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