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, other than certain experimental stations trying to generate power at the level of utility companies. Nowadays, everything from lawn lights to full power supply systems for homes are available. However, there is actually another method for generating electricity that has been in use for some time; that of heating water.

Steam generation plants have been in use for decades; as a general rule the water is heated by burning coal, oil or natural gas. The heated water is then turned to steam, which drives a turbine and 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 and this has become 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. The turbine doesn’t ‘care’ what heats the water that turns the blades that produce electricity; and using solar heated water is significantly less polluting than other methods, even taking the component manufacturing effects into account.

Some day solar power may well provide a significant percentage of the total energy needs..

One such method is that used in ordinary solar water heating systems, which typically use collector panels on top of 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 is a difficulty.

At any one time the total sunlight received in a given area is fixed; this will vary depending on cloud cover, dust in the air and other factors. However, it can’t be adjusted upwards because we cannot control the sun’s output – by adjusting how that energy is used, we can control the amount of usable energy and how it is applied.

More efficient collector systems make that possible and one of these 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. The quality and shape of the mirror determines exactly how focused and to what geometry this will be. A circular parabola, like a satellite dish, focuses to a point. A cylindrical parabola focuses to a line and that shape concentrates the energy received into a smaller area – this makes it possible to use the same energy to raise the water temperature much higher than by other methods.

Through the use of parabolic troughs and other shapes, solar heating collectors can raise the water temperature to as much as 428F (220C). Water boils at 212F (100C) and 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 – following the basic principles 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 suitable 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 solar power 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.