EW-R-4: Water efficiency of thermal power plants

The image shows an aerial view of a nuclear power plant with a cooling tower emitting water vapour at the edge of a river.Click to enlarge
Water-efficient cooling systems are less dependent on freshwater, less vulnerable to drought periods
Source: Photograph: © fototrm12 / stock.adobe.com

2019 Monitoring Report on the German Strategy for Adaptation to Climate Change

Table of Contents

 

EW-R-4: Water efficiency of thermal power plants

As a result of increased efficiency and measures such as multi-use or recycling, the application of freshwater for cooling purposes declined significantly. In 2010 it had decreased by a third compared to 1991 figures. Overall, the demand for coolant water for use in thermal power plants will play a diminishing role in the course of energy transition.

The line graph represents the amount of water for single use (with a significant decreasing trend) and water efficiency (with a significant increasing trend) from 1991 to 2016 on a scale indexed to 100 for 1991. The additionally depicted time series for electricity generation of thermal power plants, which extends to 2017, shows a quadratically decreasing trend.
EW-R-4: Water efficiency of thermal power plants

The line graph represents the amount of water for single use (with a significant decreasing trend) and water efficiency (with a significant increasing trend) from 1991 to 2016 on a scale indexed to 100 for 1991. The additionally depicted time series for electricity generation of thermal power plants, which extends to 2017, shows a quadratically decreasing trend.

Source: StBA (environment statistics; monthly report on electricity supply)
 

Water shortage as a problem for conventional thermal power plants

In hot and dry summers, the supply of freshwater for cooling purposes can become a bottleneck for electricity generation in thermal power plants which are dependent on the availability of coolant water. However, thermal power plants make a minor contribution to electricity generation in the course of energy transition. The demand for coolant water will therefore play a diminishing role in the future progress of energy transition.

So far the energy industry is still by far Germany’s largest consumer of water. More than half of all the groundwater and surface water abstracted in Germany is used in the process of energy supply, especially for refrigeration purposes in thermal power plants.

Just under 95 % of the water used for cooling purposes in energy supply is used in continuous-flow cooling systems. Commercially speaking, continuous-flow cooling systems were considered the most efficient; that is why this became the most common type of cooling system applied in German power plants. On the other hand, this is also the most water-intensive cooling system. The coolant water is abstracted from a water body and used for cooling just once in the power plant’s steam cycle. Subsequently, the heated water is returned to the water body. Dependent on the location, cooling towers may be used in this process in order to reduce the temperature of coolant water and to avoid any undesirable or prohibited heating effects in rivers into which the water is returned.

In order to pre-empt shortages, it is possible for instance to decrease the coolant water demand for thermal power plants by means of technical measures. The use of circulatory cooling systems can result in a distinct decrease of water demand in thermal power plants. In this case, cooling can take place in an open system (wet cooling) or a closed system (dry cooling). In open systems, water abstraction from water bodies is required only for the compensation of evaporation losses; compared to continuous-flow cooling, this amounts to just 2 to 3.5 %.

In dry cooling the heat is discharged to the air by means of convection using a heat exchanger. In this case, there is no evaporation loss, i.e. the requirement for water is minimised. It is also possible to combine the two systems in so-called hybrid coolers.

Alongside the increasing use of water-saving technologies, the technical optimisation of thermal power plants plays an important part in water efficiency. In past years it was possible to achieve a considerable increase in the degrees of efficiency of power plants by using fossil-fuel energy carriers. As a result of such developments water efficiency increased continuously. At the same time, nuclear power plants and hard-coal power plants make a minor contribution toward electricity generation. Consequently, it is not quite foreseeable at present what importance might be attributed to a water-saving application of coolant water.

 

Interfaces

EW-I-3: Reduced power generation due to ambient temperature in thermal power plants

WW-R-1: Water use index

WW-I-4: Low water

 

Objectives

Consideration of technical methods and enhancements to achieve more efficient cooling in power plants in line with the principle of proportionality (DAS, ch. 3.2.3)

Determining and assessing potential supply risks and establishing measures for the reduction of any such risks (DAS, ch. 3.2.9)