Solar Electricity Generation By Water

Using solar cell arrays to produce electricity is a now-familiar application. Most applications that use PV (photovoltaic) modules are still small scale, except for certain experimental stations trying to generate power at the level of utility companies. Still, everything from lawn lights to full power supply systems for homes are available.

But there's another way of generating electricity, one that's actually been in use for some time: heating water.

Steam generation plants have been in use for decades. Usually, the water is heated by burning coal, oil or natural gas. The heated water is turned to steam, which drives a turbine. That circular motion can be used to generate electricity.

Michael Faraday, the great 19th century British scientist and inventor, discovered that if a coil of wire is turned near a magnet, electricity is produced. That effect is the basis for countless applications that use a generator to provide power. The same basic principle is at work in turbines, only in this case the turning is provided by steam power.

But the turbine doesn't 'care' what heats the water that turns the blades that produce electricity. And using solar heated water is significantly less pollution producing than other methods, even taking the component manufacturing effects into account.

One such method is that used in ordinary solar water heating systems, which typically use collector panels atop a roof. The water is heated by the greenhouse effect and then passes down a series of channels and pipes into a storage tank.

But there's a difficulty.

The total sunlight received in a given area at one time is fixed. It will vary depending on cloud cover, dust in the air and other factors. But it can't be adjusted upwards, since we can't control the sun's output. However, by adjusting how that energy is used, we can control the amount of usable energy applied and how.

More efficient collector systems make that possible. One is the parabolic mirror method.

A mirror shaped roughly like a section of a sphere can focus the sun rays to approximately a point or line. Exactly how sharply focused and to what geometry is determined by the quality and shape of the mirror. A circular parabola, like a satellite dish, focuses to a point. A cylindrical parabola focuses to a line. That shape concentrates the energy received into a smaller area. That makes it possible to use the same energy to raise the water temperature much higher than by other methods.

By using parabolic troughs and other shapes, solar heating collectors can raise the water temperature to as much as 428F(220C). Water boils at 212F (100C). That extremely high temperature water creates steam under very high pressure in a contained vessel. The steam is then used to power a turbine to produce electricity.

Since the temperature and pressure are high, the conversion efficiency of the device is correspondingly high. That's the result of a basic principle of the physics of heat. That makes it possible to create solar electricity generation devices that are as high as 40% efficient. PV (photovoltaic) panels range from roughly 10-15% efficiency.

Of course, such systems may not be for the average homeowner. Yet. But businesses are beginning to experiment with them as the cost of coal, oil and natural gas rises and the price of solar systems comes down. Some day it may well provide a significant percentage of the total energy needs of the average person, who could receive electricity from large solar turbine-based plants.