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Water supply projects are particularly well-suited for renewable energy applications. Distributed renewable energy sources, such as photovoltaic solar, wind, and in-conduit or micro hydropower should be utilized for new and existing water projects whenever practicable to reduce greenhouse gas emissions, protect utilities and their customers from spikes in fossil fuel costs, and decrease the water demand associated with conventional sources of electric power.
It takes a tremendous amount of energy to reliably supply clean drinking water in the United States. It is estimated that moving and treating water in the U.S. accounts for approximately 4% of the country’s electricity consumption. In the first detailed study of its kind, the California Energy Commission found that 19% of the electricity, 30% of natural gas and 88 million gallons of diesel fuel are consumed each year as a result of water use in California – the State Water Project, which delivers water from the San Francisco Bay-Delta to Southern California, is the largest single user of energy in California. Indeed, energy consumption by water and wastewater utilities is generally on the order of 30-60% of a typical city’s energy bill.
Considered in the context of climate change, the water and wastewater sector will need to significantly curtail its energy use and greenhouse gas emissions. While water and wastewater provisions already account for a significant share of total U.S. energy demand, the following trends suggest that water-related energy use in the United States is poised to grow at an accelerated pace:
Groundwater - Declining aquifer levels as a result of unreplenished groundwater withdrawals can increase the lift, and thus the pumping energy, required to extract water from groundwater resources. Sea level rise due to climate change is projected to result in saline groundwater moving landward as saltwater intrusion, further diminishing the availability of local, low-energy water supplies for coastal communities. Freshwater aquifer depletion in areas with underlying brackish groundwater can result in contamination and require more energy for treatment.
Water Treatment- More stringent water quality standards could require the adoption of new technologies that increase the energy required for water and wastewater treatment.
Power Generation- Power plants already account for 52% of total U.S. water withdrawals (both fresh and saline) and one out of every four gallons of nonagricultural freshwater consumption. Technologies being considered to reduce greenhouse gas emissions, such as carbon capture and sequestration and concentrating solar power, require up to one third and twice as much water, respectively, for cooling than conventional thermoelectric power generation. If current trends persist, consumption of water for electricity production – which is growing fastest in the West, where water resources are already over allocated – could more than double by 2030, resulting in even greater pressure on existing water supplies.
As you can see, there are a number of reasons to suspect that the energy and resultant greenhouse gas emissions required to provide reliable drinking water supplies is going to keeping climbing unless we make some changes. In addition to water conservation, efficiency and reuse, powering water projects with clean and renewable energy is a great way to reduce the carbon footprint of water use and help address climate change.
Power Water Projects with Clean, Renewable Energy
With the price of fossil fuels likely to increase due to growth in demand and future regulations limiting greenhouse gas emissions, deploying renewable energy projects in conjunction with water supply projects can stabilize and ultimately reduce energy costs over the life of a project. Photovoltaic solar, wind, and in-conduit or micro hydropower
The intermittency issues associated with sources of renewable energy makes them ideal for powering pumping stations because water can be pumped when the energy is available and stored for later use when renewable energy output declines. Furthermore, hybrid systems of wind and PV solar (equipped with or without backup generators) have been shown to provide reliable, uninterrupted power because wind and solar function independently of each other.
A variety of environmental gains can be achieved by utilizing renewable energy for pipeline projects, including water, land and air emission benefits. Electricity or diesel fuels are most commonly used to power pumping stations and both are carbon intensive. Using renewable energy can help offset the additional greenhouse gas emissions that would result from the new energy demands of the pipeline project.
Because these energy demands are related to a water supply project, it is important to note the water savings that can be achieved by utilizing certain types of renewable energy. On average, 2 gallons of water is consumed for every kilowatt hour of electricity produced in the United States, which means that new water supply projects powered with conventional energy have the potential to increase water demands. PV solar, wind and in-conduit hydropower require virtually no additional water to operate, an important consideration given the growing scarcity of water.
Building transmission lines to connect pumping stations to existing electric power supplies can result in significant land-use changes, environmental degradation and capital costs. Deploying renewable energy applications can avoid the substantial environmental and capital costs associated with building new transmission lines to remote pumping stations.
Examples of Renewable Energy for Water Projects
A number of water supply projects have already utilized renewable energy technologies, providing a proven track record for these approaches. In California, for instance, water agencies are currently the largest customer group for solar installations, with 20 MW of generation currently in operation or under construction, and nearly 50 MW pending with request for proposals going out. A few examples of solar installations for water supply projects include:
The Las Gallinas Valley Sanitation District in San Rafael, CA, built a series of solar panels that generate 571 kilowatts of electricity. When compared to the cost of using grid-tied electricity, the system is expected to save $136,000 in the first year alone, while eliminating 890,000 pounds of carbon dioxide emissions annually.
In 2004, the Palmdale Water District installed a 950-kW wind turbine at a water treatment facility for an installed cost of $2.1 million. The turbine is expected to offset all of the facility’s energy consumption and recoup installation costs in under 10 years.
The Inland Empire Utilities Agency in California has initiated a solar power project expected to generate 2.5 MW of energy and save about $200,000 a year in energy costs.
The Desert Water Agency in Palm Springs, CA, relies on a 300-kW solar photovoltaic system to offset energy costs. Originally projected to have a 10 to 11-year payback, increases in energy prices of nearly 30% mean that the system’s payback period will likely be significantly less.
The Las Vegas Valley Water District has been operating solar photovoltaic systems at six reservoir and pumping station sites since June 2007 with a combined capacity of a 3.1 MW. The system cost $23.4 million to build and is being paid back through actual annual energy savings of approximately $725,000 annually and through the sale of renewable energy credits to a local electric utility. This yields a payback period of 11.6 years for a system with a projected lifetime of 35 years.
In September 2009, Secretary Salazar signed Secretarial Order No. 3289, entitled “Addressing the Impacts of Climate Change on America’s Water, Land, and Other Natural and Cultural Resources,” which mandates the development of integrated mitigation and adaptation strategies within the Department of the Interior. In order to help DOI – and the country as a whole – meet climate change mitigation and adaptation goals, it is imperative that the energy costs of providing safe and reliable drinking water is minimized first through water conservation, efficiency and reuse, then through the adoption of renewable energy technologies to power energy intensive water operations.