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About the Solar Panels

About the Solar Panels

Where are the panels?
What's a watt?
How did the project start?
How do they work?
How much power do they generate?
What are they used for at UVM?

 


Where are the panels?
     The panels are located on the south facing roof of UVM's Cage Central Heating Plant near the library and the UVM Bookstore, Burlington, VT (44N, 73W) . They were placed here because it is a central location of campus where more people can walk by and see them. It was also convenient to install and monitor the equipment from the Central Heating Plant. The Cage Plant phone is 656-2649 

How big are they?
     There are forty-eight 120-Watt panels made by AstroPower, Inc. The solar cells are made from recycled semi-conductor wafers used in the computer industry. They cover 500 square feet of roof space. At the time of installation it was the largest solar array on a Vermont school.



How did the project start?
     The UVM solar panel project was initiated by Richard Wolbach, the energy management engineer at Physical Plant Department, who had taken a course about solar energy with Leigh Seddon, adjunct professor in engineering and CEO of Solar Works Inc. When it came time to replace the roof on the central heating plant, Rich thought it should include solar panels since it has an almost ideal orientation and provided a large surface visible to many passers-by. He presented the idea to the UVM Environmental Council which presented the idea to the University administration. Funding was provided in part by the Department of Energy's Million Solar Roofs program and UVM's Physical Plant Department.


How much power do they generate?
     The total array is rated for 5,760 watts DC under Standard Test Conditions (1000 Watts / square meter). Actual AC output varies depending on factors such as atmospheric haze, inverter efficiency, and the incident solar angle of the season. This is enough power to light 250 energy efficient light bulbs (20 watts each). The average amount of energy these panels generate per day is 19 kilowatt-hours (kWh).  In summer it can be more, and in winter it will be less, due to the number of daily sun-hours. 19 kWh is enough energy to power:
  • 95 energy efficient light bulbs for ten hours, or 
  • 9 TVs for 10 hours, or 
  • 9 desktop computers for 10 hours.
In full sun the system will produce between 4 and 5 kilowatts of AC electricity.
Under partly cloudy conditions the system will produce 3 to 4 kilowatts of AC electricity.
On a cloudy day the system will produce 1 kilowatt of electricity or less.

What about snow in winter?
     Because solar panels are dark in color and positioned facing south, snow melts off the panels rather quickly when there is available sunlight . 

Seasonal changes
     In Vermont, the amount of sun that the panels receive varies considerably from month to month.  The peak for solar energy is in the summer months (May through August) when the panels can produce over 700 kilowatt-hours (kWh) per month. The average Vermont home uses 500 kWh per month. 
     There is a dip in solar energy production in the winter months (November through January) due to shorter days. During these months production may fall to around 300 kWh per month.  An average Vermont home that relies solely on solar panels would require an additional power source. The UVM photovoltaic system is a grid-connect system.  It is connected to the city of Burlington's electric grid and the solar panels serve as a supplemental power source.



What's a watt?
     A watt is a measurement of power. Power is a rate at which work is done or energy transferred. One watt is equal to one joule per second. The unit is named for James Watt (1736-1819), the British engineer whose work on steam engines would help to bring on the industrial revolution.

A 100 watt incandescent bulb left on for ten hours uses 1,000 watt-hours of energy. 1,000 watt-hours is called a kilowatt hour (kWh).
 
 

For the more technical definition go to Terms Defined



How do they work?
     The solar panels are photovoltaic (PV) cells (photo means 'light', voltaic means 'energy').  Each panel is made out of mono-crystalline silicon, a semiconductor material also used in the manufacturing of computer chips . When light hits the semiconductor it is absorbed and part of its energy is transferred to the semiconductor.  The energy knocks electrons loose allowing them to flow freely through a circuit.  PV cells also have electric fields that force the freed electrons to flow in a certain direction. This flow of electrons is an electric current. By putting metal contacts on the top and bottom of a PV cell the electric current can be channeled and used to power any electrical device. 


What are they used for at UVM?
     The power  generated by the panels helps power the Central Heating Plant, operating in parallel with the Burlington Electric system. 

     These panels are not enough to power all of UVM's energy needs but serve as a demonstration to educate the public about solar energy.


Terms Defined (More technical definitions)

Power (P) - Rate of energy transferred.  Calculated as the product of Volts and Amperes. Units of WATTS.

      P = V * A 

Energy (E) -  Ability to do work. Also defined as the amount of power produced or consumed over a specific interval of time. In mathematical terms, the integral of power over time. Units of KILOWATT-HOURS. Energy can be calculated as follows: 

 But for this purpose we can approximate energy as follows. 

Kilowatt-hour (kWh) - A discrete unit of energy equal to 1000 watt-hours or 3.6 kilojoules (kJ) of energy. One kilowatt-hour equals 3,412 British Thermal Units (BTU's) and 2,655,224 foot-pounds. One kilowatt-hour is equivalent to the energy needed to carry 91 pounds from sea level to the top of Mt Everest (29,035 ft).

Last modified May 31 2004 12:11 PM

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