Ask the EcoGeek: The Power Cost of Solar
by EcoGeek.org on 07.12.07
Dear Mr. EcoGeek,
I've heard that it takes more energy to produce photovoltaic cells than the cells will ever produce throughout their lifetime. Is there any truth to that, or are those naysayers just saying nay?
David
Spokane, WA
Short Answer:
Those naysayers are just saying nay! But that doesn't mean there's not more to this story.
Long Answer:
This myth was probably perpetuated by studying solar panels created for NASA. If you need something extremely efficient for use in outer-space, yes, then it doesn't matter how much energy you use to create the panel. But for use hear on Earth, it's ridiculous for anyone to say that solar panels consume more energy than they produce.
Of course, doing anything in this world takes energy. Whether it's building power lines or shipping oil from Saudi Arabia, it takes energy to make energy usable. In fact, there's a nifty number that puts all of this into perspective. It's called the “energy balance”, and it is, in short, the amount of energy you get out divided by the energy you put in.
So, for corn ethanol, for example, we get 1.3 units of energy for every 1 unit we put in, so its energy balance is 1.3. Whereas for Brazilian sugar cane ethanol, we get 8 units of energy for every one we put in. As for gasoline, its energy balance is about 5.
So what does this have to do with solar? It is a bit incorrect to apply energy balance to solar panels, because they don't actually contain the energy, so it's not something that I've ever actually seen done. But I think it makes sense to fudge it a bit in light of your question.
Data from a study(pdf) from Energy Environment and Economics Inc. showed that the average solar panel gets five times more energy out than was originally put in. Roughly the same “energy balance” as gasoline.
Still, no one is satisfied with that number. Thousands of scientists, engineers and business people are working, right now, to increase solar's energy balance, and many have done it substantially. The simplest and most common methods include making sure that the panels are always at a 90 degree angle to the sun, increasing the life of the panels, and decreasing the amount of photovoltaic (PV) material needed in the panels.
As PV material (usually polysilicon) is energy intensive to create, a lot of folks are trying to figure out how to use less of it. One common method is to use mirrors or lenses to concentrate the sunlight on a relatively small amount of polysilicon material. Additionally, a whole other branch of the solar industry is trying to make solar panels from less energy intensive materials, including the much touted copper indium gallium selenide (CIGS) thin-film solar panels.
There may be some economic reason to not be an early adopter of solar, but there is certainly no doubt that they produce a lot more energy than they consume. And soon, they'll be producing even more.
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Of course, solar water heaters and passive solar design have far lower entry costs. Just put a black painted bottle of water out on the fire escape on a sunny day !
cool stuff how come people never mention on how much we would save if we recycled all our garbage
I think the EROEI figures may be slightly adrift in the article above. The values I have are:
Corn Ethanol - 1.3 (correct)
Sugarcane Ethanol - 0.8 to 1.7 (not as high as 8!)
Gasoline - 10 (not as low as 5!)
Can the author attribute the values he has?
As far as the comparison between solar PV and other energy sources is concerned, surely one thing that needs to be taken into account is that the EROEI figures cannot be directly compared.
Presumably with a Solar PV panel the whole-life energy produced is being compared to the energy costs of production. This means that the energy is being produced over (let's say) 20-25 years, but the energy to produce the panel is all being taken up front.
Surely this is a little bit like the problem with carbon offsets like planting trees - say you cause one tonne of carbon to be emitted and then plant trees that will sequester one tonne over 100 years - it's not going to do the job when we need it most, which is now!
Sorry about this post - I always forget to click the checkbox to subscribe to the entry - why can't this be a default setting?
I found EROEI estimates from 8 to 10 on other articles covering Brazilian sugarcane ethanol. In any event here is a link to a Popular Mechanics article stating that Brizilian sugarcane/beet ethanal has a much higher EROEI than corn ethanol.
http://www.popularmechanics.com/blogs/energy_family_news/4213318.html?nav=RSS20
I just started using with solar cells myself. I like how I can power small electronic devices without have significant loses on the transformer and rectification. I find I used far too much lighting in the past. Now I have a 1.4 Watt lightbulb next to my notebook computer when I am working. That represents a lot less cooling load during the summer. I switch to my inverter when I have more pressing demands.
Solar is a good transitionary technology because the same basic infrastructure - batteries and control mechanisms - can be used to accommodate other power sources such as wind generators. So although I realize I am not recovering my costs in the shortrun, I'm definitely much happier and resourceful now.