Beyond Electricity: Photovoltaics Harvest Sun and Rain


Your rooftop solar system doesn’t have to sit idle in the midst of a downpour. Aside from harnessing the sun’s energy, photovoltaic (PV) panels can also provide an opportunity to collect rainwater. With water supplies becoming an increasing concern, more states in the U.S. are embracing rainwater harvesting as an effective means for water conservation. As rainwater catchment systems become more attractive, some residents see solar PV panels as a versatile tool to aid self-sufficiency.

Engineer Lyndon Than, who transformed his Ontario bungalow into an energy efficient passive house, has been exploring the option of collecting rainwater with his solar PV panels.

“The fact that PV panels are glass-clad means they present a premium surface for rainwater collection. The trouble is that they are not designed for this task, which I certainly feel they should be,” Than says. “In fact, I would like to see PV panels made as large interlinking panels that shed water all the way down the roof.” This would improve the quality of the water, he adds.

Questions have been raised regarding the quality of water harvested off photovoltaics. Researchers at the United States Geological Survey conducted a study to measure the potential of heavy metals leaching from PV panels into the harvested rainwater. They concluded that a newly installed (amorphous silicon thin film) solar panel would increase concentrations of cadmium and lead in potable water. As far as non-potable purposes, the metal concentration levels were low enough that the water could safely be used for activities like toilet flushing, irrigation, laundry, etc.

The study did not, however, address the use of filtration systems. Today’s filtration systems run the gamut of purification techniques, from the state-of-the art systems used by developing nations to eliminate bacteria and viruses to the simple method of adding sand to make rainwater drinkable. Some purifiers use ceramic filters to absorb pesticides and organic compounds while others utilize ultraviolet light to kill bacteria. There are also solar-powered water purification systems, but the ones sold commercially are often designed for remote locations, or areas where the water is highly contaminated. For the do-it-yourself individual, solar purification systems can even be constructed with household materials.

Harvesting rainwater has been a touchy subject in recent years. Until 2009, it was illegal in Colorado to collect rainwater from your roof, but the state now allows small-scale collection. Eleven other states and the U.S. Virgin Islands also impose laws for rainwater harvesting. However, recent droughts and concerns with water shortages have been encouraging state governments to allow rainwater collection for home use, according to the National Conference of State Legislatures.

For residents who already catch rainwater, the addition of roof-mounted PV panels should not present compatibility issues. “I don’t see any problem with solar [photo]voltaics on a water harvesting roof,” said permaculture expert Penny Livingston-Stark.  “As ever, you need mechanisms to ensure the stored water is actually clean. If you're going to drink it that's doubly important.”

The increasing need for fresh water, combined with the current energy crisis could make solar PV systems a more attractive option for their multi-faceted role in our sustainable future. 

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 - Author of Solar Reviews

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