In the last fifty years we have learned how to turn the energy from sunlight directly into electricity. This process is called photovoltaics (PV). This is possible due to the photoelectric effect. When photons hit certain substances, they free electrons and produce electricity.

1. Photovoltaics (PV) are made out of cells, which are wired together into a module. Many modules can be put together to make an array. We can generate useful amounts of electricity from a PV array.
   
   
2. Each cell produces 0.5 volts when sunlight hits it. Lots of these cells can be put together to produce much higher voltages.
   
   
3. The surface area of a cell and the intensity of the light hitting it determine the current. Cells can also be wired together to produce higher amounts of current.
   
   
4. Today PV captures 6-15% of the sun's energy falling on that cell. One square meter of PV at 10% would produce 100 Watts. Remember that sunlight reaches the earth at 100 Watts per square meter.
   
   
5. PV cells produce DC power. This can be used directly, or it can be converted to AC power with an inverter.
   
   
6. PV produces clean power. After the manufacturing process there is no waste product, and nothing is used up. In addition, no water is needed to produce electricity from PV. In one month, a 1-kilowatt PV system will save approximately 150 lbs of coal, keep about 300 lbs of CO2 out of the atmosphere, and save 105 gallons of water.
   
   
7. Since nothing is used up, PV cells keep working for a long time. Some last for more than 30 years.
   
   
8. PV is renewable. The amount of sunlight we use today to produce electricity will not affect the amount we will have for use tomorrow.
   
   
9. PV can be located at the site where electricity is needed. This reduces distribution losses. When electricity is transmitted over long distances, up to 50% of the electricity is lost in the process. These are called distribution losses.
   
   
10. Because sunlight is diffuse, it takes a lot of space to produce enough electricity to meet our current needs. It would take 0.5% of this country’s land mass to meet all our energy requirements. This is about 18,000 square miles or 1/6th the state of Arizona!
    
    
11. Solar energy is inconsistent. It is only produced when the sun is shining. At night we must use energy stored during the day, or we must use another source of electricity. The same is true for cloudy days. One way to store the energy from PV is to use batteries. During the day they are recharged and at night electricity is withdrawn.
    
    
12. Electricity from PV is more expensive than from conventional sources. However, it does not have a lot of hidden costs. Hidden costs are those that aren’t paid for directly when a product is purchased. Instead, hidden costs are paid for later in other ways such as through taxes and reduced environmental quality.
    
    
13. PV can be used to power homes, telecommunications equipment, satellites, water pumping, and other things in remote areas where there is no other power source. PV can provide clean power to villages and homes in developing countries. This is especially important for health care. PV can be used to power refrigerators that keep vaccines alive. These systems are called “stand alone” PV systems if they have batteries, and "direct application" systems if they do not.
    
    
14. PV can provide clean power to urban dwellers who choose to obtain their energy from the sun in order to have less of a personal impact on the environmental. This can be done with a "Line Tie" PV system which is connected to the utility grid. This system does not require batteries. However, batteries can provide backup so that if there is a power outage, the PV system can power critical appliances.
    
    
15. There are different ways to make PV materials. The traditional way is to grow a crystal from molten silicon. The Crystal is then cut into cells that make up a PV module. This is a very costly process, involving a great deal of time and energy. The latest PV technology produces thin film cells. This is a more efficient process, and promises to make PV more affordable in the near future.

Tucson Electric Power is a joint owner of a new manufacturing and research facility in Tucson. The company, GLOBAL SOLAR manufactures thin film PV.

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