The ugly side of solar panels

New research shows, albeit unintentional, that generating electricity with solar panels can also be a very bad idea.

The manufacture of just 1 square meter of solar panels generates between 7,500 and 31,400 kilograms of greenhouse gases. An average household needs at least 8 square meters of solar panels for electricity generation alone, which boils down to a global warming debt of a whopping 60,000 to 940,000 kilograms of CO2. These numbers equate to 12 to 188 intercontinental flights (see comments). In some cases, producing electricity by solar panels releases more greenhouse gases than producing electricity by gas or even coal. (Picture: Sungazer)

Producing electricity from solar cells reduces air pollutants and greenhouse gases by about 90 percent in comparison to using conventional fossil fuel technologies, claims a study to be published this month in “Environmental Science & Technology”. Good news, it seems, until one reads the report itself. The researchers come up with a solid set of figures. However, they interpret them in a rather optimistic way. Some recalculations (skip this article if you get annoyed by numbers) produce striking conclusions.

Solar panels don’t come falling out of the sky – they have to be manufactured. Similar to computer chips, this is a dirty and energy-intensive process. First, raw materials have to be mined: quartz sand for silicon cells, metal ore for thin film cells. Next, these materials have to be treated, following different steps (in the case of silicon cells these are purification, crystallization and wafering). Finally, these upgraded materials have to be manufactured into solar cells, and assembled into modules. All these processes produce air pollution and heavy metal emissions, and they consume energy - which brings about more air pollution, heavy metal emissions and also greenhouse gases.

Energy mix

The ecological burden of energy use depends on the way electricity was generated. Therefore, the researchers bring into account 3 scenarios. One is based on the average European energy mix, another on the average American energy mix (which is about 45% more CO2-intensive). A third scenario uses the figures of the recent “CrystalClear” European Commission project, which investigated the real energy mix used by 11 European and American silicon and PV module manufacturing factories. Since they use comparatively more gas and hydropower, this is the best case scenario. The researchers investigated 4 types of solar cells: multi-crystalline silicon (with an efficiency of 13%), mono-crystalline silicon (14%), ribbon silicon (11.5%), and thin-film cadmium telluride (9%).

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"The optimistic conclusions of the researchers are based on a life expectancy of 30 years and solar insolation in the Mediterranean"

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The scientists come up with figures concerning the amount of greenhouses gasses emitted per kilowatt-hour of electricity delivered by one square meter of solar cells. They do that for every type of cell and for the three different scenarios. Thin film solar cells get the best score with 20.5 grams of CO2 (*) in the European energy mix and 25 grams of CO2 in the American energy mix. In spite of their lower efficiency, they are more eco-friendly because they need less material and no aluminium frame. In spite of their high efficiency, mono-crystalline silicon cells score worst, with 43 grams of CO2 in the EU, and 55 gram of CO2-equivalent in the US. All other types and scenarios fit between these two extremes.

Solar insolation

However, these conclusions are dependent on some assumptions, most importantly solar insolation (the amount of sunlight that the cells receive) and lifetime expectancy. For solar insolation, the researchers choose 1,700 kWh per m² per year, which is the average of sunlight in Southern Europe. For lifetime expectancy, they choose 30 years. From these variables, they calculate the total lifetime electricity generation of one square meter of solar cells. Next, they divide the amount of CO2 emitted for the production of one square meter of solar panels by this lifetime electricity generation – and that’s how they achieve their conclusions.

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"Surprisingly, the key data of the calculation (the amount of CO2 emitted per square meter of solar panels) are nowhere to found in the report"

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Surprisingly, the key data of the calculation (the amount of CO2 emitted per square meter of solar panels) are nowhere to found in the report. That’s remarkable, since these data are the most objective numbers available. Even so, they can be calculated by multiplying the obtained results (in gram CO2 emitted per kilowatt-hour of generated electricity) by the lifetime electricity generation. This calculation gives the amount of greenhouse gases emitted for the production of one square meter of solar panels, regardless of the assumptions on solar insolation and lifetime expectancy.

2 to 20 flights

Once calculated, it’s not so surprising that the researchers choose not to write these figures down. In the best case scenario, one square meter of solar cells carries a burden of 7,527 kilograms of CO2. In the worst case scenario, that becomes 31,416 kilograms of CO2. An average household needs at least 8 square meters of solar panels for electricity generation alone (make that 10 in the US), which boils down to a global warming debt of a whopping 60,000 to 940,000 kilograms of CO2. These numbers equate to 12 to 188 intercontinental flights (see comments for details of the mistake, see paragraph below for the correct version). 

Once calculated, it's not so suprising that the researchers choose not to write these figures down. In the best case scenario, one square meter of solar cells carries a burden of 75 kilograms of CO2. In the worst case scenario, that becomes 314 kilograms of CO2. With a solar insolation of 1,700 kWh/m²/yr an average household needs 8 to 10 square meters of solar panels, with a solar insolation of 900 kWh/m²/yr this becomes 16 to 20 square meters. Which means that the total CO2 debt of a solar installation is 600 to 3,140 kilograms of CO2 in sunny places, and 1,200 to 6,280 kilograms of CO2 in less sunny regions.  These numbers equate to 2 to 20 flights Brussels-Lissabon (up and down, per passenger) - source CO2 emissions Boeing 747.

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"Solar panels mounted on gadgets are completely insane"

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According to the researchers, producing the same amount of electricity by fossil fuel generates at least 10 times as much greenhouse gasses. Checking different sources, this claim is confirmed: 1 kilowatt-hour of electricity generated by fossil fuels indeed emits 10 times as much CO2 (around 450 grams of CO2 per kWh for gas and 850 for coal). Solar panels might be far from an ideal solution, but they are definitely a better choice compared to electricity generated by fossil fuels. At least if we follow the assumptions chosen by the researchers.

Northward

Logically, if we make the same calculations for a solar insolation of 900 kWh/m² (the yearly average in Western Europe and in the Northeast and Northwest USA), the results get worse. In the worst case scenario (US grid, mono-crystalline silicon), emissions rise to 104 gram CO2 per kilowatt-hour of solar generated electricity, which makes solar panels only 4 times cleaner than gas. Now let’s play a bit with the life expectancy. If we combine this lower solar insolation with an expected lifetime of only 15 years, the worst case scenario becomes 207 grams of CO2 per kilowatt-hour – just 2 times better than gas. Agreed, this is the worst case scenario, and even in that case solar panels are still a better choice than fossil fuels. But it becomes quite hard to describe them as a “clean” source of fuel.

This map (click to enlarge) shows the amount of solar energy in hours, received each day on an optimally tilted surface during the worst month of the year. For a more detailed view of solar insolation (in kWh/m²/yr) see the links above.

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 "A better strategy would be to use already available solar panels to produce more solar panels"

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The life expectancy chosen by the researchers is, well, just an expectation. It’s true that most manufacturers give warranties of 20 to 25 years, so technologically speaking a life expectancy of 30 years is not implausible. However, there are other than technological reasons that may lead to a significantly lower life expectancy. The scientists note that the environmental score of solar panels will improve, because they are becoming more efficient each year. (They also become thinner, so less energy is needed to make them). Most likely they will also become cheaper.

Life expectancy

That means that in 15 to 20 years time, if the evolution in efficiency carries on the way it does now, a solar panel with an efficiency of 10 percent produced today will have to compete with cheaper solar panels that have efficiencies of about 20 percent. Moreover, and that’s a fact that the researchers are not taking into account, solar cells degrade in time. Typically, the warranty given by solar cell manufacturers covers just 80 percent of power output. All this means that it may make economic sense to substitute older panels with newer panels before they are 30 years old. Again, even in that case the ecological score will probably still be better than the one of fossil fuels, but the point is that the gap can become very small.

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"All this does not mean that PV solar energy should not be promoted. But some facts have to be faced"

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For rooftop and ground-base installations, the eco-friendliness can be good or doubtful, depending on the solar insolation and the life expectancy. But if we consider solar panels mounted on gadgets like laptops or mobile phones, solar energy becomes a plainly bad idea. If we take a life expectancy of 3 years (already quite optimistic for most gadgets) and a solar insolation of 900 kWh/m² (quite optimistic too, since these things are not lying on a roof), the result is 1,038 gram CO2 per m² kWh in the worst case scenario (high-efficient mono-crystalline cells produced in the US). Of course, these panels do not have a size of 1 m², so the amount of CO2 is lower. But that does not change the fact that That means that it is better for the environment to power a gadget with electricity generated by coal, rather than by a solar panel.

Now what?

All this does not mean that PV solar energy should not be promoted. For one thing, it’s much better using silicon wafers to make energy generating equipment instead of energy guzzling equipment (like computers, mobile phones and car electronics). But some facts have to be faced. First, solar cells are far from a zero emission technology. Two: solar panels can be a doubtful choice in less sunny regions. Three: solar panels mounted on gadgets are completely insane. Four: solar cells should be recycled. Five: some law or incentive should be introduced to guarantee a life expectancy of 30 years. And if possible, solar thermal power should have priority over solar PV power.

It should be realized that solar panels first raise the amount of greenhouse gasses before they help lowering them. If the world would embark on a giant deployment of solar energy, the first result would be massive amounts of extra greenhouse gasses, due to the production of the cells. A better strategy would be to use already available solar panels to produce more solar panels. The scientists calculated that the ecological burden of solar panels can be halved if 100 percent of energy in the factories would be delivered by solar energy.

I did not do the calculations for air pollution and heavy metals, but since these are mainly produced by energy use for production, the conclusions must be similar.

© Kris De Decker (edited by Vincent Grosjean)

(*) in the text, “CO2” stands for CO2-equivalents (which means other greenhouse gases are included).

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Comments

[Jerry]

(23)

While this article has some valid points, its arguments are now obsolete. Using a new nanotechology based ink, NanoSolar corporation is producing 100's of feet of solar panel per minute. No foundries, no highly toxic metals. No need for huge amounts of energy consumption (CO2) like with crystalline silicon cells. The new ink based panels cost a tiny fraction of silicon. This technology is going to change the world as we know it.

I've built solar panels by hand and while I can't vouch for the numbers in this article, there are most certainly environmental negatives that come with using silicon cells. I was poisoned when I handled silicon cells without gloves and I'm still dealing with the effects of that experience.

[Jay Draiman]

(22)

Renewable Energy Manufactures/suppliers should use their own product to manufacture.

The manufacturers’ of Solar Panels and other forms of renewable energy with related support products manufactures/suppliers - should have at least the decency to practice what they preach what they market to the public.
That would be the best marketing approach I can think off.
If they believe in the product, they should utilize it to its fullest potential.
It will give the manufacturer the actual experience of utilizing the product on a daily basis, view and experience any improvements that are needed, implement the improvements and capitalize on that improvement to improve the product and its performance.
This will instill confidence in the public to purchase the product.

Jay Draiman, Energy Analyst

[Kris De Decker]

(21)

If you would read more than one article on this website, you would realise how ridiculous your accusation sounds. You, on the other hand, are paid by the renewable energy industry.

And if you send cowardly comments like this without mentioning even a pseudonym or an e-mail adress, you should remember that your ISP shows up in the web traffic analysis - especially relevant when you send "anonymous" comments from the server at your job.

[DC Power Systems]

(20)

you must be paid by the Oil industry.

you are spreading lies.

[Kris De Decker]

(19)

Mr. Fthenakis, you don’t say anything about the chosen solar insolation?

The conclusions of your study are that “at least 89% of air emissions associated with electricity generation could be prevented if electricity from photovoltaics displaces electricity from the grid”.

That is a deceptive message since it implies a solar insolation of 1,700 kWh/m²/yr, which is everything but self-evident. Germany, for example, the world leader in solar PV power, has much less sun than that.

If I would have been one of those expert peer reviewers, I would have advised you to attach the following sentence to your conclusions: “...if the solar insolation is 1,700 kWh/m²/yr”. You know damn well that most media don’t get further than the summary.

The 3 year life expectancy mentioned in the article concerns gadgets like mobile phones and laptops, not rooftop panels. You should read the text carefully.

Yes, my surname sounds very different from yours. So what?

[Vasilis Fthenakis]

(18)

Kris De Decker exhibits great ignorance about PV technology and life cycle impacts with his comments. The study in ES&T that he cites, undertook year-long independent expert peer reviews before it was accepted for publication by this most prestigious journal. Just a couple of remarks to some of his points that deserve an answer. Degradation losses of 0.5% to 1% /yr are included in our studies; the low number is confirmed by utility (e.g., TEP, AZ) records and the utility posts on the web daily perfomance of their biggest plant Springerville). The numbers of gCO2/kWh that De Decker (is this a real name?) demonizes us for not showing!! are intermiadiate numbers in a LCA. The final numbers with which PV can be compared with nuclear and fossil are g CO2/kWh. The former can easily be backcalculated from the later.
His assumptions about 3 yr life expectancies are rediculous. PV flat modules have confirmed lifes of 30 yrs and their structures can well last 60 yrs, but consevatively, we used 30 yrs for both.

Dr. Vasilis Fthenakis
Brookhaven National Lab and Columbia University

[Kris De Decker]

(17)

Speaking of toxic chemicals -- there is a story on Grist linking to this page and to an article in the Washington Post, called "Solar energy firms leave waste behind in China". An excerpt:

"Because of the environmental hazard, polysilicon companies in the developed world recycle the compound, putting it back into the production process. But the high investment costs and time, not to mention the enormous energy consumption required for heating the substance to more than 1800 degrees Fahrenheit for the recycling, have discouraged many factories in China from doing the same."

As one reader comments on Grist: "This is not a problem of technological feasability but of social irresponsibility. This isn't like nuclear energy which produces a waste no tech can deal with".

And that's correct, but it shows again that PV has potential negative sides, and they should be accepted if we want it to be a solution instead of a new problem.

http://www.grist.org/news/2008/03/10/solar/

http://www.washingtonpost.com/wp-dyn/content/article/2008/03/08/AR2008030802595.html

[BCL]

(16)

Actually, having worked in the semiconductor industry, I was happy to see somebody perform this analysis. I always wondered if the energy going into producing those solar panals was more than what came out. I was actually worried that they might take more energy to make them than they produce! Fortunately this turned out not to be the case -- but there are other concerns. Manufacturing of the panels does use huge amounts of water (this depends on the specific process used to make the panels, but it could be as high as a 1000 gallons per sq. ft. Also, there are a host of toxic chemicals used in the proces as well which might make solar less attractive. Of couse, non VC based systems are much better over all.

[Kris De Decker]

(15)

Ron: everybody makes mistakes. The fact that I fess up, might be a reason to trust me and accept the conclusions that stand up. If not, prove me wrong.

The scientists come to their conclusions starting with a solar insolation of 1700 kWh/m²/yr and a life expectancy of 30 years. You don't have to be a mathematician to conclude that the results are 4 times worse when you halve both the solar insolation and the life expectancy.

I saw quite some blogs just posting the 89 percent advantage of solar energy, because they did not bother reading the paper. At least, this news should be accompanied by the fact that it is based on two subjective assumptions, no?

[Ron Swenson]

(14)

Would I trust any conclusions drawn by someone who blithely makes a mistake of 2 orders of magnitude? (That said, I do appreciate that you fessed up!)

I would prefer to resort to the conclusion of the folks who wrote the original article on which this opinion piece is based:

"At least 89% of air emissions associated with electricity generation could be prevented if electricity from photovoltaics displaces electricity from the grid." See http://pubs.acs.org/cgi-bin/abstract.cgi/esthag/asap/abs/es071763q.html

[jim]

(13)

Rushing through the article, I reflect on the idea that solar cells might become dramatically cheaper to produce in a few decades due to materials research and production technologies. Solar cells tend to diminish output over time, but still can be productive with a fractional output. They might be useful for hundreds of years if sufficient real-estate exists to recycle them as low-yield units where possible. Design technologies already exist that greatly extend the output of cells, by external focusing of sunlight on cells and the use of susbstrate cooling systems. I remember a member of my computer club some thirty years ago who went on to wealth and fame in part for his self-focusing cell systems that achieved a record for output for given parameters (Midway Labs, 1980's). Unfortunately, Paul Collard did not fully appreciate the importance of cooling systems to preempt premature aging and his systems succumbed to declining output in only a year or two. However, new experimental systems are promising. Don't write them off completely. You might be disappointed.
Lots of research:
http://www.redrok.com/main.htm

[Kris De Decker]

(12)

Andy, thanks a lot, you are right.

The lifetime electricity generation = efficiency x solar insolation x performance ratio x lifetime

My calculation (for the best case scenario) was: 9 x 1,700 x 0.8 x 30 = 367,200 kWh/m²

Of course, it should be:
0.09 x 1,700 x 0.8 x 30 = 3,672 kWh/m²

Unfortunately, that does not change the conclusions of the article, since I overestimated both C02-emissions and electricity generation.

But it does mean that the number of intercontinental flights is hugely overestimated. The C02 cost of 1m² of solar panels is not (in the best case scenario) 7,527 kg but 75 kg. And in the worst case scenario it is not 31,416 kg but 314 kg.

Thanks. Can I hire you as a proof reader? :)

[Andy Simpson]

(11)

I think that you should check your calculations. They looked a bit suspect to me because the amount of energy used to make the panels would cost more than the wholesale price of panels. So I checked:

Looking at the best case scenario, you say that a square metre of solar panel will cause 7,527 kg of emissions, given an emission intensity of 20.5 g/Kwh. That implies that the panel generates 7,527/0.0205 Kwh over its 30 year life time (the 30 years comes from the study).

7,527/0.0205 Kwh = 367,170 over 30 years.
That's 367,170/30 = 12,239 Kwh/ year - not bad, but sadly not possible given a solar intensity of 1700 Kwh/year.

[Kris De Decker]

(10)

What's the use of sending me this link? It's the same page that I am linking to in the article, it's the same study we are talking about here. So what's your point then? Just believe whatever the experts say and shut up?

[A concerned Reader]

(9)

http://pubs.acs.org/cgi-bin/sample.cgi/esthag/asap/html/es071763q.html

"... Overall, all PV technologies generate far less life-cycle air emissions per GWh than conventional fossil-fuel-based electricity generation technologies. At least 89% of air emissions associated with electricity generation could be prevented if electricity from photovoltaics displaces electricity from the grid."

[david_42]

(8)

Having followed the solar industry for over 40 years, I'll make a few observations. First, solar thermal for large installations is 2-3 times as efficient as photovoltaics AND uses far less materials. It is also very easy to build energy storage into thermal systems. Second, there is a class of gadgets where photovoltaics is just about perfect. Those are remote sensing and sparsely populated operations. The solar panel/cell phone/gell battery kiosk for emergancy phones is a good example of the latter. Installing them along I5 in California cost 1/4 as much as a wired system and that included building the cell towers and relays.

In the middle ground, powering homes and businesses, the cost effectiveness of solar depends strongly on the ability to push excess power back into the grid. Home power loads are seriously out of sync with supply. My peak loads are at night in mid-winter. At noon in the summer, I need almost nothing.

[Kris De Decker]

(7)

A message to the guys at fark.com, calling me an "idiot" and an "asshole" :

Obviously, some of you didn’t get further than the three first words of the headline. I did not write that solar panels are a bad idea (except for gadgets), nor that we should burn coal or build more nuclear plants instead. However, being an advocate of solar energy myself for years, I was shocked by the amount of energy needed for the manufacture of one square meter of solar cells – and by the fact that the authors of the study try to hide that. Yes, solar energy is the future, among other renewables, but I think these figures show that it might be better to use solar panels where there is as much sun as possible. In deserts, solar insolation can be 6,000 kWh/m²/yr, and more. That makes solar cells 40 times more eco-friendly than burning fossil fuels.

[Joe]

(6)

Its great to see both sides of an arguement. I generally agree with the conclusions, but I think we should consider the longer term future and not focus so much on current limitations of what is still a relatively immature technology.

As with any new technology, PV will become more efficient, cheaper and cleaner to produce. In order for this to happen we (Governments / NGOs / Individuals) need to invest more time and money into making PV viable, e.g. through regulations, technical standards, R&D, manufacturing processes and generating consumer demand.

As more electricity is generated from PV (and other renewable sources), the manufacturing of such technology will become less carbon-intensive.

In terms of using PV for gadgets, I agree its difficult to justify over such a short life expactancy. However, this will change as manufacturing costs / carbon emissions decrease and efficiencies increase. I do have a problem with the manufacturers of these gadgets as they intentionally design their products to last such short periods - this is where regulations should be put in place for increasing life expectacy and making the manufacturers responsible for the disposal of 'old' products.

[Soren]

(5)

Before jumping to the conclusion that gadgets should be "powered by electricity from coal," I think one needs to examine the CO2 costs of the *batteries* almost all gadgets use to store power. And the often-inefficient transformers that are used to charge those batteries. For a desktop calculator, at least, the PV modules are often *in place* of batteries. If other devices can have smaller batteries by adding solar panels for more frequent recharging, the CO2 cost might go down ... probably not enough to pay itself back in the three-year lifespan of the device, but perhaps bringing it out of the "insane" level.

Maybe most gadgets with PV have the same size batteries as if they had no PV, but to assume that you can attach a coal plant directly to your cellphone (or even to a land line telephone, which has lots of batteries at the telco) seems like jumping to conclusions too quickly.

I don't have PV on my house yet ... first has been a reduction to 60 kWh/mo of electricity, now is installing a 1.6 GPM shower head, and next will be a solar thermal collector to heat the house and water (I still consume at least 10 therms of gas each month in the cooler months).

[Frank Schanzenbächer]

(4)

"Style remains a matter of taste". I am German, and I know the are around Bodensee. Its one of the most beautiful places in Germany. I do not see the solar panels as an disadvantage, in terms of messing up the scenery. I rather see it as an advance in time. Want to have some wood/clay/tarsheet tiles to absorb or reflect the light, or to use it wisely to regain the energy? Mr. Cleaver, its your brain playing a trick on you. What you consider nice, might appear dirty to others. Apart from that, there are other type of solar panels coming up. Translucent ones as brown/red and black are available. Only a matter of time.

The article seems quite one sided. Comparing the "worst case solar scenario" (old panels, bad location, little use) to best case gas. And still points out that it would only be twice as little CO2. Trying to write good things to be bad. Imagine a car would produce 50g of CO2 instead of 100g, by giving the same distance and power of engine... It would be a breaker...

[Martin Cleaver]

(3)

That's not the only "ugly side" so solar panels. I am a great believer in the benefits of solar energy and other alternatives to oil, but a recent journey through Southern Germany made me think. Many picturesque old villages around the Bodensee are now defaced by huge shiney dark-blue panels. Whole farmhouses have been hidden behind them. Surely someone could pay a little attention to the aestetics of things. Just because it's "Good for the Earth" doesn't excuse "Bad Taste". Please will someone look into alternatives? Say - slate grey, terracotta bronze?
Just plastering our world full of ugly blue sheets is not the answer. :(
Martin

[Kris De Decker]

(2)

Efficiency and size don't matter. The problem with gadgets is their short life expectancy and the amount of solar insolation they receive. It takes some years before a roof-top mounted solar panel delivers as much energy as was needed to produce it. This so-called "energy payback time" depends on the type of solar cell and the amount if sunlight it receives. The problem with gadgets is that they don't receive much sun (they are not mounted on a roof to absorb all available light) and thet their life expectancy is at best 2 or 3 years. That means they will be discarded before the solar cell had the chance to produce more energy than was needed to produce it.

[JuandeSant]

(1)

Very interesting article indeed… Even when "The ugly side of solar panels" is maybe a little extreme, it is true that the carbon footprint of manufacturing any piece of technology cannot be neglected.

Maybe I've skipped over some section, because even when I think I understand the logic for no solar panels in gadgets (low efficiency of small panels, while manufacturing cost increases per square cm), maybe it should be more explicitly expressed.