	Concentrating Solar Power and Its Water Use

Large-scale deployment of concentrating solar power (CSP), a renewable energy technology for generating electricity, has the potential to affect the availability of water resources in the Southwest for other uses. Because the water demand of CSP is highly dependent on the type of CSP facilities constructed (e.g., whether thermal storage is included and whether wet cooling is used) and their locations, and because the data for these evolving technologies are preliminary, there remains much uncertainty about the impacts of CSP on Southwest water use. Water resource constraints are likely to prompt adoption of more freshwater-efficient technologies, or decisions not to site CSP facilities in certain locations. However, water constraints do not necessarily preclude CSP in the Southwest, given the ability to reduce the freshwater use at CSP facilities. The quantity of electricity produced at these facilities, the water intensity per unit of electricity generated, and the local and regional constraints on freshwater will shape the cumulative effect of CSP deployment on southwestern water resources, and the long-term sustainability of CSP as a renewable energy technology. Site-specific and cumulative water resource implications are among many factors (e.g., cost, climate and air pollution emissions, land and ocean impacts, wildlife and the environment impacts) to be weighed when judging the tradeoffs between different energy options. Convergence of Solar Abundance and Water Constraints

In arid and semi-arid regions like the Southwest, or other areas with intense water demand, water supply is an issue for locating any thermoelectric power plant, not only CSP. The cumulative impact of installing multiple thermoelectric power plants in a region with existing water constraints raises numerous policy questions. This concentration of CSP in a region of the country with water constraints has raised questions about whether, and how, to invest in large-scale deployment of CSP. Why is there concern specifically about the CSP water footprint? The water intensity of electricity from a CSP plant with wet cooling generally is higher than that of fossil fuel facilities with wet cooling. Options exist for reducing the water consumed by thermoelectric facilities, including CSP facilities; however, with current technology, these options reduce the quantity of energy produced and increase the energy production cost. A Trend Toward More Freshwater-Efficient Cooling

The trend for new thermoelectric generation, including CSP, in water-constrained areas is toward more freshwater-efficient cooling. Water-Efficient Cooling Technologies

Alternatives to wet cooling can significantly reduce the freshwater footprint of CSP. Most electricity siting and water planning, management, and allocation decisions are delegated to the states. Whether and how the federal government should promote water conservation, efficiency, markets, and regional- and state-level planning and collaboration is a matter of debate, and actions in these areas often occur on a piecemeal or ad hoc basis. At the same time, federal policies (e.g., energy, agriculture, and tax policies) can affect water-related investments and water use, and operations of federal facilities can affect the water available for allocation.
As the 111th Congress considers energy and climate legislation, the land and water impacts of renewable technologies are receiving greater attention. The cumulative impact of installing numerous thermoelectric power plants on the water resources of the Southwest, a region with existing water constraints, raises policy questions.
Solar Abundance and Water Constraints Converge. Many Southwest counties are premium locations for siting solar electricity facilities, but have constrained water supplies. One policy question for local, state, and federal decision-makers is whether and how to promote renewable electricity development in the face of competing water demands. A principal renewable energy technology being considered for the Southwest is concentrating solar power (CSP), which uses ground-based arrays of mirrors to concentrate thermal solar energy and convert it into electricity. The steam turbines at CSP facilities are generally cooled using water, in a process known as wet cooling. The potential cumulative impact of CSP in a region with freshwater constraints has raised questions about whether, and how, to invest in large-scale deployment of CSP. Much uncertainty about the water use impacts of CSP remains because its water demand is highly dependent on the location and type of CSP facilities constructed (e.g., whether thermal storage is included and whether wet cooling is used), and because the data for these evolving technologies are preliminary.
Water Consumption and Electricity Generation Tradeoffs. In arid and semi-arid regions like the Southwest or in other areas with intense water demand, water supply is an issue for locating any thermoelectric power plant, not only CSP. The trend is toward more freshwater-efficient cooling technologies for CSP and other thermoelectric generation. Why is there concern specifically about the CSP water footprint? CSP facilities using wet cooling can consume more water per unit of electricity generated than traditional fossil fuel facilities with wet cooling. Options exist for reducing the freshwater consumed by CSP and other thermoelectric facilities. Available freshwater-efficient cooling options, however, often reduce the quantity of electricity produced and increase electricity production costs, and generally do not eliminate water resource impacts.
The quantity of electricity produced at these facilities, the water intensity per unit of electricity generated, and the local and regional constraints on freshwater will shape the cumulative effect of CSP deployment on southwestern water resources and the long-term sustainability of CSP as a renewable energy technology. Water resource constraints may prompt adoption of more freshwater-efficient technologies or decisions not to site CSP facilities in certain locations.
Next Steps. Water constraints do not necessarily preclude CSP in the Southwest, given the alternatives available to reduce the freshwater use at CSP facilities. Moreover, water impacts are one of many factors (e.g., cost, climate and air pollution emissions, land and ocean impacts, wildlife and the environmental impacts) to be weighed when judging the tradeoffs between different energy options. States are responsible for most water planning, management, and allocation decisions and electricity siting decisions. Whether and how the federal government should promote water conservation, efficiency, markets, and regional- and state-level planning and collaboration is a matter of debate. At the same time, federal policies (e.g., energy, agriculture, and tax policy) can affect water-related investments and water use, and operations of federal facilities can affect the water available for allocation.