By Christian Flinn
Desalination, the process of extracting salt from seawater and similar sources to create potable water for everyday use, is becoming increasingly important on a global scale in places where water resources are scarce and facing pressure from expanding populations and environmental changes. California is no exception and independent water producer, WaterFX, has begun fundraising for what it believes to be a solution for the drought-ridden State in the form of a $30 million desalination plant known as HydroRevolution.
HydroRevolution, which is essentially a commercial version of a demonstration plant that operated in the Panoche Water and Drainage District in 2014, would take advantage of the abundance of solar energy potential in the State by using it to power the plant in its entirety. In order to comprehend the importance of the proposal, understanding what desalination is and how it works is crucial.
The desalination process entails removing enough salt to ensure that any resulting water contains “less than 1,000 parts-per-million (ppm)” of salt, the maximum threshold of salinity that is still suitable for human consumption. While somewhere between 250-500 ppm of salt is normal in drinking water, both in terms of taste and health considerations, the main difference between desalinized water and regular tap water is that any desired nutrients or chemicals must be added to desalinized water because the process it goes through rids it of all components that are not water molecules. Though the quality of the produced water itself is something to consider, the most widespread concern is the cost of the process. This cost, in turn, largely depends on three things: method, source, and power supply.
Looking first at the method, it is important to note there are three processes widely used for desalination today: thermal distillation (TD), electrodialysis (ED), and reverse osmosis (RO). HydroRevolution would utilize TD, the most common of the three. At its most basic, TD involves evaporating the source water, thus separating it from salt and other particles, and then condensing the resulting water vapor into liquid form. Though TD has been around for decades, HydroRevolution claims that its method of powering the process, as well as its initiative in finding a source other than seawater, will demonstrate the plant’s benefits in terms of cost and environmental impact.
At this point, understanding the energy cost and source differences of the process becomes crucial. Desalination is an energy-intensive process and, depending on how high a source’s salinity levels are, separating the water molecules from any other particles present can become challenging and expensive. For example, one project in Carlsbad, California – a part of San Diego County – utilizes traditional RO that, in this case, is heavily reliant on fossil-fuel generated electricity. RO cost per cubic meter of water produced (m3) is somewhere between $7.98 and $29.00 for low capacity plants. For Carlsbad specifically, this translates to around “$3 billion over 30 years for only about 7 percent of the county’s water needs.” Here assuming that costs can be reduced over time as economies of scale take effect.
HydroRevolution would tackle the challenge differently by designing the plant to run entirely on solar energy. In doing so, HydroRevolution’s costs of energy production as well as equipment maintenance plummet, with the bulk of the cost being the initial investment in the enormous parabolic mirrors (known as heliostats) required to capture enough sun to power the process. For comparison, the initial investment in a large RO plant with a capacity of 200,000m3/day is around $160 million whereas the initial investment in a solar powered TD plant of comparable capacity and size is around $380 million. The flip side, as mentioned previously, is that in the case of the solar powered plant costs plateau, relatively speaking, for the life span of the heliostats (anywhere from 20-30 years) as energy production is essentially free and maintenance costs are low. In the case of an RO plant, which utilizes a series of filters to desalinize the source water, initial costs may be lower but maintenance costs over time are high as the filter membranes must be replaced every two to five years and require specific technical knowledge to do so. The other advantage of solar powered TD is environmental, as solar energy produces no greenhouse gases and may help alleviate pollution and combat global warming.
In terms of cost specifically for HydroRevolution, then, it must be noted that exact numbers have not been disclosed as the project is still undergoing its first round of funding for $10 million. Given the project’s chosen source, however, a few considerations apply. HydroRevolution is, by desalination standards, a small-to-medium sized plant. Part of this is attributed to its source of salinized water. While most desalination plants use seawater as their primary source, HydroRevolution would be sourced from an estimated 326 billion gallons of irrigation runoff, tainted by selenium and other minerals, that has been collected over the years by drains embedded under the surrounding 44,000 acres of farmland in the Panoche Water and Drainage District. WaterFX claims HydroRevolution would price water competitively according to the estimated value of treating and eliminating the contaminated drainage water as well as the market value of an additional supply of supplemental water. Pricing would be competitive due to the energy-cost savings mentioned above and the longevity of the project, which has an estimated life-span of 25-30 years depending on weather conditions and basic maintenance.
While not necessarily revolutionary in terms of methodology, using irrigation run-off as a source of salinized water is the project’s cornerstone. Its process revolves around a 377-foot-long heliostat that reflects and focuses the sun’s rays on an oil-filled pipe that runs the length of the structure; WaterFX calls the assembly a SkyTrough. The focused solar energy heats the oil in the pipe, which runs to a treatment plant where it is used to boil water. This water is then condensed, leaving salt and mineral residue behind. The completed commercial plant would have a total of 35 SkyTroughs and an annual production capacity of around 4.5 million gallons of water.
Aaron Mandell, WaterFX’s chairman, said “unlike a seawater desalination plant, these are much smaller and more distributed plants…the value of what we’re doing is not just the water we produce, but eliminating the drainage water.” What’s more, the overall goal of the project is to demonstrate and promote the feasibility of solar energy’s role in the process and in reducing overall long-term costs – both monetarily and environmentally. In this sense, these plants are particularly well positioned because while any desalination plant will produce a salt or other material byproduct, many of them simply rerelease said byproduct into the environment (seawater sourced plants, for example, discharge any resulting salt back into the ocean). HydroRevolution, according to Mandell, would be different in this respect as well.
Because salt would not be the only byproduct in question, HydroRevolution may have a second revenue source outside of its direct water production. The most logical recourse would be the processing and selling of the highly concentrated solid particles left over after desalination, particularly Gypsum (for building materials) and Selenium (which can be used as a health supplement). The plant, then, would be an example of a crucial urban need being met via renewable energy and the recycling of waste. It could demonstrate the possibility to overcome the prohibitive energy cost of desalination on a small scale and help alleviate water issues in struggling communities and in turn even help reduce the community’s carbon footprint. The greatest potential of the project, once again, lies in its scalability and, through this, its ability to become a viable alternative as a water source to overused reservoirs and drought-ridden rivers and springs.
For more information, please contact Christian Flinn at firstname.lastname@example.org.