# Archives

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## Two sources on energy, and using heat

I was reminded yesterday, after posting more on the cost-effectiveness of energy sources, to point out an interesting new book on the economics of energy. The book is Sustainable Energy With the Hot Air by David MacKay, a physics professor from Cambridge University. What’s important about the book is that he pays hard attention to the numbers, and demonstrates that certain types of alternative energy are likely to never make sense, while others are more promising.

I only have a few faults to pick with the book, and he’s not unaware of them. He decides to express energy in the odd unit of “kilowatt-hours per day” as he feels this will make numbers more manageable to the reader. Of course with time in the numerator and denominator, it’s a bit strange to the scientist in me. (It’s the same as about 42 watts.) In a world where we often see people say “kilowatt” when they mean “kilowatt-hour” I suppose one deserves credit for using a correct, if strange unit.

My real quibble is over his decision to measure energy usage at the tank, so that an electric car’s energy usage is measured in the battery, while a gasoline car is measured in the fuel tank. Today we burn fuel to make electricity, and so electric cars actually consume 3 times the energy they put in the batteries. That’s a big factor. MacKay argues that since future energy sources (such as solar) might generate electricity without burning fuel, that this is a fair way to look at it. This is indeed possible but I think it is necessary to look at it both ways — how efficient the vehicles are today (and will be if we still generate electricity from heat) and how they might be in the future. Generating electricity from heat does complicate the math of energy in ways that people can’t agree on, so I understand his temptation.

Yesterday I was also pointed out to a solar power site called SolarBuzz. This is a pro-solar-panel site, and is rare in that it seems to do its math right. I haven’t looked at all the numbers, and I am surprised wthat with the numbers they show that they are such boosters. Their charts of payback times all focus on power costs from 20 to 50 cents/kwh. Those costs are found in Europe, and in the tiers of California, but the U.S. national average is closer to 10 cents, where there is no payback. They also use 5% for their interest rate, a low rate that is only found in strange economic times such as these — but justifiable in a chart today.  read more »