By guest blog poster Matt Seitzler, PE, The Davis Energy Group
Drought and Water Usage
As a result of last year’s record low rainfall, at the beginning of this year California Governor Jerry Brown declared a state of emergency asking all of California to conserve water during what would end up being an unprecedented three-year drought. Today California faces this drought where nearly 58% of the state is classified by the U.S. Drought Monitor1 as being in an “exceptional level” of drought; it’s highest level of drought intensity classification. This heightened state of awareness regarding water has brought the issue of water usage across all sectors of society into focus. One area of particular interest not often discussed, is the issue of water usage in the production of electricity. As the US population grows the stress on freshwater resources is now becoming evident especially in areas like the Southeast of the US, where in some cases water usage via the generation of electricity is greater than that used by residences within certain areas2. In fact in the report Burning our Rivers: The Water Footprint of Electricity, the authors calculate that, for an average US household, the amount of
water consumed for electricity generation to meet household loads—using the current portfolio of generation technologies—is five times that of the average water consumption.
Water Footprint for Electricity
All types of electric power generation use water in some form, but not surprisingly this amount is not the same across generation technologies. As a part of the Burning Our Rivers report, the authors analyzed the water footprint for traditional electricity generation sources (coal, nuclear, and natural gas) as well as emerging resources like renewable energy technologies (solar thermal, geothermal, photovoltaics (PV)). Comparison of water usage is based upon the determination of the water footprint of each
technology in gallons per mWh. Water footprint is classified in terms of the sum of the amount of water used, or withdrawn, and the amount of water wasted, or consumed; usually as a result of evaporation of stored water. One item to note is that while the water footprint is useful in comparing generation technologies, another important aspect not captured in the volumetric water footprint are the thermal effects of certain power generation technologies on the surrounding environments. As water is often used to cool facilities and then it is ejected into the environment, this practice has been shown to adversely affect nearby ecosystems causing algae and loss of animal species.2
Figure 1. Lifecycle Water Use of Electricity (Gallons/MWh)
Water and PV
The Burning our Rivers report analyzes water use during the upstream or manufacturing phase and during the on-site power generation phase of each of the technologies included. In the chart above, findings from the report show that PV is the second overall least users of water on a gallons per MWh basis. Additionally, the production of PV modules and equipment was found to require a minimal amount of water withdrawn and nearly no water consumed during the manufacturing phase. In the on-site power generation stage of the analysis, PV with its low water use requirements during operation and maintenance enabled it to be the second least user of water in that category as well.
Commonly, PV facilities require small amounts of water in their maintenance typically due to the cleaning of module surfaces resulting from soiling from the environment. Previously done by hand, with the introduction of robotic cleaning devices, the use of water can be more precisely controlled while even some manufacturers are reporting positive cleaning results using robotic cleaning devices without the use of water at all.
So, while the use of PV for power generation might require the use of more land and possible animal habitat, it would not be at the cost of additional water loads and the introduction of thermal load into the environment. With the introduction of new energy storage technologies coupled with a beneficial water footprint, PV is poised to be an even more sustainable way to meet our electric power generation needs.
 US Drought monitor website: http://droughtmonitor.unl.edu/Home/StateDroughtMonitor.aspx?CA
 Burning Our Rivers: The Water Footprint of Electricity, by W. Wilson, T. Leipzig, and B. Griffiths-Sattenspiel, www.rivernetwork.org