Even with some winter rain in California, the state, and much of our nation, still suffers from on-going drought. The issue draws attention to industries with heavy water usage, in this case, electric generation.

California state law demands utilities obtain 33 percent of their power by 2020 via “renewable sources”, such as wind, solar, and geothermal. However, some solar farm projects have come under scrutiny for how much water they use to generate electricity.

Specifically, a project to build two solar panel plants in the California desert – Genesis Solar and Mojave Solar – both received features in the New York Times. The article noted the plants would use a bit more than 1.24 billion gallons of water each year to generate 500 megawatt/hours of electricity between the two of them. These, “wet cooling” projects, which use a significantly larger amount of water than “dry cooling” projects must constantly replenish water lost to evaporation.

It should be noted that there is a trade-off – “dry” projects are not believed to be nearly as efficient as “wet” projects when it comes to generating electricity.

While 1.24 billion of anything sounds like a lot, when it comes to other forms of electricity production, how do these solar plants measure up? Current, more standard, power plant technology – specifically nuclear energy production – returns about 98 percent of the water used back to the environment. The total percentage use of water nationwide for electricity production is about 3.3 percent of all freshwater, less than half of all residential use.

In a recent study by the National Renewable Energy Laboratory (NREL), solar energy was ranked as having the highest water usage rate out of all forms of energy production. At 786 gallons of water per megawatt produced, the waste from solar energy stands out among its rivals.

However, comparing facility water use side by side is a bit tricky as there are many different types of plant cooling and re-use systems. That being said, according to the NREL, nuclear plants use around 672 gallons per megawatt hour of electricity produced. This is the equivalent of about 22 gallons used per household served by a nuclear power plant. Keep in mind that about 98% of this water, used from nuclear plants, returns back to the environment.

The same study shows that coal-fired plants used approximately 687 gallons per megawatt hour while natural gas plants use a comparatively low amount at around 198 gallons per megawatt hour. Clearly, when it comes to initial water consumption levels, natural gas far outweighs most other means.

Out of all means of production, solar energy is certainly the biggest drain on water resources necessary per megawatt-hour of electricity harnessed. The surprisingly high levels of water consumed by solar panels points to needed improvements for the advancement of efficiency and safety.

When most people think of solar energy, the last thing on their minds is water waste.

Water is one of earth’s most precious resources. Nobody lives without it. It is our duty to preserve these resources by developing technologies and improving infrastructure across the full spectrum to continue to limit its waste during energy production.