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# Enough With the Solar Power 'Magic,' Please!

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Re: Solar powered cars
1/10/2014 2:33:33 AM
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@Henry, rtapl.  I went back and watched the Ford video again.  They claim 1.5 m2 of panels and 300W output - that's 200w / m2 or 20% efficiency.

The "Carport" is shown as 4.3 x 5.3 m = 22.8 m2 of concentrator lens, that's 15.2 times the area of the panels, and they are claiming an 8x increase in power as  result.  Considering the difficulty in precisely positioning the car, that's probably reasonable, but I'd still question whether you can drive any solar panel that hard?  And that's a big carport for a small car, I wish my garage at home was that big...

Again taking their figures, not ones I've estimated, that gives 300W x 8 x 5 hours - 12 KWH.  Depending on the driving, that would give up to a bit more than an hour of driving per day.  So it would be feasible for shortish commutes.

Anyone able to knock any holes in that?

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Re: Watt-hours
1/10/2014 2:25:02 AM
A lot of innacuracies there.

Today converter don't have a 50% conversion ratio but more around 80% to 90%

It's not the 1.5m² of the solar cell surface you have to take into account, it's the canopy surface (around 20m²) that will be concentrated onto the car roof top.

The solar cells used there are multilayer type that can convert that amount of concentrated solar energy to electricity. Ford says 8x concentration, so not all of the 20m² equivalent surface will be converted, but more around 10m² with 20% ratio.

Those cells are already working as prototype with real 8x factor, but there's still the self-heating issue to take care of.

Nothing magic here.

So you can full-charge a car battery in one day... if the battery is not too big. If you want a bigger car and/or longer range then it will work for 50% of the full charge, that's is still good to have.

The stupid thing in this business model is that you'd better have 50m² of standard solar cells on your house roof top and charge your car with them, it will be cheaper.

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Re: Solar powered cars
1/9/2014 11:58:02 PM
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I consider 1\$ per watt "cheap" and they are more than 15% efficient.   I am sure Ford understands "cold"  since they are headquartered in Detroit.

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Re: Solar powered cars
1/9/2014 11:46:33 PM
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@rtapl123 The last (relatively expensive) panels I bought were    a little less than 15% efficiency. Sunpower panels ar about 16% while Sanyo panels are around 17.25% efficient. The cheap panels are a lot lower efficiency. Concentrators are an interesting option, but it's pretty easy over power a panel - especially during winter cold.

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Re: Solar powered cars
1/9/2014 10:35:44 PM
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Somehow the author has his head in the sand.  15% is not the max efficiency for even cheap cells these days.  Concentrators are typically over 30%.  Does anybody check these articles before publishing them?

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Re: Solar roofs for cars?
1/9/2014 9:39:59 PM
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I've also lived off-the-grid for the past 9 years and I totally agree with the points in this article.  However, I will throw out one small point in favor of the concept.  With more and more electronics installed in the car, or potentially plugged into the car these days, it's nice to have a modest power source that doesn't require the car to be running.  Dead batteries would be a thing of the past!  I've often wished for an integrated solar charger for my car, but granted, this usage doesn't require or even justify a lot of fancy technology.

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Re: Solar powered cars
1/9/2014 3:32:30 PM
I drive a LEAF, and it is solar powered. But indirectly of course. I have 6kW of solar panels on my home roof. The electricity produced is put back on the grid. Thanks to net metering I get credit for that and help produce power during higher demand times of the day. Then I charge my car at night when demand is low. Eliminates thestorage problem for now. I hoping the organic/inorganic flow cell batteries solve that significant problem.

My LEAF gets 4 miles per kWh on average with about half my driving on the highway.

In December, the solar array produced 25 to 70 kWh per week (The snow is NOT helping, the array is at a low roof angle so it doesn't slide off, takes a while to melt.)

I use about 30kWh per week driving, so plenty of excess to help power my home. I'm hoping that in the other three seasons most of the house power is covered too.

Thanks to rebates (50% from utility, 30% tax) I'll pay about \$8,000 or less for the system. It should payoff in 5-10 years depending on how fast electric rates rise, and meanwhile I'm not driving my car on coal.

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Re: Watt-hours
1/9/2014 2:01:45 PM
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&jeremybirch - thanks - do you think you could increase the output of your panels by 8 times with a lens?  That's fairly key to making this work.   And a typical parking space is 4 x 3 metres - thats 12 square metres - assuming 15% solar cell efficiency and 50% conversion losses that's 4.5 KWH in a 5-hour charge, not 15 KWH as in my workings.   I'm pretty dubious of Ford's figures.

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Re: Watt-hours
1/9/2014 1:55:55 PM
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@majortom84 - if you are looking at start-stop city driving I think the consumption would go up if anything - though you do have zero consumption at traffic lights and hopefully regenerative braking helping a bit.  In suburban or industrial areas you could have parking lots covered in carports with fresnel lenses but in inner cities it would be more difficult.

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Re: Watt-hours
1/9/2014 11:00:42 AM
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No holes to poke, but I do wonder if the numbers look any better if you assume 25-30mph, say for city driving.  (Heck, if I were stuck in the desert I would be happy with 10mph.)  Wind resistance is much less than half, I think.  Yes, of course in a city it is more difficult to come by direct sunlight.

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