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Joined: Jul 2004
Posts: 9,669
Likes: 6
Paul, I am in Florida and I still can't make the numbers work. The only reason I considered it was for "after the storm" and my collectors would probably be solid waste in the next county anyway.

Greg Fretwell
Joined: Mar 2005
Posts: 1,213
I was greatly disappointed when I looked into this, too- after we lost power for 8 days after Hurricane Isabel, I wanted to add solar power so I could power my fridge and some lights/TVs during another outage, and sell back energy when the grid was working. But it's just SO expensive!

I'd posted these calculations before, but I think it's pertinant. I apoligize for all the [super]s- I wrote this up for another forum that had superscripts that the UBB on this board doesn't support:

* Average Solar Flux for North America: 150 W/m[super]2[/super] -This is representative of the US Northeast and Europe, and accounts for weather.
* Best Average Solar Flux in the US southwest is 240 W/m[super]2[/super]
* Northern US December average 71 W/m[super]2[/super]
* Winter levels will be appx 80% of this value
* US Annual Energy Consumption in 2003: 6.22 ExaWatt-hours (equivilent to 325 billion tons of oil)
* Typical electrically heated household energy use during coldest week of winter: 24,000W
* Typical instantaneous power requirement for a refrigerator: 1200W
* Combined contribution of solar, geothermal and wind in 2003: less than 2%
* Solar Panel Efficiency: 8.25% (commercially mass produced a-Si, the only feasible material at the scale we're talking! See Unisolar whitepaper #1 below.)
* Thermal de-rating of solar panels for US winter weather: 15% for a-Si, 35% for crystalline silicon.
* Typical loss due to dirt, dust, etc: 3%+
* Inverter efficiency: 94%
* Wiring efficiency: 97%
* Transformer efficiency: 95%
* Battery efficiency: 80%

* Energy required to manufacture a-Si panels:120 kWh/m[super]2[/super] (432 MJ/m[super]2[/super]) as a generously conservative estimate. I don't know if this counts mining, refining, transportation, installation, cabling, power conversion, substations, transmission, etc, etc and I'm pretty sure it doesn't.
* Energy required to mount an a-Si panel: appx 120 kWh/m[super]2[/super] (432 MJ/m[super]2[/super])

* Solar energy absorbed annually per m[super]2[/super] in US Southwest desert:
365 days * 24 hours * 240W/m[super]2[/super] = 2,100 kWh

* Solar energy absorbed annually per m[super]2[/super] in US Northeast:
365 days * 24 hours * 150W/m[super]2[/super] = 1,314 kWh

* Losses in conversion, wiring, etc:
.97 * .94 * .97 * .95 * .80 = 32% loss, 67% efficiency

* Break-even point for energy for a-Si Solar Panels and installation in US Southwest desert:
240kWh/m2 / (240W/m2 * 8.25% * 67% * 24 * 365) = 2.1 years

* Break-even point for energy for a-Si Solar Panels and installation in US Northeast:
240kWh /m2 / (150W/m2 * 8.25% * 67% * 24 * 365) = 3.2 years

For this that missed the significance of this, it means spending 2-3x our entire annual energy consumption on solar panel production alone.

If the south-facing roof of a 200m[super]2[/super] (~2000ft[super]2[/super]) typical house in the Arizona desert was covered in a-Si solar panels:
240W/m[super]2[/super] * 100 m[super]2[/super] * 8.25% * 67% = 1300W (about enough to run a refrigerator)

If the south-facing roof of a 200m[super]2[/super] (~2000ft[super]2[/super]) typical house in the US was covered in a-Si solar panels:
150W/m[super]2[/super] * 100 m[super]2[/super] * 8.25% * 67% = 829W (about enough to run a typical PC desktop with 17" CRT monitor). It would take 42 houses like this to provide the energy one house requires for electric heating.

If the south-facing roof of a 200m[super]2[/super] (~2000ft[super]2[/super]) typical house in the US Northeast in winter was covered in a-Si solar panels (assuming no snow):
71W/m[super]2[/super] * 100 m[super]2[/super] * 8.25% * 67% * .85 = 321W (4 houses combined could run a Mr. Coffee). It would take 75 houses like this to provide the energy one house requires for electric heating.

Cost of 8% efficient a-Si solar panel: appx $1000/m[super]2[/super]
Cost of installation: appx $100/m[super]2[/super]
Cost of 10kW inverter: $12000 (For surge. An electric range draws 10kW.)
Cost of storage batteries: $200/kWh
Cost of cabling: appx 1x material cost
Cost of electrical installation: appx 2x electrical material cost

100m[super]2[/super] of solar panels: $100,000
Cost of panel installion: $10,000
Batteries required to store 2 day’s worth of energy at 1300W average: $13,000
Cost of inverter: $12000
Cost of electrical installation: $20,000
Total cost of 1300W Arizona or 564W northeast partially-solar-powered house calculated for above: $155,000.

Area of solar panels in the southwest US desert required to supply US with total electricity demands:
6.22Ewh / (1300W * 24 * 365) = 54,000 km[super]2[/super]

Number house-sized solar panels spread evenly throughout the US required to supply US with total electricity demands:
6.22Ewh / (829W * 24 * 365) = 856 million house-sized panels (compared to 120 million households in the US, which includes aparments and townhouses)- works out to about a quarter acre of solar panels per every family in the US. BUT, that's lopsided as most of that comes from the summer. If we go by straight winter values, it works out to closer to 17 acres of solar panels per family.

US GDP: $ 11.75 trillion
856 million house-sized panels: $158 trillion


Since we're using very large numbers here:
1,000 Thousand Kilo k
1,000,000 Million Mega M
1,000,000,000 Billion Giga G
1,000,000,000,000 Trillion Tera T
1,000,000,000,000,000 Quadrillion Peta P
1,000,000,000,000,000,000 Quinillion Exa E

* It would literally take a solar panel larger than Wales to supply UK with their annual electrical consuption. And probably require most of Scotland to be turned into hydoelectric resevoirs to feed the grid at night and on rainy/cloudy days.

[This message has been edited by SteveFehr (edited 02-26-2007).]

Joined: Feb 2002
Posts: 375
I figured that the income from $15-20K would pay my electric bill forever.

It is certainly a better investment to put the money in a business investment rather than into solar panels.

Joined: May 2003
Posts: 2,876
e57 Offline OP
Steve was that a solar powered calculator? It must be on fire! [Linked Image]

I am truely impressed....

Mark Heller
"Well - I oughta....." -Jackie Gleason
Joined: Jun 2005
Posts: 821
I didn't realize solar energy isn't as advanced as it seems. The Home Depot and British Petroleum make it seem like the we're nuts for not using it when it's clearly available. I don't want to trigger a political debate (ECN policy violation), but a little energy conservation can't be all bad.

Joined: May 2003
Posts: 2,876
e57 Offline OP
Dare I say it, the reason I posted this was for a 'green' apprentice who used to work for a Solar company who as absorbed too much of the Sales Literature [Linked Image] whom I have gotten into heated debates about solar with. (I wish he would pop in on the topic.) When I told him that I really didn't believe in solar as being viable or effective (key words) in the grand scale.... he scoffed. I will admit I did use hash words for what I think of it. But said he would be surprised how many Electricians don't buy into solar at this stage of its development.

Note that there are many way to look at the varied calculation. (Steves' is hash, and right along my thinking) But for many, the calculation is balanced with a very heavy dose of currency allotment for how one might feel about how the impact the environment. But this is not the cleanest method of producing electricity by any means - something I feel that people often turn a blind eye to - Because they think the trade off is worth it, but if you bounce the numbers (the electrical ones) around, solar is very ineffeciant vs. cost, value of return in production i.e. kW output, and of course the pollutants it took to make it. Because it (the technology) is in it's infancy... Moving ahead full scale with it at this stage is actually more wastefull.

Personally I would like to see better made wind-generators that work.... You get way more bang for the buck with them, and the have much higher output.

Mark Heller
"Well - I oughta....." -Jackie Gleason
Joined: Jul 2004
Posts: 625
As a guy named "SolarPowered", I guess I just have to weigh in on this subject. [Linked Image]

First off, the name is in reference to a peculiar characteristic of my body. My body is solar powered--when the sun is shining, I'm bright and happy and energetic; when the sun goes away, I go into hibernation. I don't have solar power running my home, nor do I design solar power systems for people.

That said, I do have a pretty keen interest in the subject, and have been following it for a long time.

My take on solar power is right in line with what mostly everyone else here has been saying--at the current level of technology, solar power isn't viable as a mass replacement for other power sources. The economics just aren't there. To make it almost look economically viable requires large subsidies from the state in form of rebates for much of the cost of installing the system, and from the power companies in the form of "net metering", which is really a big loss for the power company.

One major issue that hasn't come up yet is the issue of energy storage--these solar power systems don't produce anything when the sun's not shining. There's really no cost-effective technology available at this time to store energy during the day for use at night. Most systems use lead-acid batteries. Like all batteries, they wear out eventually. When you amortize the cost of the batteries over their lifetime, it ends up that you're paying $.25-$.50 per kWH just to store the energy, not counting the cost of the rest of the system.

From what I can see, if we as a society decide that we must curtail the burning of fossil fuels, the only viable techology at this time that could replace fossil fuel on a large scale is nuclear power.

[This message has been edited by SolarPowered (edited 02-27-2007).]

Joined: Mar 2005
Posts: 1,213
If y'all think solar is bad... solar panels look like nuclear reactors compared to the energy efficiency of ethanol! I still can't fathom why in the hell we're embracing ethanol like it's some miracle replacement for oil when it actually takes more energy to grow and process corn and soy into fuel then we get from burning ethanol. (OK, there's still debate on this- but the debate isn't whether it's a viable energy source, it's whether there's a net energy loss or if it's just ridiculously inefficient)

Solar has its niches; it's both economically and energy efficient when used in remote applications where wiring is impractical. Remote weather stations, for instance. I ran those calcs assuming solar heat and typical US power loads- if a home were to "cheat" and use gas heat & cooking and have no A/C and a minimum of other loads and use the electric grid in lieu of a battery storage system, it begins to look a little better. And honestly, every little bit helps- if we can put 10 square meters of solar panels on each new home in arizona, it will reduce our overall need for coal by that much.

[This message has been edited by SteveFehr (edited 02-27-2007).]

Joined: Jan 2005
Posts: 5,316
Cat Servant
One problem I see with "solar power" discussions is what I tend to think of as the "Russian syndrome." That is, the issue is discussed in terms of central planning, and massive arrays. This is, I believe, an incorrect application of solar.

Now, I have installed a dozen or so 'solar power' systems that were neither large, nor tied into the grid. These systems have worked well.
The application? Powering bus shelter lights and traffic signs. In these applications, they work well. The role of solar may be to maintain, rather than power. I see them powering small, stand-alone loads, rather than as part of a power distribution system.

Joined: Jul 2004
Posts: 9,669
Likes: 6
The real weakness of solar is still the battery. Getting 1000 deep cycles out of a battery is about all you can count on. That is why the net metering is really the only practical way to go. On a small scale that works fine but the electrical infrastructure still needs to be able to handle a cloudy day so the real saving to the utility is not as great as we could expect. I see a similar problem with the electric car. A few people having an electric car is not a problem but if we had 50 million people who net meter their solar arrays and then come home and plug in their car right after dark we will need a whole lot more generating capacity, not less. People seem to forget all of that "car" energy has to come from somewhere.

Greg Fretwell
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