Solar Cogeneration Start-up Adds Cooling Capability to Its Heat and Electricity Portfolio

Capturing and converting 60% of incident solar energy - as compared to the less than 20% for conventional silicon solar PV cells -is big news for any company. Silicon Valley start-up Cogenra's concentrating solar PV (CPV)-solar thermal co-generation technology has been a hit with its primarily commercial and industrial base of customers because of its increased efficiency. Now the company's ready to take that up a notch, extending the functionality of its solar heating and electricity co-generation system to include cooling.

Absorption chilling, and chillers, have been around for quite some time. They've even been applied to and used in solar energy systems before, but Cogenra's "just taking it to the next level," CEO Gilad Almogy told Triple Pundit in an interview, "to get the best of both worlds." The ins and outs of absorption chilling

Using high temperatures in a cooling system may be counter-intuitive, but that's the way absorption chilling and chillers work. In contrast to conventional mechanical chillers - the air conditioners we all know and love so much on those long, hot summer days - absorption chillers use heat to evaporate water contained in a low pressure environment. That circulating, cooler fluid then captures heat from its surroundings - be it another stream of flowing liquid or the air in the open space of a room, thereby cooling it.

Evaporating all the water would put a halt to the process so some of the now cooler and circulating water always remains in the system. At the same time, the evaporated water is absorbed and condensed into another liquid - in the Cogenra system's case, lithium bromide - to recharge the system. The lithium bromide solution is then heated to evaporate the water it contains. That's circulated back through the system, starting the cycle all over again.

Cogenra's path to solar co-generation commercialization
Based in Mountain View, California, Cogenra was founded around three years ago when Almogy, formerly a senior vice president with Applied Materials - the industry leading provider of solar PV cell fabrication equipment - hit on the idea of developing a technology that could capture and convert solar energy more efficiently with co-generation. Doing so, he figured, would result in a alternative, renewable energy technology capable of producing usable energy at a cost low enough to compete with conventional and other renewable energy alternatives without any subsidies.

Producers of the solar photovoltaic (PV) cells that produce electricity had been, and continue to hit a fundamental physical barrier that limits solar PV cells' to energy conversion efficiencies to around 20%, Almogy explained.

With backing from Khosla Ventures, Almogy began designing a system that would capture the significant amount of heat that strictly solar PV cells, panels and systems leave behind. He came up with an innovative design for a concentrating photovoltaic (PV) technology that also captures sunlight's heat, overlaying, or under-laying, a solar thermal energy aspect to a CPV system's design.

From the solar PV aspect, Cogenra's solar co-generation technology uses tiny, curved, custom designed and manufactured glass mirrors to concentrate sunlight around 10x and focus it on industry-standard high-efficiency crystalline silicon (c-Si) solar PV cells with conversion efficiencies of around 15% to produce electricity.

The CPV cells are carefully place around all-black piping system wherein distilled water with a bit of antifreeze liquid is circulating. Incident sunlight heats the circulating fluid to temperatures sufficient for a wide range of process and space heating needs, from those used in food processing, pharmaceutical manufacturing and a range of other industrial processes to producing hot water for laundries and space heat to meet building/household needs.

Reaping the added benefits of cooling to solar co-generation

Incorporating a solar thermal aspect to their CPV technology boosts the Cogenra system's overall energy conversion as high as 60%. That translates into significant dollar savings and makes it economical for Cogenra's customers, a growing base that includes some close to home, such as the Sonoma and Napa Kendall-Jackson wineries and the fitness center on Facebook's campus in Menlo Park.

With the successful installation of around 20 systems among its first wave of customers, Cogenra's been looking farther afield. It now has several dozen solar CPV electricity-and-heat co-generation projects in various stages of development at customer sites in four other countries.

Wedding a heating aspect to CPV technology was a good place to start out because it's straightforward and improves the economics significantly. Cogenra's customers can typically expect a payback on their investments in about five years, according to Almogy.

Now Cogenra's taking its solar CPV-thermal co-generation technology a step further by adding a cooling aspect to it. Customer requests have been a primary driver underlying its efforts, Almogy explained.

In contrast to space heating, where less sunlight is available in winter when your heating needs go up, there's a positive correlation between the amount of sunlight available for a solar energy system and daily as well as seasonal needs when it comes to cooling, he continued. "The moment you talk about cooling, there's a perfect correlation between hot and sunny and cooling, so for us it's a perfect way to meet customer demand," he told TriplePundit.

Cogenra did need to modify and augment its technology to add an absorption chilling cooling aspect to it. For heating uses, "you need to provide the heat at somewhat higher temperature depending on whether it's space heat or process heat, but for cooling you want the temperature to be above 70 degrees Celsius, which is straightforward using concentrating solar thermal technology.

"You want to get electricity from the solar PV out first. The electricity's worth more money, and it can drive a mechanical chiller (a conventional AC unit), then heat is left over than can drive an absorption chiller, so the overall cooling output is higher than any other alternative."

Producing both electrical power and heat, Cogenra's competing against electric utilities as well as natural gas, propane distributors. The economics varies country by country, though Cogenra's initial success has been in the U.S., Almogy explained.

While Europe and the U.S. have well developed natural gas distribution grids, that's not the case in many countries around the world. "We definitely see a future in the Middle East, South America, India, and somewhat in southern Europe," he related. "If you're off the natural gas grid, you're a great potential customer for us immediately."

Southern California Gas Co. (SoCalGas) is the first to install a Cogenra solar CPV-heating and cooling cogeneration system, annoucing the launch of a multi-year demonstration project at its Energy Resource Center in Downey, California. Looking to help commercialize the system, SoCalGas is betting that it will attract the interest of businesses across the region. Cogenra's also working with a large, multinational provider of cooling equipment (which Almogy could not disclose) to take its business up a level in scale and scope.

Solving Solar's Energy Storage Problem

There's one other key aspect that improves the operational efficiency and cost of Cogenra's solar CPV-thermal co-generation technology: energy storage. Finding a cost-effective means of storing the intermittent energy produced from solar PV and other renewable energy systems continues to be industry's most significant challenge.

Hot water can very easily be stored in tanks, Almogy pointed out. "The extension to cooling does two things: it affords a good correlation [between incident solar energy] and the need for cooling, but even without that, it's very easy to store hot water in a tank and later use it to drive cooling in the evening. That can make solar a firm source of renewable energy."

*Photo courtesy: Cogenra