Photovoltaics are solid-state semiconductor devices that convert light directly into electricity. They are usually made of silicon with traces of other elements and are similar to transistors, light emitting diodes (LEDs), and other electronic devices. The photovoltaic device (usually called a solar cell) consists of layers of semiconductor materials with different electronic properties. Most of the material is silicon. A thin layer on the front of the cell is treated with phosphorous to give it a negative character. The interface between two layers contains an electric field and is called a junction.

Light consists of particles called photons. When light hits the solar cell, some of the photons are absorbed in the region of the junction, freeing electrons in the silicon. If the photons have enough energy, the electrons will be able to overcome the electric field at the junction and are free to move through the silicon and into an external circuit. Some of the more commonly available units generate 5W to 10W per square foot of collector surface.

The direct current (DC) from the solar panel is converted to alternating current (AC) through an inverter. The inverter provides the following safety features:

• any necessary protection required by the electric utility
• over and under voltage protection from DC injection
• less than 5% harmonic distortion
• automatic disconnect from the grid when power on the grid is lost
• all AC and DC overcurrent protection and disconnects

Penn State has two 2,000 Watt Solar PV systems installed thanks to the Solar Schools program and Conectiv Energy.

The first one installed is located on the roof of The Main Building at Penn State - Delaware Valley.

The second is located on the roof of the Physical Plant Building at University Park.

The intent is to track performance (kWh generated), cost avoidance, and maintenance costs. The electricity generated is fed into the electrical distribution system of the buildings and reduces the amount of power purchased from the utility. The approximate installed cost is $19,000 per system. These systems were donated to Penn State by Conectiv Energy.

The following table summarizes the average measured performance for each system.  The analysis assumes a best case scenario with the solar cells off-setting electric demand at full capacity for all twelve months of the year.  Maintenance costs are not considered at this time.

The economics of these systems are not very favorable considering the anticipated lifetime of 30 years.  The solar radiance available in Pennsylvania is about 3 kWh/m²/day.  The solar radiance available in the Southwestern parts of the US is about 7 kWh/m²/day. It is expected that this same system would produce 6000 to 7000 kWh per year in the Southwest, and would therefore have a 20-30 year payback, which is within the expected lifetime of the equipment.

PSU Solar Campus-wide Application:

The University Park campus has approximately 79 acres of roof area.  If 75% of this roof area could be covered with Solar PV panels they would produce about 26,000,000 kWh per year, or about 10% of the consumption at University Park.  Based on the installation price of the 2 kW systems above, the installation would cost $255,000,000.