Cooling tower of the unfinished Chernobyl reactors 5 and 6
A new study by Michelle T. H. van Vliet, John R. Yearsley, Fulco Ludwig, Stefan Vögele, Dennis P. Lettenmaier, and Pavel Kabat released in Nature Climate Change finds that climate change will impact the 91% of US and 78% of European power that is produced by thermal power plants. In the near future, power potential is expected to be reduced from 4 to 16%, with the possibility of a complete system collapse tripling or more.
Thermal Power Plants
Power plants that use heat to produce electricity are thermal power plants. This includes nuclear, coal, solar thermal, gas, and geothermal. Gas is often used in a gas turbine peaking power plant. Such power plants are quickly turned on and off but, historically, have been the most expensive to run. Other plants use the heat to produce steam in a Rankine cycle.
The Rankine Cycle
An old but still common way to make electrify is to boil water to produce steam in a Rankine Cycle to turn a turbine. It is highly inefficient and water-wasteful to let that steam escape after it has done its work, so it must be cooled to a liquid (condensed) and returned to a boiler to complete a cycle.
Condenser Types
Cooling the steam takes place in a condenser. It is most efficient to cool the steam with the coldest possible substance, but cost dictates that it should be cooled from a readily available source. There are two common variations. The first is to directly take in water from a river or lake and pass it over pipes containing the steam. The second also uses a liquid condenser but the water is pumped to a cooling tower where some of it is allowed to evaporate. (You have no doubt seen this water vapor rising from cooling towers.) Although this uses less water, a supply is needed to replace what has evaporated. The once-through method was used in the US mostly before 1970 and the wet cooling tower was used mostly after that time.
A third method uses air to cool the steam (using a dry cooling tower). Because the air is so much warmer and cannot contain as much heat, this is the least efficient and most expensive method, but it is in some cases the most practical option. In a window air conditioner, it is the air-cooled condenser (part that looks like a radiator on the outside) that makes the unit so bulky. A liquid-cooled condenser would be about the size of a thermos.
The Cooling Water
Most of the water used for cooling is freshwater. Together, Europe and North America consume 86% of the water used in the world to cool thermal power plants, 43% of all surface water comsumption.
Prior to construction, power plants are required to specify the source of water resources, including details such as how much water they will use, seasonal variations, and anticipated temperature differences. But what has not been anticipated in some studies now decades old is the warming climate.
The Warming Climate
Base water temperatures are now expected to rise. Water flow will decrease. Neither of these futures was foreseen during original construction. Power plants will be required to cease operations to avoid operating outside the regulated and design boundaries. This is not wild speculation. Last year we reported this has already happened in Tennessee. Not surprisingly, the study also concluded the problem will be most severe in the Southeast US. And in a more recent article, geothermal was being pursued in East Africa because severe seasonal drought was making hydroelectric unreliable.
Options
Preparations must be made prior to increasingly severe weather. We will have to shift to power generation that does not need water, like solar photovoltaics and wind power. Or, at some cost, we must adapt present thermal power plants to limit water use and make them work acceptably in the midst of higher temperature disruptions. A government that does nothing for four years, waiting for the next election cycle, is not an option.
Image Credit: Cooling tower of the unfinished Chernobyl reactors 5 and 6 by Timm Suess (CC BY-SA 2.0)
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