A solar collector system to produce electricity AND clean water.

a solar collector system
A solar collector system
This year, farmers in California's Central Valley won't receive any water through the federal irrigation program, a network of reservoirs, rivers, and canals that is normally replenished yearly by ice melt from the Sierra mountains. Crippling water shortages have made desalination technology more attractive. A solar collector system uses the sun to produce heat. The heat separates salt and water through evaporation. This has fewer environmental repercussions than traditional methods of desalination that rely on fossil fuels to generate electricity. 
In a solar collector system, a solar trough that looks like a jumbo-sized curved mirror, collects energy from the sun's rays and transfers that heat to a pipe filled with mineral oil. The mineral oil feeds the heat into a system that evaporates the salty water being treated. Steam is produced, which condenses into pure liquid water. The remaining salt solidifies and can be removed. That salts can be used in other industries as building materials, metals, or fertilizers. In order to operate continuously, the solar trough is very large so that it collects extra heat during the day. The energy is stored and used to run the system at night when the sun isn't shining.
By using sun as the fuel source, a solar collector system uses roughly one-fifth of the electricity consumed by traditional desalination plants. Less electricity means lower operating costs. With conventional desalination, electricity makes up 50-60% of the water costs. A typical desalination plant in San Diego operates at about $900 per acre-foot, while it costs around $450 to produce an acre-foot of water with a solar collector system. (An acre-foot is 325,000 gallons, or the amount of water it takes to cover an acre at a depth of one foot). A solar collector system also helps solve an issue that has long plagued irrigated land. Soils in the arid west of San Joaquin Valley naturally contain a lot of salt as well as high concentrations of metals, like selenium, which can be toxic to humans and wildlife. When the soil is irrigated, the salt, selenium, and other elements become concentrated in the drainage water that collects under the crops. In the past, drainage water have been discharged into rivers, wetlands, and aquifers in the San Joaquin Valley. Now, that otherwise unusable water can be diverted to a solar collector system and turned into irrigation water again.
During a drought-free year, the federally run Central Valley Project provides enough water to irrigate 3 million acres of agricultural land. Last year, farmers only received 20% of their allotment. The lack of water is not just worrying for growers. It affects all people who eat food. One third of the nation's produce is grown in the Central Valley — composed of Sacramento Valley in the north and San Joaquin Valley in the south — and the deep water cuts mean that more than half a million acres of crop land will be left unplanted. Some scientists predict California's drought could last as long as a century. Going forward, the state is going to need a substantial water supply that doesn't rely on the aqueduct system. However, in order to counter California's drought, the push must be toward renewable desalination plants rather than fossil-fuel dependent facilities that further contribute to climate change.
Many desalination facilities, including the $1 billion Carlsbad plant set to open in 2016, use a process known as reverse osmosis that forces seawater through billions of tiny holes that filter out salt and other impurities. This method can produce fresh water on a large scale, but has economic and environmental drawbacks. It uses an immense amount of electricity and only about half of the seawater that goes into the system comes out as clean water. The remaining half is dumped back into the ocean as salty brine where it can be harmful to marine plants and animals.  By contrast, a solar collector system has a 93% recovery rate, meaning that for every 100 gallons of water that goes in, 93 gallons of usable water are spit out.
The Panoche Water District in Central Valley is home to the first demonstration plant, a 6,500-square foot system that is capable of producing around 10 gallons of freshwater a minute, or roughly 14,000 of freshwater each day. When the demonstration plant is operating in commercial mode, running 24 hours a day, it can put out 25 to 30 gallons of freshwater a minute.
The pilot project, funded by the California Department of Water Resources, will hopefully prove that a solar collector system system is more reliable and affordable than other freshwater sources.
The water that's being treated by the pilot plant streams in from a canal that collects salty drainage water from around 200 farms in the area and brings it to a single location. In the pilot phase, the clean water that's produced is blended back in with the drainage water, but a commercial plant would send the water back to farmers through a series of canals that are already in place.
Additionally, small-scale systems could be used by individual farmers on site to recycle their own drainage water. The Sahara Forest project in Qatar and an Australian company called Sundrop Farms are using the technology to grow food in greenhouses. The goal is to eventually be able to treat salty groundwater in addition to drainage water.

The High Concentration Photovoltaic Thermal: coming to a neighborhood near you.

The High Concentration PhotoVoltaic Thermal (HCPVT) system uses a large mirrored parabolic dish attached to a tracking system to position the dish at an optimal angle to the sun. The HCPVT system concentrates solar radiation 2,000 times and converts 80 percent of the incoming radiation into useful energy.

- High Concentration PhotoVoltaic Thermal system able to convert 80% of the sun’s energy. 
- System can deliver electricity and potable water in remote locations.
- Design based on a large dish-like concentrator and cooled photovoltaic chips.

A team of researchers are working on a solar concentrating dish that will be able to collect 80% of incoming sunlight and convert it to useful energy. The High Concentration Photovoltaic Thermal system will be able to concentrate the power of 2,000 suns. As an added bonus, the researchers state that the system would be able to supply fresh water and cool air wherever it is built at one third the cost of current comparable technologies. A $2.4 million grant from the Swiss Commission for Technology and Innovation has been awarded to develop the system. IBM, Airlight Energy, ETH Zurich and Interstate University of Applied Sciences will all be developing the prototypes and various components. A prototype of the HCPVT system is currently being tested at IBM Research - Zurich. Additional prototypes will be built in Biasca and Rueschlikon, Switzerland as part of the collaboration. 

"We plan to use triple-junction photovoltaic cells on a micro-channel cooled module which can directly convert more than 30 percent of collected solar radiation into electrical energy and allow for the efficient recovery of an additional 50 percent waste heat," said Bruno Michel, manager, advanced thermal packaging at IBM Research. "We believe that we can achieve this with a very practical design that is made of lightweight and high strength concrete, which is used in bridges, and primary optics composed of inexpensive pneumatic mirrors -- it's frugal innovation, but builds on decades of experience in microtechnology. 

"The design of the system is elegantly simple," said Andrea Pedretti, chief technology officer at Airlight Energy. "We replace expensive steel and glass with low cost concrete and simple pressurized metalized foils. The small high-tech components, in particular the microchannel coolers and the molds, can be manufactured in Switzerland with the remaining construction and assembly done at the installation. This leads to a win-win situation where the system is cost competitive and jobs are created in both regions." 

The solar concentrating optics will be developed by ETH Zurich. "Advanced ray-tracing numerical techniques will be applied to optimize the design of the optical configuration and reach uniform solar fluxes exceeding 2,000 suns at the surface of the photovoltaic cell," said Aldo Steinfeld, Professor at ETH Zurich. 

"Microtechnology as known from computer chip manufacturing is crucial to enable such an efficient thermal transfer from the photovoltaic chip over to the cooling liquid," said Andre Bernard, head of the MNT Institute at NTB Buchs. "And by using innovative ways to fabricate these heat transfer devices we aim at a cost-efficient production." 

The sun's rays are reflected off the mirrors onto liquid cooled photovoltaic chips; with each chip able to generate 200-250 watt hours over an eight hour day in a sunny region. More than 30 percent of collected solar radiation can be converted into electrical energy and the hundreds of chips in each unit collectively represent 25 kilowatts of electricity generation capacity. The researchers believe they can achieve a cost per aperture area below $250 per square meter, with a levelised cost of energy less than 10 cents per kilowatt hour. 

The HCPVT system is designed around a huge parabolic dish covered in mirror facets. The dish is supported and controlled by a tracking system that moves along with the sun. Sun rays reflect off of the mirror into receivers containing triple junction photovoltaic chips, each able to convert 200-250 watts over eight hours. Combined hundred of the chips provide 25 kilowatts of electricity. Replacing expensive steel and glass with concrete and pressurized foils, the HCPVT is less costly than many other similar installations. Its high tech coolers and molds can be manufactured in Switzerland, and construction provided by individual companies on-site. Through their design, IBM believes they can maintain a cost of less than 10 cents per kilowatt hour.

The entire dish is cooled with liquids that are more effective than passive air methods, keeping the HCPVT safe to operate at a concentration of 2,000 times on average, and up to 5,000 times the power of the sun. The system will also be able to create fresh water by passing heated water through a distillation system that vaporizes and desalinates up to 40 liters each day while still generating electricity. It will also be able to provide air conditioning by a thermal absorption chiller.

The liquid cooling system, 10 times more effective than passive air cooling, keeps the chips at a safe temperatures up to a solar concentration of 5,000 times. The heated liquid presents another opportunity for energy harvesting in heat recovery, with the potential for approximately 50% of the waste heat being utilised. The heated liquid can be used for desalination while still generating electricity.
Based on information by the European Electricity Association, IBM claims that it would require only two percent of the Sahara’s total area to supply the world’s energy needs. Cost effective and efficient, the HCPVT system could be vital to developing nations. Remote locations could also benefit from the technology, eliminating the need to build a large integrated infrastructure. Several prototypes of the dish will first be built in Biasca and Rüschlikon, Switzerland.

Background – Today solar photovoltaics (PV) remains the fastest growing power generation technology by installed capacity in the world. Yet, the technology has its limitations, most importantly its low efficiency (around 15% for direct solar irradiation) compared to other power generation technologies. A substantial improvement of this efficiency is obtained by the Concentrating Photovoltaics (CPV) technology. Optical concentrators are used to increase the solar radiation density on the PV cell, which leads to a reduction of cell area needed for the same amount of power production. Since concentrators (e.g. parabolic dishes) use cheaper materials and are often easier to manufacture than PV cells, there is a notable potential for overall cost reductions. Furthermore, CPV uses the more expensive triple junction PV cells that reach comparatively high efficiencies, especially at high solar concentrations. Using the same amount of land, CPV systems can produce more electricity, more efficiently and using much less PV material than conventional PV systems.

While High Concentration PhotoVoltaic (HCPV) systems achieve high conversion efficiencies, the cost of produced electricity remains comparably high. Main reasons are the high cost of involved materials (PV cells and concentrator) and system complexity due to tracking and cooling. An approach to reduce the cost of electricity generation is to utilize the thermal energy harvested during the cooling of the PV cell.

Goal – The goal of the project is to realize a cost-competitive High Concentration PhotoVoltaic Thermal (HCPVT) system able to convert 80% of the collected solar energy into useful electrical and thermal output. Materials for a low-cost large dish-like concentrator and a high performance receiver are exploited for mass-production. The main commercial goal is a solar technology that increases the conversion efficiency from solar-to-electrical beyond 22 percent and allows additional recovery of at least 50% thermal energy. Solar radiation is concentrated 2000 times onto a receiver holding an array of triple junction PV chips able to extract half of the incoming energy as heat while maintaining the solar cells at safe temperatures. 

 A three-year, $2.4 million (2.25 million CHF) grant from the Swiss Commission for Technology and Innovation has been awarded to scientists at IBM Research (NYSE: IBM); Airlight Energy, a supplier of solar power technology; ETH Zurich (Professorship of Renewable Energy Carriers) and Interstate University of Applied Sciences Buchs NTB (Institute for Micro- and Nanotechnology MNT) to research and develop an economical High Concentration PhotoVoltaic Thermal (HCPVT) system.

Based on a study by the European Solar Thermal Electricity Association and Greenpeace International, technically, it would only take two percent of the solar energy from the Sahara Desert to supply the world's electricity needs*. Unfortunately, current solar technologies on the market today are too expensive and slow to produce, require rare Earth minerals and lack the efficiency to make such massive installations practical. 

The prototype HCPVT system uses a large parabolic dish, made from a multitude of mirror facets, which are attached to a sun tracking system. The tracking system positions the dish at the best angle to capture the sun's rays, which then reflect off the mirrors onto several photovoltaic chips -- each chip can convert 50 watts over a eight hour day in a sunny region. The entire receiver combines hundreds of chips and provides 25 kilowatts of electrical power. The photovoltaic chips are mounted on liquid coolants to absorb the heat and draw it away. With such a high concentration and a radically low cost design scientists believe they can achieve a cost three times lower than comparable systems.

Water Desalination and Cool Air

Current concentration photovoltaic systems only collect electrical energy and dissipate the thermal energy to the atmosphere. With the HCPVT packaging approach scientists can both eliminate the overheating problems of solar chips while also repurposing the energy for thermal water desalination and adsorption cooling. 

To capture the medium grade heat IBM scientists and engineers are utilizing an advanced technology they developed for water-cooled high performance computers. With computers water is used to absorb heat from the processor chips, which is then used to provide space heating for the facilities. In the HCPVT system, instead of heating a building, the 90 degree Celsius water will be used to heat salty water that then passes through a distillation system where it is vaporized and desalinated. Such a system could provide 30-40 liters of drinkable water per square meter of receiver area per day, while still generating electricity with a more than 25 percent yield or two kilowatt hours per day -- a little less than half the amount of water the average person needs per day according to the United Nations, but a large installation could provide enough water for a city. 

Remarkably, the HCPVT system can also provide air conditioning by means of a thermal driven absorption chiller. An adsorption chiller is a device that converts heat into cooling via a thermal cycle applied to an absorber made from silica gel, for example. Adsorption chillers, with water as working fluid, can replace compression chillers, which stress electrical grids in hot climates and contain working fluids that are harmful to the ozone layer. 

Scientists envision the HCPVT system providing sustainable energy and potable water to locations around the world including southern Europe, Africa, Arabian peninsula, the southwestern part of the United States, South America, and Australia. Remote tourism locations are also an interesting market, particularly resorts on small islands, such as the Maldives, Seychelles and Mauritius, since conventional systems require separate units, with consequent loss in efficiency and increased cost.