PV, Solar Thermal, and Light Bulb All In One


BrightPhase Energy, a Denver-based startup, has created the solar equivalent of a one-man-band: The Photensity. Inside this square box, three different technologies are employed to harness sunlight. Firstly, 18% efficient silicon solar cells are mounted on a set of Venetian blinds to deliver PV electricity. Secondly, thin fluid-filled pipes absorb thermal energy which can be used to heat a house’s water supply. Finally, because the aforementioned blinds can be rotated to let in sunlight, the Photensity also “harnesses” sunlight by acting as a skylight during sunny hours (when there is no sun, it turns on an electric light). All told, BrightPhase claims that after tallying up all of the energy that the Photensity provides – in terms of electricity, heat and light – they calculate the cost at $1.80 per watt. Now, we know that any time we get a quote like that, it must be taken with a grain of salt, since there are a lot of assumptions that go into it. For example, since the Photensity allows sunlight in, it counts those lumens as energy generated. How do you translate lumens into watts? If you do so by using light bulbs as a standard, what kind of light bulbs? If you’re basing the number on incandescent bulbs, it will in a sense inflate the wattage that the device is actually producing.

However, I’m less concerned about how the $1.80 is calculated and more concerned about how these devices will actually work. The Photensity aspires to be a replacement for a skylight, but it offers a lower-quality light than a skylight, since its light casts shadows of the solar modules. And it can only be applied to architecture that facilitates skylights – which means it can’t be used to retrofit, say, a large warehouse. And, reportedly, a trial in a California Wal-Mart revealed some issues with the functionality of the device itself. What I wonder is: how much PV and thermal energy do you lose by incorporating the sunlight element? Is it really worth it? Or did BrightPhase simply find a way to report a lower cost-per-watt by incorporating the “wattage” of sunlight? (Source: http://www.ecogeek.org)


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