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December 7th, 2006


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01:43 pm - Nifty solar cell news.
Here's some exciting news about 40% efficient solar cells. If they can combine this level of efficiency with the newer thin-film cells that can be mass produced in vast quantities, I'd like to see these things covering the roofs of every house in the US. The best idea would be to find a way to either bond high efficiency thin film solar cells to roof shingles or to make them in large sheets capable of being cut to size and then make such roof coverings mandatory for all new houses and replacement roofs on existing houses. A rough calculation gives (averaged over 24 hours) more than 10 KW per roof, which is a fairly impressive amount of energy.
Current Mood: pleasedpleased

(9 comments | Leave a comment)

Comments:


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From:b00jum
Date:December 7th, 2006 10:42 pm (UTC)
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I want it as a covering for the top of my Prius, so it can partially recharge when parked.
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From:heron61
Date:December 7th, 2006 11:01 pm (UTC)
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Also an exceedingly good idea.
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From:antayla
Date:December 8th, 2006 12:36 am (UTC)
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You probably won't have to make it mandatory if it is economically effective :P.

Yeah, I really hope they can make it work, and that it is chemically sustainable. The last thing we need is more economy based on non-renewable/non-recycleable power sources that pollute the environment.
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From:heron61
Date:December 8th, 2006 03:50 am (UTC)
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You probably won't have to make it mandatory if it is economically effective

Except that roofing companies don't particularly care about people generating power and many people would object to the initial expense of having a solar roof, despite the fact that it would save them money in the long term (especially since the Public Utility Regulatory Policies Act of 1978 [congrats to Jimmy Carter, who both suggested and signed this law]) means you can actually sell power back to a power company. One vital function of government is to take over long-term planning when the populace won't.
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From:onyxrising
Date:December 8th, 2006 03:47 am (UTC)
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I've heard something about the manufacturing process for solar cells creating ozone-damaging emissions. Do you know if this is still a factor, or has that issue been resolved. It was a big reason we hadn't gotten any.
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From:heron61
Date:December 8th, 2006 03:54 am (UTC)
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The older manufacturing methods solar cells that used thick silicon wafers wasn't all that clean - it was pretty much identical to making semiconductor chips, which is notoriously polluting. I'm fairly certain that some of the newer varieties of solar cells, especially the thin film cells produce considerably less in the way of pollution, but I don't have actual stats on them. Of course, the best way to judge them is to compare the output of pollution from making them to the output of pollution produced from burning fossil fuel to generate the amount of power a solar cell can produce in its lifetime (typically 20-25 years, perhaps longer with some of the newer ones). Sadly, I don't have that data, but I'm certain it exists somewhere.
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From:jonathansfox
Date:December 8th, 2006 12:46 pm (UTC)
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You'd need more than 43 kW worth of panels on a house to generate an average of 10 kW over a day. That'd be $129,000 per house. Assuming you could fit 43 kW worth of panels on the roof (and I don't think you could), 10 kW over 24 hours gives 87,600 kWh of energy annually, compared to an annual consumption of a little over 10,000 kWh per household. To completely offset energy consumption (assuming a decent weather area: Alaska, for example, is not included), you'd only need about 5 kW worth of panels, or $15,000. You could probably fit this on the roof of most houses, at least if the 40% efficient cells were used.

If we estimate that for every household in the United States (measured in persons), there is a 1 in 20 chance that a home is being re-roofed that year (there are more housing units than households, some housing units are multi-family, and cheap roofing may not last that long, while good roofing lasts longer), the cost for subsidizing $15,000 of solar cells for every re-roofing in the United States would require the energy budget be raised by about $75 billion. By my estimates, your proposal of mandating and subsidizing the full price of solar roofing (with the goal of neutralizing household energy usage) would cost the equivalent of around 3% of the current total budget, or 16% of the annual military budget, assuming $3/watt solar roofing.

After 20 years, most homes in the United States would have solar roofing, with a total expendature in the range of $1.5 trillion dollars, crudely assuming that inflation and population growth are offset 1 to 1 by falling prices on solar panels. For this change to be permanent, it's best to assume that we would need to make the expendature permanent, at least in the medium term.
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From:heron61
Date:December 8th, 2006 07:41 pm (UTC)
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Assuming you could fit 43 kW worth of panels on the roof (and I don't think you could)

At the equator, sunlight is around 1 KW/square meter. With 40% efficient solar cells and a rough reduction of latitude, you get around 300 Watts/square meter, requiring roof area of 1500 square feet, which is a fairly reasonable number. The reason to go with this much cell area is not just to power the houses, but also to sell electricity back to the local power company (a process made legal in the US through the Public Utility Regulatory Policies Act of 1978) and so reduce overall energy usage.

Looking at the numbers more closely, per capita electricity consumption in the US is 12 Mwh. If we assume 3 people per house we can actually reduce the total from 87.6 mWh to 36 mWh (requiring only 620 square feet). I would also assume that if solar cells were manufactured on such a vast scale, costs would go down due to economies of scale. Let's assume a fairly modest 30% reduction in costs. So, now we have $37,000 per roof, which is only 7.4% of the total budget and would vastly reduce other energy costs. 64% of the US population lives in single family homes, so in 20 years 64% of all US electricity usage would be solar.

For your more modest proposal, reducing the military budget by 12% seems like a very small price to pay for the benefits gained, assuming that the solar cells have a lifetime of at least 20 years (IIRC older style solar cells had a lifespan of around 25 years, so that seems reasonable).
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From:jonathansfox
Date:December 8th, 2006 08:47 pm (UTC)
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Using the estimates on Wikipedia/Solar_power, I estimate a 24 hour average oy 300 Watts/square meter before the 40% reduction is applied, giving me about 120 Watts/square meter afterwards, and 3855 square feet. Even if we throw that out and go with 1500, my old home was only 1200 square feet on the outside, and it was a $360,000,000 house. My previous estimate is based on extrapolation from estimates of current SV roofing, as you still have to take into account roof angle and the resulting shading, assuming your roof isn't flat.

I agree that in isolation, it's not all that expensive of a proposal compared to the military, but I can't help wondering if there would be more cost effective measures to achieve the same goal, given the same budget. On one hand, aiding power companies instead wouldn't help make individual home owners into power plants, but on the other, it would probably be less expensive and free up more government resources for use in other pursuits. Perhaps an alternative voluntary subsidies for solar roofing (I believe Oregon already has this to a certain extent) coupled with construction cost offsets for power companies seeking to build solar or other renewable generation facilities. As you said, roofing companies don't really care about electricity -- but power companies care very much, and likely wouldn't need much prodding, if we merely made it economically viable.

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