Current Limits of Renewable Electricity

In the past few years, the world realized the tremendous challenge of higher consumption of electricity, as well as the waste associated with its production. Consequently, renewable energies have gained a unique position as clean substitutes for limited and polluting fossil resources.

Introduction to Various Technologies

There are four main technologies for producing electricity and heat using renewable energy sources.

Hydroelectricity is the main source of electrical power from renewable sources. For centuries already, the flow of a river has given mankind free energy for the development of a number of industrial applications. The hydro-electric dams that turn hydraulic power into electrical power mostly serve peak load requirements. They do not operate all the time and are mainly activated when a sizeable amount of energy needs to be supplied for a given period of time. The dam helps store a vital quantity of water, which can then be used when decided to rapidly supply an important amount of energy. The crucial point is to regularly reconstitute the “stock” of energy. The natural flow of the river provides this “stock“. There are also pumping stations which can use the electricity provided by other plants at times where consumption is low to pump the water back upstream from the dam in order to build “stock” (Barre and Merenne-Schoumaker 2011). This can then be reused when an additional amount of electricity is required during peak load time. When presenting hydroelectricity, one often thinks of large electric dams such as the Three Gorges Dam in China, which can produce up to 22.5 GW, or the equivalent of 20 nuclear units. There are also small hydroelectric dams which produce less than 10 MW of electricity. These plants disturb the environment to a lesser extent than large ones and are an interesting alternative for rural electrification.

The development of solar electricity has been spectacular in recent years. There are two main technologies to produce electricity out of sun power. The first one is photovoltaics. It uses sunlight to produce directly electricity from photoelectric effect in a semiconductor. This is the most deployed technology. The second is concentrated solar technology (also called solar thermal), in which solar radiation is used to heat up a coolant, similar to what happens in a thermal power plant. The vapor or gas produced is then used to activate the rotation of turbines to produce electricity via an alternator.

Wind-based electricity is also widely deployed. Wind is used to run directly the turbine which, following the same principle, produces electricity with an alternator.

Yet another energy type is geothermal energy. It recovers natural heat deep in the ground and brings it up to the surface where it is used to heat up a coolant or directly heat homes. Geothermal electricity power requires drilling more than 1500 m into the ground in order to reach high enough temperatures. When drilling is less deep, geothermal energy is essentially being used for domestic or district heating.

Finally, tidal power uses marine currents to run turbines, following the same principles as wind power.

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