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Author Topic: Solar Cell Misconceptions  (Read 1863 times)
K5END
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« on: January 16, 2010, 06:08:47 AM »

Lately I have heard some misconceptions about solar-cell power. The real advantages of solar-cell power are the simplicity, and the ubiquity and reliability of sunlight. But there seems to be some thought that solar power will save money or save the Earth. Not so, at least with today's technology. I am referring to solar cells; solar-thermal power is another matter.

Environmental Myth
Regardless of ones opinion on alleged global warming and whether the phenomenon exists or not, solar cells are NOT "green" power. I've read reports that with current technology, the manufacturing process alone requires more energy to produce the solar cell device than the expected lifetime energy output of the solar cell. So its use is unlikely to reduce output of Carbon-dioxide or the so-called greenhouse gases.

Economic Myth
If you considering using it for economy, do a little math and see if it makes sense, economically to use the solar panel versus your utility. One model I like to use is the "three year payoff." It works like this. If a capital investment will eliminate a monthly recurring operational cost, the savings should pay off the capital investment within three years. Even in desert climate where sunlight is plentiful, my back of the envelope calculation, based on best case scenario of 12 hours average sunlight daily during the first three years of use and current KWH rates in my area it is at least 3 times more expensive per kilowatt-hour. Realistically it would probably take more than 10 years to pay off the investment, and that is assuming these delicate cells survive all circumstances and are used during every sunny moment. Now, that is just for the use of the power. If on the other hand, you live in the outback, installing poles and electrical lines out to your shack may outweigh the cost of several kilowatts' worth of solar cells. But, then you have to consider that wires and poles require less maintenance and are more durable than the solar cells.

Bottom line is, sometimes it makes sense to install solar cells. But for a primary source of electricity in typical circumstances, it is not a good alternative to conventional means, including standby generators.

« Last Edit: January 16, 2010, 06:11:38 AM by K5END » Logged
N2EY
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« Reply #1 on: January 16, 2010, 07:49:19 AM »

K5END writes: "I've read reports that with current technology, the manufacturing process alone requires more energy to produce the solar cell device than the expected lifetime energy output of the solar cell."

I think those reports were in error.

Check out this one:

http://www.csudh.edu/oliver/smt310-handouts/solarpan/pvpayback.htm

Since that paper was written, better manufacturing techniques and more-efficient technologies have shortened the payback time.

K5END: "So its use is unlikely to reduce output of Carbon-dioxide or the so-called greenhouse gases."

I think the more important issue is resource depletion.

K5END: "If you considering using it for economy, do a little math and see if it makes sense, economically to use the solar panel versus your utility. One model I like to use is the "three year payoff." ...If a capital investment will eliminate a monthly recurring operational cost, the savings should pay off the capital investment within three years."

Why only three years if the capital investment will last longer?

The method I use is to compute the ROI compared to putting the money in the bank or a good bond.

K5END: "Even in desert climate where sunlight is plentiful, my back of the envelope calculation, based on best case scenario of 12 hours average sunlight daily during the first three years of use and current KWH rates in my area it is at least 3 times more expensive per kilowatt-hour."

A key factor is how much someone pays per kilowatt-hour. Rates vary all over the place. I pay about 18 cents per kilowatt hour, how much do you pay? (Be sure to include distribution and connection charges)

K5END: "Realistically it would probably take more than 10 years to pay off the investment, and that is assuming these delicate cells survive all circumstances and are used during every sunny moment."

But are the panels really so delicate?

More important, what will happen to utility prices in those 10 years? If they go up, the payback time can be shortened dramatically.

K5END: "installing poles and electrical lines out to your shack may outweigh the cost of several kilowatts' worth of solar cells. But, then you have to consider that wires and poles require less maintenance and are more durable than the solar cells."

Maybe. OTOH, if a tree falls on the line you may be without power for a long time.

In such cases the usual response is to have a backup generator - but the cost of such a generator has to be considered too.  

K5END: "Bottom line is, sometimes it makes sense to install solar cells. But for a primary source of electricity in typical circumstances, it is not a good alternative to conventional means, including standby generators."

I think that's too broad a statement. Each situation has to be judged on its merits, and actual calculations done. Just the variations in residential electricity costs alone will make PV panels worthwhile in one place and not another.

And the calculations need to be redone over time. As utility prices rise and PV panel prices drop, the practicality of PV systems will change.

IMHO the most logical approach is to check out what energy improvements give the most return on investment. For example, improving the insulation in a house and replacing low-R-value windows and doors may have a much shorter payback time *and* make the house more comfortable and valuable. Replacing an inefficient appliance or HVAC system may add up to big savings. Judicious replacement of incandescents with CFLs and LEDs is a good idea. Just turning stuff off when not in use can save lots of energy.

73 de Jim, N2EY
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WX7G
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« Reply #2 on: January 16, 2010, 09:56:45 AM »

Interesting. Let's run the cost numbers in 'real time.' I don't know what the answer will be until I hit the Post button:

Inputs:
1) Solar cells presently run $4.80 per watt peak

2) Estimate 8 hours per day effective peak output 365 days per year in the California desert

3) Estimate a life of 30 years

4) Use 10 cents per kWh for electricity pricing

Answers:
A) Total energy ouput over the 30 year life is 88 kWh

B) Cost of 88 kWh is $8.80

Conclusions:
Assuming the cost of a solar cell reflects manufacturing energy costs only - that is, $4.80 of electricity was used to manufacture the cell - it takes 16 years before the solar cells hits energy break even.

Even with the extreme assumption of cost = electricity a solar cell will output more energy that was used to manufacture it.
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WX7G
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« Reply #3 on: January 16, 2010, 10:10:57 AM »

http://www.csudh.edu/oliver/smt310-handouts/solarpan/pvpayback.htm

This author calculates 1.6 to 8 years energy payback depending on technology. This is for solar cells installed in Europe.

I see photovoltaic power as something that might be done over a 50 year period. The same with thermal solar energy. Energy storage for nightime use must be installed also. This can take the form of mechanical storage (compressed gas, elevated water) or chemical storage. This could take the form of hydrogen produced by electrolysis and then burned in turbines or used in fuel cells.

'Fossil' fuels will run out and inevitably alternative energy sources must be developed. Time will tell but solar is the most area-efficient followed by wind. Bio mass requires more land and water than we have. Hot fusion might or might not be tamed in the time frame required to replace fossil fuels.
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K5END
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« Reply #4 on: January 16, 2010, 11:09:08 AM »

Jim, you've answered your own question.

It is because of the multiple unknowns of the future that 3 years is considered a maximum reasonable expectation for payoff on a capital investment against a recurring operating cost.

However, I should have been more specific. It's unwise for a consumer to invest in electronic or semiconductor technology against a lengthy return. The prices drop too quickly.

Solar cells have good application. But the recent craze I see is a bit blind. It reminds me of masses of lemmings all running the same direction, until they are all swimming...briefly.
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K0BG
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« Reply #5 on: January 16, 2010, 11:42:05 AM »

Thin film solar cells aside, this argument is like global warming. Irrespective of the truth, the opposite side will never relent. That said...

Using current technology, Larry is correct. Assuming David's calculations are correct, even thin film payoffs are way out there, even if they last as long as David suggests (30 years). The real problem is, they don't!

One of my very good friends owns 5 commercial repeater sites, all of which are powered by solar arrays. Granted they're atop mountains, and the weather more severe perhaps. But, average life time is closer to 6 years. A few might stretch to 10, but one has to remember the power has to be there, and when their output sags, off the hill they come. Same goes for the lead-acid batteries they charge.

Now, if you really want to get into an argument...

Let's start talking about the manufacturing cost of Li-ion batteries for hybrid vehicles. Or how about their unsafe at any speed tires which account for a goodly percentage of the fuel savings?

Or that in some (most actually) applications, a regular old alkaline AA offers better overall cost economy than any rechargeable.

Or even better, CFL! Oh God, don't let me get on that soap box!
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N2EY
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« Reply #6 on: January 16, 2010, 01:05:13 PM »

K5END writes: "It is because of the multiple unknowns of the future that 3 years is considered a maximum reasonable expectation for payoff on a capital investment against a recurring operating cost."

I think that's very shortsighted. A lot of worthwhile things won't pay for themselves in three years.

K5END: "It's unwise for a consumer to invest in electronic or semiconductor technology against a lengthy return. The prices drop too quickly."

But the only reason they drop quickly is because people invest in them!

Look at computers, what they used to cost, and how limited they used to be. The only reason they got better/faster/cheaper was because people bought them. If everybody had sat on their hands until P4 machines running Win7 were developed, we'd have never gotten them.

K5END: "Solar cells have good application. But the recent craze I see is a bit blind. It reminds me of masses of lemmings all running the same direction, until they are all swimming...briefly."

Lemming mass suicide is a complete myth:

From Wikipedia:

"The myth of lemming "mass suicide" is long-standing and has been popularized by a number of factors.... Even more influential was the 1958 Disney film White Wilderness, which won an Academy Award for Documentary Feature, in which staged footage was shown with lemmings jumping into sure death after faked scenes of mass migration. [9] A Canadian Broadcasting Corporation documentary, Cruel Camera, found that the lemmings used for White Wilderness were flown from Hudson Bay to Calgary, Alberta, Canada, where they did not jump off the cliff, but in fact were launched off the cliff using a turntable.[10]"

Despite all that, one of my favorite "Far Side" comics shows a mass of lemmings jumping off a cliff, with one holding his knees and yelling "CANNONBALL!"

I agree with WX7G: Solar is a long-term thing, to be phased in, not a quick all-purpose magic-bullet solution. It's important to get all the facts and make smart decisions based on them. And the 800 pound gorilla is resource depletion; even if you don't care about pollution, climate change, or the trade deficit, eventually (years to decades) we'll run out of economically-recoverable fossil fuels. The time to get ready for that is now. Of course, the more alternative sources we build, the farther out depletion will be.

Here in the Northeast, wind energy is part of the solution, for example. I don't think we'll ever see 100% wind or solar electric power, but those technologies can make a big dent.

I think the really BIG problem is that too many people want a simple, one-shot no-thought magic answer to problems. Real solutions don't usually work that way.

For example, take hybrid cars. They're great for city-type driving because they recover energy that would be wasted in braking, and because they don't idle the engine as much. On the highway, their advantage is minimal. So a hybrid may be right for one driver and wrong for another.

Or consider CFLs. In general lighting applications where they are turned on and left on a lot, they're very good. For applications where they're on and off frequently, or not used much, such as in a closet, incandescents are better.

And sometimes the solutions are old-fashioned and simple. A few years back, I put up a clothesline in the back yard, and when weather permits, I hang the clothes rather than running the electric dryer. Saves money, the clothes get a good airing, and the peak demand on the power plant is reduced at the most critical time (hot summer days).

73 de Jim, N2EY
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N6PJB
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« Reply #7 on: January 16, 2010, 01:21:35 PM »

Real world

System cost:$33K for 5KW

PG&E rates are tiered. The first 330KWH are $0.085/KWH. The uppermost tier is $0.52/KWH.

Annual PG&E bill prior to solar system:$3600
Annual PG&E bill after: $635

If energy costs do not go up in the next 11 years and there is no nuclear winter or other calamity, it should pay for itself in those eleven years.

The next 20 years will be free. Time will tell.
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WX7G
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« Reply #8 on: January 16, 2010, 02:39:50 PM »

The quoted life of the solar cells I looked at is 20 years. Satelites run solar cells for quite some time with satelite lives of 20 years and more being aimed for. So, long life solar cells will be available.

Now as oil supplies begin to run out we will run more things on electricity (transportation will move from oil to electricity). The electricity can be supplied by coal fired plants for some time. But then coal supplies will begin to run out. Energy prices will climb such that solar and other technologies will be cost competitive.

Based on the technology of today solar looks like the winner. The 29,000 TwH of energy (that is total energy, not just electricity) used in the U.S. each year could be supplied by 38,000 sq miles of solar cells. This is a square 200 miles on a side.

[Calculations based on 10% efficient solar cells operating at peak power an effective 8 hours per day, 365 days a year].

The 'market' can be left to solve this. There might be glitches - big glitches - along the way during energy supply disruptions. Or, government can provide (more) subsidies to hasten the transition and reduce or eliminate supply disruptions. National security as well as pure economics play into this.

Bottom line: Solar cell produced electricity is not cost competitive yet. As oil, coal, and natural gas prices go up and solar cells prices go down the point will be reached where solar cells are the lowest cost energy source.
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N2EY
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« Reply #9 on: January 16, 2010, 02:55:05 PM »

The mention of solar cells in space remined me of Oscar 7.

from wikipedia:

AO-7 was launched 15 November 1974 and remained operational until a battery failure in 1981. On 21 June 2002 the satellite was heard again on its 2 meter beacon (145.9775 MHz CW) after 21 years of silence, and 27 years in space.

AO-7 is still working, after 35 years in space.

73 de Jim, N2EY
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K5END
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« Reply #10 on: January 16, 2010, 03:15:07 PM »



K5END: "Solar cells have good application. But the recent craze I see is a bit blind. It reminds me of masses of lemmings all running the same direction, until they are all swimming...briefly."

Lemming mass suicide is a complete myth:


I do love these discussions. Roll Eyes

Are we talking about solar cells or arctic rodentia here?

It was imagery, color, a metaphor...a hyperbole.

C'mon, work with me here.
« Last Edit: January 16, 2010, 03:26:43 PM by K5END » Logged
K5END
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« Reply #11 on: January 16, 2010, 03:25:50 PM »

Here is my prediction as of January 16, 2010.

I think our main source of energy 20 years from now will be lemmings on hamster wheels. We'll just put a bowl of water in front of the cages where they can see it, and they will do their best to run toward it and drown themselves.

For high power applications they will use an iMax screen with HD films of the arctic from the point of view on an iceberg and blow cold air towards the lemmings faces. This will get the little buggers in high gear.
« Last Edit: January 16, 2010, 03:27:46 PM by K5END » Logged
K5END
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« Reply #12 on: January 16, 2010, 07:32:37 PM »

The mention of solar cells in space remined me of Oscar 7.

from wikipedia:

AO-7 was launched 15 November 1974 and remained operational until a battery failure in 1981. On 21 June 2002 the satellite was heard again on its 2 meter beacon (145.9775 MHz CW) after 21 years of silence, and 27 years in space.

AO-7 is still working, after 35 years in space.

73 de Jim, N2EY

Jim, I know you know that the solar cells you buy as a consumer will not last 35 years.

In any case, will you and I last another 35 years?
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TANAKASAN
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« Reply #13 on: January 17, 2010, 04:15:34 AM »

A far better source of free energy is to use a slice of buttered toast and a pussycat, let me explain.

If you let a slice of buttered toast fall it will always land butter side down on the rug and if you let a pussycat fall it will always land on its feet. So, by strapping a slice of toast* (butter side up) on the back of a pussycat and then letting it fall there will be a conflict between the toast and the cat. This will result in a rotational movement as both the toast and the legs of the cat attempt to land on the rug. The only problem is recovery of the energy from a rapidly spinning cat hovering above the floor.

Tanakasan

*If you are unable to strap the toast to the cat (some object to this) epoxy or three inch nails make a suitable substitute.
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N2EY
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« Reply #14 on: January 17, 2010, 05:44:15 AM »

K5END writes: "Jim, I know you know that the solar cells you buy as a consumer will not last 35 years."

How does anyone know that? They just might.

I have lots of things that were supposed to not last as long as they have which are still going strong. And other things that fell apart much sooner than advertised.

The panels on AO7 are over 35 years old and still working - in a space environment!

K5END: "In any case, will you and I last another 35 years?"

I might.

Point is, somewhere between the demand of payback in 3 years and payback in 30 years there's a good decision point.

And one thing we know is going to happen is that utility prices will go up.

73 de Jim, N2EY
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