Burning coal to generate electricity has serious problems related to climate change and air pollution, but it’s also too thirsty to keep up. If the average home in the US received all of its electricity from coal, about 370 eight-person hot tubs full of water would have been wasted to generate that electricity. Now that wind and solar are as cheap as they are, it’s time to leave our freshwater alone.
How does that add up? Well, let’s start with the water usage per MWh and work up the numbers. According to the Union of Concerned Scientists:
Like all thermoelectric power systems, coal plants require cooling. Three major options are available: once-through, wet-recirculating, and dry cooling. About 53 percent of coal plants in the United States use once-through cooling, about 40 percent use wet-recirculating, and less than one percent use dry-cooling. Table 1 shows water requirements in gallons per megawatt-hour (MWh, or thousand kilowatt-hours) of electricity production. (Despite their name, dry-cooling systems still require water for system maintenance, cleaning, and blowdown, as explained below).The UCS summarized this from an extensive study that is worth reviewing in detail.
A little math tells us that this represents a range of from 11 to 27 gallons (49-120 litres) per kWh is withdrawn from fresh water supplies. This water must be present in sufficient volume and temperature that there is enough thermal variance for cooling the high temperatures in thermal plants, and global warming is already causing coal and nuclear plant shutdowns and reductions in service. This water is heated and much of it is returned to groundwater such as lakes and rivers, causing thermal pollution problems, so while the water is “clean,” it is still causing environmental challenges. Some of it is lost entirely to evaporation, perhaps ⅓ to ⅔ of a gallon (1–3 litres) per kWh consumed.
According to the US EIA, the average home in that country used 10,932 kWh per year in 2014, which means that just electricity use for the average family powered by coal would withdraw about 120,000–300,000 gallons (530,000–1,300,000 litres) annually, and about 3,000–7,300 gallons (13,400–33,000 litres) is lost entirely, ignoring the thermal shock and pollution. That would fill up to 360 eight-person hot tubs, and waste about nine hot tubs worth over the sides.
This isn’t the entire story, of course. Coal extraction and transportation is harder to pin down and varies widely as well. Strip mining buries freshwater sources, coal washing requires and pollutes enormous volumes, and slurry pipelines require enormous volumes of water as well.
And coal burning is responsible for freshwater pollution, of course. The EPA calculates that burning coal generates over 50% of mercury emissions in the USA, and sulphur removal from coal plants produces about 200,000 lbs per year of sludge waste per plant, which also involves water usage.
The moderately silly idea of making coal generation much more expensive by adding carbon capture and sequestration would require a lot of water too, as:
Adding carbon capture and storage to a coal plant would increase its water consumption 45 percent to 85 percent.
This should, of course, be compared to solar and wind energy, which withdraw virtually no water per kWh, consume no water per kWh, and pollute no water per kWh in the creation or transportation of their fuel. They also heat exactly no water in already-heated groundwater in the generation of electricity.
When reading the dense graphic below, don’t forget to look at each category of water usage for each type of generation. You’ll note that wind and solar only show up once, in the no-cooling-required category, while coal, natural gas, and nuclear show up all over the place.
This isn’t to imply that wind and solar have zero water usage per kWh on a full lifecycle basis, but the amount consumed during raw material extraction, refining, manufacturing, construction and operation is virtually non-existent on a per kWh basis compared to thermal generation technologies.
WATER CONSUMPTION–WIND AND SOLAR
Coal generation consumes, overheats, and pollutes far more water than any reasonable person or organization would think worthwhile. If coal generation were presented as a technology today for the first time, it would be laughed out of boardrooms just based on water issues alone. It’s only the legacy of use that makes it seem reasonable at all.
Water usage is just one of the ways in which coal generation is a vastly inferior product to alternatives. The compromises were reasonable in the industrial revolution, but not any more.
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