Water and energy

Last month, several nuclear power stations in Europe had to shut down during a heat wave (and consequent period of extreme electricity demand) to avoid releasing overheated water back into the environment.  As many other astute observers have pointed out, this pokes another big hole in the arguments that nuclear is our best choice of carbon-neutral generating technology.  A power plant that goes down precisely when you need the most power is almost useless for the current grid.

It also brings up the broader point of the role of water in electricity generation.  Nuclear is not the only technology that uses water for cooling.  Coal plants, including “next generation” IGCC plants mostly use water for cooling (air cooling can be used, but it makes them less efficient, and hence more expensive to run, and is seldom used in practice.)

This is a problem because water, in most countries is under-priced.  Resources that are under-priced tend to be overused, since the user does not have to bear the full cost of supply.  This is the cause of a large number of ills, such as the drying up of the Aral sea due to irrigation for cotton farming.  It is not only poor countries who don’t have enough water.  In the US, mispricing means that almost every aquifer is being pumped at much faster than sustainable levels.  In this context, it seems certain that power plants are also paying too little for the water they use for cooling.

 With a looming need to increase farming to supply biofuels, it is more important than ever that water be priced appropriately, especially in planning scenarios for power plants.  When water is under-priced, generation technologies which use more water are likely to be inappropriately favored in comparison to technologies which use little or no water for generation.

 Like nuclear, thermal electric systems are usually water cooled.  Fossil-fueled power plants account for approximately 39 percent of the water used in the United States, second only to agriculture. For coal plants, this typically amounts to 3 gallons of water (Texas study) or 0.5 gallons (NREL study) for every kWh produced (25 gallons are used for cooling, but only 3 evaporate in the process).  Nuclear, Biomass, and Oil fired plants also require large amounts of water lost as steam in the cooling process.   Some Solar thermal technologies also require significant water for cooling.

Water use by large hydropower projects is more complex, since water in reservoirs is more useful for some purposes (recreation) but often less useful for wildlife.  However, there is no question that reservoirs increase evaporative losses.  An NREL study quantifies these losses in the US.  Overall, in the US evaporative losses average over 18.2 gallons per kWh of hydroelectric power generated.  These numbers vary widely depending on the reservoir, from 2-3 gallons per kWh in cool northern states, up to over 100 gallons per kWh in KY, OK, SD, and WY.  Keep in mind that a lot of these reservoirs have other uses besides power generation, such as storing water for dry seasons, but the numbers can be mind-boggling.

Technologies which use little water include gas turbines (both natural gas and gas from renewable sources such as landfill gas), and geothermal (the water is typically re-injected into the ground).

Wind, photovoltaic, and wave power require no water to generate electricity. 

Energy efficiency, by its nature, uses no water.  Readers will recognize that as an ongoing theme: Given the choice, it is better to avoid using a kWh than it is to generate a kWh (regardless of source… even renewables have environmental impact.)

Renewable energy advocates should also be advocating for more rational water pricing, especially in planning scenarios.  Water use in generation will eventually come to be recognized as a significant cost (and source of uncertainty, as France found out last month).  The sooner this happens, the better for everyone.  Pricing water properly will not only save water, it will help move us to renewable energy technologies.

Investors may do well by concentrating their investments on low water use technologies, especially in parts of the world where water is (or will soon be) scarce.

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