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By Robert Rapier on Jul 24, 2007 with no responses

Solar Redux

The previous essay on solar energy got picked up and linked to from a number of places. Between those links and the original blog entry, some of the comments I read were largely in left field, and many of them didn’t come close to representing my actual position or arguments. Maybe that’s partially my fault for spending all of 20 minutes writing the post. Which brings up another point: It seems like the less time I spend on a post, the more comments and hits it gets. But I digress.

So, let me clarify a few things.

1. I am not against biofuels. In certain situations, biofuels may be (and probably are) an appropriate solution to the problem. In fact, I continue to work on solutions to biofuel problems, and I wouldn’t waste my time doing this if I didn’t think there were some applications. My argument is that we won’t, as many people believe, displace large amounts of petroleum with biofuels. Presuming we can is presuming that technology that does not currently exist will inevitably be invented.

2. I am not against technology. I love technology – especially biotechnology. But I am well aware of the “technology will save us mentality.” Technology doesn’t always proceed as you think it should, and it doesn’t always respond to monetary incentives. If it did, cancer and AIDS would no longer be with us, and 40 years after the moon landing, a manned Mars expedition wouldn’t still be a distant dream.

3. This is not a new revelation for me. I have long believed that our future must be electric for at least 4 reasons. First, is the photosynthetic efficiency that I discussed. Second, internal combustion engines are notoriously inefficient relative to electric motors. Third, we have a lot of rooftops available that will not compete with arable land. And finally, electricity can be produced from a tremendous diversity of sources. Start with biomass, solar, wind, hydro, nuclear, natural gas, coal – all are easily converted into electricity. Contrast that with the uncertainty of a future based on cellulosic ethanol and algal biodiesel. If we are to embark on a Manhattan Project to get off of our petroleum dependence, we should direct our efforts toward an eventual electric transportation infrastructure.

4. As one person argued, “solar collectors don’t self propagate.” True, but biofuels don’t self-harvest and convert themselves to useful end products. Once the solar panels are in place, they keep giving for a long time.

5. The rapeseed example is merely a thought experiment. Don’t spend too much time worrying about all of the implications of planting a majority of our land in rapeseed, or whether instead I should have planted palm oil or corn everywhere. It is just an example to frame the problem. But I do not believe, as some have suggested, that using land that is presently non-arable is going to provide a fraction of the yields you would get from planting all the arable land in rapeseed. So, I think it is a very conservative thought experiment.

6. Several people have suggested that I am just wrong about biofuels; that technological advances will change everything. All I can say is that hope is a wonderful thing. But you better plan for contingencies in case those visions of algal biodiesel fail to materialize.

7. Yes, I know that SI units are better in the context of a scientific paper. And I do use SI units in the chapter. But for most casual readers in the U.S., a yield of gallons per acre is going to be more meaningful than a yield of liters per hectare.

8. I am aware that biomass is stored energy. But you can’t harvest all of that stored energy and use it, or you will rapidly deplete the soil. This is why you will never convert anything close to theoretical photosynthetic efficiency into liquid fuels. And theoretical photosynthetic efficiency is still far short of solar cell efficiency.