If you're not a daily reader of the Arizona Republic then you probably missed an op-ed on solar energy written earlier this summer by Arizona Senator Jon Kyl. Instead of spending his (staff's) valuable time penning a letter to promote the burgeoning solar industry in his home state, Kyl decided to take a highly-specified shot at utility-scale solar power. The senator sees "conventional concentrating solar power" as a central threat to Arizona's water supply:
"While it's true that Arizona's sunny climate is ideal for solar-energy production, its arid landscape poses significant challenges to the deployment of solar systems that rely more heavily on water than other forms of energy production."
To be sure, we here at Ecocentric are very sensitive to the connection between water and energy, including electricity generation's alarming dependence on water supplies. And the senator is right to call for energy policymakers to pay more attention to the affects of all forms of energy generation - fossil fuel, nuclear or concentrating solar - on the nation's waters. However, by lumping together all types of solar technology as "solar systems," the Senator brazenly ignores the distinction between solar photovoltaic technology - used in the typical rooftop solar panel - which uses virtually no water and concentrating solar power which has a higher water demand. And, his choice to highlight solar energy generation in particular, especially in a state that relies on similarly-thirsty fossil and nuclear energy production, strikes me as a little disingenuous.
Yes, the report is correct in stating that large-scale concentrating solar power plants can consume a lot of water if they rely on conventional wet cooling. But just as conventional power plants are now using unconventional methods for cooling, solar power plants have a wealth of options at their disposal.
A recent Renewable Energy World interview with energy consultant Babul Patel provides a great introduction to many of these options. I'm not going to lie - the interview is a shamelessly nerdy discussion about cost-benefits, the Rankine cycle and operational efficiency, so to pull a few highlights:
- The simplest idea is to use hybrid wet and dry cooling systems, where wet cooling kicks in only when the temperatures are too high for dry cooling to work effectively. According to Patel, such a system would require about 10 percent of the water that a plant would use if it relied exclusively on wet cooling.
- Concentrating solar plants could also use treated wastewater for its cooling needs, just as many fossil and nuclear power plants already do (http://www.netl.doe.gov/technologies/coalpower/ewr/pubs/reclaimed%20water.pdf). (PDF) According to Patel, as long as a power plant is sited near a population center, the cost of piping in wastewater is minimal.
- Or a plant could use virtually water-free solar photovoltaic technology, or could tap into saline aquifers, or be more efficient by recycling water for different uses - the list of technologies and strategies goes on and on.
There's also a bigger picture here. Some arid states withdraw tremendous amounts of water for agriculture, which in Arizona accounts for a staggering 68 percent of the state's annual water use. Another 25 percent of the state's water use is residential, and much of that goes towards keeping lawns green and pools full.
So how much of the state's water withdrawals goes towards cooling power plants? Thanks to many of the water-efficient technologies described above, less than 2 percent.
Nearly all solar power plants will require some amount of water, just as nearly all conventional power plants do. But in Arizona there are far larger pressures on the state's freshwaters than utility-scale solar power plants. The solar industry is implementing creative and forward-thinking strategies to reduce its water use, so Senator Kyl should take a moment to consider: if he sees a threat to his state's water supply when he visits a new emissions-free solar power plant, what does he see when he drives by neighborhood after neighborhood of lush, green desert lawns?