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Solar CHP Innovations Offer Efficiency Kick, Future Energy Storage Options

In late April IBM announced a new partnership with Airlight energy, ETH Zurich and Interstate University of Applied Sciences Buchs NTV. The group won a US$2.4 million grant from the Swiss Commission for Technology and Innovation to develop a low-cost high-concentration photovoltaic thermal (HCPVT) system.

The system uses mirrors to concentrate the sun 2000 times. According to Bruno Michel, manager of advanced thermal packaging at IBM Research in Zurich, the system is built on trackers that are made from low-cost molded concrete for the "lowest base cost possible". A parabolic dish made from mirrors is mounted on the tracking system, which reflects the sun's rays onto several microchannel liquid-cooled receivers that contain hundreds of triple-junction PV cells, which amount to 25 kW of capacity.

Beneath the cells, a liquid composed of antifreeze and corrosion deterrent is piped mere centimetres behind the cells to absorb heat, which is enough to also drive a water desalination process. The coolant maintains the cells at almost the same temperature for a solar concentration of 2000 times, and can keep them at safe temperatures up to a concentration of 5000 times.

"We reach a 25 percent system-level electrical efficiency (and about 30 percent chip level efficiency) with a PV junction temperature of 100-105°C and a coolant temperature of 90°C," explained Michel. "The overall recovery efficiency is 80-85 percent. We lose (less than) 15 percent in the primary optics. Losses in the secondary optics are captured as heat and contribute to the 50 percent heat recovery."

The system also provides cooling through a thermal-driven absorption chiller. "Absorption 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," said Michel.

Researchers hope this device will be an all-in-one answer in areas that are in dire need of low-cost electricity, heating and cooling, and water purification, such as the Middle East. According to IBM, the system could provide 30 to 40 litres of drinkable water per m² of receiver area per day, while still generating 2 kWh of electricity per day. That's "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."

The research group believes that using low-cost materials for the major base components, manufacturing the small high-tech components in Switzerland and assembling the device in the region where it will be installed will have huge benefits.

"This leads to a win-win situation where the system is cost competitive and jobs are created in both regions," says Andrea Pedretti, chief technology officer at Airlight Energy. "The design of the system is elegantly simple."

Solar cogeneration produces both electricity and thermal energy. Solar photovoltaic (PV) systems convert the sun's rays into electricity at typically less than 20 percent efficiency, and the heat given off by the system goes to waste. Cogeneration captures that heat and applies it, in this case, to water purification.

These systems boast some major benefits. During the US east coast's battering by Superstorm Sandy, many praised solar energy systems for weathering the storm and providing ongoing emergency power. Unlike other generator systems that ultimately had a set amount of power available until the fuel ran dry, solar was able to produce power indefinitely (there were several reports of kind citizens bringing solar energy to several communities to provide power for charging phones, etc).

Emergency situations aside, solar cogeneration advocates argue that, on a typical day, renewable systems will give you the most for your money. Compared to the volatile fossil fuel market that accounts for rising utility costs, solar promises a stable, clean source of energy for as long as you own the system. And according to a recent report from Pike Research, Residential Combined Heat and Power, residential CHP has the ability to aid aging transmission systems in many countries where there are growing numbers of blackouts and brownouts: its distributed nature makes the transmission systems less vulnerable to outages on the centralised power grid.

New Innovations

One company that is at the forefront of the residential and commercial solar combined heat and power industry, Cogenra, is now breaking into the cooling market and recently announced that it is providing cooling solutions on an international scale for Johnson Controls with their YORK absorption chillers.

Cogenra is “first and foremost a CPV company,” said Mani Thothadri, vice president of products at Cogenra. At first, the lowest hanging fruit was to utilize the heat produced by the modules, which led to a good part of its business and has allows it to move to other ventures, such as cooling. So instead of just using about 15-20 percent of the sun’s energy, Cogenra systems use about 75 percent by taking advantage of the waste heat in different ways.

The system is composed of silicon PV panels that are assembled on a single-axis tracker. Attached to this system is a parabolic trough with flat mirrors that concentrate the sun 10 times to heat up the panels, and a water chamber that captures the heat. 

The newer cooling absorption chillers integrate into most building components, according to Gilad Almogy, chief executive officer and founder of Cogenra. The chillers require temperatures of about 95 degrees Celsius, so Cogenra’s modules can now perform in these conditions, according to Thothadri.

“The thermally driven chiller adds another 50 percent output to those chillers,” said Thothadri. In other words, “if you compared us to a standard PV-based solution, our solution would be 50 percent higher output.”

Cogenra is not stopping there. According to Thothadri, it is currently working on a storage solution with a grant from the California Energy Commission received in February 2013. Congenra is using the money to research driving the heat output from their modules up to 100-120 degrees Celsius. At the point, it will be able to store hot water in a low-cost, low-pressure storage tank and drive it through low-temperature turbines, similar to geothermal energy systems, to produce electricity when necessary. 

Not only would this be able to provide power at night and during peak hours, “it will be dispatchable,” said Thothadri. “If clouds come in and disrupt PV production during the day, you can kick-start the turbines and offset what you lose.”

In the short-term, Thothadri believes the systems will benefit distributed generation and commercial applications like data centers and help displace fossil-based energy security applications like generators. In the long-term, Congenra sees its energy storage solutions benefiting a range of customers on a wider scale as more PV enters the grid, similar to what Germany is now experiencing – hence their recent energy storage incentives.  

Thothadri did not give a specific timeline for the release of Congenra’s energy storage solution, but promised the industry will hear more about it soon.

“Our first commercialized product came out in July 2011, our first pilot for cooling was released in July 2012,” he said, “and you can extrapolate when a storage based solution will happen. Don’t expect July, but we are working towards getting a solution and pilot out there.”

Lead image courtesy Cogenra


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Volume 18, Issue 3


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