Water for Energy: Reducing the Carbon Water Footprint

Water for Energy: Reducing the Carbon Water Footprint

Water and energy are inextricably linked and mutually dependent, with each affecting the other’s availability. Water is needed for energy generation, energy source support, and energy fuel development. Conversely, power is needed for water pumping, purification, and portable water delivery. This linkage provides many opportunities for reduction of the carbon footprint of the water energy nexus. There is a significant need for a system-level understanding of the processes and choices so as to guide development to best address the challenges. This paper will explore options available to the technology and policy community to generate electricity from water driven power plants. The interest is driven by two observations:

1. Water driven power plants have virtually no carbon imprint after development.

2. Many of the new approaches generate baseload renewable power with no requirement for intermittent nature driven processes e.g. wind and sun. This is also true to some extent of many of the older approaches such as hydropower that is only interrupted by drought or required maintenance.

Water as an energy source:

Conventional hydropower: In generating electricity, hydroelectric power plants do not release carbon dioxide (CO2). Government research has found that a large hydroelectric power station emits the equivalent of between 10 and 30 grams of CO2 for each kilowatt-hour (kWh) of electricity it generates. To the extent our energy is a result of hydropower, there is virtually no carbon footprint in operation.

Hydropower with energy storage: Pumped storage hydropower is usually not a source for energy. The hydraulic, mechanical and electrical efficiencies of pumped storage determine the overall cycle efficiency, ranging from 65 to 80%. If the upstream pumping reservoir is also used as a traditional reservoir the inflow from the watershed may balance out the energy loss caused by pumping. If not, net losses lead to pumped hydropower being a net energy consumer. However, if the pumping is derived from renewable energy sources, the carbon footprint has the potential for being relatively small.

Small hydro: Studies have estimated significant potential for increased deployment of hydropower in the United States, with additional generation capacity of at least 80,000 megawatts, mostly provided through the development of new small and micro hydroelectric plants (accounting for nearly 59,000 megawatts).

Hydrokinetics: Hydrokinetic technologies produce renewable electricity by harnessing the kinetic energy of a body of water, the energy that results from its motion. Since water is 832 times denser than air, our tides, waves, ocean currents, and free-flowing rivers represent an untapped, powerful, highly-concentrated and clean energy resource. Estimates suggest that the amount of energy that could feasibly be captured from U.S. waves, tides and river currents is enough to power over 67 million homes. 

Osmotic power: This is the energy available from the difference in the salt concentration between seawater and river water. The osmotic power process can convert the pressure differential between two water streams into hydraulic pressure that can be used to drive a turbine to produce electrical energy. The technology works in unison with the turbines to cost-effectively enable stable, reliable, environmentally friendly energy production anywhere freshwater and salt water are available.

Geothermal: Geothermal has a long history in the United States-the first plant opened in 1971. The vast majority of the country’s 66 geothermal plants with at least one megawatt of capacity are in the Southwest, mostly in California. Within California, more than three-quarters of generation comes from two counties: Imperial home to the Salton Sea, home to the Salton Sea resource area and Sonoma, home to the world’s largest geothermal field, the Geysers. The 11 plants by the Salton Sea generate about 400 megawatts of electricity, and researchers have estimated that an additional 2,000 megawatts could be available. By comparison, there are currently only 3,700 megawatts of generation nationwide.

Lagoon Power: One of the newest and most interesting water driven power plant is the plan to generate electricity from tidal lagoons. This effort is being led by the United Kingdom but the US indicates backing from the Department of Energy. There are six lagoons in the project-four in Wales and one each in Somerset and Cumbria. They will capture incoming and outgoing tides behind giant sea walls and use the weight of the water to power turbines. The cost of generating power from the project will be very high but subsequent lagoons will be able to produce electricity much more cheaply. The series of six lagoons could generate 8% of the UK’s electricity for an investment of $45B.