Solar Energy To Feed the Grid

Most renewable energy technologies derive their impetus from the enormous energy delivered by the sun. For example, wind farms are driven by air moved primarily by temperature changes caused by the sun between geographic regions. And hydroelectric plants use water driven into pondage or run-of-river power plants by the sun’s effects on evaporation, condensation and rainfall. And then we solar power, harnessing energy directly from sunlight. There are two main technologies that are called “solar power”:

(a) Heat recovery systems collect energy radiated by the sun onto a fluid which then drives a steam turbine or an induction generator. There are several ways to do this. One is to pass water through a series of pipes with parabolic mirrors focusing sunlight onto the pipes to concentrate the radiated energy. The water is trurned into steam that drives a turbine, and the turbine turns a synchronous generator to produce alternating current (AC).

(b) By directing the sun’s rays onto photo-voltaic cells that produce electricity. Photovoltaics, or PV, use the photovoltaic effect of semiconductors to generate electricity directly from sunlight into direct current (DC). A variant, concentrated photovoltaics, uses lenses to concentrate sunlight into a smaller panel of high efficiency PV. The DC is passed through inverters to obtain alternating current (AC) than can be stepped to higher voltages and delivered to the electric grid.

Curiously enough, both these methods are called “solar” power.

thermal – use solar heat to run a steam turbine or an induction generator. For further discussion, we’ll refer to the steam turbine system by its commercial name – SEGS for the solar energy genrating system developed by Solel, and to the induction generator as SES for Stirling Energy Systems, developer of that design.