August 3, 2009

Solar Power in the Sunshine State (part 1)

By: James Stevenson, Extension Specialist, Pinellas County Extension

Solar Thermal

Using the sun’s energy to power our lives is really nothing new; it has been around since the 70s, right? Actually humans have been using solar power as long as we have been human. Using the sun to warm our homes, dry our clothes, heat water and even defeat foes are only a few ways humans have harnessed solar power throughout the centuries. Every hour, enough sunlight reaches the earth to meet the world’s energy needs for a year.

With almost too-late attention being paid to renewable energy sources, the sun is again front-and-center in Florida’s energy future.

We enjoy an average of 200 sunny days here in the Sunshine State. In addition, Florida has 85% of the maximum solar resource available in the US, only being outdone by the southwestern states.

Yet with all this free solar energy, we still depend on non-renewable resources that are not even produced in Florida. 37% of our energy comes from burning coal. Although coal is very abundant in the US, it still needs to be transported to Florida’s power plants. In 2008, the US IMPORTED 34,000 tons of coal from countries as far away as Australia, Indonesia and China.

Next on the list is petroleum. It is no surprise that we depend on foreign oil to power our lives. But did you realize the scale? In April 2009, the US imported 360 million barrels of oil. Just in April.

21% of our power plants are fueled with natural gas. Our very own Progress Energy just this year switched from its oil-fired units to a combined natural gas/steam turbine system. The pipeline that supplies our natural gas stretches from Mobile Bay in Alabama, across the Gulf of Mexico and into Manatee.

Florida has several nuclear power plants as well, and combined they provide 18% of our energy needs. This leaves us with 3%; the amount of renewable energy that is consumed in Florida. This is a combination of solar, wind and geothermal.

Solar energy comes in the form of light and heat. Energy produced from light is called photo-voltaic and the sun’s heat is referred to as solar thermal.

It is possible to take advantage of solar thermal power and depend less on your local service provider. 20% of your energy bill goes for the heating of water. A solar water heater can bring that percentage down to 0.

There are three basic types of solar water heaters available in Florida; the pumped, or direct circulation system, the integral collector storage (ICS) system and the thermo-siphon system.

All these systems involve some sort of solar heat collecting device usually placed on the roof. Within this structure (flat rectangular metal boxes) are pipes containing the potable water supply from the household.

A pumped, or direct circulation system, uses an electric pump to bring the water into the rooftop heating unit, and then, once heated, into a holding tank back on the ground. A controller regulates the movement of water through the system, using a series of thermostats and valves.

The integral collector storage (ICS) system uses the home’s water pressure to circulate water through the system. With this set-up the rooftop unit actually serves as a storage unit, not just a heating chamber. On demand, water is pulled from this rooftop tank into a small auxiliary tank.

The thermo-siphon system uses thermophysics (!) to work. Cool water is introduced into the collector on the roof, at the bottom of the collector. As the water is heated it expands and rises to the top of the chamber and out into a holding tank, also on the roof. Then, just as the ICS system, the home’s water pressure drives the system and brings heated water back down to ground level.

ICS and thermo-siphon systems do not require the electric pump or controller to keep things moving. Those two components may also be powered by sunlight as well, with the light being transformed directly into electricity, or by photo-voltaics. This fascinating and very modern technology will be our next Timely Topic.

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