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Solar Energy in Wisconsin
By William Hurrle, Community Builders and Niels Wolter, WisconSUN
2000, updated 2003

Introduction
Solar Energy System Output

Orientation

Siting

It simply feels good to be plugged into the sun, into natural flows of energy Ė just like it feels good to garden, walk in the woods, or canoe on a lake.

Some people think there is not enough sun in Wisconsin for solar energy systems. They are wrong! Madison is at 43o North latitude, the same as Rome. During the summer, Wisconsin receives about 75% of the annual solar energy received by the deserts of Arizona and Southern California (Figure 1).

U.S map

Figure 1. The average radiation received by a horizontal surface in June. Units are in kilowatt-hours per square meter.

One benefit for photovoltaic (PV) solar energy systems in Wisconsin is that the annual peak of the solar resource (and a PV systemís output) occurs on sunny summer days. This corresponds exactly with utilitiesí highest energy demand periods Ė and their highest energy charges.

During Wisconsinís winter, especially in November and December, there is less sun, an average of only 2.5 hours of sun per day available to power PV systems. However, on clear days with snow cover, there is up to a 60% output increase from light reflected off snow. And the efficiency of crystalline PV cells is improved in the cold. Thus on cold, sunny Wisconsin winter day, crystalline PV systems will have their highest output, higher than similar systems in the deserts of Arizona.

Two solar energy systems are well suited to Wisconsin:

  • Solar electric photovoltaic (PV) and
  • Solar hot water (SHW) systems.

Solar strategies such as passive solar design are also very effective in Wisconsin, but are not covered here.

PV systems are based on materials, most commonly silica, which produce a current of electricity when struck by sunlight. This electrical current is then modified, using an inverter, to produce an alternating current of a very high quality. The PV system can either be connected to your home and the local electric utility or be independent of the utility grid.

Most SHW systems collect solar energy using fluid-filled pipes, located in a glass covered panel. The pipes typically contain a propylene glycol solution that will not freeze during Wisconsinís winter. A pump circulates the propylene glycol solution from the solar panel to a heat exchanger located in the hot water tank. Heat moves into the hot water tank across the heat exchanger. A second pump circulates the solution from the tank back into the solar panel. Typically, the hot water tank can also use another fuel, such as natural gas, electricity or propane.

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