Solar PV Panel Shading, a New Consideration for ROI?

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solar panel shade helps energy efficiency

One of the essential questions we ask with solar PV installation is “what will the return on the investment (ROI) be?” Many considerations are used to calculate a result. Researchers at the UC San Diego Jacobs School of Engineering, under the direction of professor for environmental engineering Jan Kleissl, have recently provided us with yet another consideration to incorporate into these equations — the energy efficiency benefit of solar panel shade. Using a thermal infrared camera, they were able to calculate the value of solar panel roof shading.

An ROI calculation weighs benefits, including costs avoided, against the costs of the project. Estimates are often required, but a more useful calculation is possible when exact components are known. This study helps on that front by putting numbers on air conditioning savings resulting from solar panel shade. The study was done over three days in April using a laboratory building on campus. The building roof has different sections: without solar panels, with tilted panels, and with flush panels. The panel shading caused a reduction in air conditioning costs equal to a 5% increase in electricity provided by the panels, the researchers found. It was a chance discovery when undergraduates were asked to take thermal images of the ceiling while waiting for another conference.

At night, the panels tended to keep the ceilings warmer. Air circulation beneath the tilted panels lessened the heat transfer. There are other strictly conservation measures that give larger returns. These would include highly reflective roofing materials or paint and increasing the insulation in a roof. Both of which were outlined in a memo by the Secretary of Energy, Dr. Chu, calling for more energy efficiency in government buildings. Although the benefits are presently less for PV panel shading, future designs might now incorporate a better understanding of these benefits.

More research will show how the results from this building compare with other buildings. Future work should include creating a model for predicting the benefits. Someday, we may have solar panels that are also optimized to give the most shade benefits.

For further reading:

  1. For an Energy Efficient Cool Roof, Try Poplar Leaves
  2. How To: Cheap or Free Solar Panels

Photo Credit: mikebaird

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