NEXUS researchers haven’t just looked at the water needs of renewable energy sources, they have also looked at how water itself can generate energy.

In every water delivery system throughout the United States, pressure-reducing values (PRVs) continually lower the high pressure of water so that it is suitable for customer use. NEXUS scientist Dr. Mehdi Etezadi-Amoli, at the University of Nevada, Reno (UNR) is investigating the potential for this process to also generate electrical power, using waste energy from the reduction process. To do this Etezadi-Amoli and his UNR team have looked at the efficiency of the water delivery system in Northern Nevada and proposed a scheme to convert the wasted energy into electricity.

By converting the electrical power into Direct Current (DC), the researchers can store energy in batteries, so that it can be used later to provide fixed power. Alternatively, the energy can be converted into alternating current (AC) to be pumped back to the power company or the distribution system.

“This is a renewable energy source that converts the wasted energy in PRVs to electricity,” Etezadi-Amoli says. “Water distribution stations can use the generated power to supply their local loads and even sell the extra amount to power companies.”

As water can be scarce in desert environments, NEXUS scientists have investigated the use of impaired waters and other sources of water that ordinarily would not be used for potable purposes in solar energy production. But using such water resources requires them to be “cleaned” and cleaning water is a process that requires energy.

To address this challenge, NEXUS researcher Dr. Sage Hiibel and his UNR team have developed an ingenious technology that supports both solar energy and water treatment. This technology uses waste heat from solar energy generation to power water treatment and the treated water for cleaning and other on-site needs.

The NEXUS technology hinges on a process called direct contact membrane distillation (DCMD), an emerging water treatment technique that can be used to treat many non-potable waters. In the symbiotic technology, waste heat from a solar energy facility supplies the energy required to warm impaired waters that are then processed through membranes to produce purified water that can be used to clean the solar panels or mirrors.

“This technology can be used to provide the clean water needs of the solar facilities. Because it uses low-grade waste heat to drive the process, it can be a sustainable option for solar facilities,” Hiibel says. “If we are careful and collect the water used for cleaning, we can reuse that water multiple times to maximize our water efficiency in arid environments.”

Expanding on the symbiosis between solar energy and water, Batista and Ahmad have also investigated using solar energy to pump shallow brackish groundwater to generate freshwater that could be used for solar energy generation or other purposes.

Groundwater aquifers that lie deep beneath the land surface already supply 15% of the Las Vegas water requirements. Now scientists are questioning whether shallow groundwater, which typically contains more salts and is known as brackish water, also has the potential to provide much needed water for human and industrial use. To generate usable water from a shallow source it is necessary to pump and to treat that water, as it typically contains high levels of total dissolved solids. Desalination techniques can remove dissolved solids from such brackish water to produce freshwater but it’s an energy-intensive process.

To test whether using solar energy to pump and treat shallow groundwater may be a viable option the NEXUS scientists have investigated the costs and benefits of using energy generated from solar PV panels to pump and desalinate a brackish shallow groundwater source in the Las Vegas Valley using a model.

The researchers findings imply that solar power was capable of supplying the energy for desalination of the shallow groundwater but constructing a solar plant of the required size might not always be feasible. But the team did find that using solar power to fuel the freshwater generation, instead of a fossil fuel energy source, made for a reduction of carbon emissions to the tune of 4,700 metric tons of carbon dioxide a year in the Las Vegas valley.

“Although the cost of pumping and treating brackish water with solar energy may not be significantly cheaper, there are intangible benefits associated with the process such as decreased carbon dioxide emissions, and an additional secure water source,” Batista says.