The process of turning solar energy into electric energy is called the photovoltaic (PV) effect. Each solar electric system is made up of several modules each containing many PV cells. It is in these cells that the PV effect takes place.

PV cells are made of semiconducting materials, usually silicon, similar to those used in computer chips. When sunlight is absorbed by these materials, the solar energy knocks electrons loose from their atoms, allowing the electrons to flow through the material to produce an electric current.

Many different manufacturers make solar electric systems. Four different manufacturers are providing the equipment installed at the schools.

Each system produces about 2,800 kilowatt-hours each year or about enough electricity to power 40% of a home. Put together, these 10 systems produce enough energy to supply four average homes. The electricity produced is used in the schools.

The electrical current produced in the PV cells is a direct current (DC). An inverter installed near the solar panels converts the direct current to alternating current (AC) so it can be used by the school.

An electric meter records the amount of electricity produced by the system, called kilowatt-hours, and sends electronic signals to the data acquisition system (DAS) where this information is recorded.

Each school also has a weather station, and DAS instruments at the weather station record wind speed, temperature and the amount of solar energy reaching the solar panels. The DAS receives signals from the weather station and electric meter. It runs a computer program to calculate and record the weather conditions and electrical output of the system every 15 minutes.

The school's electrical distribution panel receives electricity generated by the solar system, combines it with other electricity supplied by MGE and routes it to the school's classrooms to power lights, computers, and other devices.

School PV Equipment

SMA Sunny Boy string inverters convert the DC power generated from these arrays to AC power used in the schools.

Monitoring equipment will record:

• Instantaneous power output.
• Cumulative energy output.
• Solar insolation (how much light is hitting the array).
• Temperature and wind speed.

• Installed by H&H Electric, a local electrical contractor.
• Purchased from RWE Schott Solar, Waltham, Massachusetts, a solar systems distributor.