Solar PV: Still Too Carbon Intensive
Monday, September 13, 2010 at 10:18AM 
A friend of mine sent me a link to a recent Mother Jones article that attempts to dispel the "myth" that the benefits of photovoltaics are limited because they are energy intensive to produce. Unfortunately the article over-simplifies a relatively simple math problem, and in doing so it reaches an incorrect conclusion. Here's what I wrote back:
The issue with PV is not limited to whether they produce more energy than is consumed during manufacture, as suggested by the MJ article. Mathematically, even if you get the energy back in one year, it would still take many years to get a net carbon benefit from PV, assuming you ever get one. The reason is that PV currently provides a tiny fraction of our electrical energy (about one-half of 1%), and so the industry would need to grow exponentially for many years to make any significant contribution to the energy supply. During the period in which a carbon intensive industry is growing exponentially, the carbon emission rate of that industry is also growing exponentially. During the exponential growth years for solar, the carbon emissions will exceed the carbon offsets for that year and, depending on the rate of growth and the actual energy payback time, the emissions will offset the gains from most or all prior years. The faster solar grows, the more net carbon it will emit in each year. The benefits, if any, are way down the road, and they only occur if you extinguish the growth of the industry. Sad but true.
I built a pretty cool mathematical model to prove this to myself, but the proof is barely needed. It's fairly obvious, thinking about it, that trying to solve a carbon problem by ramping up a highly carbon-intensive industry is going to be a losing proposition.
As far as the energy payback for PV being 1.7 years or less, as suggested by the article, I don't put much faith in those numbers. PV payback studies generally neglect or underestimate the energy consumed by the wholesale, retail, installation, maintenance, repair, and disposal chain. Ask a solar installer how much fuel their trucks consume and how much heating and air conditioning energy they consume, add it all up and compare it to the energy generated by the systems they installed in a year, and prepare to be disappointed.
A far more pertinent question about our energy predicament is, why are we focused on energy-intensive solutions rather than efficiency solutions? I have my own answers, but why do you think is the reason?
I hope this was helpful, and all the best. - Mark
Reader Comments (6)
Kevin @ <a href="http://www.SoleraGroup.com"> Solera Home Improvement</a>
Because efficiency leads to greater resource use - not less. As long as Efficiency is part of the energy solution mantra (and inarguably it has been a HUGE part of the thrust of modern energy efforts), we're still travelling to the music of the Talking Heads ("we're on the road to nowhere, come on inside, Takin' that ride to nowhere, we'll take that ride...").
From the steam engine to the transistor to Energy Star programs that let us build bigger houses (but more efficiently, mind you!)...to efficient use of manual labor, for that matter; every great leap in efficiency has been one more nail in the coffin of Mother Earth. Or to quote another song I like (by Rush), "we fight the fire...while we're feeding the flames."
Gear change...
And I agree that simply paving the planet with PV is no solution - but not because of the carbon balance question: it seems ludricrous to suggest that (and maybe you're not), despite the fact that creating panels causes carbon it's not orders of magnitude better than burning fossil fuels - which ALWAYS ALWAYS ALWAYS produce pollution...FOREVER. Stoichiometry, baby! So I guess one question would be whether your model compares the emissions per kWh, for example, of fossil-fired electricity versus PV-generated. I mean, it seems like it must be the case that the curve for the PV-generated kWh falls off exponentially and - assuming a long enough life - asymptotes (can that be a verb?) to zero. Are you saying that the area under the PV curve is net negative relative to manufacturing (and yes, transportation and all), and therefore doesn't justify PV production? That would indeed be a significant reality and kick in the teeth for solar prponents. (And I'm not saying I know - I'm asking.)
Because I doubt you'd disagree that whatever source(s) get chosen in the long term, they have to be based on collecting a (very small) fraction of average incoming solar energy. So if PV can't justify itself long term, what are the alternatives you suggest that DO justify themselves?
...and if you say biomass, or burning anything, I'm gonna kick you in the shin ;-) Not really, it's just that I have this nagging question that wonders how burning anything, i.e. chemically converting what was once part of a closed-loop nutrient cycle into ash, heat, carbon dioxide (again, stoichiometry), and of coursre electricity/heat can be considered sustainable. How does a forest continue long term when we annually remove tons upon tons upon tons of what was - before us - destined to be the building blocks of the next generation of flora and fauna?
Anyway, didn't mean to try to answer for you. I just wonder if 1. PV is truly unjustifiable and 2. what WILL work to supply energy needs loooooong term?
Anyway, I'll add one more just in case.
I don't understand the exponential growth years argument. Obviously if the industry experiences perpetual exponential growth, then there's an issue. But the idea is that there will be exponential growth until such time that fossil fuels are replaced with "sustainable" sources, at which time growth must flatten out. ...or at least become more linear, which I admit still isn't an answer.
But when discussing PV, there are really two questions here:
1. Are the carbon emissions (and other impacts) associated with PV from raw material to installed system worse than the emissions from fossil plants necessary to provide the energy the panel will offset over 30 years? If not, then at least we're doing better.
2. Are the carbon emission associated with PV greater than the Earth's ability to assimilate those effects? (We absolutely know that's true for fossil). Further, what is the primary source of carbon emissions in the "PV Cycle?" Couldn't PV be bootstrapped to supply its own perpetuation?
I'd argue that without tying use to long term average solar input, ANY solution is unstainable. I guess I don't see any reason to single out PV (or nuclear or fossil for that matter in the context of the real issue) - no other technology will do much better if the disconnect between (true solar) supply and demand persists. No matter whether it's done on a municipal grid or an interstate one.
I know you have lots of research - perhaps you could point out a single, definitive source that demonstrates your claim that PV sucks... but that perhaps goes beyond the apparent speculation of the above post so that we, the laypeople, aren't forced to endure the same grueling years of time you've invested. After all, we're not all engineers who've spent over a decade delving expertly into energy issues ;-)
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