Frying eggs from 93 million miles

away - now that's power

What is the role of solar energy in Green Power Switch?

Solar energy will constitute a small but important part of Green Power Switch's energy resources.  Its capacity will be 225 to 250 kilowatts -- an amount that demonstrates TVA's leadership among Southeastern utilities in its commitment to solar energy.

How is solar energy generated?

It's generated by photovoltaic (PV) systems.  PV systems consist of semiconductor cells or modules that convert sunlight directly into electricity, plus such additional equipment as an inverter that changes direct current to alternating current (which is what people use in their homes).  The PV cells are connected in the form of flat panels that can be mounted on rooftops or canopies or integrated into roofing shingles and other building materials.

How much electricity will a PV system produce?

It ranges from 4 to 50 kilowatts.  On average, a 10-kilowatt PV system located in the Tennessee Valley will generate approximately 16,500 kilowatt-hours of electricity per year, or a little more than the total amount of electricity used in a typical home.

How are solar sites selected?

TVA has asked power companies participating in the market test to help identify sites that offer high visibility and good opportunities for public education.  These might include such high-traffic areas as visitor centers, museums, or schools.  Of course, the sites must also meet the necessary physical criteria; a southern orientation, good exposure to the sun, and the appropriate amount of structural support and space for placement of the PV panels.

Will the PV systems produce electricity all the time?

No.  Depending on the season, they will ordinarily generate power from 8 a.m. to 6 p.m., reaching maximum output between noon and 1 p.m.   Since solar energy won't be a primary element in the power mix, batteries or collection and storage systems will not be used.  When the PV systems aren't producing power, TVA's other resources will continue to supply reliable electricity.

Can PV systems produce power on cloudy days?

Yes.  PV modules generate electricity when the weather is cloudy, although their output is diminished.  On a dark, overcast day, a PV system might receive only 5 to 10 percent of the usual amount of sunlight it needs, so power output would decrease proportionately.

Do PV systems work well in the cold?

PV modules actually generate more power at lower temperatures.  The reason is that like most other electronic devices, they operate more efficiently when it's cooler. PV systems generate less energy in the winter than in the summer, but this is due to the combination of fewer daylight hours and lower sun angles, not to cooler temperatures.

What about breakage?  Don't most modules contain glass?

PV modules are designed to withstand any potential rigors of the environment, including arctic cold, desert heat, tropical humidity, winds of more than 125 miles per hour, and one-inch hail at terminal velocity.  In spite of this very durable construction, though, the glass may break under and extremely strong impact.

How does the cost of solar energy compare to that of traditional electricity?

Solar is one of the cleanest energy sources available, but it's also one of the most expensive.  By creating more demand, TVA hopes to stimulate further technological development that may help bring the cost down over time.  For now, electricity produced by solar photovoltaic sources is more expensive than that produced by common sources like coal.  A typical coal-fired generating unit currently produces electricity for a little more that a penny per kilowatt-hour.  The cost of producing electricity using solar photovoltaic sources is about 60 cents per kilowatt-hour.