Introduction and Structure - Renewable Energy: Technology, Economics and Environment - page 15

1.4.2 Power generation technologies
In the following, the main system elements of conventional power generation sys-
tems are outlined. In addition, two reference systems are defined, for which the
costs are calculated on the basis of investment, operation, maintenance, and fuel
costs. These calculations allow for a comparison of power generation by conven-
tional plants with the corresponding renewable energy option. Additionally, se-
lected environmental effects are discussed.
Economic analysis. Thermal power stations convert part of the energy contained
in fuels (e.g. hard coal, lignite, natural gas, crude oil) into electrical energy. For
this purpose, often power plants based on steam cycles and/or gas turbines are
used. In the following, the main system characteristics of such technologies are
briefly described. However, engines used for power generation by stand-alone
systems (e.g. mountain lodges), for standby power supply, and partly for covering
the peak demand, have not been addressed.
− Steam power plant. The main components of steam power plants based on coal,
natural gas or crude oil include furnace, steam generator, turbine, generator,
water cycle, flue-gas cleaning (depending on the applied fuel dust filter, flue-
gas desulphurisation and denitrification) as well as control and electro technical
devices. Coal-fired power plants additionally require fuel treatment (such as
coal grinding). To date, for the common modern hard coal and lignite fired
power plants, fuel is combusted in a pulverised way. For power plants with a
capacity below 500 MW, also fluidised-bed systems are in use. Oil and gas-
fired boilers are generally equipped with a conventional burner firing. The
downstream steam generator transfers the energy released during the oxidation
of the fuel to the water cycle, thereby generating steam which is subsequently
relieved by a multi-stage steam turbine. The thermal energy which has been
converted into mechanical energy is then transferred to a generator which
transforms it into electrical energy. To close the cycle, the steam that exits the
turbine is condensed by a cooling system and re-transferred to the steam gen-
erator by a feed-water pump. Currently, steam turbine power plants are charac-
terised by net efficiencies of up to 45 % and above.
− Gas turbine power plant. Gas turbine power plants mainly consist of turbo-
compressor, combustion chamber, turbine and generator. First, the compressor
pressurises ambient air sucked in from outside, which is subsequently trans-
ferred to the combustion chamber. Within this combustor the pressurised air
chemically reacts with the fuel under release of heat. Downstream, within the
turbine, the flue gas is relieved to ambient pressure and thus released at rela-
tively high temperatures into the atmosphere; a generator coupled to the turbine
shaft transforms the provided mechanical energy into electrical energy. With
38 %, the net efficiencies of gas turbine power plants are slightly below those