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Über dieses Buch

This is the first book dedicated to solar gas turbines, providing fundamental knowledge and state-of-the-art developments in the field. A gas turbine is a heat engine in which a mixture of fuel and air is burned in a chamber that is an integral part of the flow circuit of the working fluid. The burnt gas mixture expands and turns the turbine, which can be connected to a generator for electricity production. Solar gas turbines offer an important alternative to conventional gas turbines driven by non-renewable, polluting fossil fuels such as diesel or natural gas. The book provides a comprehensive overview of the topic as well as numerous illustrations.



Chapter 1. Introduction to Solar Gas Turbines

Fossil fuels are the main source of primary energy worldwide. Nevertheless, heavy reliance on these fuels is contributing to environmental degradation. In addition, concerns about energy security are arising from the consideration of depletion of the reserves of fossil fuels, fossil price fluctuations, rising competition from evolving consumer countries, political conflicts in areas which are rich in hydrocarbons and high economic impacts which ensue when there is disruption in the energy supply. In this vein, international and national policies are being reviewed to increase the share of renewable energy in the energy mix. A gas turbine engine is one of the technologies which can be driven by renewable energy resources such as solar radiation and biofuels. This engine exhibits higher thermodynamic performance compared to the widely exploited steam cycle. Existing gas turbines are designed to operate on conventional fuels and, therefore, they need modification before solar energy can be integrated on the inlet side of the turbine. Solar radiation can be converted to high-grade heat (up to 1773 K) using concentrating solar power technology. These levels of temperature are suitable for solarisation of the gas turbine system.

Amos Madhlopa

Chapter 2. Gas Turbine Fuels and Fuel Systems

Fossil fuels, especially oil and gas, are the major sources of heat for conventional gas turbines. The heating value of a fuel (Hf) is one of the most important factors to consider when choosing a fuel. Traditionally, gas turbines operate on high calorific fuels such as natural gas (Hf = 39–46 MJ kg−1) and Diesel no. 2 fuel oil (Hf = 42 MJ kg−1). A recent estimation of the reserves of fossil fuels shows that the production of these fuels will be constrained by the projected reserves. Consequently, there is a need to find alternative sources of energy, and biofuels are promising to be a sustainable option of supplying energy. Combustibility of biofuels has been demonstrated at laboratory and pilot scales. Nevertheless, combustion difficulties such as atomization and emission of NOx are still challenges to the wide-exploitation of biofuels in the gas turbine engines with the present combustion features. Nuclear energy is another possible source of heat for driving gas turbines but commercial nuclear power plants are commonly based on the steam Rankine cycle. Research work is going on in the area of high-temperature gas reactors for exploitation with closed cycle gas turbines.

Amos Madhlopa

Chapter 3. Solar Radiation Resource

The sun is the main source of renewable energy. It emits radiation at an equivalent black body temperature of about 6,000 K with a constant intensity outside the earth’s atmosphere. Only direct (beam) radiation is available outside the earth’s atmosphere. As solar radiation propagates through the atmospheric matter, it is attenuated, producing direct and diffuse components which reach the earth surface. Only the direct component can be focused and is, therefore, useful in the development of concentrating solar power (CSP) technologies. Absorption of solar radiation by a receiving surface is maximum when the angle of incidence is zero, and the surface is said to receive direct normal irradiation. The recommended minimum annual sum of direct normal irradiation for CSP technology to be economically viable is 2,000 kWh/m2, and many locations within the sunbelt meet this threshold. It has been found that the worldwide technical potential of CSP is estimated at 3,000,000 TWh/year which significantly exceeds the world electricity consumption level of about 29,000 TWh/year in 2015. This level of solar energy resource availability is attractive for the advancement of the solar gas turbine technology.

Amos Madhlopa

Chapter 4. Main Components of Solar Gas Turbines

Major components of a solar gas turbine (SGT) for generating electricity are solar field, compressor, combustion chamber (combustor), turbine and generator. The solar field comprises concentrators and receivers. Four widely exploited concentrating solar power (CSP) technologies are the parabolic trough concentrator (PTC), linear Fresnel reflector (LFR), parabolic dish concentrator (PDC) and solar tower (ST). Of all the CSP technologies, the ST system exhibits the highest potential for solarisation of gas turbines. The compressor helps to increase the pressure of the working fluid before it enters the solar receiver (or combustor where combustion of fuel–air mixture proceeds). Pollution control is one of the factors that influence the design of modern combustors. Turbines operate at very high temperatures and so they need to be cooled to avoid overheating and material failure. To enable generation of electricity, an electric generator is linked to a turbine. Many processes take place in a SGT, which require proper control to ensure the right output is obtained at a given time. A detailed discussion of the major gas turbine components has been presented in this chapter. It is shown that the receiver and combustor are critical components in the development of the SGT system.

Amos Madhlopa

Chapter 5. Thermodynamic Cycles of Solar Gas Turbines

Thermodynamic cycles play a vital role in the development of solar gas turbines. Currently, the Rankine cycle is the most-widely exploited engine cycle in concentrating solar power (CSP) technology. However, this cycle exhibits high loss of low grade heat at the condenser. In view of this limitation, researchers are paying attention to gas cycles. The Brayton cycle (gas turbine) is a good candidate for solarisation because it has a higher thermodynamic efficiency than the Rankine cycle. Based on flow path, gas turbines are classified into three basic types: (a) closed cycle gas turbine (CLCGT), (b) open cycle gas turbine (OCGT) and (c) semi-closed cycle gas turbine (SCLCGT). It is also possible to combine the Brayton cycle with a bottoming cycle such as the Rankine cycle to yield a combined cycle which is advanced with high thermodynamic efficiency (>50%). Many studies have examined the solarisation of the CLCGT and OCGT systems. In spite of the environmental and other potential benefits of the SCLCGT, integration of this cycle with the CSP technology is scarce. So, a conceptual semi-closed cycle solar gas turbine (SCLCSGT) has been proposed in this book.

Amos Madhlopa

Chapter 6. Configurations of Solar Gas Turbines

Components of a gas turbine can be assembled together in many ways, thereby yielding a wide variety of system configurations. It is possible to use multiple units of each type of component (such as compressor, combustor, turbine and shaft). The configuration of a gas turbine, which is also influenced by the intended application, affects the optimal performance of the system. This flexibility in gas turbine configuration provides a good opportunity for the development of the solar gas turbine (SGT) technology. Major configurations of SGTs can be generally classified into solar-only or hybrid categories. Recovery of heat from the exhaust helps to augment the efficiency of the power plant. In this vein, a review of the literature shows that both recuperative and regenerative types of heat exchangers were used on the exit side of the turbine in previous work. Based on the theory of heat exchangers, it is shown in this chapter that recuperative exchangers are most suitable for heat recovery downstream of the turbine. Hybridization and inclusion of a thermal storage unit enhance the performance of SGTs.

Amos Madhlopa

Chapter 7. Design and Testing of Solar Gas Turbines

System design and testing are important processes in the development of any technology. Usually, it is desirable to theoretically optimize the design of a solar gas turbine (SGT). Based on simulation results, a real SGT system can be constructed and tested. At present, prototyping of SGTs is based on modification of the existing conventional gas turbine engines. A review of previous work shows that there is a deficiency in Standards for testing of concentrating solar power technologies. Some initiatives are under way to bridge this gap, which may also facilitate the development of relevant standards for testing SGTs. A limited number of projects have been implemented to test the performance of SGTs. Most of these projects are at demonstration scale, and there is lack of commercial-scale SGT power plants. Some challenges to the development of the SGT technology have been presented and discussed.

Amos Madhlopa

Chapter 8. Economic Performance of Solar Gas Turbines

Usually, decision-making about project development is influenced by the costs and benefits over the lifetime of a project. Costs and benefits of a project can be analyzed using several methods, which fall into two groups: (a) methods without time value and (b) those with time value of money. Two widespread indicators of methods without time value are payback period and average rate of return on investment. However, cash flows take place over a certain period of time. Consequently, methods with time value are more relevant, and they include net present value, discounted payback, internal rate of return and levelized cost of energy (LCOE). Some advantages of LCOE over NPV are: (a) the absence of restrictions on project scale, (b) LCOE is independent of energy technologies, and (c) LCOE is applicable even when energy technologies are of different types. Attractive theoretical values of LCOE have been reported (as low as 0.06 US$/kWh) for solar gas turbines (SGTs), which compare very well with LCOE values (0.092-0.095 US$/kWh) for some coal power plants. This indicates that the economic performance of the SGT technology is theoretically approaching parity with conventional thermal power plants.

Amos Madhlopa


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