Solar Southwest Initiative

Most people think of rooftop or poletop solar panels when then think of solar energy. These applications of solar energy are called photovoltaic panels or modules, which use a specially prepared material that generates electricity when light hits it. Sometimes there are also small to medium-size solar thermal collectors on rooftops which are used to heat domestic hot water; these have become popular in some regions of the world as an inexpensive alternative to natural gas water heating.

Solar Thermal Electric or CSP (Concentrating Solar Power)

Unlike the mostly smaller installations of photovoltaic or solar water heating, solar thermal electric plants are very large installations that may stretch for many acres or even square miles. The large expanse of solar collectors contain mirrors that are oriented via motors to track the sun across the sky. When the sun strikes the mirrors they concentrate the rays of the sun on a receptor. Different designs of solar thermal power plant concentrate more or less rays of the sun on the receiver, yielding a lower or higher temperature at the of concentration on the receiver.

The receiver contains a liquid which absorbs the heat of the sun. The liquid, oil, water or molten salt, is called the heat transfer fluid. In most solar thermal electric plants, the heat transfer fluid is pumped some distance to either a power block or a storage tank.

In the power block, a structure that contains machinery, the heat from the heat transfer fluid is run through heat exchanger inside a steam generator or, if heat transfer fluid is itself water, it is alllowed to evaporate creating steam. The pressure of the expanding steam is used, as in a conventional power plant to drive a turbine that turns the coils of a generator that generates electricity. Power engineers are quite familiar with the latter part of the CSP process as this type of power block is quite common.

Those few current CSP power plants that have the storage tanks work almost exactly the same way, except the heat from the heat transfer fluid is stored in a storage tank. The heat is then tapped into by pumping out heated fluid to the steam generator when power is needed. Current storage facility designs lose about 1% of stored heat per day, a negligible amount. The storage tanks enable a solar thermal electric plant to dispatch power at any time that there is stored heat in the tanks. Dispatchable power is more valuable to the managers of the grid than non-dispatchable power.