Solar photovoltaic systems that make electricity directly from sunlight are one of the most promising technologies for clean renewable energy. While solar PV has many positive attributes (e.g. clean, renewable, quiet, etc.), there are two primary drawbacks:
- They are intermittent (meaning that they only create juice when the sun is shining).
- They have a low energy intensity (meaning that the amount of energy per unit of area is small, especially when compared to large scale fossil or nuclear plants).
The intermittency problem, like certain chronic medical conditions, can’t be cured, (not unless you use satellites that continuously track the sun and beam energy back to earth) though it can be managed with storage capacity and a smart distribution system (grid).
The intensity problem can be addressed in two ways. First, because solar is available everywhere, its intensity is less important if it’s used in a distributed manner. If, for example, you can power your home with panels installed on your roof, you don’t care that much if they take up your whole roof or half your roof, except that the latter will probably cost less. A factory on the other hand will likely not have enough roof space to meet its total energy demand and would instead have to settle for some fractional solar contribution.
The other way that intensity can be improved is by improving efficiency, which has been the subject of a great deal of research. That means increasing the amount of usable energy produced per unit of sunlight. Solar panels are relatively inefficient (22 percent is a good number today). What’s worse is that their efficiency tends to drop off under high temperature. And since their job is to sit out in the sun, getting hot is something that will happen regularly. That’s where today’s story about Naked Energy picks up. Naked Energy is a new British start-up company that claims to have invented a hybrid solar technology that can produce both electricity and hot water. The tubular solar collectors produce hot water which is not only useful in itself but it also helps to regulate the temperature of the panel, keeping it from getting too hot, which improve its efficiency. Independent testing has found Naked Energy’s Virtu solar collector to be 46 percent more efficient than conventional PV systems.
There are drawbacks, however. Since water is also required, both installation and maintenance are more involved and more costly. The company says they are currently working on self-cleaning vacuum sealed tubes that only have to be filled once. However, because of all the energy the system delivers, they claim an ROI of 13 percent over 25 years. You can think of it as a small scale combined heat and power (CHP) system.
That is exactly the approach being pursued in the US by Cogenra, which specializes in solar cogeneration. But while Naked Energy is aiming its products at the residential market, Cogenra is after bigger fish. They recently installed a 240 kW system at the Kendall Jackson winery, which they claim will save the company $30,000 in annual energy costs. According to Cogenra, their collectors capture and convert 75 percent of the sun’s energy into either electricity or hot water, either of which would otherwise need to be purchased, most likely from a fossil fuel source. You can see Cogenra’s video here.
[Image credit: Courtesy of Naked Energy]
RP Siegel, PE, is the President of Rain Mountain LLC. He is also the co-author of the eco-thriller Vapor Trails, the first in a series covering the human side of various sustainability issues including energy, food, and water in an exciting and entertaining format. Now available on Kindle.
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