Sciencemadness Discussion Board

Energy balance of solar cells?

jgourlay - 27-3-2014 at 07:38

Question about photovoltaics: are they able to supply enough energy over their useful life, in real world conditions, to replenish themselves?

By "replenish themselves", let me give an example. Let's say I was to give you, in one lump quantity, all of the photovoltaics a major size solar cell plant can produce. You go set these up in a sunny spot. Now, over the course of the useful life of those cells, will they produce enough power to refine all steel, copper, etc to make the raw materials for the machines to produce the cells. Will they in addition provide enough power to refine all the raw materials for replacing the cells themselves as well as providing the power to run the 'operation' of producing a replacement set?

I was having an 'energy' discussion the other day where we did some back of the napkin calcs showing that an offshore oil platform produces at a minimum an amount of BTU's about 3 orders of magnitude greater than what is necessary to refine and machine all the steel necessary for the entire chain of industry necessary for producing an oil operation from scratch.

I was wondering if solar does the same.

macckone - 27-3-2014 at 08:09

For solar cells the ROI is hard to quantify because the 'working life' hasn't been well established and also depends on the battery storage component if one is used. Generally the batteries don't take a lot of energy to recycle but the silicon used can be quite energy intensive to produce. I don't know if there is any data yet on recycling solar cells or repair of solar arrays.

jgourlay - 27-3-2014 at 08:35

The machinery used in solar cell production is all what you call "heavy"machinery as well. Many tons of steel needing smelting, many tons specialized concrete and rebar for the rigoursly specified foundations in these plants. Then there are energy costs of actually building and maintaining the plant.

Recycling is problem a minor savings. Recycling is, for example, an important part of keeping the cost of aluminum down. But only because the melting point is so low and the purity requirements for cans so loose. Aluminum, as an industry, would be almost unviable if it weren't from essentially free geothermal energy available in iceland (or is greenland?)

Tsjerk - 27-3-2014 at 09:09

I do not completely agree with the statement aluminium can only be produced with ''free'' energy. There is quite a big aluminium industry in the Netherlands which works on natural gas.

Dutch natural gas costs about 35 euro cents / m3. While for example English gas costs 6,56 dollars / MMBTU. 1 MMBTU being 27,9 m3, one m3 would be 0,23 dollar. As good as half the prize.

With or without taxes could make some difference, but the statement aluminium production wouldn't be viable without free energy is nonsense.

And besides that, if it wouldn't be viable, than the prize of aluminium would just go up.

Since when did we start to write aluminum instead of aluminium? I'm in a office with Spanish, English and German people, I'm Dutch and anyone agrees with me it should be aluminium.

jgourlay - 27-3-2014 at 09:26

Aluminium vs Aluminum: reminds me of the recent fight when Portugal began to discover that they were no longer relevant on the world stage and therefore could not effectively stop Brazil from being the final authority on questions of what vocabularly and grammer formed "Proper" Portugese.

Energy cost: not knowing anything about the specific industry you cite in the Netherlands, I can't comment. I would ask whether that industry primarily in remelt, or in smelting bauxite? It certainly makes sense to have many aluminum foundries sprinkled all over the globe during remelt: transport is expensive. But breaking bauxite is energy intensive in the extreme.

The benefits of aluminum are clearly described in text books at least as far back as the 1910's. As was the arc method of refining. But it wasn't until 'cheap' energy you actually saw it commonly used outside of the military.

The US does have several bauxite refiners. However, I'm told that the existence of that industry is largely undergirded by US military requirements about where strategically important components are produced. Sort of the same reason the Herstal group still exists in Belgium.

Tsjerk - 27-3-2014 at 10:03

I really don't see why the Portugal issues has anything to do with the aluminium/aluminum question. There is no group (I won't go to language) in the world that uses aluminum when referring to the element Al, except for the people from the US. I wouldn't exactly count the citizens of the US in as being a final authority on questions of what vocabulary and grammar to be English.

A quite big proportion of the world's inhabitants speak and write English, A quite small proportion of the US inhabitants speak or write a language besides ''English''. At the moment I'm trying to learn proper English as I'm doing an internship abroad (UK), and I have to admit learning English from the internet is being made more difficult by people from the US.

The aluminium industry in the Netherlands are breaking bauxite. Using the electrochemical pathway.

Edit: I have to apologize. I am assuming you are from the US, or am I wrong?

[Edited on 27-3-2014 by Tsjerk]

macckone - 27-3-2014 at 10:21

I am not sure what lead or silicon recycling has to do with aluminum/aluminium recylcing. Lead recycling does not require
much in the way of heat and is relatively easy to recycle.
Easier even than aluminum. Silicon recycling is not common today.
But given the difficulty of producing silicon in the first place
repair and recycling are likely to be much more common in the future,
much as aluminum is today. Aluminum is recycled because
virgin aluminum is extremely energy intensive much like silicon.
None of this really answers the OP's question.

jgourlay - 27-3-2014 at 10:41

"There is no group (I won't go to language) in the world that uses aluminum when referring to the element Al, except for the people from the US."

Many years ago, I dated an art school student. Big head lights, long hair, liked it when you pulled it. Anyway, we were having a little lovers spat over "PC vs Mac". I said, "nobody uses a Mac!"

She says...."except the cool people, the ones who matter."

By the way, this is not really where I wanted this thread to go, but I'm just following your lead. :D

jgourlay - 27-3-2014 at 10:42

Where you to recycle silicon, can the dopants be refined out?

Tsjerk - 27-3-2014 at 11:31

@ jgourlay, You just made my point, thank you.

Polverone - 27-3-2014 at 14:47

Yes, solar PV has a positive net energy return. A fairly recent review is:

Energy Policy 45 (2012)
The energy return on energy investment (EROI) of photovoltaics: Methodology and comparisons with fossil fuel life cycles
Marco Raugei, Pere Fullana-i-Palmer, Vasilis Fthenakis

I have noticed that literature reviews, including this one, tend to underestimate the EROI of current practice because they are working with figures a few years out of date on silicon production, wafering, cell efficiency, etc.

This study, like many, assumes a 30 year lifetime of useful output. That is a reasonable middle-ground assumption. The Energy Return on Investment calculations are sensitive to lifetime, since a doubling or halving of useful life means nearly a doubling or halving of lifetime EROI. There is at least a significant minority of modules that will maintain useful output long beyond 30 years. There is also a significant minority of modules made in the last few years that will fail much earlier, since marginal manufacturers struggled to reduce costs by any means possible (including untested ones) during the post-2010 capacity glut that slashed average selling prices.

PV modules have no (deliberately) moving parts to wear out; the main causes of degraded output are soiling, damage to internal electrical connections from differential thermal expansion and fatigue, potential induced degradation to cells and electrolytic corrosion if moisture infiltrates the module, light induced cell degradation with amorphous and p-type silicon cells, encapsulant browning or frosting, and gross encapsulant failure with module delamination. All of these problems except for soiling can be designed around with proper choice of cell materials and connections and encapsulation. Silicon modules built with fatigue-resistant cell connections, good encapsulant materials, and n-type silicon -- like those from Sanyo or SunPower -- may well be producing at high levels 60 yeas in the future. It was only in 1979 that production of solar modules for terrestrial use started on any large scale, so historical data goes back 35 years at most.

For a review of PV output degradation in long term field trials, see:

For a nice technical article on the industrial shift to n-type silicon and its resistance to light induced degradation, see:

Beware of researching this topic outside peer reviewed literature because there are a lot of people writing from the gut on the topic.

hyfalcon - 27-3-2014 at 14:50

Talk about topic drift. To answer the OP, considering that most solar panels have an expected operating lifespan of 20-25 years, then I would say yes they are price competitive. If you use them for more shall we say "experimental" purposes and store your energy in oxidizers instead of batteries. They can be very cost effective.

jgourlay - 31-3-2014 at 13:17

Thanks gents, that's exactly what I wanted to know!