Clean Tech 101

Water-Energy Nexus

Energy and water share a very close relationship, a nexus, which if understood could solve water and energy problems.

A considerable amount of water is required to produce energy. Water is used for cooling steam electric power plants fueled by oil, coal, nuclear power and natural gas as well as the generation of hydropower. During fuel extraction, production and refining, large quantities of water are needed.

Similarly, a considerable amount of energy is needed for the treating and transportation of water. Energy is used for the extraction, movement and treatment of water for irrigation and drinking. It is used to collect, treat and dispose wastewater.

When water is used by industries and households especially through cooling and heating, energy is consumed.

Energy and water policy, management and planning must be combined to motivate innovation, encourage conservation and make sure that energy and water are used wisely.

End users, for instance, households and commercial establishments play a key role. By minimizing the amount of water consumed, end users not only conserve water but energy also. This can save money on utility bills.

Water Requirements of Energy Production

Electricity generation is processed in a number of ways that include thermoelectric generation, hydroelectricity, solar generation and wind energy generation. Each of the methods and their water consumption are discussed briefly below:

Thermoelectric Power Generation

Thermoelectric power plants make use of a fuel source for heat generation that drives generators and turbines for the production of electricity. Most of the thermoelectric power plants use steam turbines. With steam-electric turbines, heat generated from a nuclear reaction or fuel combustion boils water in order to create steam that drives a generator and a turbine for electricity generation.

Steam, passing through the turbine, is sent to a heat exchanger where cooling is done with water as a coolant. The water amount is withdrawn and consumed by thermoelectric power plants depending on several factors, which include fuel source, power cycle, plant efficiency and the cooling system.

In this case, either ground or surface water is used for pollutant and cooling scrubbing operations. Air and thermal emissions modify the quality of aquatic ecosystems and surface waters.

Hydropower and Wind Generation

Hydropower is the generation of power from the kinetic energy of moving water. Large amounts of hydropower is obtained from hydroelectric dams. Hydroelectric systems comprise of a reservoir, a dam and a powerhouse.

Water released from the dam is sent to the powerhouse where the water movement drives a turbine and generator producing electricity. In terms of quantity, reservoirs lose water due to evaporation.

Reservoir and dam operations modify water temperatures, flow timing, quality and aquatic ecosystems.

A wind turbine that includes a rotor with blades and an electricity generator is mounted on a tower that is higher than the ground surface where wind speeds are more constant and higher. Wind energy generation uses minimal amount of water for blade washing during operation.

Solar Photovoltaic Power Generation

Solar cells are used in solar photovoltaic technologies for the direct conversion of sunlight to electricity. Solar panels comprise of cells with semiconductors, normally silicon, that is capable of photon absorption from the sun, emitting electrons that become part of an electric current.

Utility-scale solar PV uses large solar panel arrays that feed electricity into transmission grids. These make use of minimal amount of water for panel washing during operation.

Other Energy Applications that Require Water

In oil and gas exploration, water is needed for drilling, hydraulic fracturing and well completion. Certain unconventional oil and gas resources have high water demands. In oil and gas production, water is needed for enhanced oil recovery. During production, large volume of impaired waters can be generated.

Coal and uranium mining can generate large water quantities that contain contaminants and impact the ecosystem. Production of ethanol and biofuels require water for growing biomass.

Water is also used for oil and gas refinery operations. Water is used for hydrostatic testing in energy pipelines, slurry transport in coal, slurry pipelines, and slurry mining of oil and gas storage caverns.

Energy Requirements for Water Treatment

Water treatment and transportation of water and wastewater requires 1 – 18% of electrical energy in urban areas. Treating water to drinking standards also requires energy.

Conventional methods are no longer enough to treat the levels of contamination in today’s water. Water supply and sewage disposal also require energy.

To describe it in simple terms, energy is used in five stages in the water cycle. These are:

  • Extracting and conveying water: Water extraction from streams and rivers or pumping the same from aquifiers then conveying the same over hills and into storage facilities is an energy-intensive process.
  • Water treatment: Water treatment plants make use of energy for the pumping and processing of water.
  • Water distribution: Energy is required for water transportation.
  • Water usage: Energy is consumed by end users for water treatment with filters or softeners for the circulation and pressurizing of water with irrigation systems and circulation pumps and for cooling and heating water.
  • Collection and treatment of wastewater: Energy is used for pumping wastewater to the treatment plant, to aerate as well as filter it to the plant.

By being careful about the amount of water used, we bring down the demand on the energy-intensive systems that deliver and treat water.

Quality and Quantity

For both water and energy, quantity and quality matter. The quality of water is determined by impurity concentration, constituents suspended, or dissolved in water and also by its physical characteristics such as temperature and color.

Water quality can be impacted considerably by energy-related projects. Water used for cooling in power stations is returned to the river with a higher temperature that may be harmful to marine life. Mining may destroy complete landscapes including streams.

Conclusion

The nexus between water and energy is gaining awareness mainly due to the wastage and inefficiency in the way both the resources are being used. Generation of electricity, transmission, distribution and storage have serious inefficiencies in many parts of the world.

In the same way, there are inefficiencies in water distribution systems. This connection implies that significant efficiency gains in the use of water will bring down electric power requirements, which will result in water savings that would have been used for power generation.

In simple terms, saving water saves energy and saving energy saves water. The more energy is saved, the easier it becomes to minimize the harmful effects of greenhouse gas emissions.

The more water saved, the easier it becomes to secure valuable freshwater resources and maintain a healthy climate-resilient environment.

References:

Kris Walker

Written by

Kris Walker

Kris has a BA(hons) in Media & Performance from the University of Salford. Aside from overseeing the editorial and video teams, Kris can be found in far flung corners of the world capturing the story behind the science on behalf of our clients. Outside of work, Kris is finally seeing a return on 25 years of hurt supporting Manchester City.

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