IBM “sunflowers” to supply off-grid energy, water, and cooling

Equipped with an array of multi-junction photovoltaic chips, each of the IBM'sunflowers' can supply the energy needs of several homes (Image: Airlight Energy/dsolar) Click on this picture for VIDEO

Equipped with an array of multi-junction photovoltaic chips, each of the IBM ‘sunflowers’ can supply the energy needs of several homes (Image: Airlight Energy/dsolar)
Click on this picture for VIDEO

Using a number of liquid-cooled microchannel receivers, each equipped with an array of multi-junction photovoltaic chips, each HCPVT can produce enough power, water, and cooling to supply several homes.

Looking rather like a 10-meter (33 ft) tall sunflower, IBM’s High Concentration PhotoVoltaic Thermal (HCPVT) system concentrates the sun’s radiation over 2,000 times on a single point and then transforms 80 percent of that into usable energy.

Using a number of liquid-cooled microchannel receivers, each equipped with an array of multi-junction photovoltaic chips, each HCPVT can produce enough power, water, and cooling to supply several homes.

Swiss-based supplier of solar power technology, Airlight Energy, has partnered with IBM Research to utilize IBM’s direct wam-water cooling design (adapted from use in IBM’s SuperMUC supercomputer), water adsorption technologies, and leverage IBM’s past work with multi-chip solar receivers developed in a collaboration between IBM and the Egypt Nanotechnology Research Center, to develop and produce the system.

Using a 40-sq-m (430.5-sq-ft) parabolic dish coated with 36 plastic foil elliptic mirrors just 0.2 mm thick, the HCPVT system prototype concentrates the sun’s radiation onto a number of liquid-cooled receivers, each of which contains an array of 1×1-cm2 (0.39 × 0.39 in2) chips that each generate “up to 57 watts of electrical power when operating during a typical sunny day.” Combined, the whole system produces a total of 12 kW of electrical power and 20 kW of heat over that same period.

Micro-structured conduits pump treated water around these receivers to carry away excess heat at a rate that is claimed to be 10 times more effective than passive air cooling. Although the water is still subsequently heated to around 85-90° C (183-194° F), the removal of heat from the chips keeps them at a relatively cool safe operating temperature of around 105° C (221° F). Without this cooling, the concentrated energy of the sun would see the chips reach temperatures of over 1,500° C (2,732° F).

“The direct cooling technology with very small pumping power used to cool the photovoltaic chips with water is inspired by the hierarchical branched blood supply system of the human body,” said Dr. Bruno Michel, manager, advanced thermal packaging at IBM Research.

The HCPVT system can also be adapted to use the cooling system to provide drinkable water and air conditioning from the hot water output produced. Salt water is passed through the heating conduits before being run through a permeable membrane distillation system, where it is then evaporated and desalinated. To produce cool air for the home, the waste heat can be run through an adsorption chiller, which is an evaporator/condenser heat exchanger that uses water, rather than other chemicals, as the refrigerant medium.

The creators claim that this system adaptation could provide up to 40 liters (10 gallons) of drinkable water per square meter of receiver area per day, with a large, multi-dish installation theoretically able to provide enough water for an entire small town.

All of these factors, – waste energy used for distillation and air-conditioning combined with a 25 percent yield on solar power – along with the setup’s sun tracking system that continuously positions the dish at the best angle throughout the day, combine to produce the claimed 80 percent energy efficiency.

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High Concentration PhotoVoltaic Thermal: Harness the Energy of 2,000 Suns

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Today on Earth Day, scientists have announced a collaboration to develop an affordable photovoltaic system capable of concentrating solar radiation 2,000 times and converting 80 percent of the incoming radiation into useful energy.

The system can also provide desalinated water and cool air in sunny, remote locations where they are often in short supply.

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 microchannel-liquid cooled receivers with triple junction photovoltaic chips — each 1×1 centimeter chip can convert 200-250 watts, on average, over a typical 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 micro-structured layers that pipe liquid coolants within a few tens of micrometers off the chip to absorb the heat and draw it away 10 times more effective than with passive air cooling.

The coolant maintains the chips almost at the same temperature for a solar concentration of 2,000 times and can keep them at safe temperatures up to a solar concentration of 5,000 times.

The direct cooling solution with very small pumping power is inspired by the hierarchical branched blood supply system of the human body and has been already tested by IBM scientists in high performance computers, including Aquasar. An initial demonstrator of the multi-chip receiver was developed in a previous collaboration between IBM and the Egypt Nanotechnology Research Center.

“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 in the region of 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.

With such a high concentration and a radically low cost design scientists believe they can achieve a cost per aperture area below $250 per square meter, which is three times lower than comparable systems. The levelized cost of energy will be less than 10 cents per kilowatt hour (KWh). For comparison, feed in tariffs for electrical energy in Germany are currently still larger than 25 cents per KWh and production cost at coal power stations are around 5-10 cents per KWh.

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, including Aquasar and SuperMUC. With both computers water is used to absorb heat from the processor chips, which is then used to provide space heating for the facilities.

“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.”

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 porous membrane 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 town.

Remarkably, the HCPVT system can also provide air conditioning by means of a thermal driven adsorption 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.

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Researchers Develop Effective Thermal Energy Storage System

Energy storage using the concrete method cost only $0.78 per kilowatt-hour, far below the Department of Energy’s goal of achieving thermal energy storage at a cost of $15 per kilowatt-hour.

Engineering researchers at the University of Arkansas have developed a thermal energy storage system that will work as a viable alternative to current methods used for storing energy collected from solar panels. Incorporating the researchers’ design into the operation of a concentrated solar power plant will dramatically increase annual energy production while significantly decreasing production costs.

Current storage methods use molten salts, oils or beds of packed rock as media to conduct heat inside thermal energy storage tanks. Although these methods do not lose much of the energy collected by the panels, they are either expensive or cause damage to tanks. Specifically, the use of a packed rock, currently the most efficient and least expensive method, leads to thermal “ratcheting,” which is the stress caused to tank walls because of the expansion and contraction of storage tanks due to thermal cycling.

“The most efficient, conventional method of storing energy from solar collectors satisfies the U.S. Department of Energy’s goal for system efficiency,” said Panneer Selvam, professor of civil engineering. “But there are problems associated with this method. Filler material used in the conventional method stresses and degrades the walls of storage tanks. This creates inefficiencies that aren’t calculated and, more importantly, could lead to catastrophic rupture of a tank.”
As an alternative to conventional methods, Selvam and doctoral student Matt Strasser designed and tested a structured thermocline system that uses parallel concrete plates instead of packed rock inside a single storage tank.

Thermocline systems are units — bodies of water, such as oceans and lakes, for example, but also smaller units that contain fluids or gas — with distinct boundaries separating layers that have different temperatures. The plates were made from a special mixture of concrete developed by Micah Hale, associate professor of civil engineering. The mixture has survived temperatures of up to 600 degrees Celsius, or 1,112 degrees Fahrenheit. The storage process takes heat, collected in solar panels, and then transfers the heat through steel pipes into the concrete, which absorbs the heat and stores it until it can be transferred to a generator.

Modeling results showed the concrete plates conducted heat with an efficiency of 93.9 percent, which is higher than the Department of Energy’s goal and only slightly less than the efficiency of the packed-bed method. Tests also confirmed that the concrete layers conducted heat without causing damage to materials used for storage. In addition, energy storage using the concrete method cost only $0.78 per kilowatt-hour, far below the Department of Energy’s goal of achieving thermal energy storage at a cost of $15 per kilowatt-hour.

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via University of Arkansas, Fayetteville
 

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