March 28, 2008

Solar Thermal Energy, Another Way To Capture The Sun's Energy

When talking about solar power most conversations revolve around photovoltaic (PV) cells, but there is another solar technology that may surpass the capabilities of PV production. Solar thermal energy is gaining ground among production companies (and I've blogged about it here, here and here.

Solar Thermal energy is a way of capturing the sun's energy by concentrating a large field of mirrors onto a single point in a tower. The tower has huge tubes filled with oil that is heated at the concentration point and the incredibly hot oil is used to turn water to steam which turns turbines. Sounds like a long complicated process but really its not (consider the process of coal mining all the way to electricity in your house, this is a far more complicated process).

The advantage solar thermal energy has over PV technology is that it can produce energy even at night or during cloudy days. The efficiency of storing heat is much better than converting solar to electrical power and then storing it (not to mention much, much cheaper). Think of it this way. Your laptop stores about as much power as a 4 quart thermos. If you turn on your laptop and put some hot water in a thermos which one will lose its energy first? Unless you have a very very expensive battery in your laptop the thermos will far outperform it at energy storage. And the laptop's storage components run in the hundreds of dollars while the thermos costs $15 max. Ausra, a company leading the solar thermal charge has developed a storage system that is 93% efficient. Even under theoretical conditions PV cells can't begin to touch that type of conversion efficiency.

The efficiency of storing heat is a major major advantage for solar thermal energy, and the ability to store and ramp up production in mere minutes means that the plant can operate as a base grid powerstation or a peak production plant.

Looking at the timeline of peak energy usage there is a very steady pattern of electricity demands being the highest in the late afternoon and early evening of the summer months. Most of that is fueled by air conditioning as the heat of summer pounds down. So it is hottest and brightest when we need the most energy and this technology works best during the hottest and brightest times of the day, sounds like a pretty damn good fit to me.

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