Electrical Infrastructure at Hoover Dam.

Sizing Up Electricity’s Water Footprint

In water to make energy, water use

 

Estimating the Water Footprint of Different Electricity Generation Methods

2013 paper by Meldrum et al., takes a crack at creating the water footprint of the entire life cycle of different electricity generation technologies, and in so doing reveals a lot of gaps in water resource data. Water withdrawal and consumption estimates (learn about the important differences) for electricity generation are tough to make because there are so many variables involved in the estimates.

Besides the water needs of different fuel sources and generation technologies – coal, gas, nuclear, hydropower, solar, geothermal, wind – there are other factors to consider:

  • How much water is required in the fuel cycle to extract, process and transport fuels to a power plant?
  • How much water is needed to construct a plant or make all the necessary components?
  • How long is the plant expected to generate electricity?
  • How about the water needed to decommission the plant?

Authors of the 2013 paper screened thousands of scientific papers, government reports and corporate sustainability reports in an attempt to answer these questions.

How much water does generating electricity require?

It depends. In fact, there is significant variation as illustrated by the paper’s supporting dataDespite all the variability (and limitations to available data), there are some important generalizations that can be made:

Thermoelectric Power Plants

In the United States, a high percentage of electricity is generated by thermoelectric power plants.

  • These facilities use fossil fuels – coal, oil and natural gas – or nuclear fuels to boil water for steam to spin turbines and generate electricity.
  • While water used for cooling steam at conventional thermoelectric plants dominates the water footprint of most sources of electricity, the amount of water needed for the fuel cycle – extracting, processing and transporting fuel – and construction of plants can be substantial.
  • For thermoelectric technologies, more water is consumed during the operations phase –which primarily means cooling – than any other phase of electricity generation. (This includes solar thermal power plants which use large fields of mirrors to concentrate sunlight and heat water, producing steam that spins turbines; similar to nuclear, gas and coal-fired plants.)

Non-thermal Renewables

Non-thermal renewable technologies that have no need for cooling water, like wind and solar photovoltaics, have a much lower total life cycle water use than thermoelectric generation technologies. It’s worth noting that most of the water consumed by non-thermal renewables is for the manufacture of equipment, though this is much less than thermoelectric power plants require.

Hydroelectric Generation

Hydroelectric generation’s water footprint ranges from small to large depending on how evaporation from the surface of the artificial reservoir created behind the dam is factored into the accounting. A paper, authored by Mekonnen and Hoekstra provides the scientific support for the claim that “hydroelectric generation is in most cases a significant water consumer,” depending upon if it is “merely an in-stream water user or whether it also consumes water.”

Carbon Capture and Sequestration

Carbon capture and sequestration is a set of technologies that can greatly reduce carbon dioxide (CO2) emissions from new and existing coal- and gas-fired power plants and large industrial sources. They are anything but water-friendly – they can increase water consumption by 75 percent and water withdrawals by up to 97 percent.

It’s important to note that the authors qualified the estimates presented in their paper, referring to them as “few in number, wide in range and…of questionable original quality.” Yet this paper represents an important first step towards creating a true water footprint of electricity by collecting many of the estimates that have been made. 

Fuel Cycle

For coal, natural gas and nuclear, the water demand of the fuel cycle may be small when compared to cooling, but still represents a significant water use. Fuel cycle refers to the complete fuel production chain which consists of the following main stages: (1) extraction, processing and transport of primary fuels; (2) refining or other conversion processes; and (3) transmission and distribution to the site in which the fuel will be consumed.

Why Thermoelectric Power Plants Are Particularly Problematic

According to the Union of Concerned Scientists (UCS), thermoelectric generation’s dependence on cooling water poses a problem “during times of drought or other water stress, when water is simply not available in the required volumes or at the required temperatures.” In recent years, power plants have been forced to temporarily shut down or reduce output due to drought or reduced water supplies. According to UCS, that trend will continue – the changing climate will continue to place thermoelectric power plants at higher risk. In contrast, wind and solar photovoltaic systems do not require water to generate electricity.

When a plant unexpectedly shuts down or has to reduce its electrical output, there are impacts to a reliable and affordable power supply both in the short term and long term. This is another reason why renewable power sources like solar and wind have become increasingly attractive and practical.

There are also ecological impacts to consider: Under normal operations, power plants across the nation kill hundreds of billions of fish and aquatic life every year because of their cooling water intake systems. Also, the warm or hot water that is discharged back into the source like a river or lake, can be detrimental to aquatic species. Power plants that operate during drought conditions and water scarcity can exacerbate this impact.

Why Does Electricity’s Water Footprint Matter?

In a water-constrained world, electricity production’s reliance on ample supplies of water throughout its life cycle is an issue that demands attention – whether it’s the significant evaporation from the manmade reservoirs formed behind hydroelectric dams or power plant cooling systems that draw water (hundreds of millions or even billions of gallons over the course of year) from lakes, rivers, oceans or aquifers.

By relying more on non-thermal renewable energy technologies such as wind and photovoltaics, electricity’s water footprint can be reduced, and other environmental benefits can be achieved, such as a reduction in carbon emissions and a lower impact to ecosystems. In addition, reduced reliance on water buffers electricity generation and grid stability in times of water stress thereby minimizing the risks of shut downs.

As the researchers from the 2013 paper suggest, there are a lot of unknowns for many of the life cycle stages of electricity, meaning there’s a big opportunity for researchers to determine how much water electricity generation actually requires. Fuel sources and technologies that fall on the low end of the water footprint spectrum must play a major role in meeting electricity demand going forward.