HISTORY AND PRESENT STATUS OF GREEN TECHNOLOGY

The advent of Metal Age around 3500 b.c.e. also witnessed the beginnings of writing and the development of systems of weight and measures which resulted in the formation of urban, state-based societies with developed economies. Trade and industry played an important role in the development of ancient Metal Age civilizations. Metal smelting increased the demand for wood thereby leading to extensive deforestation which led to the complete disappearance of forests in many parts of the world. As the energy needs of the people multiplied further, they began to depend on traditional sources of renewable energy to supplement their energy needs.

3.3.1 ANIMAL POWER

The domestication of wild animals dramatically increased the amount of energy available to humans. Horses, donkeys, and oxen were used to draw the wheeled vehicles such as carts and wagons. In Asia, elephants have been tamed and used for travel, transport, and war since ancient tunes. Other animals that have been used for travel and transport through the ages are dogs, llamas, reindeer, camels, and water buffalo. The plow was used for the first time to make use of annual energy in the preparation of fields, thereby providing a functional link between animal keeping and crop production. At present, while the draught annual power (DAP) is expanding in Africa, in Asia and Latin America, it is persistent. Even in highly developed countries such as Spain, Portugal, and Greece, DAP remains an important energy source in small farms. In the United States, many farms profitably run by Amish fanners solely depend on animal power. Animal power, though an old technology, has many benefits. It is a renewable source of energy, generally affordable and easily accessible, to smallholder fanners who are responsible for much of the world’s food production. Annual power can be used as a sustainable and environment-friendly technology for rural development.

3.3.2 HYDROPOWER

The ability to utilize the power that moving water provides (hydropower) was a major green technological revolution. The history of hydropower starts as early as classical antiquity. It was used as the major source of energy prior to being replaced by coal during the early industrial revolution.

3.3.2.1 WATERWHEELS

The ancient Greeks have often been credited with the development of waterwheels though it was a work of art rather than of science. Waterwheels invented by the Romans around 600-700 b.c.e. consisted of the wooden wheel, powered by water flow and fitted with buckets that lifted water for irrigating nearby lands. Ox-, camel-, and human-driven waterwheels were also used for simple irrigation purposes. Waterwheels basically consist of two designs: a horizontal wheel with a vertical axle and a vertical wheel with a horizontal axle. The latter is further divided into undershot, overshot, and breastshot waterwheels according to where the water hits the wheel. The first ancient Greek waterwheel was an undershot waterwheel as the water passed underneath the wheel. Toward the fifth century c.e., the sudden shortage of human energy (slaves) and animal labor forced the Roman Empire to seek new energy sources. This search led to the dependence on waterwheels to perform certain works that once the slaves completed. Watermills utilize the flow of water to spin the waterwheels which then powers a drive shaft that would then complete mechanical tasks such as grinding of grains to produce flour, crushing olives to produce oil, sawing, and moving bellows and water hammers for metallurgy. These watermills later became a major energy source for textile production processes such as spinning, weaving, cleaning, trimming, as well as cloth thickening. They were also used in the paper mills and mining industry before the industrial revolution. The early steel manufacturing industries of Europe during the 13th century even used watermills for hammering.

The overshot waterwheels developed during the Middle Ages. The first scientific evaluation of the waterwheels was made by a British civil engineer, John Smeaton, during the mid-1700s. His findings led to the development of the breastshot waterwheels which were capable of harnessing significantly larger flow rates than was possible with the overshot model. The conversion to water power of the spinning jenny, the mechanical machine used for cotton cloth manufacturing, in 1769, commenced the development of several water- powered mills in England, France, and later in the United States. Though by 1830 in England, the use of coal replaced the use of hydropower in cotton spuming mills; in France and the United States, hydropower remained the major source of energy.⁸ In 1824, the use of curved buckets on undershot waterwheels to extract the maximum fluid momentum from the fluid stream was first demonstrated by Jean-Victor Poncelet, a French engineer. He also adjusted the rotational speed of the wheel such that water left the buckets with very low velocity than when it entered it. These additions increased the efficiency of the waterwheels to more than 60%.⁹ From around the tenth century to the nineteenth century c.e., the number of waterwheels continued to increase in numbers across both Eastern and Western civilizations, such as that they cluttered rivers and obstructed boat traffic. Toward the end of the nineteenth century, the vertical wooden waterwheels underwent several innovations and were replaced by ones in iron which increased its efficiency (80-90%) for low to moderate head chutes and a power range of 10-50 kW per unit.⁹

3.3.2.2 WATER TURBINES

With its large size acting as a major shortcoming, waterwheels began to be replaced by water turbines which were comparatively smaller but more efficient. The major difference between a water turbine and waterwheel was the swirl component of the water which then passed energy to a spinning rotor. This enabled the turbine to be much smaller than a waterwheel of the same power. The migration from waterwheels to turbines took almost 100 years.

Hydroturbines are basically of two types: the impulse turbines and the reaction turbines. The concept of a water turbine was developed independently by Dr. Barker in England in 1744 and in 1750 by Johann Andreas Segner in Germany.⁸ In 1832, a French engineer, Benoit Foumeyron, developed the first industrial turbine which was installed for the bellows of a metallurgical propeller-type. In 1843, with some improvements made by Uriah Boyden to the Foumeyron turbine, the Boyden turbine was introduced in the United States. The Foumeyron and Boyden outward-flow turbines remained a prominent technology in the hydraulic industry as well as in other fields of research for more than 70 years even though it was later superseded by other advanced models. In 1849, Janies B. Francis developed a scientific turbine design method and, after making several improvements to the inward-flow wheel design, installed the first full-scale water turbine at Boott Cotton Mills. As the Foumeyron and Francis turbines were not functional for chutes higher than 120 m, in 1854 in France, Louis-Dominique Girard designed an impulsion turbine to solve this problem. However, the problem of wheel erosion in the case of high chutes still remained. It was in 1866 that Samuel Knight developed the tangential waterwheel which utilized the water from a dam at a high elevation. This was an impulse turbine which made use of a high-pressure nozzle from which water originated was directed slightly off- center to the buckets on the wheel, in such a way that energy was not wasted via water splashing. In 1878, Lester Allan Pelton modified the Knight wheel and developed the Pelton turbine which had a double bucket design with a half-cylindrical profile. This design overcame some of the inefficiencies of the Knight wheel and has to date been used as the reference turbine for high chutes, hi 1912, Victor Kaplan created the Kaplan turbine, a propeller-type turbine with an intent to deliver large powers from veiy low chutes.⁸-⁹ The use of hydropower was promoted by energy-intensive industries such as aluminum smelters and steelworks. On September 30, 1882, the world’s first hydroelectric power plant, Appleton Edison Light Company, began operation on the Fox River in Appleton, Wisconsin. Hydroelectricity is a form of energy that harnesses the power of moving water to generate electricity. Since 1889 onward, all hydropower projects were aimed at electricity generation. The 22.5 GW Three Gorges hydroelectric power plant in China is the largest hydropower generating facility ever built. Though not mentioned here, many other turbines were designed and manufactured, as well as several dams were also established during this period. The world’s total installed capacity of hydropower in 2018 was estimated to be 1292 GW with electricity generation reaching 4200 terawatt-hours (TWli). Globally, hydropower is produced in 157 countries (Table 3.1), with 47 countries adding an estimated 21.8 gigawatts (GW) of hydropower capacity into operation in 2018. With Brazil increasing its installed capacity by 3.7 GW in 2018, it thereby reached a total capacity of 104 GW and so has now overtaken the United States (103 GW) as the second-largest country with respect to hydropower capacity (Table 3.2). Currently, hydropower contributes almost two-thirds of the renewable electricity generation, without which the objective of limiting climate change to 1.5 or 2 °C above preindustrial levels would likely be impossible.

TABLE 3.1 Total Installed Capacity and Hydroelectricity Generation of Different Continents in 2018

GW, gigawatts; TWli, terawatt-hours.

Source: All data in this table are selected based on information provided by International Hydropower Association in 2019.

TABLE 3.2 Top 10 Countries with the Most Hydroelectric Capacity.

GW, gigawatts.

Source: The information on the countries in this table is based on information provided by International Hydropower Association in 2019.

3.3.2.3 THE T ROM PE

A hydraulic air compressor (НАС) or “trompe” as it was originally known is an ancient Italian technology developed in 1588 that utilizes falling water to provide air supply for smelting furnaces. The trompe is a simple device that consists of one or more vertical wooden pipes through which water is channeled via gravity. Upon descent, constriction in the vertical pipe produces a low pressure which causes air to be sucked into the water from an external port, thereby providing a constant air supply. At the bottom of the pipe, the air gets separated from the water and rises to the top of the separation chamber from where it goes to the take-off pipe which can then act as the power source. As the НАС produced compressed ah' without moving any parts, it was a quite reliable and efficient device. Starting in 1896 almost 18 gigantic HACs were built mostly in the United States, Canada, Germany, and Sweden. Since the air in the trompe undergoes isothermal compression, it does not affect the captured air’s temperature, which otherwise would get heated up, thus preventing overheating of any machinery powered by it. The design of HACs was unproved further making it all the more efficient and practical. The compressed air produced can be used to power machinery in mining operations, aerate the water, atomize paint, and also serve several other functions.¹⁰

3.3.3 WIND ENERGY

Keeping in mind the fact that anything that moves has kinetic energy, humans began investigating ways to generate useful forms of energy from the power of the wind. Though wind power is a cost-effective, domestic, and sustainable source of energy, it being an intermittent source of energy that cannot be made or dispatched on demand, cannot be relied on for continuous power supply. The basic design of a wind energy device includes the horizontal axis wind turbine and the vertical axis wind turbine (VAWT); the classification being based on the axis of rotation.

3.3.3.1 WINDMILLS AND WIND PUMPS

While a windmill is a structure used to harness the power of the wind into rotational energy for the purpose of grinding grains, the wind pump uses wind power for pumping water from deep wells back to the surface, for the drainage of water from marshy areas, as well as for automated inigation of fields in areas surrounded by streams and river. The wind pumps were often coupled to an Archimedean screw, Egyptian noria, or Persian waterwheel; all of them are early pump concepts that could elevate water to a height of 5 m. Prior to the industrial revolution, other applications of wind-powered machines included extraction of oils from oilseeds, nuts, grains, lumber sawing, ventilating of mines, manufacture of gun-powder, and snuff tobacco. Interestingly, it was even used for lopping bee hives into town under siege during warfare. The simplest windmill sails comprised cloth sails attached to the rotating aims or blades. Later, wooden frames covered with cloth began to be used as common sails in order to attain better structural stability. However, when the mills run out of grain and the millstones run dry igniting a spark, there were chances of the common sails catching fire. In cold weather, the cloth sails used to get wet and frozen too. hi order to avoid friction-induced fries, a combination of wood and metal was used, and in such instances, the cloth sails were found to last 40-50 years. Modem wind generators utilize wood and glass epoxy, fiberglass, aluminum, and graphite composite materials for their construction.

Although the history of wind-powered devices is quite obscure, it was found that vertical axis wind rotors probably originated around 200 b.c.e. at the Persian-Afghan borders (Seistan), while the horizontal axis windmills of Europe followed much later around the 12th century c.e.¹¹ While the Seistan rotors were driven by drag forces, the European designs were driven by lift forces. During the 17th century b.c.e., King Hammurabi of Babylon made ambitious plans to irrigate the fertile plains of Tigris and Euphrates Rivers using the vertical axis wind pumps.¹² The Dutch engineers, around 14th century c.e., initiated making improvements to the existing windmill and wind pump designs. The rotors on many of these Dutch mills were twisted and tapered in the same way as modem rotors. The first Dutch marsh mills were started around 1400, and by 1600, there were almost 2000 of them operathig to drain almost 2 million acres of land in Holland. It was during the mid-1700s that the Dutch settlers introduced windmills in America. During the American Revolution, wind pumps were used to pump water to make salt on the islands of Bermuda and on Cape Cod. In 1759, John Smeaton through a series of experiments improved the efficiency of windmills and wind pumps, thereby laying the foundation for the aerodynamic theoiy of wind machines. During the mid-1800s, a need for a distinctive small wind pump for the settlers in American West resulted in the development of American multiblade windmill design. It consisted of a vertical steel structure with a multibladed drag or impulse propeller at the top that caught the wind. The rotational motion of the blade was converted into a linear motion to pump water and cany out functions like irrigation, cattle drinking, and also as a water supply for steam locomotives.¹³ Between 1850 and 1970, further modifications of these systems made in the United States resulted in the establishment of over 6 million wind pumps all over Australia, North America, South Africa, and South America, and many were also exported from the United States and Australia to developing countries.¹²¹³ Wind energy remained a major source of energy prior to Industrial Revolution but later the availability of cheap and plentiful petroleum coal lagged the interest in harnessing wind power which was unreliable at the same time required a high capital cost. However, in different rural areas of the world, vertical axis windmills and wind pumps are still being erected by enterprising fanners for inigation as well as drainage purposes.

3.3.3.2 WIND TURBINES

A wind turbine is a windmill like structure but specifically built to generate electricity. Professor Janies Blyth, a Scottish electric engineer, is considered a pioneer in this field as his holiday home in Marykirk was the first known structure in the world to have electricity using wind power in 1887. The American engineer, Charles Brush, has also often been credited as a pioneer in the field. Denmark, in 1891, was the first country to use wind turbines to meet the demand for electrification of rural areas. Poul La Cour, a Danish scientist, was in charge of the experimental station during this period. The wind turbines used were 23 m in diameter and had power outputs between 5 and 25 kW. Being equipped with storage batteries (100-300 A-h capacity), they were capable of meeting energy demands for up to 10 consecutive windless days.¹² In 1903, La Cour founded the Society of Wind Electricians, and in 1904, the society held its first course. He was the first to discover that wind turbines with fewer blades that spin faster are more efficient than those with many blades that spin slower. After World War I, most wind generators transitioned from a drag or impulse system to an airfoil system similar to air propeller thereby significantly improving their power coefficients.

In 1929, the first VAWT, known as the Darrieus turbine after its inventor George Darrieus, was introduced in France and later spread worldwide, and is still in use today.¹⁴ In 1931, the first wind-powered system to be connected to an existing power supply grid was built at Yalta on the Black Sea. It had a rated power of 100 kW in an 11 ms^-1 wind. The Yalta wind turbine was functional for almost 10 years until it was destroyed during the Second World War. In 1934, Palmer Cosslett Putnam designed the world's first megawatt-size wind turbine that was manufactured by the S. Morgan Smith Company of York, Pennsylvania. It is also considered as the predecessor of the two-bladed turbines built by the United States in the late 1970s and early 1980s.¹⁵ It was connected to the local electrical distribution system in Vermont, United States and was designed to operate at a wind speed of up to 33 ms^-1. The Smith-Putnam wind turbine had a rated power of 1000 kW in a wind speed of 13.4 ms^-1. The turbine was capable of producing 1250 kW, and it operated for about 1000 hours before an overstressed blade failure in 1945. Fuel shortages and rising demand for electricity, after the Second World War, instilled widespread interest and research in the potential of wind power to provide electricity. However, between the 1950s and 1960s, the increased interest and expectation of producing cheap electricity via nuclear fission diminished the developments of wind turbines.

During the late 1960s, as people became more aware of the environmental consequences of dependence on fossil fuels, a renewed interest in the use of wind energy was ignited. Despite the diverse and technically successful developments and research projects in the field post-1970s, none of them lead to commercial exploitation, as throughout the postwar period (1945-1973), fossil fuels became progressively inexpensive and cheap. Though wind turbines provided a free energy source, the cost of the power so harnessed was determined by the initial cost of the machine and to a certain extent by its maintenance and running cost, and hence, electricity thereby obtained was considered more expensive than that obtained via coal, gas, or oil. However, post-1973, antinuclear protests and sharp rises of unit oil prices spurred some politicians to realize the finite extent of earth’s fossil fuel reserves. This initiated research and development programs in wind turbines in some of the more developed countries. In the United Kingdom, the Energy Technical Support Unit for the Department of Energy evaluated the potential of wind energy as a source for generating electricity. During this period, the common misconception that large multiscale megawatt rotors (MOD series of turbines) offered low energy costs than smaller turbines was corrected. Research in the field suggested the use of more medium-sized wind turbines, at the same time, could produce more energy less expensively. Medium-sized wind turbines of 10-20 m diameter were found to have payback periods of 6-9 years when functioning in parallel to an existing electrical grid system. This led to the widespread development of microturbines of 22 kW.¹²¹⁴ The involvement of the US government in wind energy research and development (R&D) after the oil crisis of 1973 was another major milestone in the history of wind turbines. This resulted in the evolution of the commercial wind turbine market from domestic and agricultural (1-25 kW) to utility interconnected wind farm applications (50-600 kW). The US Federal funding and the Public Utility Regulatory Policy Act of 1978, which forced companies to purchase a particular amount of electricity from renewable sources, promoted the first large-scale wind energy penetration in California, resulting in the installment of over 16,000 wind turbines (20-350 kW) between 1981 and 1990.¹¹ However, with the withdrawal of federal tax credits by the Ronald Reagan administration by the early 1980s, wind rush in the United States collapsed. The 1990s witnessed the demise of the United States’ largest manufacturer, Kenetech Windpower. During this period, the focal point of the wind turbine manufacturing industry moved to Europe, particularly Denmark and Germany.¹⁵ Though Denmark attained self-sufficiency in oil a decade later, it still continued its wind development program in order to reduce GHG emissions. During a 15-year period, pioneers in the field made all their inventions and theories available for all, thus enabling the successful development of the wind power industry. It was during this period that some of the large wind turbine manufacturing companies such as Vestas, LM Wind Power, Nordtank, Spanish Gamesa, Micon, and Bonus were founded. Large wind farms were created, and offshore wind farms were bom, and as the concent over GHGs grew, the development continued further (Table 3.3). The largest wind farm in the world is the Jiuquan Wind Power Base in China. Also known as the Gansu Wind Faint, it has about 7000 wind turbines with a total installed capacity of 7.96 GW. The farm is set to be expanded to have a total capacity of 20 GW by 2020. In 2018, 50.1 GW of wind power was added thereby increasing the overall capacity of all wind turbines installed worldwide to 596.4 GW. This covered up to 6% of the global electricity demand. While Germany, Spain, Italy, and France showed weak development in the wind market, countries like China, India, and Brazil as well certain African countries showed robust growth (Table 3.4).

TABLE 3.3 World’s Biggest Wind Fauns.

TABLE 3.4 Global Wind Installations (2017-2018).

GW. gigawatts.

Source: Pitteloud (2018).

3.3.4 SOLAR ENERGY

The sun plays a vital role in life on earth. With the solar energy received on earth being plentiful, totally renewable, and directly or indirectly being the origin of all energy sources, the potential of the sun’s energy to satisfy all our energy needs is immense. Humans have been tinkering with this idea since the dawn of time. They have admired the sun and frequently personified and worshipped it as a deity, and many cultures still continue to do so. Apart from the metaphysical approach, the sun’s energy found many practical applications. Solar energy technologies are basically of two types: solar thermal technologies and photovoltaic (PV) technologies. Solar thermal technologies use solar energy to generate heat, and then if needed, electricity is generated from that. PV technologies generate electricity directly from solar energy (Table 3.5).

TABLE 3.5 Largest Solar Power Plants of the World.

MW. megawatts.

3.3.4.1 PASSIVE SOLAR HEATING OF BUILDINGS

The basic principle of a passive solar building is that it is built in such a way that it maximizes the exposure of the building to the south, thereby capturing solar energy and further insulating the enclosure to trap the heat within. Neolithic Chinese villagers around 6000 b.c.e. had the sole openings of then houses face south in order to catch the low winter sun rays to warm their interiors. The overhanging thatched roof would keep the high summer sun rays off their houses thereby cooling their interiors. Socrates and Aristotle too advised similar constructions of houses in the third century b.c.e. and often considered as the pioneer of the present passive heating and cooling techniques.¹⁶ The ancient Egyptian Pharaohs solar heated their palaces using black pools of water which captured solar energy by day, and during the night, the hot water was allowed to circulate through pipes on the palace floor. This system helped maintain warmth during the night while lowering the temperature during the daytime to a certain extent. Solar heat assisted the hypocaust system of mechanical heating in the ancient Roman baths built around 212 c.e. Glazing the south-facing windows helped trap heat in the baths, thereby reducing the usage of fuel. Thick walls, hollow tiles, and wooden shutters over the windows helped further to retain heat in the baths. Transparent glass, the Romans discovered, helped in admitting sunlight and also trapping heat in desired spaces. Dining the sixth century c.e., sunlight was so important to the Romans that a legal precedent for solar rights was actually established and solidified in the Justinian code of law. Around 700-1300 c.e., the south-facing cliff dwellings were chosen by the Anasazi people in the American West to make use of the winter sun to provide warmth. Between the 1500s and 1800s, the south-facing greenhouses, which trap solar heat energy within, were built by the wealthy Europeans who wanted to grow exotic plants in the colder climate. New England “saltbox” houses of the 17th century, the Swiss farmhouses of the 18th century, and the solar houses of the twentieth century are all examples of passive solar buildings.

3.3.4.2 SOLAR FURNACES AND COOKERS

hr a solar furnace, high temperature (up to 6330 °F) is obtained for industrial purposes by concentrating the solar radiation onto a substance using a number of heliostats or tumable minor. Back in the seventh century b.c.e., magnifying glasses were used to concentrate the sun’s rays and light a fire. By the third century b.c.e., Greeks and Romans were known to bounce off sunlight of “burning mirrors” to light torches for religious ceremonies. Ehstorians claim that as early as in 212 b.c.e., Archimedes, a Greek inventor, made use of the reflective properties of highly polished bronze shields to concentrate the sun’s rays to set fire on the Roman ships attacking Syr acuse. Georges-Louis Leclerc, Comte de Buffon, French scientist, and naturalist, in 1695, used a mirror to focus sunlight and achieve a temperature high enough to bum w'ood and melt lead as well. Antoine Lavoisier, in 1782, focused sunlight using a lens and achieved temperature as high as 3000 °F, capable enough to melt previously unmeltable platinum. The largest solar furnace opened in 1970 at Odeillo in the Pyrenees-Orientales in France employs an array of plane mirrors to gather sunlight, reflecting it onto a larger curved mirror. Asia’s largest solar furnace was built in Uzbekistan in 1981 and is also known as the Sun Institute of Uzbekistan. The energy thereby obtained can be used for hydrogen fuel production, foundry applications, and high- temperature testing.

Solar cooker or oven is a device which utilizes the solar energy to heat, cook, or pasteurize food items and drinks. The principle behind the solar furnace and solar cooker remains the same. The world’s first documented solar oven was developed in 1767, by Swiss naturalist and physicist Horace Benedict de Saussure. The so-called “hot box” plate collector consisted of a well-insulated box with three layers of glass that trapped solar heat achieving a cooking temperature of 230 °F. Saussure’s invention inspired and informed several others including Augustin Mouchot (French inventor) who saw the great commercial potential of solar appliances in France’s sun-rich, fuel poor colonies of North Afr ica and Asia. In 1877, he devised solar cookers for the French soldiers in Algeria and received the support of the French government to pursue fiill-time research. Unfortunately, better political relations with England restored France’s supply of coal, thereby diminishing interest in solar energy harnessing. The first recorded history of solar cookers use in India dates back to 1876, when William Grylls Adams, a British engineer, developed an octagonal oven in Bombay, India. This helped ease the energy shortfalls and depletion of wood fuel in Colonial India.¹⁷ Baltimore inventor, Clarence Kemp, in 1891 patented a commercial solar water heater for bathing and dishwashing that enjoyed widespread popularity in California. The solar box-type cookers were later commercialized by an Indian pioneer M.K. Ghosh in 1945. Many companies with the help of the Indian government have since then and up to the 1980s harnessed solar energy for cooking purposes. This led to the installations of two of the world’s largest solar cookers in India at the Timpati and the Shirdi Sai Baba temple, where solar energy is used to cook food to feed lakhs of devotees on a daily basis. Though in the 1950s, scientists and researchers devised and constructed solar ovens, they failed due to the availability of lower fuel alternatives. However, the oil crisis of the 1970s again spurred interest in the use of solar energy in China and India. The 1970s in the United States was sound with the several types of concentrating and box-type solar cookers developed by Barbara Kerr using recycling materials and aluminum foil. During 1979, Dr. Bob Metcalf and his student Marshall Longvin performed water pasteurization using box- type solar cookers. India and China during the 1980s expanded the national promotion of box-type solar cookers. In 2000, Paul A. Funk proposed a solar cooker power curve tool that was used to evaluate the heat-storing capacity of solar cookers.¹⁸ Countless styles of solar cookers are continuously being developed by researchers and manufacturers in an intensive effort to enhance the capacity of solar cookers.

3.3.4.3 CONCENTRATED SOLAR POWER

Concentrating solar power (CSP), also known as concentrated solar thermal systems, concentrates a large area of sunlight onto a receiver, which then converts it to high-temperature heat. The generated heat is then used to drive traditional steam turbines or engines that create electricity. Currently, there exist four different CSP technologies, namely, the parabolic trough collector (PTC) technology, linear Fresnel collector (LFC), the Stirling dish collector (SDC) system, and the earliest tower solar power (TSP). The earliest documented use of PTC technology was in 1913, in Maadi Egypt for generating steam that helped drive a 73-kW pump which in turn was used for irrigation purposes. The first LFC prototype was built by Giorgio Francia, an Italian mathematician, at Lacedernone-Marseilles solar station in 1963. The pioneer SDC system was demonstrated in Southern California from 1982 to 1985 by Advanco Corporation. The earliest TSP technology was exhibited by constructing a plant named EURELIOS in a large valley, about 30 km from the sea in Adrano, Sicily, Italy in 1976. The ability of the solar tower technology to generate large-scale electricity (10 MWe) was demonstrated by Solar One plant that was built in California, United States, in 1982. The first commercial-scale CSP plant named SEGS I was built in California in 1984 by using PTC technology to generate 14 MWe; then by 1990, the capacity of the SEGS plants was increased to 354 MWe. Between 1991 and 2005, because of the falling of fuel prices and other policy changes, no CSP plants were built. However, since 2006, the ability of these plants to limit GHG emissions and other environmental impacts of energy generation spurred an interest again in CSP plants. At present, Spain with a total installed capacity of 2.3 GW is considered the largest producer of electricity using CSP technologies. With an estimated 513 MW addition in 2018, the global installed capacity via CSP reached 5.5 GW.¹⁹

3.3.4.4 PV CELLS

A PV cell or solar cell is a device that converts light into electric current using the PV effect. It was not until the 19th century that the potential of turning sunlight into electricity was discovered. The history of solar PV cells unveils with Alexandre Edmond BecquereTs, a French scientist, discovery of the PV effect in 1839. While experimenting with an electrolytic cell made up of two metal electrodes placed in an electrically conducting solution, electricity generation was found to increase when exposed to light, hi 1873, Willoughby Smith, a British electrical engineer, discovered the photoconductive potential of selenium. This discoveiy was followed by that of William Grylls Adams and his student Richard Evans Day’s discoveiy in 1876 that selenium creates electricity when exposed to light. A few years later, in 1883, an American inventor, Charles Fritts, produced the first solar cells by coating selenium with a thin layer of gold. Though these selenium cells were not as efficient as modern-day PV cells (less than 1% light-to- electrical energy conversion efficiency), for the fust time it was proved that light, without heat or moving parts, could be converted to electricity. The paper published by Albert Einstein in 1905 on the photoelectric effect and how light carries energy helped understand the potential of solar energy in generating electricity. By the beginning of the 20th century, Silicon PV cells having five times greater efficiency than selenium PV cells began to be developed. In 1953, Daiyl Chapin, Gerald Pearson, and Calvin Fuller lined by Bell Telephone Laboratories developed a solar PV cell by doping strips of silicon with boron and arsenic. This was the fust modem PV cell which at first had an efficiency of 4%, and later through modifications was increased up to 11%.

During the early years, when the cost of PV cells was high and the efficiency low, they found applications only in space programs for which cost was not a problem but reliability was vital. For those manufacturing solar cells, the increasing demand for it in space meant a booming industry. The United States’ Vanguard satellite, in 1958, was the first satellite to use radios powered by solar energy (less than 1 W). Solar PV cells still remain the accepted energy source for satellites today. The first drivable solar car was a vintage model 1912 Baker Electric car converted to run on PV cells by the International Rectifier Company in 1962. In 1982, Hans Tholstrap and Larry Perkins were the first to cross continents in a solar car, the “BP Solar Trek” making it the world’s first practical long-distance solar-powered car.²⁰ Though during the 1960s and 1970s, the cost of PV cells remained high, the development of large single crystals of silicon for use in integrated circuits moderately brought down the prices of raw materials. The rising oil prices increased the demand for solar power. Starting in the 1970s, the work of Elliot Breman at Exxon resulted in the development of cheaper PV cells. He discovered that using silicon from multiple crystals brought down the prices fivefold than when using silicon from a single crystal, thereby increasing their terrestrial demand. Throughout the 1970s and 1980s, the ready availability of PV cells found a market in navigational buoys and remote telecommunications stations. During the 1970s, the idea of applying solar cells to pump water²¹ was put forward by Dominique Campana, a graduate student in Paris. The working model of her idea was later translated by French physicist Jean Alaine Roger who developed the world’s first practical PV pump on the island of Corsica.⁵² In 1973, the University of Delaware was credited with the construction of the first solar building named “Solar One” which ran on a hybrid supply of solar thermal and PV power. It was the first instance building-integrated PVs was used, that is, the building did not use solar panels; instead, it had solar cells integrated onto its rooftop. In 1982, ARCO Solar develops the first solar power plant in Hesperia, California which generates 1 MW hr"¹ at full capacity. Two years later, a second solar plant was developed in Carizzo plains, California with 100,000 PV arrays generating 5.2 megawatt (MW) at full capacity. Though the power plants fell into disarray with the return of oil (after the 1973 oil crisis), these plants demonstrate the potential for solar power production.

While single crystal silicon remains the most important and efficient base for solar cells, during the 1990s, polycrystalline silicon being cheaper became popular. PV research and development continued, and cheaper thin-film amorphous silicon PV cells were developed. Thin-film solar cells based on other materials such as cadmium telluride (CdTe) and copper indium gallium diselenide attracted attention and offered as a cheaper alternative to silicon.²² However, over the years, the reduction in the cost of silicon cells coupled with its high efficiency established its dominance in the solar industry. PV cells began to be used in warning lights, horns on offshore oil rigs, lighthouses, railroad crossings, and even in remote and isolated places where the traditional electricity grid was not available. In 1995, Thomas Faludy filed a patent for a retractable awning with integrated solar cells for use in recreational vehicles (RVs), and it remains one of the popular ways to power RVs to date. By 2005, do-it-yourself solar panels started becoming popular. In 2019, the National Renewable Energy Laboratory in Colorado developed the multi-junction or stacked solar cells with a record-breaking efficiency of up to 45%.²³ The consumer demand for solar panels increased as the price of solar panels decreased from S300 per watt in 1956 to $2.99 per watt in 2019.²⁴A solar plant constitutes of a single generating station designed by a single developer or consortium and most often with a single export connection to the grid. Solar parks, on the other hand, may be defined as a group of colocated solar power plants. Marry of the largest solar power facilities are installed in China and India (Table 3.4). The total installed capacity of solar PVs reached 480.3 GW

(excluding CSP) in 2018 (Table 3.6), with solar PV additions of around 94 GW.

TABLE 3.6 Solar PY Installed Capacity Worldwide.

GW. gigawatts.

Source: IRENA (2019).

So far, the evolution of the solar industry has been remarkable with several milestones reached in recent years with respect to advancements in technology, installations, cost reductions, and establishment of key solar associations. The use of solar power spans various industries and contributes power to hundreds of different gadgets and technologies all over the world. Over the past 20 years, the solar cell industry has grown dramatically and is often accepted as an effective solution for rising energy needs. In 2018, the world solar power installed total capacity reached 485.8 GW, up slightly by 93.7 GW than last year.¹⁹ 3.3.5 GEOTHERMAL ENERGY

Geothermal energy constitutes the thermal energy generated and stored in the earth’s crust; transmitted via conduction/convection through various rocks and natural groundwater reservoirs called aquifers. The energy thus obtained is a sustainable, renewable source of energy as the heat extracted is small compared to the immense magnitude of the earth’s heat content. While high and medium temperature resources (approx. > 100°C) are used for power generation, low-temperature resources (approx. < 100°C) are suitable for direct uses such as recreation, heating, and drying. A brief historical outline of different practical applications of geothermal energy is discussed in the following text.

3.3.5.1 DIRECT USE AND DISTRICT HEATING SYSTEMS

Prehistory is abounding with the pieces of evidence pointing to the practical uses of geothermal energy for bathing, cooking, washing, as well as other religious rituals. It was during the beginning of the seventh century b.c.e that the Etruscans considered as the “fathers of geothermal industry” developed their civilizations in the central part of Italy with their settlements and cities built near springs, geothermal manifestations, and products of hydrothermal activity such as alabaster, travertines, iron oxides, sulfur, silica, kaolin, borate, alum, and thermo-mineral muds. Being veritable bartering goods, they were of great economic value to the Etruscans. These minerals were mainly used in pottery, production of enamel, ointments, medicines, and paints. They were also used in the dying of glass, wool, and cloth. A practice still active in the Larderello region in Italy is the production of enamel using borax, which is recovered from boraciferous springs. Many of these hydrothermal products were popularized by the trade of the Etruscans in the Mediterranean Basin. They valued the healing properties of the geothermal waters as well as of its salts and thermo-mineral muds. The practice of geothermal bathing and balneotherapy which was first developed by Etruscans was later perfected by the Romans from the second century b.c.e. The Romans instilled the thermal practice for healing and recreation even in localities lacking geothermal manifestations using artificially heated water. The fall of the Roman Empire in 476 c.e. resulted in a strong decline in thermal bathing as well as extraction and use of most by-products of terrestrial heat everywhere in Italy and in the territories of the old Roman Empire. This lasted for the whole Early and most of the High and Late Middle Ages. From about the 15th century, balneotherapy in the Italian thermal spas underwent a new blooming even though it never reached levels attained in Roman times.²⁵ The direct utilization of geothermal energy for cooking and therapeutic purposes by ancient people of the world such as the Mexicans, Chinese, Japanese, Greeks, Indians, Turks, Arabs, and Maoris for thousands of years is well documented.

Geothermal heat pumps (GHPs) utilize the relatively constant heat of the earth to provide heating, cooling, and domestic hot water for buildings. Medium-temperature geothermal energy (70-150°C) is itsed for these purposes. Although the Romans and the Chinese built primitive pipelines to pipe thermal waters and steams for bath, the use of geothermal energy for space heating became common only after the development of metal pipes and radiators. The oldest known geothermal pipeline (a duct of stones, slabs, and clay) was made in Iceland around the 13tlr century to heat an outdoor bath pool. The earliest documented case of residential heating in the world using geothermal energy was in the 14th century in Chaude Aigues (France). In 1930, the first municipal district heating system using geothermal water was invented in Reykjavik, Iceland, where hot water was piped from a spring 25 km away, and residents used it not only for heating their houses but also for hot tap water. Presently, more than 90% of the population of Iceland live in houses heated by geothermal water. Greenhouse fanning using geothermal water was started in Iceland in the 1920s and was later adopted and has been operated for several decades by several countries including the United States, New Zealand, Greece, Hungary, Macedonia, Italy, Romania, Russia, China, and Japan. Large- scale district heating systems have also been installed in many of these countries. The extraction of salt from seawater using geothermal springs is known in Iceland since the 18th century. In 1828, Francesco Larderel replaced the use of firewood in the traditional boric acid industry with the natural terrestrial heat as process heat, thereby solving the problems associated with the wood shortage. This was the first industrial utilization of geothermal energy. The world’s first geothermal wells constructed for the boric acid industry were also developed during this period by the manual drilling of small diameter (10-12 cm) shallow wells (6-8 m depth), located near the natural lagoons in Larderello, Italy.⁵⁶ It was during the 1950s that the first large-scale industrial application of geothermal steam was utilized in a pulp and paper mill in Kawerau, New Zealand.²⁶ Geothermal steam- operated air conditioning was first developed in a hotel in New Zealand in the late 1960s. Since the 1960s, in different countries, geothermal steam, heat, and water began to be used in various industries for drying, washing, and dyeing of different products. Nowadays, low-temperature geothermal energy (20-60 °C) finds use in aquaculture (fish farming and algae production), animal husbandly, and even soil heating. There has been a steady increase in the number of countries depending on geothermal energy for direct application with currently almost 73 countries utilizing geothermal energy with a total output of 75.9 TWh per year.²⁷

3.3.5.2 ELECTRIC POWER GENERATION

Electricity generation using geothermal steam or hydrocarbon vapor is a much more recent industry dating back to the beginning of the 20th century. On July 4, 1904, at Larderello, Italian, businessman Prince Piero Ginori

Conti powered five bulbs from a dynamo driven by a reciprocating steam engine using geothermal power. In 1905, by using an old Cail steam engine, he increased the power production to 20 kW which he then used to light the Laderel borax factory as well as to drive some small electric engines. Prince Ginori classified the geothermal wells into wet and dry. The wet wells were used in the extraction of boric acid as they produced both water and steam. The dry wells were used to generate electricity as they produced only dry steam and the quantity of steam produced depended on the depth of the well. Despite the shallow depths of the well (average 100 m), the flow rates until the early 1900s were between 6 and 20 tons per hour. Within a decade, in 1913, the first geothermal power station was also built here with an installed capacity of 250 kW_(e) which exported power to the local regions from 1913 to 1916. Natural steam was used to heat and evaporate fresh water which was then used in firm to feed the steam turbines constructed by the Italian company Franco Tosi. Using a similar prototype, a much larger and more complex power plant with three Franco Tosi turbo-altemators of 2500 kW each was built in 1916. Following the path set by Italy, in 1919, Japan successfully drilled some wells at Beppu and started producing electricity at a small scale in 1924. It was only in 1966 that geothermal electricity began to be produced here at an industrial scale. In the United States, even though the first well was drilled in California in the Geysers area as early as in 1925, geothermal electricity was generated by Pacific Gas and Electric only hr 1960. Since 1958, China and New Zealand also started generating geothermal electricity.²⁸ Geothermal power plants are basically of three types: “dry” steam, flash, and binary. The Geysers hr the United States and the Larderello in Italy are “dry” steam reservoirs as they produce steam with very little water content. The steam produced is directly used to run the turbine. A flash power plant is used in the case of a hot water reservoir like that of Wairakei in New Zealand, wherein hot fluid with temperature greater than-lSO^C is brought up to the surface through a production well, whereupon being released from the pressure of the deep reservoir, some of the water flashes into steam in a “separator.” This steam is then used to power the turbines. The binary power plant or the organic Rankine cycle power plant was first demonstrated in 1967 in the Soviet Union and later introduced to the United States in March 1970 by B.C. McCabe, Chairman and CEO of Magma Energy, Inc., a subsidiary of Magma Power Company.²⁹ Binary power plants make use of low-to-rnedium enthalpy reservoirs with temperatures (85-150 °C) not hot enough to flash enough steam but instead generate electricity by transferring the heat to a low-boiling point binary liquid. This binary liquid then flashes into vapor which is then used to power the turbine. This technology thus facilitated the use of much lower temperature energy resources than were previously recoverable. At present, 24 countries generate electricity using geothermal energy, and almost 11 other countries including Australia, France, Germany, Switzerland, Japan, the United Kingdom of Great Britain, and Northern Ireland are developing and testing geothermal systems.²⁷ Geothermal installed capacity increased by 587 MW in 2018, thereby reaching a total capacity of over 14.3 GW by the end of 2018. With geothermal power resources limited to the tectonically active regions of the world, only a few countries use geothermal power, and the United States remains the global leader in generating geothermal power (Table 3.7). Turkey and Indonesia accounted for about two-thirds of the new capacity installed in 2018. The largest geothermal power plant is the Geysers Geothermal complex located in the United States with an installed capacity of 1.5 GW (Table 3.8).

TABLE 3.7 Installed Geothermal Capacity Worldwide in 2018.

GW. gigawatts.

Source: IRENA (2019).

TABLE 3.8 Some of the Major Geothermal Power Plants in the World.

MW. megawatts.

3.3.6 TIDAL POWER

Tidal power is a type of hydropower that converts the energy of the tide into power or other valuable types of energy. Tidal power draws on energy inherent in the orbital characteristics of the earth-moon system, and to a lesser extent from the earth-sun system. Though being predictable, it is an intermittent source of energy that supplies energy only when the tide surges. While the rise and fall of the tides—in some cases more than 12 m—creates potential energy, the flows due to flood and ebb currents create kinetic energy. Both forms of energy can be harvested by various tidal energy technologies.

3.3.6.7 TIDE MILLS

A tide mill is a water mill driven by the rise and fall of the tide in bays and estuaries. These ancient tide mills relied on the enhanced potential energy within a small basin created with the help of a dike closing off a small bay; sluices installed helped fill up the basin during high tide. The paddlewheel constructed turned when the basin emptied at the ebb, thus transforming the potential energy into mechanical force driven mainly for rasping and dyeing of woods, grinding of cereals, corns, and salt as well as in the manufacturing of tobacco stems. Tide mills were also used to provide fresh water for the city like the mill on the London Bridge. The exploitation of tidal motion for energy has a long history, and tide mills with waterwheels have been known for the best part of a millennium in Europe and elsewhere. The tide mill at Nendrum Monastic site on Stanford Lough on the east coast of Northern Ireland built as early as in 619 c.e. is presently considered as the oldest mill in the world. During the 10th century c.e., the Arab geographer described the Persian Gulf mills he found at Basra hi the Tigris-Euphrates delta (Iraq), explaining how the water turned the wheels as it flowed back to the sea. Apart from these mills, tide mills appear to be very much a European, Atlantic Basin technology. Around 1066-1086 c.e., mills in Europe were built at the entrance to the port of Dover on the English Channel. This technology was later exported to Australia. In the Netherlands, where the earliest known mills were built in 1200, almost 20 mills have been reported. The number of mills increased steadily throughout the Middle Ages. By 1300, there were 37 mills in England alone, after which tide mills were built infrequently. Many of the tide mills began to be replaced by windmills as the former were occasionally damaged and destroyed by storms. During the 16th century, in Germany, while tide mills were built in the Hansa City—State of Hamburg, no mills existed along its North Sea Coast. The tidal range was increased and mills were established by using canals as reservoirs and damming certain river branches. Though the perfect location for tide mills is on coasts with a wide tidal range, it does not appear to be the sole determining factor as the Iberian Peninsula with its narrow tidal range had the highest number of tidal mills (some 100 tide mills) in the world. During the 14th and 15th centuries, new mills were built in Britain, near Plymouth and Southampton. From around the 15th century, the construction of tide mills with abutments consisting of strong breakwaters was encouraged as they provided protection against severe storms. The Great voyages of the 15th century and the discovery of America by Columbus in 1492 accelerated the number of the mills built in the following century. In 1613, the French aided by Micmac Indians introduced the first double function tide mills, which made use of both incoming and outgoing tides, at Port Royal (Nova Scotia) in North America. Later in 1635, the fust tide mill in the United States was built in Salem (Massachusetts). The growth in the number of mills along the Atlantic coast during the 17th and 18th centuries was attributed to the development of grain crops and the colonization of America. During the 19th and 20th centuries, tide mills were built in Spain, in the North, and around Cadiz. Overall, approximately 800 mills were built on either side of the Atlantic and the North Sea, with over 500 mills on the European littoral. All of these mills were of local importance with the entire industry of the village centered on the mill. The idea of tide mills thus dotted the coasts of England, Wales, France, Portugal,

Spain, Belgium, the Netherlands, Germany, Denmark, Canada, the United States, and China. Despite the mechanical energy produced (30-100 kW) being sufficient for local needs, by the mid-20th century, the use of tide mills declined dramatically as a result of the appearance of the electric motor, need for long-distance transmission of energy, and the advent of power economics. The doom of tide mills started in England and Wales around 1900. Though some of these mills survived World War II, by 1950 they were either abandoned or converted for other uses. The mills in Spain and France also closed down during this period.³⁰

3.3.6.2 TIDAL POWER PLANTS (TPPS)

Tide mills may be considered as the forerunners of TPPs that generate electricity. Both the tide mill and TPP comprise a powerhouse, a barrage, and a retaining basin. While the mill transforms the extracted energy into mechanical power, the TPP using tidal turbines transforms kinetic energy into electrical energy. The design of a typical tidal turbine is very similar to that of an offshore wind turbine; however, the former can function independently of weather and climate change. At present, there exist more than 30 different tidal turbine designs under different stages of development: with MCT SEAGEN geared tidal turbine as one of the most advanced ones. Basically, the exploitation of tidal energy involves two approaches. The first one utilizes the rise and fall of the sea level through entrainment which includes either the traditional barrage method or the lagoons. The second approach is analogous to the harnessing of wind power, that is, it utilizes the local tidal currents. The most common and simplest form of power generation is the ebb-flow generation. However, it is also possible to reverse the process and generate power using the flood tide instead of the ebb tide. Another possible mode of operation makes use of both the ebb and flood tide to generate electricity. Due to the high cost for the construction, operation, and maintenance of TPP, only a few commercial projects have been commissioned to date.

Since the 1920s, the idea to transform the ocean’s energy into electricity has been formulated with several abortive attempts. A serious proposal for barraging or damming the Severn estuary, with a mean tidal range of 8 m, was made in 1925, and this particular option continued to be examined till 2010. However, following the Severn Tidal Power Feasibility Study (2008- 2010), the British government concluded that there was no strategic case for building a barrage but to continue to investigate emerging technologies.

Iii 1930, the United Kingdom built a TPP with a 16-kW scheme installed at Avonmouth Docks. Apart from small plants built in China during the late 1950s, it was in 1966 that the world’s first commercial TPP was built by Electricite de France on the Ranсe Estuary in Brittany, France. The La Ranсe tidal power station is a typical example of a tidal energy barrage system. It consists of 24 bulb tidal turbines with a power rating of 10 MW each, thereby having a total power rating of 240 MW. The turbines are placed along with a dam-like structure that directs the energy of the incoming tide directly through the turbines, forcing the blades of the rotor to rotate. The kinetic energy of the rotors is then converted to electricity by the built-in generator. In 1968, Russia began operating a TPP at Kislaya Guba, with a power rating of 0.4 MW. The Kislaya Guba tidal power station too employed a bulb turbine. The Annapolis Royal Generating Station built in 1984 in the Bay of Fundy in Nova Scotia, Canada, is the only tidal electricity generating station in North America. With doubts expressed as to the economic returns while using a bulb turbine, the Annapolis Royal Generating Station utilized the Straflo turbine; a straight-flow turbine with rim type generator. The turbine was, in fact, a modified version of the axial flow turbine patented by Leroy Harz in 1919 and was suggested as a more economic and better efficient system. The Straflo turbine has a generator built into the rim of the turbine runner, enabling the unit to operate in low-head conditions while keeping most of the generator components out of water. It has a power rating capacity of 18 MW. Being installed only in Annapolis power station, the experience with the 18 MW Straflo turbine design is limited.³¹ Though since the 1950s China has installed several small-sized power stations, it was only in 1986 that a large-scale power station, the Jiangxia tidal power station, was established with a power rating capacity of 3.9 MW. The Haishan and the Rushankou power stations are other tidal power projects of China.³² The Uldolmok Tidal Power Station is the first plant commissioned by the South Korean government with a power rating of 1 MW. Later in 2011, another tidal power station of Korea, the Sihwa Lake Tidal Power Station, with an installed capacity of 254 MW became the world’s largest power station. It employs the bulb turbine but, unlike most TPPs, power is generated only with tidal inflows. The Swansea Bay tidal lagoon project (United Kingdom) and the MeyGen tidal array project (Scotland) are some of the large-scale tidal projects currently under development. The European Marine Energy Center (EMEC) established in 2007 is the world’s first dedicated marine energy testing center to be fully equipped for the testing of tidal and wave energy technology. A similar testing facility, Fundy Ocean Research Centre for Energy, was undertaken by Canada in 2009 in the Minas Passage area of the Bay of Fundy.

In addition to the substantial up-front investment of time and money for its development, tidal barrage systems also cause considerable environmental changes. Artificial lagoons that enclose only an area of coastline with a high tidal range are a proposed alternative to tidal barrages, which often consists of structures spanning the entire estuary. The Swansea Bay in the United Kingdom and the Yalu River in China have both been suggested as potential locations for artificial lagoon-style power plants. However, many planners and engineers favor the development of a tidal current system with respect to a tidal entrainment system, mainly because it is cheaper to implement and has a comparatively lesser impact on the environment. The earliest documented attempts to harness the power of tidal currents began in the early 1990s in the waters of Loch Linnhe in the Scottish West Highlands. The project involved a turbine held mid-water using cables hanged from a seabed anchorage to a floating barge. Planning and development of tidal current powered systems were carried out during the mid-to-late 1990s, and it was only fr om the beginning of the 21st century that such systems were ready to be tested. In 2001, in the Strait of Messina along the Sicilian coast (Italy), a large floating vertical axis Kobold turbine with an installed capacity of 20 kW was tested as a part of the Enemrar project. Bristol-based Marine Current Turbines (MCT) Ltd., in 2002, installed a small-scale tidal power device, Aquanator, that uses rows of hydrofoils to generate electricity from water currents at the Clarence River, New South Wales, Australia. In 2003, they demonstrated a 300-kW horizontal axis tidal turbine, the Seaflow turbine, that they installed off the coast of Devon, the United Kingdom. MCT installed the world’s first commercial-scale prototype, SeaGen, with an installed capacity of 1.2 MW in Strangford Narrows in Northern Ireland in 2008. Later in 2018, it was successfully decommissioned after having exported over 11.6 GWlr during its lifetime. In 2003, the Hanrnrerfest Strom system installed a 300-kW pillar-nrounted horizontal axis system in a fjord environment in Norway. In December 2011, the company successfully deployed its 1 MW precommercial tidal turbine at EMEC’s tidal test site. The device delivered its first energy to the grid in February 2012. Several other models were also developed in Norway, the United Kingdom, the United States, Germany, South Korea, the Netherlands, Australia, Spain, Sweden, France, Japan, Holland, Italy, and Canada.³³

Placed stationary on the seabed, the most common tidal device typically requires a current of 2.5 rn/s or faster to produce electricity cost-effectively.

Though this may be achievable in areas with high marine current inflows, the need to gain energy from watercourses with not too low current velocity remained unmet. This led to the invention of tidal kite turbines by Vienna Austrians Ernst Souczek and Wolfgang Kmentt around 1947.³⁴ Their invention consists of a holding a turbine, held to a rope anchored at the bottom of the sea, in a floating condition with the help of an underwater earner connected to the turbine, thereby creating a dynamic buoyancy. In other words, the tidal kite turbines convert tidal energy into electricity by moving through the tidal stream. Even though many others advanced the underwater kite and paravane electric generating systems, the breakthrough in the field happened to be in 2004 with the invention of the Deep Green (then called Enerkite) by Magnus Landberg. In 2007, Minesto, a Swedish marine energy company, develops two models of its Deep Green tidal kite, which is capable to operate in low-velocity (1.2-2.4 m/s) tidal currents. They began installing the infrastructure for its Deep Green pilot project at Holyhead in May 2018. Less than 6 months later, in October 2018, Minesto successfully generated electricity via slow-current water for the first time with its DG500 model turbine capable of generating 500 kW power which is equivalent to around 1800 solar panels.³⁵ Though the initial objective was to produce 10 MW to cover the energy needs of 8000 households, it has now been extended to produce 80 MW. Due to the expensive initial cost, tidal power remains a relatively new technology that holds immense potential to satisfy the increasing demand for energy.

3.3.7 WAVE ENERGY

The possibility of converting the wave energy into useful forms of energy has inspired numerous inventors resulting in the registration of more than one thousand patents by 1980. The earliest such patent was filed in Paris by Pierre-Simon Girard and his son in 1799. However, to date, no viable technology exists that has gained merit as a frilly functional commercial product capable of harnessing wave energy. In 1910, in France, Bochaux- Praceique constructed a device that utilized the wave energy to light his home at Rayon, near Bordeaux. This was the first oscillating water column (OWC) type of wave energy device to be developed. A former Japanese navy officer, Yoshio Masuda with his experiments on wave energy devices since the 1940s, may be considered as the father of modem wave energy technology. The wave energy-powered navigation buoy installed with air turbines, later named the OWC, developed by him, was commercialized in Japan since 1965. The oil crisis of 1973 created a renewed interest in wave energy as it did in other renewable energies. In 1976, Masuda promoted the construction of a barge (80 m x 12 m), named Kaimei, that was used as a floating testing platform housing several OWCs equipped with different types of air turbines. In 1974, the Salter’s duck or the Nodding duck, a laboratory prototype invented by Prof. Stephen Salter, of the University of Edinburgh, Scotland, in a small-scale controlled test could stop 90% of the wave motion with its curved cam-like body and convert 90% of it into electricity. As the oil prices went down in the 1980s, wave energy funding drastically reduced. In 1985, two full-sized (350 kW and 500 kW rated power) shoreline prototypes were installed at Toftestallen, near Bergen, Norway. In 1990, two fitll-sized OWC prototypes were constructed in Asia at the port of Sakata, Japan (60 kW) and also at Thinrvananthapurarn, India (125 kW). In 1991, a small (75 kW) OWC shoreline prototype was deployed at the island of Islay, Scotland. Recently facing the consequences of climate change, there is again a growing interest worldwide for renewable energy, including wave energy. The first commercial wave energy system, the Islay LIMPET (Land Installed Marine Power Energy Transmitter), was installed at Islay island, Scotland in 2000. The 500-kW wave energy collector decommissioned irr 2018 was connected to the national grid. The first-ever wave farm was constructed by the Scottish company, the Pelamis Wave Power off the coast of Portugal in 2008. The farm started delivering 2.25 MW using its three Pelamis generators. The current trials, farms, and cormnercial installations are located in Hawaii (Azura Wave and BOLT Lifesaver), Sweden (Sotenas), Spain (Mutriku Wave Power Plant), Israel (SDE Sea Wave Power Plant), and Greece (SINN Power). Currently, The European Marine Energy Centre, in Orkney, Scotland established in 2003 is the world’s first marine energy test facility and has supported the deployment of more wave and tidal energy devices than at any other site irr the world. The worldwide resource potential of coastal wave energy has been estimated to be 2.11 TW; however, at present, the energy harnessed by the wave is still minimal, with an overall capacity under 15 MW. The area with the highest wave energy potential lies in the western seaboard of Europe, the northern coast of the United Kingdom, and the Pacific coastlines of North and South America, Southern Africa, Australia, and New Zealand. Compared to wind and solar energy, government and cormnercial research and development into wave power have paled.

Ocean Thermal Energy Conversion (OTEC) method is another method of extracting energy from the ocean which utilizes the temperature difference between the deep cold ocean water and the warm tropical surface waters. However, because of the availability of only low-temperature difference (20-25 °C) and the requirement of very large volumes of water needed to be brought to the surface, electricity is generated at low efficiency. Though in 1870 the French novelist Jules Veme introduced the idea of OTEC in one of his books, it was only in 1881 that Jacques Arsene d’Arsonval, a Frenchman physicist, conceptualized the physical development of trapping theimal energy stored in the ocean. In 1930, his student Georges Claude built the first OTEC plant (22 kW capacity) inMatanzas, Cuba. Though research continued throughout the 1940s and 1950s, the availability of cheaper alternatives for power generation halted all work in the field. A more practical compact and economic OTEC power plant was developed by J. Hilbert Anderson and Janies H. Anderson Jr. in 1962. The mid-1970s witnessed a renewed interest in OTEC research and development due to the Arab oil embargo and consequent skyrocketing of oil prices. The United States, Japan, and India each have conducted and continue to pursue research on small-scale OTEC power plants. In 2015, Makai Ocean Engineering launched the world’s largest operational OTEC power plant (100 kW capacity) at the Natural Energy Laboratory of Hawaii Authority. Capable of producing electricity 24 h a day throughout the year, it was connected to the US electrical grid in August 2015.

As most of the tidal and wave energy projects established are relatively small-scale demonstration and pilot projects of less than 1 MW, ocean energy represents the smallest portion of the renewable energy market. Marine energy (Table 3.9) (wave, tide, and ocean energy) generation capacity reached 532 GW in 2018, with only 2 GW additions in the last year.¹⁹ More than 90% of this total is contributed by two large tidal barrage facilities (Table 3.10). By the end of 2018, there were more than 90 tidal power technology developers all around the world, with more than half of them employing a horizontal axis turbine. Other tidal devices included the vertical axis turbines, oscillating hydrofoil, Archimedes screw, and Venturi as well as tidal kites. With respect to wave energy converters, there were at least 200 companies developing wave energy converters of various types including attenuator, point absorber, oscillating wave surge converter, OWC, overtopping/tenninator device, rotating mass, bulge wave, and others. Though development activities to harness the enormous potential of the ocean are being carried around the world, the resource remains largely untapped.

TABLE 3.9 Marine Energy Capacity Installed Worldwide (2017-2018).

GW, gigawatts.

Source: IRENA (2019).

TABLE 3.10 Biggest Tidal Power Plants Constructed in the World.

MW. megawatts.

3.3.8 BIOENERGY

Bioenergy is considered as a renewable source of energy as it refers to energy obtained from recently derived organic materials such as wood, agricultural crops, or organic waste. On the other hand, although fossil fuels are originally derived from organic matter, they are considered as a nonrenewable source of energy, as they are formed over many millennia through several biological and geological processes. Energy obtained from biomass may be used for the production of transportation fuels, electricity, heat, and other products. Even though accepted as a renewable source of energy, biomass at the point of combustion is not carbon neutral. In fact, biomass is less energy-dense than fossil fuels and contains higher quantities of moisture and less hydrogen, thereby emitting more GHGs per unit of energy produced than fossil fuels. It must, however, be noted that while the burning of fossil fuels releases carbon that has been locked up in the ground for millions of years, burning biomass emits carbon that is part of the biogenic carbon cycle. Proponents of the carbon neutrality of biomass also propose that during combustion, biomass releases back the same amount of CO, absorbed by it from the atmosphere during its growth phase, hence resulting in a zero-net balance of CO, emission. Though most of the governments, considering biomass as a renewable energy source, promote its use as a green solution to climate change, the scientists, as well as the environmentalists, have been raising concerns for years with respect to the emissions produced by burning biomass.

With the controversy over whether bioenergy is clean energy or not still persisting, a brief history of our dependence on bioenergy is outlined. Biomass-based energy is the oldest source of consumer energy used since the dawn of human civilizations for heating and cooking, and is still the largest source of renewable energy used worldwide.

3.3.8.1 BIOPOWER: HEAT, LIGHTING, AND POWER GENERATION

Solid biofuels: Prior to the 19th century, wood was the primary fuel for the whole world for heating and cooking. Interestingly, prior to the early 20th century, in the United States, wood-buming fireplaces, cookstoves, and heaters were commonly found in households. Interpolation studies conducted by FAO suggest that wood used for bioenergy production increased from 2 billion m³ in 1970 to 2.6 billion m³ in 2005. This indicated that by 2030, approximately, 3.8 billion in³ would be needed. However, the use of energy- efficient woodstoves in developing countries has significantly reduced the consumption of firewood. Even then, today nearly 40% of the world population mainly belonging to rural areas of developing countries in Asia and sub-Saharan Africa rely on firewood to satisfy their energy demands.³⁶ Cellulosic biomass has also been used traditionally for heat in the past and ash obtained then is used as fertilizers. While the combustion of firewoods is the most energy-efficient way to utilize bioenergy, it being bulky could not be used for small automated heating systems for controlled fuel value. This led to the increased use of wood chips for heating and electricity generation since the beginning of the 21st century. Being expensive than firewood, wood chips are not used in rural areas of developing countries. In the United States, however, wood chips are less expensive than firewoods and so are widely used for heat, hot water, and electricity. Cofiring in which wood chips are combusted along with pulverized coal to drive steam turbines is also being practiced. With incentives being available in the form of Renewables Obligation Certificates for electricity and Renewable Heat Incentive in the

United Kingdom, the use of biomass for energy needs lias increased significantly in the last years. In the United Kingdom, wood chips used to feed large power plants are imported from North America and Latin America and constituted about 51 million tons a year in 2013. There exist about 3019 such plants that use wood chips as its fuel source in Europe.³⁶ In the United States, there exist 222 power plants directly fueled using wood chips with an annual production of 57.6 billion kWh of electricity from wood chips, thereby accounting for 1.42% of the total produced electricity. The world biopower generation capacity was 70 GW in 2010, and it is projected to increase to 145 GW by 2020. With respect to wood chips, wood pellets as well as other biomass pellets are more processed biofuel products hence making them more expensive than wood chips. Thus, the use of wood pellets is limited to residential heating of developed countries. Wood pellets are also used for power generation in countries like China, the Netherlands, the United Kingdom, Japan, and Germany. The global production of wood pellets in 2012 was 19.1 million tons, and the projected increase in 2020 is 45.2 million tons. The rapid increase in wood pellet production in different countries poses severe environmental hazards as more forests and wetlands are being cleared. Woodfire with a typical temperature below 850 °C is unable to melt metals. To overcome these drawbacks, charcoal was produced by the heating of wood in a kiln or retort at about 400 °C in the absence of air until no visible volatiles are emitted. The use of charcoal in metallurgy can be traced back to the Bronze Age (around 3000 b.c.e.). In China’s Tang Dynasty (700 c.e.), charcoal was designated as governmental fuel for cooking and heating. With an energy content of 28-33 MJ kg"¹, it bums without smoke and flame giving a temperature as high as 2700 °C. Today charcoal is usually made into briquettes for barbecuing and also continues to be used for cooking, heating, air, and water purification, art drawing, as well as steel-making. In 2015, worldwide an estimated 3.7 billion m³ of wood was extracted from forests, of which 50% (i.e., 1.86 billion m³) was used as fuel by either directly burning or by converting into other forms of wood fuel. Of this 1.86 billion m³, 17% (i.e., 315 million m³) was used as charcoal. More than half of this was produced in Africa (62.1%) followed by America (19.6%) and Asia (17%) with small quantities in Europe (1.2%) and Oceania (0.1%). In 2018, the global production of wood pellets for producing electricity and heat reached an estimated 35 million metric tons. The largest producer and exporter of wood pellets in 2018 was the United States (7.3 million tons). Unsustainable wood harvesting and production of charcoal can cause emission of GHGs along with forest degr adation and deforestation. However, the impact can be lessened to a certain extent if charcoal is produced via sustainably managed resources and improved technologies. Though renewable electricity generation sources like wind, solar, and hydro can replace fuelwood and charcoal, the requirement of large up-front investment for them causes the latter to be preferred more.

Wood was the first fuel used for lighting. Resinous pitch oozing from coniferous trees was found to be very flammable and luminous when burned and so were used as torches almost 3000 years ago. By medieval times, the processing of pitch from coniferous trees became a trade governed by guilds. Archaeological evidence of oil being burned in lamps originated almost 4500 years ago in the ancient city of Ur, Mesopotamia. Olive and sesame oils were most commonly used during this period. Since the early Egyptian civilization, tallow (rendered and purified animal fat) has been used for lighting, initially, within lamps, but later began and continued to be used to make candles for almost 2000 years. The pithy stalk of rushes was dipped in animal fat, and a prototype of the candle was made in Egypt. When dried and used, it burnt brightly. These were also used throughout Europe, and in some places, they continued to be used until the 19th century. Evidence of modem candles consisting of a small wick and a thick, hand-formed layer of tallow emerged from Rome during the first century c.e. Annual oils, especially from fish and whales, were used in Northern Europe. Around the 18th century, sperm whale oil was found to be an excellent illuminant and became widely used in colonial America. Far more superior candles were produced when in 1825 French chemists Michel Chevreul along with Joseph Gay patented stearin, a tallow derivative. Ethanol became a common fuel, as feedstock was abundant, and it could be produced by anyone with a still. In the early 19th century, lamps burned many different fuels including all kinds of vegetable oils (castor, rapeseed, peanut, and olives), animal oils (especially whale oil and tallow fr om beef and pork), refined turpentine from pine trees, as well as alcohol (especially wood alcohol and grain alcohol). By the 1850s, the US patent office recorded almost 250 different patents for different fuels, lamps, wicks, and burners used for illumination, hr the 1820s, the most common fuel used was a dangerous mixture called the burning fluid composed of turpentine and alcohol, and was popularized by Isaiah Jennings in New York in 1830. In 1835, a mixture of one part turpentine with four parts alcohol and a small amount of camphor oil extracted from the camphor tree (used for aroma) was patented by Henry Porter of Bangor, Maine and came to be popularly known as the “Porter’s burning fluid.” Despite the risks associated with the mixture, its demand increased, hr 1856, Henry Porter’s business in Boston was taken over by Rufus H. Spalding, who then became the sole manufacturer of Porter’s Patent Composition. And so alcohol blends replaced the expensive whale oil by the late 1830s in most of the country. By 1860, thousands of distilleries churned out at least 90 million gallons of alcohol per year for lighting. However, with the isolation of paraffin wax from petroleum products in 1830, high-quality candles began to be made from it cheaply. The candle industry thus made a transition from biomass-based to petroleum-based industry around the 1860s. With the advent of kerosene, coal gas, and incandescent light bulb, the candle industry declined.³⁷

Gaseous biofuels: Anecdotal pieces of evidence suggest that biogas was used in Assyria back in the 10th century b.c.e. for heating bathwater. However, it was only in 1630 that Jan Baptista van Helmont, a Belgium scientist, found that the decaying organic material produced flammable gases. Later in 1776, Count Alessandro Volta concluded that there was a direct correlation between the amount of organic matter decaying and the amount of corresponding gas produced. During the period between 1804 and 1808, John Dalton and Humphrey Davy working independently established that the combustible gas produced was methane, hi 1859, the first recorded anaerobic digester plant was established in Bombay, India. A Frenchman in 1881 developed a crude version of the septic tank, named “automatic scavenger,” to treat wastewater via anaerobic digestion. The success of the anaerobic digester resulted in the introduction of this system in the United States in 1883. In 1895, the term “septic tank” was coined by Donald Cameron, an Englishman who constructed a watertight covered basin to treat sewage by anaerobic decomposition. The increased efficiency and successful treatments of septic tanks inspired the local government of Exeter, England, to make use of the methane evolved from septic tanks for lighting its streets in 1895. Commercial use of biogas in China has been attributed to Guorui Luo who in 1921 constructed an 8 m³ biogas tank fed with household wastewater. Microbiological research work in an attempt to identify best anaerobic bacteria and digestion conditions for promoting methane production was conducted by US scientist A.M. Buswell and his colleagues in the 1930s. The sharp rise in fossil fuel prices in the early 1970s stimulated interest in the use of anaerobic digestion systems for energy as well as industrial wastewater depollution.³⁸ Currently, worldwide there exist approximately 50 million microscale digesters with almost 42 million of those operating in China and another 4.9 million in India. Almost 700,000 biogas plants operate in the rest of Asia, Africa, and South America. These microscale digesters may be operated as stoves for heating and cooking, thereby replacing the high emission solid fuels like firewood and charcoal. The generation of heat and electricity using a combined heat and power plant is an established technology used worldwide. Electricity generation via biogas plants increased from 46,108 GWh in 2010 to 87,500 GWli in 2016 (a growth of almost 90% in 6 years), hi 2018, there were more than 10,000 digesters in Europe as well as almost 2200 sites in all 50 US states producing biogas for electricity and heating.

Upgradation of biogas to biomethane plants, though new, is now a proven technology. Globally, there exist almost 700 plants that upgrade biogas to methane. There are over 540 upgrading plants in Europe, followed by 50 in the United States, 25 in China, 20 in Canada, and the remaining few in Japan, South Korea, Brazil, and India. While certain plants upgrade biogas to be used as vehicle fuel, others inject it to the local and national grid. Many plants are also beginning to capture CO, to be used in greenhouses and the food and drink industry.³⁹ Syngas produced via the gasification or pyrolysis of plant materials is another gaseous biofuel that can also be used dir ectly to generate electricity. The raw material most commonly used for syngas production is woody biomass low in nitrogen and ash content. Global biopower capacity increased by almost 6 GW in 2018 reaching an estimated 115.7 GW.¹⁹ The total electricity generated via biomass increased by 9% from 532 TWli in 2017 to 581 TWli in 2018. While the European Union remained the largest generator of bioelectricity by region, the country which produced the largest amount of electricity was China. Other major producers of bioelectricity were the United States (69 TWli), Brazil (54 TWli), Germany (51 TWli), India (50 TWh), the United Kingdom (35.6 TWli), and Japan (29 TWli).

3.3.8.2 BIOFUEL

Currently, biomass is the only renewable source of feedstock material to produce liquid fuel. The history of biofuels roots back into the earliest automotive days during which the first cars were built to run on biofuels rather than fossil fuels. In 1826 in the United States, Samuel Morey developed the first internal combustion engine (ICE) which used a mixture of turpentine and alcohol to power a small boat up the Connecticut River at 7 and 8 nipli (miles per hour). German engineer Nikolaus August Otto in 1860 developed another ICE that ran on ethanol fuel blend. During the 1860s, the main obstacle which prevented ethanol from being used as an engine fuel in the United States was the imposition of tax on alcohol to fund the civil wars.

Henry Ford, in the period between 1908 and 1925, mentioned ethanol as the fuel of the future and used it to power tractors and his model T cars. The United States witnessed an increased demand for ethanol as necessitated by the shortage of raw materials and natural resources during the years of World War. The 1973 oil crisis further spurred interest in the use of ethanol as a fuel. The fust pilot bioethanol plant with a distillation column was established at South Dakota University in 1979. During the 1980s, the US Environmental Protection Agency (EPA) headed gasoline phaseout resulted in increased demand for ethanol as an octane booster and volume extender. Throughout the 1990s, methyl tert-butyl ether (MTBE) derived from fossil fuels was used in most of the oxygenated gasoline markets. However, restrictions on the use of MTBE as a fuel oxygenate led to the rapid growth of ethanol production in the United States since 2002. Fermentation of vegetable biomass results in the production of ethanol. Starch/sugai-based crops such as sugar cane, sugar beet, sweet sorghum, com, wheat, barley, potato, yam, and cassava are used for the commercial production of bioethanol. Bioethanol produced from such food crops is called “first generation” biofuels, while that produced from non-food crop lignocellulosic plant materials is called “second-generation” biofuel. World’s fust commercial-scale cellulosic ethanol plant, the Cres- centino Biorefinery, Crescentino, Vercelli in Italy started operating in 2013. Run by the Italian company Beta Renewables, it has an annual production of 20 million gallons of ethanol. Coimnercial production of second-generation ethanol is expected to grow in the future, as an alternative to gasoline. “Third-generation” biofuels based on improvements in the production of biomass takes advantage of energy crops such as algae. The world’s largest ethanol producers, POET and Ar cher Daniels Midland, are from the United States. The global coimnercial bioethanol production has increased from 15.1 billion liters in 1990 to 106 billion liters in 2018.⁴⁰

In the 1890s, Rudolf Diesel invented the diesel engine which ran on different fuels including vegetable oil. A French Otto Company at the World’s Fair in Paris at 1900 demonstrated a peanut oil fuel-based diesel engine. However, widespread availability and low price of fossil fuels discouraged further research for developing vegetable-based fuel. Still, experiments conducted in various countries identified that the main problem with using vegetable-based fuel to run diesel engines was its high viscosity. During World War II, fuel shortages necessitated research to find ways to convert vegetable oil to diesel. Several attempts were made to overcome the problem associated with the high viscosity of vegetable-based fuels, hi 1937, George Chavanne, a Belgian scientist, presented and patented the “Procedure for the transformation of vegetable oils for their' uses as fuels.” It was the Brazilian scientist, Expedito Parente, who developed the first industrial-scale biodiesel production process in 1977. Later in 1989, the world’s first commercial-scale biodiesel plant which produced biodiesel from rapeseed began operation in Asperhofen, Austria. The world production of biodiesel has steadily increased from 7.4 million tons in 2000 to 45 million tons in 2019.

Both biodiesel and bioethanol display comparatively higher oxygen content and greater dissolution capacity with respect to fossil fuels and hence are corrosive to the engine, fuel storage, as well as to the distribution system. In order to overcome these problems, drop-in biofuels are suggested as an alternative. As the name suggests, they can be readily dropped into the existing fuel system without any significant modification in engine or infrastructure. Drop-in biofuels, currently at the research and development stage, are biomass-derived liquid hydrocarbons that are functionally equivalent to the existing petrol distillate fuel. Currently, the dominant pathway to making drop-in biofuels is the oleochemical/lipid pathway wherein animal and vegetable oils are hydrotreated to produce biofuels. To date, this remains the only pathway to produce significant amounts of drop-in biofuel. Currently, the commercialization of this technology is still in progress.

In an attempt to produce fuels similar to fossil fuels, human beings began treating vegetative biomass in a simulated high-temperature (300-900 °C), high-pressure, oxygen-free environment. However, the final product of such pyrolysis: biochar (the black, solid residue), bio-oil (the brown vapor condensate), and syngas (the uncondensable vapor) was little like fossil fuels. Although about 3000-5000 years ago, a similar technique was used in ancient China and by indigenous Amazonians to produce charcoal and biochar, respectively, the pyrolysis of biomass to produce bio-oil for use as fuel is quite recent. There are basically two types of pyrolysis with respect to the heating rate: fast pyrolysis and slow pyrolysis. Since the development of fast pyrolysis, various types of reactors (bubbling fluidized bed, circulating fluidized bed, ablative pyrolysis, vortex, rotating cone pyrolysis, vacuum, etc.) have been developed since the 20th century for the production of bio-oil.⁴¹ Though containing combustible components, crude pyrolysis bio-oil due to its high moisture and acid content is instable, corrosive, viscous, and difficult to ignite thus requiring significant upgradation before it can be used as a petrol distillate fuel alternative. The past few decades have investigated a number of techniques (e.g., hydrogenation, esterification, emulsification, etc.) to upgrade crude bio-oil to use as a substitute for heavy fuel oils to power static appliances such as electric generators, turbines, furnaces, engines, and boilers. The bio-oil produced is used as heating fuel and sometimes as potential industrial feedstock material for chemicals, lubricants, thickeners, paints, and so on. Although there are a number of pilot plants that convert woody biomass to bio-oil, techniques that are economically feasible and industrially applicable are still under development. Hence, commercial production, as well as utilization of biofuel as a petrol fuel alternative, faces many technological challenges.

At present, the volume of renewable diesel in the world is about 5 billion liters, and production is mainly dominated by freestanding facilities based on hydrotreating.⁴² In 2018, with increased production of 10 billion liters made in the year, the global production of all biofuels (ethanol, biodiesel) reached a total of 154 billion liters. The United States and Brazil have dominated the biofuels market together producing nearly 70% of all biofuels in 2018, followed by China (3.4%), Germany (2.9%), and Indonesia (2.7%).⁴³