Utility Grid with Hybrid Energy System
The most basic form of power generation and transport during the last century was centralized power generation by coal, gas, or nuclear power plants and transmission of power by centralized utility or smart grid. Although this system served well urban communities, the operations were thermally inefficient, harmful to environment, and did not serve the communities who did not have access to smart grid. As pointed out in Chapter 1, efforts to integrate renewable and distributed low-density energy sources (like solar and wind) in smart grid have forced grid to be multifaceted and multifunctional in a number of different ways. First, the inclusions of renewable energy sources and homogeneous or hybrid energy storage devices made the utility grid hybrid. Second, in order to capture distributed low-density energy sources, localized microgrids are created which can either be connected to a main grid or be operated independently. Third, to provide power supply to very remote areas, off-grid hybrid renewable energy operations are created. It is clear that energy generation, storage, and transport structures became more multifaceted and hybrid in nature. Efforts to make power generation more efficient (i.e., cogeneration) or to better handle the emission of harmful C02 emission also made grid more multi-functional and hybrid. In this chapter, we address the development of hybrid utility or smart grid. Subsequent chapters will address the issues of hybrid storage, microgrid, and off-grid operations.
As pointed out above, smart grid can become a hybrid energy system in a number of different ways. In cogeneration, hybrid energy is produced from one source of power generation by utilizing waste heat for heating/cooling purposes or for generating an additional source of power. In recent years, significant efforts are being made to generate additional power from waste heat from numerous micro and macroscale operations using thermoelectricity. Large-scale power generation from coal, gas, or nuclear energy produces significant amount of waste heat, which can also be used to generate additional power (such as in combined cycle power generation) or used as excess heat for industrial or domestic heating and cooling needs. Hybrid power can also be produced, as shown by ExxonMobil, by using CO, produced from the power plant to generate more power using fuel cell technology. Thus, in these cases, hybrid energy system either improves process efficiency or reduces harmful environment impact.
The future energy industry will require less use of fossil fuel and deeper penetration of renewable sources of energy in the overall energy mix. The present book shows that the use of renewable sources (particular solar and wind energy which are intermittent) will require a hybrid mode to supply power or heat in a stable manner. Thus, a hybrid energy system will be the preferred mode for deeper penetration of renewable sources. My previous book  showed that hybrid energy can also be provided by using co-fuel (coal and biomass) or co-energy (nuclear and renewable sources) for power generation.
As mentioned in Chapter 1, this book divides grid transport into three levels: large macrogrids, microgrids, and off-grids which include mini-grids, nanogrids, and stand-alone systems for rural areas, islands, and remote locations. Large grids may be further divided into developed and developing grids. Thus grid system for power transport can be sub-divided as:
- • Large developed grid. The US electricity grid is an example of a large developed grid, providing reliable energy at a low cost. Primary storage markets for large grids include ancillary services, transmission deferral, and customer demand charge reductions. Increasing reliability and reducing diesel fuel use are not primary concerns. The use of hybrid energy in a large developed grid is discussed in this chapter.
- • Large developing grid. India is an example of a large developing grid.
A large developing grid provides low-cost energy, relative to the cost of a diesel generator, but blackouts are common. Increasing reliability is an important market for developing grids. The use of hybrid energy for a large developing grid is discussed in this chapter .
- • Microgrid. Examples may include universities, hospitals, and military bases. A microgrid is connected to a larger grid but has the ability to produce its own electricity for demand charge and resilience purposes. Microgrids may be further subdivided by the size of the load. Microgrids are created to harness distributed energy resources at medium- to low-voltage levels. Chapter 5 describes in detail the workings of hybrid microgrids.
- • Off-grid (mini-grids, nanogrids, and stand-alone systems) systems in rural, islands and remote locations. Examples include mines, off-grid communities, and, of course, islands. Islands and remote locations are not connected to a larger grid and generally face higher energy costs because most energy production comes from diesel generators. Although, as shown in Chapter 6, in recent years, HRES is penetrating more and more in off- grid operations, reducing diesel fuel use and increasing level of HRES with the help of energy storage are the primary objectives of the off-grid market.
Besides three levels of grid transport mentioned above, a hybrid energy system also contains homogeneous or hybrid storage devices which are particularly important to harness hybrid renewable sources. This is illustrated in details in Chapter 4. In this chapter we focus on the changing nature of the large developed or developing macrogrid.