Page 307 - Handbook of Energy Engineering Calculations

fuel plants are also under development. Future developments project 1-GW
solar-power towers being used. Tax credits for solar power will help
accelerate its wide-scale adoption.
A promising application of solar energy is combining solar power with
conventional combined-cycle (steam- and gas-turbine) power plants. The

solar power is integrated with the combined-cycle steam plant in several
different ways. Some experts are predicting that combining solar energy with
fossil-fuel plants will be the eventual answer to reducing greenhouse gas

emissions. Working fluids (steam or oil) in solar systems (sometimes called
farms) are delivering temperatures as high as 1000°F (538°C), and higher.
Steam generated by solar energy in solar farms can be used to (a) heat
feedwater for the steam boiler; (b) be fed to a gas-turbine heat-recovery steam
generator (HRSG) to increase the steam output to the steam turbine, thus

increasing its electrical output; (c) feed solar-generated super-heated steam to
the main steam turbine in the plant to reduce the fossil-fuel consumption.
These, and other designs, promise many fuel savings for combined-cycle

plants, while reducing the carbon footprint of such plants. Steam produced by
various solar-energy plant designs can range from low-pressure saturated
steam to superheated steam, giving designers a wide range of design options.
Solar energy, while more expensive than most other sources of alternative
energy, will eventually become an important source of power worldwide.

Numerous engineers and scientists are working on ways to reduce the cost of
converting solar energy to electricity. A major breakthrough may not be far
away.

Thus, at this writing (2011), two 280-MW concentrating solar-power
stations are planned for the United States—one in Arizona and one in
California. These plants will use parabolic troughs that concentrate the sun’s
rays onto a heat-absorbing pipe that uses a molten-salt fluid to heat water to
generate steam for a turbine-generator. Heat can then be stored in the molten

salt that is held in storage tanks for use during the night and on cloudy days
when sunshine is not available. Some 6 hours of heat storage will be
available from the storage tanks. Each plant will have about 2700 parabolic

troughs to collect heat from the sun, and each plant will occupy some 1700
acres (688 hectares) of land. New transmission lines are expected to serve
each plant.