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Concentration of CO2 in the Atmosphere

Local Solar Co. Developing Unique Approach to Generate Electricity

Norwich Solar Technologies’ SunTrap™ concentrating solar system. Images courtesy of NST

George Harvey

The U.S. Department of Energy (DOE) supports some innovative technologies through the Small Business Innovation Research and Small Business Technology Transfer program. Of special interest here is a grant given to Norwich Solar Technologies (NST) for its unique approach to concentrating solar thermal power for generating electricity on a continuous basis, 24 hours per day.

Green Energy Times has run numerous articles about the innovative technologies from NST. Most of them have been about solar photovoltaic (PV) systems in the New England area. Here, however, we are dealing with a different technology, which has been under development for some time.

Many people are familiar with concentrating solar power. We might think of the 392-megawatt (MW) Ivanpah plant, in California, with its 173,500 heliostats, following the sun to focus light on three big towers that glow brightly when the sun is shining. Or we could recall the 354-MW Solar Energy Generating System’s (SEGS) trough collectors, which use somewhat different technology to accomplish the same end. The first of these systems uses molten salt to transfer energy, and the later uses special synthetic oil, which is heated to about 750°F.

Both of these systems are sited in deserts in California. Both produce power reliably, but it is considerably more expensive than baseload power. And both of the plants are huge.

NST is developing a concentrating solar system, dubbed SunTrap, with intended capability to produce electricity on a 24-7 basis, with the hope that its electricity will be much less expensive, at a much smaller scale, with much smaller investment, and in wider areas of the country than the deserts of the Southwest.

McBride, Chief Technology Officer

The NST SunTrap system under development uses pressurized water as the medium for transferring and storing energy. Because it is pressurized, it can be used at much higher temperatures than the water in a tea kettle. It is heated in solar troughs, like the SEGS system, and similar temperature to SEGS I and II.

Now comes the novel part of the system, the reason for getting the grant. Storing and using this very hot water at very low cost is a key enabler for the NST/SunTrap system. Challenges include dynamically separating the hot and cold sides of the pressurized water during operation in order to achieve the lowest possible costs for bulk energy storage.

Water in the troughs can be heated very hot without boiling, because it is under pressure. At such high temperature, it can be used to heat a liquid to boiling, to drive a turbine. This is done in a Rankine system, which means that the liquid is in a closed system, so the gas that turns the turbine is all captured and condensed back to liquid for reuse. In the case of the NST system, the liquid is organic, which means that its temperature range is different from that of boiling water, and so pressurized water can be hot enough to drive the system.

Jonathan Lynch, Vice President of Research & Development

“This grant is specifically related to the pressurized water’s thermal storage.” Troy McBride, NST’s chief technology officer, told us. “Our goal is the lowest cost electricity we can generate. The novel part, which requires research funding is the storage. We just completed the nine-month proof of concept grant. Now we will build a full-scale system with the Cleco Alternative Energy Center of the University of Louisiana, Lafayette.”

The SunTrapsystem NST is building will include the concentrating solar collector, heat storage, and organic Rankine generator. It will be a hybrid-generating station with a matching PV array to produce daytime power, allowing a greater portion of heat collected to go into storage.

Under the schedule for the research in Louisiana, the project is to be completed within two years after the contract is signed. Within that time, the engineering and preparations for a respectably large project would have to be finished, the project built, and several months of testing completed, to show how a full-scale system will work.

“Our target customers are commercial, industrial, and municipal operations, universities, schools, and hospitals, in the sunbelt,” McBride said. He said the smallest systems are about 1 MW and would be big enough to supply the equivalent of 200 homes for economies of scale.

We will watch this with anticipation.

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