You are my sunshine

NELLIS AIR FORCE BASE, Nev. -- How many times have you driven down Range Road and wondered "What is the story behind those solar panels and how exactly will they work?"

The new solar energy system, which hundreds of Nellis base employees drive by every day, represents the cutting edge of solar power technology. There is a lot one can learn about the system's various parts and how they will work to transform sunlight into electricity.

"This is new technology," says Michelle Price, Base Energy manager. "These types of panels have not been used in the U.S. before."

Most people think in terms of solar panels, but it is really the solar cell that transforms the sunlight into energy. Each cell is approximately 25 square inches of crystal silicon. Metal conductors in the back of the cell transform energy from the sun directly into electricity. You may also hear these cells referred to as photovoltaic cells ("photo"=light and "voltaic"=electric).

Seventy-two solar cells make up one solar panel.

A solar panel is simply a collection of solar cells. "Solar panel" can be used as a generic term to mean anything that collects the sun's energy. When people speak of the solar panels being installed here, they are probably really thinking of the units called trackers.

Twelve solar panels make up the most common tracker here, the SunPower GPT-20. Trackers are the free-standing units that you see popping up alongside Range Road. They get their name from their ability to slowly turn throughout the day, tracking the movement of the sun. Their nicknames are "the tripods," since they are the trackers with three concrete feet. The "20" in their name refers to the 20-degree tilt of the solar panels. The SunPower GPT-20 trackers will be used on 75 to 85 percent of the solar power farm's acreage.

Another type of tracker being installed has solar cells on both the front and back of the panels. These are the Sanyo GPT-20 trackers with bifacial panels. The Sanyo GPT-20 trackers are being chosen for particular locations where they will be able to collect additional sunlight. Ten to 15percent of the farm's land will use GPT-20 trackers.

The SunPower GPT-0 is the third and final type of tracker on the new solar power farm. As opposed to the SunPower GPT-20s, the GPT-0 trackers are installed into concrete in the ground. The "0" in their name means that they lay flat with a zero-degree tilt. The SunPower GPT-0 will be used on the final 10 to 15 percent of the solar power farm's acreage.

Rows of 40 trackers will be connected by steel bars, and motors at the end of each row will turn the whole group as they track the sun. Each row will also be connected by power cords that are on the back of each tracker. The power cords will run underground alongside Range Road before connecting directly to the base electric grid.

The entire solar panel farm is sometimes referred to as a photovoltaic array.

"It just means a series of panels in a field -- basically a farm," says Mrs. Price.

The array, when completed, will consist of approximately 5,000 trackers, producing roughly 15 megawatts of power. The first five megawatts are scheduled to be connected to the electric grid in October. The next five megawatts will be connected in November with the remainder being connected in December.

Nellis' system will be the largest photovoltaic array in North America and will provide the base with renewable energy at a discounted rate. It will be a secure power source and will reduce greenhouse gas emissions. The solar power farm will ultimately supply the base with twenty to thirty percent of its total energy needs. 

Frequently Asked Questions

1. Won't the solar panels reflect light into the eyes of pilots flying overhead?

No. Most solar panels would reflect light, but the units being installed here will use special solar cells that have a black appearance. Specially chosen to complement the missions here at Nellis, these solar panels will not reflect light into pilots' eyes. In fact, they will be less reflective than lakes or other bodies of water that pilots routinely see in flight.

2. Will the solar panels get dusty? Won't this hurt their efficiency?

Yes. That is why contractors will wash them down occasionally. There will be water trucks going through and cleaning the dust off periodically. Clean solar panels will operate more efficiently.

3. Why are three different types of trackers being used?

There are a variety of trackers being installed because of the different terrain and soil types in the area. Some of the land is a capped landfill, which would have been too expensive to dig up. That is why the two types of GPT-20 trackers, with the tripods sitting on top of the land, are being installed there. In other locations, the GPT-0 trackers are suitable for being installed in the ground.

4. What will happen if the photovoltaic array goes down?

Nothing noticeable would happen. The array will be simply interconnected to the already-existing electric grid on base. Whatever electricity the array can't provide will be supplied by Nevada Power, and no one would ever know the difference. If, however, the entire grid goes down, the photovoltaic array will be shut down for safety reasons.

5. Will there be some sort of battery to save the solar power so we can use it when the sun is not shining?

No. Since the solar power farm will only produce 20 to 30 percent of the base's total energy needs, there will be none left over to store. Experts say this is for the best, since a battery for the array would have to be the size of a large building. There would be a number of safety concerns with that large of an electric battery.