Water. Desalination + reuse
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SOLAR STEAM ON DEMAND • Team: Sunvapor • Location: Livermore, CA • DOE Award Amount: $1,500,000 • Awardee Cost Share: $1,000,000 • Principal Investigator: Philip Gleckman While solar photovoltaics (PV) has benefited from hundreds of billions, perhaps even trillions of dollars-worth of subsidies from governments around the world, solar radiation has had little such investment. Dr Philip Gleckman, former chief technology officer at nu- clear giant Arriva, saw that gen- erating electricity from solar PV was too competitive compared to solar thermal for the latter to make an impact. However, he knew that steam heat itself was much in demand from industry and favourably priced, and that LOW-COST DESALINATION USING NANOPHOTONICS- ENHANCED DIRECT SOLAR MEMBRANE DISTILLATION Team: Rice University Location: Houston, TX DOE Award Amount: $1,700,000 Awardee Cost Share: $787,124 Principal Investigator: Qilin Li In conventional membrane distil- lation, heat transfer reduces the temperature difference across the membrane, bringing down efficiency. Rice University is investing $1.7m to examine how an extra light-absorbing layer of special material, nanophotonics- enabled solar membrane distilla - tion (NESMD), can simultaneous- ly convert sunlight to heat and desalinate water. Under the sun's energy, the membrane layer serves to elevate vapour pressure with no extra heat source. At the distillate-membrane interface, the vapour condenses and is collected by a stream of purified water. HAWAII SUNSHOT DESAL PROJECT Team: Natural Energy Laboratory of Hawaii Authority/Trevi Systems Location: Kailua-Kona, HI DOE Award Amount: $1,928,238 Awardee Cost Share: $2,311,938 Principal Investigator: Gregory Barbour Hawaii's project comes out of the starting gate with a buyer eager for 500 m3/d of desalinated water, the thirsty nutraceutical company Cyanotech. The project, which has the potential to become the world's largest solar- powered forward osmosis (FO) plant, is a partnership between Petaluma, CA-based desalina - tion specialist Trevi Systems, and Hawaii's green tech park, Hawaii Ocean Science and Technology Park (HOST). The Natural Energy Laboratory of Hawaii Authority (NELHA) administers HOST Park which, founded in 1974, is at 870 acres perhaps the largest single green economic development project in the world. Trevi System's special in - gredient is "a very fancy, long, linear engineered molecule which makes up the draw solution," explains founder, chairman, and chief executive John Webley. These molecules turn into coils when warmed to 60 degrees Celsius by solar thermal heat or concentrated solar power "then find a mate, and sink to the bottom or a gravity separator," says Webley. This leaves 99.5 per cent of the permeate free to be extracted for use. The team is using a variety of FO membranes and polymeric heat exchangers from third party suppliers. The project is totally powered by a solar thermal energy and aims to reduce the levelised cost of water (LCOW) to 40 per cent compared to the competition. The off-taker Cyanotech grows micro-algae on land leased from NELHA, and 500 m3/d is a quar - ter of the water it needs to pro- duce astaxanthin and spirulina for the nutraceutical market. Cyanotech has 90 acres of aquatic growing space, and currently uses the state's regular potable water — a supply that comes in at a costly $1.20 per cube. Webley's process makes use of solar heat at $0.01 per kWh with storage, compared to $0.15 to $0.16 per kWh for a photovoltaic panel and battery array. NELHA's chief programme manager Alex Leonard says: "Hawaii is a small island in the middle of a big ocean, and despite the sun, we are depend - it could be made cheaper. As a result he set up Sunvapor in California, with a view to mak- ing the product improvements that would bring down the cost of solar steam in a meaningful way, and in turn lower solar thermal desalination costs. With the DoE grant, Sunvapor is looking at two areas of in- novation that could make solar steam-based desalination more viable: reducing the cost of the collector; and creating a thermal storage solution that is suitable for industrial steam. The team is investigating a cheaper material for the struc- tural elements which support the 14 by 7 metre collectors in their perfect parabolic shape, with- standing high winds. For many decades, steel had been used for this purpose and, as a result, the structure represented 75 per cent of the cost of the entire unit. The team has settled on a renewable fibre-reinforced composite material much like lumber, using a design similar to a roof truss. "House builders have spent centuries creating a precision piece of equipment from this precise material," ex - plains Gleckman. The use of the composite can realise a 50 per cent reduction in the total cost of the unit. The second area of experi - mentation concerns an alterna- tive to the molten salt used to store the heat from industrial steam by way of latent energy storage. The solar steam reaches temperatures of 150 to 250 degrees Celcius, which is not high enough for a phase change in salt. Instead, Sunvapor is storing heat in a different phase-change material (PCM), which melts like wax at the required tempera - ture and below it, forms a solid. Philip Gleckman, Sunvapor chief executive, at a technology incubator event organised by CalSEED, the California Energy Commission programme for winners of its awards for clean energy entrepreneurs. TOPIC AREA 3 Integrated solar-thermal desalination systems 34 Far Site September 2018 Water. desalination + reuse