Water-energy nexus

The water-energy nexus[1] is the relationship between how much water is evaporated to generate and transmit energy, and how much energy it takes to collect, clean, move, store, and dispose of water.

Water for Electricity

All types of electricity generation consume water either to process the raw materials used in the facility or fuel, constructing and maintaining the plant, or to just generate the electricity itself. Renewable power sources as photovoltaic solar and wind power, which require little water to produce energy, require water in processing the raw materials to build the turbines and solar panels. If a wind turbine is mounted on a concrete or steel tower, additional tonnes of water are required in the tower's construction.

In the US, about 2 US gallons (7.6 L) of water is evaporated to create one kilowatt hour (kWh) of energy.[2] This water is consumed in thermoelectric plants which are power plants converting waste heat into electrical power and evaporated in reservoirs for hydroelectric plants. An average of 18 gal (68 L) of fresh water is evaporated to generate 1 kWh of electricity at a Hydroelectric plants.[2] The production of electricity to power one 60W incandescent light bulb over the course of a year would evaporate about 3,000 to 6,300 US gallons (24,000 L) of water.[3]

Thermal power plants require large amounts of cooling water. 39% of all freshwater withdrawals in the USA are used for thermoelectric energy production.[4] Most of the cooling water is returned but at a higher temperature, and only around 3% is actually consumed, mostly by evaporation.[5] The demand for cooling water can be in competition with agriculture and municipal demands in some areas with the demand for water for irrigation around 40% overall.[5] As a result of climate change some rivers are running lower in the summer, putting additional strain on power production.

Electricity for Water

As energy requires water, water supply and sewage disposal needs energy.[6] Drinking water must be pumped to the treatment plant, pre-treated, and then pumped to consumers. In areas where fresh water is scarce and drinking water must be brought in from a long distance, the energy footprint for this drinking water is extremely high. The energy consumed for pumping groundwater is typically between 537 kWh and 2,270 kWh per million gallons depending on pumping depth, but as an example, southern California receives potable water from the Sacramento-San Joaquin Delta which travels over low-lying mountains and requires 9,200 kWh per million gallons.[7]

Treatment of wastewater and stormwater can also consume significant energy. Combined sewer systems use the same pipes for conveying stormwater and wastewater. During precipitation events, stormwater can swell and even overwhelm the shared pipe resulting in sewer overflows, extra wastewater treatment, and flooding. There are nearly 800 cities with combined sewer systems in the US.[8] Many municipalities are in the process of installing storage tunnels and high rate treatment facilities to store and treat the large volume of storm/sewer water during precipitation events. The overflow captured and treated at these new facilities is projected to be in the billions of gallons annually per city and will only increase the water-related energy consumption in these communities. Even areas with newer, separate stormwater systems still experience infiltration and inflow of runoff in sanitary sewers and must treat stormwater at wastewater treatment facilities.

According to the River Network, the U.S. consumes at least 521 million MWh a year for water-related purposes which is the equivalent to 13% of the nation’s electricity consumption.[7] The energy required to heat water is even higher. Fuel oil, propane, electricity, and natural gas are used to heat water in the US, all together consuming the kWh equivalent of 304.2 billion kWh each year.[7] Water related energy use in California alone including the conveyance, storage, treatment, distribution, wastewater collection, treatment, and discharge sectors, consumes 19 percent of the state’s electricity, 30 percent of its natural gas, and 88 billion US gallons (330,000,000 m3) of diesel fuel annually.[9]

Water/Runoff Footprints

Water-energy nexus is a term for the interrelationship of both water and energy. Excessive consumption of both can lead to resource depletion, pollution, and an overall increase in the price for each. By conserving water and reducing runoff, the negative impacts of the water-energy nexus can be mitigated. A "water footprint" is an assessment of the amount of potable water used by an individual, community, business, or nation for outdoors irrigation and indoors. Through a Water footprint, one can learn how much water is consumed and by what. Action can then be taken to reduce water consumption from the activities with the highest impact. Low-flow aerators, toilets, and showerheads can be installed inside, while sustainable landscaping can be planted outside to reduce the need for irrigation. A Runoff footprint can be completed to assess how to sustainably reduce stormwater runoff on a site, preventing it from entering the local stormwater system and being treated at a waste water treatment plant...

See also

External links

References

  1. ↑ California Sustainability Alliance, Cynthia Truelove, Senior Water Policy Analyst, California Public Utilities Commission, http://sustainca.org/programs/water_energy/videos, sustainca.org
  2. 1 2 Consumptive Water Use for U.S. Power Production, P. Torcellini, N. Long, and R. Judkoff
  3. ↑ Water Cooler, The intertwined tale of energy and water, Rachelle Hill and Dr. Tamim Younos
  4. ↑ U.S. Energy Sustainability http://www.sandia.gov/energy-water/nexus_overview.htm
  5. 1 2 Energy Demands on Water Resources. REPORT TO CONGRESS ON THE INTERDEPENDENCY OF ENERGY AND WATER. http://www.sandia.gov/energy-water/docs/121-RptToCongress-EWwEIAcomments-FINAL.pdf
  6. ↑ Plappally, Anand; John Lienhard (2012). "Energy requirements for water production, treatment, end use, reclamation, and disposal". Renewable and Sustainable Energy Reviews] 16.
  7. 1 2 3 River Network. The Carbon Footprint of Water. http://www.rivernetwork.org/resource-library/carbon-footprint-water
  8. ↑ Trees: the New Sewers. http://www.americanforests.org/magazine/article/trees-the-new-sewers/
  9. ↑ Energy Use in California Assembly Committee on Water, Parks and Wildlife ,February 20, 2007Martha Krebs


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