Design and Implementation Issues for Hybrid Renewable Energy System (HRES)
There are two types of renewable energy sources; dispatchable like biomass, geothermal, and hydro and non-dispatchable like solar and wind. Unlike dispatchable renewable energy sources, non-dispatchable sources are available in most parts of the world and they are often preferred. To overcome the intermittency and uncertainty of non-dispatchable renewable sources and to provide an economic, reliable, and sustained supply of electricity, a modified configuration that integrates these renewable energy sources and uses them in a hybrid system mode is proposed by many researchers. Hybridization of different alternative energy sources can complement each other to some extent and achieve higher total energy efficiency than that could be obtained from a single renewable source. Multisource hybrid renewable energy systems, with proper control, have great potential to provide higher quality and more reliable power to customers than a system based on a single source. Hybrid Renewable Energy Systems (HRES) work in stand-alone or grid-connected mode [41]. Due to this feature, hybrid energy systems have caught worldwide research attention.
The applications of hybrid energy systems in remote and isolated areas are more relevant than grid-connected systems. Hybrid energy systems are now becoming an integral part of the energy planning process to supply previously unelectrified remote areas (see Chapter 6). In addition, the application of hybrid systems is becoming popular in distributed generation or microgrids, which recently have great concern. Due to advances in renewable energy technology which have improved their efficiency and reduced the cost and the advances in power electronic converters and automatic controllers which improve the operation of hybrid energy systems and reduce maintenance requirements, these advances have made hybrid systems practical and economical. Various hybrid energy systems have been installed [9, 12-22, 31-34, 40] in many countries over the last decade, resulting in the development of systems that can compete with conventional, fuel-based remote area power supplies in many applications.
Buildings, both residential and commercial, are a major source of environment pollution (about 30%-40% of CO, pollution is connected to the buildings). In recent years, a significant push is made toward zero energy buildings and other home energy systems using renewable sources. This push has also made residents of buildings not only energy consumers but also prosumers. This will create, as shown in Figures 1.2 and 1.3, enormous growth in both home and building energy management systems. The use of PV-battery and other hybrid renewable energy system is on meteoric rise.
The design process of hybrid energy systems requires the selection and sizing of the most suitable combination of energy sources, power conditioning devices, and energy storage system, together with the implementation of an efficient energy dispatch strategy [6]. The selection of the suitable combination from renewable technology to form a hybrid energy system depends on the availability of the renewable resources in the site where the hybrid system is intended to be installed. In addition to the availability of renewable sources, other factors may be taken into account for proper hybrid system design, depending on the load requirements such as, reliability, greenhouse gas emissions during the expected life cycle of the system, efficiency of energy conversion, land requirements, economic aspects, and
FIGURE 1.2 Growth in home energy management system revenue. Source: Advanced Energy Now, 2017 Market Report, prepared by Navigant Research, 2017 [41].
FIGURE 1.3 Growth in building energy management system revenue. Source: Advanced Energy Now, 2017 Market Report, prepared by Navigant Research, 2017 [41].
social impacts [9, 12-22, 31-34, 40]. The unit sizing and optimization of a hybrid power system play an important role in deciding the reliability and economy of the system.
As mentioned above, integrating renewables into the electricity grid has obvious environmental benefits. But upgrading a vast infrastructure made up of thousands of individual utility companies and a web of high-voltage transmission lines is complicated. The grid was built under a one-way model, in which power is generated at centralized sites and sent through distribution lines to end users. Renewable energy generation facilities—particularly solar and wind—are more widely distributed. Solar and wind farms can feed into the main energy grid, and small-scale installations can be plugged directly into homes. This means that the power coming into the grid from such sources on very sunny or very windy days represents a supply of excess energy that can be redirected through the grid to where it’s needed the most. In addition to demand-side management (DMS) tools like variable pricing for electricity use, new' forms of smart grid information technology are being implemented by utility companies to balance out this two-way flow' of energy.
Improving the grid to accommodate more renewable energy also means coordinating among utilities in neighboring areas to balance demand and supply and creating better forecasts of solar and w'ind output to anticipate generation levels over the course of days. Increasing the amount of renewable energy in the grid will also require a lot of batteries. Renewable energy sources sometimes generate more electricity than is needed in real time. To maintain a utility’s capacity to provide precisely the right amount of electricity to its customers, large-scale lithium-ion batteries are now being added onto renewable power sites to store that power and distribute it as needed. These large batteries can hold multiple megawatt hours (MWh) of electricity; the average American home uses about 10 MWh per year. Getting more renewable energy into the mix of sources powering the US grid will hinge on equipping more utilities and energy producers with such batteries. A key priority moving forward will be to better incentivize the development of energy storage (homogeneous or hybrid).
The National Renewable Energy Laboratory (NREL) is exploring how to better integrate the three main grid regions that make up the US energy system. These three systems operate almost entirely independently of one another, with little ability for one to send excess electricity to help meet the demands of another. As part of its Interconnections Seam Study, NREL is working with national labs, universities, and industries to develop new ways of sharing a diverse pool of energy sources across these three systems. If successful, this effort could make it easier for abundant wind energy from Texas to power systems in states like Tennessee and Maine, or solar energy from the sunny Southwest to power homes in the cloudy Northwest.
Many believe that the need to transition the grid to better accommodate renewable energy sources will continue for the foreseeable future. Any change to the resource mix requires careful planning but we know' that a high-penetration renewable grid is feasible through improved transmission and expanded deployment of energy storage and other advanced technologies. Currently RES accounts for at least 19.5% of the global electricity. We must integrate these increasing shares of renewables into our T&D (transmission and distribution) systems as soon as possible. Renewables are already saving time and cost for utilities. For example, in 2013, Idaho Power Company (IPC) received a $94 million grant from the US Department of Energy to modernize the grid, including the development of renewable energy integration tools. As part of the grant, IPC w'as able to improve its forecasting, using 15% of natural gas-fired reserves instead of 100%. This alone resulted in savings of approximately $50,000 for the utility and its customers, and IPC is seeing similar results on a consistent basis [41].
Another challenge is the injection of reactive power into the electric grid from outside power sources, such as solar energy. The utility controls the voltage levels of its system and injects energy into the grid when necessary to smooth out the natural swings in usage and keep the voltage at an acceptable level. But by renewable energies being injected into the grid, it can throw' off a utility’s synchronous generator, making it so that they can’t track where the power is coming from. In order to incorporate renewable energies into their existing infrastructures, companies must address several primary issues that can make the system unstable:
Voltage management. It is especially important to control the voltage, and companies are looking to options such as Secondary and Tertiary Voltage Regulators; reactive power compensators such as the STATCOM (Static Synchronous Compensator); battery systems for storing energy reserves; and pole transformers for remote tap control.
Frequency control. A pow'er system often has inconsistent frequencies when adding renewable energy. Companies are searching for solutions that can adjust frequency variations within a specified range by using a faster regulated response.
Controlling output fluctuations'. Absorbing excess energy in cases of excessive output fluctuations wall help companies maintain a smooth pow'er curve.
Managing electric vehicle charging. This is an increasingly complex problem as electric vehicles become more widely adopted and rapid charging can cause a sudden increase in load to the system. Batteries can be used to store excess power, minimizing the negative effects of rapid charging on the grid.
Demand response (DR): This is one of the more commonly known solutions for managing energy and is increasingly being applied to renewables as well. DR allows for the system to automatically request that users suppress power consumption during peak hours and can automatically shift any surplus power load to a later time.
All of these issues are currently being addressed as the need for HRES increases.
