It’s Not All the Same

Differentiating Solar Energy Technologies

I feel the need to say something about different kinds of solar power because, unlike wind or wave or tidal power, the methods of generating electricity from solar power are very different, yet they always get clumped into the same bucket.

Although there are many different methods to use the sun to generate electricity, two of the technologies are mainstream these days. The first is solar thermal, and the second is photovoltaic.

Solar Thermal

Reflective Troughs for Solar Thermal

Solar thermal technology concentrates the sun’s rays to heat a fluid to a boiling point. The steam is then used to drive a typical turbine (similar to one that you would find in a coal-fired generation plant). There are quite a few different kinds of solar thermal plants out there. Some use parabolic-shaped, reflective troughs to concentrate the sun’s rays onto a pipe to hear the fluid (see the above picture). Other plants use a series of mirrors strategically placed in a field concentrating the sun’s rays on a bucket of the fluid. There are many other variations on these two, but the essential concept is the same: heat a fluid with the sun’s rays and use the steam to drive a turbine.

Photovoltaic

Photovoltaic Cells

Photovoltaic technology is entirely different than solar thermal. A photovoltaic panel converts light energy directly into electricity for use in your house or office. It contains a device called a photodiode which is capable of absorbing light rays and converting them into current or voltage. Although there are many different materials that will convert light into electricity, silicon is currently used for most applications currently. This is the reason why photovoltaic panels have become much more economical recently; the price of silicon has dropped dramatically.

Other Solar Technologies

Solar Updraft Tower

The other technology you may have heard of is called a solar updraft tower. There have been a few prototypes, the most famous in Spain.  There is also a proposal for a large scale project in Australia. This technology is fairly simple: Essentially a large area is covered with plastic at a height above the ground, and then in the middle a long tube-shaped tower is inserted with turbines at the bottom. Since hot air rises, the air from under the plastic rises and escapes through the tower while turning the turbine on the way out.

Hopefully after reading this the first question you’ll ask after hearing about a new solar project is, “Solar thermal or photovoltaic?” They are very different technologies and have very different economics and implications for the world.