There's not as much hype as there once was about electric cars, but I recall my surprise on learning that you would have to run one of them for 80,000 miles before all the CO2 created by the energy used in making it had been offset by the CO2 savings generated in using it.
And that led me to a series of other questions and discoveries - like, what do you do when a dam comes to the end of its useful life? I had somehow assumed that dams just went on for ever. Apparently not. Just as trees that are standing will one day fall, burn or be cut down, dams have a useful life. When they reach the end of it, you need to anticipate this and let all the water out. The dam has to be 'decommissioned'.
And if a dam is used for hydro-electricity, how long does it take for the CO2 created by building it and running it to have been offset by the CO2 saved by generating electricity that way instead of through burning coal? A very long time, but it happens. A lot depends, of course, on the details of the dam we are talking about.
Now someone has done this for all forms of generating electricity, and I find both the methodology and the results quite fascinating. I read about it on Barry Brook's website, Brave New Climate, in an essay by John Morgan, which in turn relied on a paper by some German scientists, Weissbach et al, a preprint of which you can obtain from footnote 1 at the end of the essay.
It is all based on a formulation called Energy Returned on Energy Invested, which is shortened to EROEI. I've seen it before, but not enquired further. More on that in a moment. Morgan says that, with respect to alternative energy forms, the much-discussed storage problem (how can you best store solar energy for use at night, or wind energy when it's not needed by the grid?) is not the real problem: there is not enough surplus energy left over after construction of the generators and the storage system to power our present civilization.
What he means is that there is simply not a large enough return on investment in the alternative energy source to allow it do it anything much. The Weissbach paper, which I've read, is a long and systematic account of how you would work all that out, taking into account construction, commissioning, production, maintenance and decommissioning - of all forms of electricity generation. The results look like this.
Buffered, in the diagram, means stored: there are energy costs associated with storage, so that the buffered EROEI is smaller than the unbuffered. CCGT is gas turbine generation. Morgan argues that you need an EROEI of at least 7 to be able to do anything much with the energy you've generated. So solar, biomass and wind, all of which need storage of some kind to be practical, all fall below that figure.
We simply can't, on these figures, run a modern society on alternative energy alone, and that is a message that the alternative energy believers find impossible to accept. The Morgan and Weissbach papers provide a strong suggestion that we either rely on what we have, or shift to nuclear - or of course add nuclear to our present fossil fuel system. But there are few supporters of nuclear among those who criticise fossil fuels. Barry Brook, however, is one.
During a day spent in hospital recently I was fascinated to see the degree to which every single piece of apparatus in such a place relies on electricity, and how the health system is based on the belief that there will always be sufficient power to respond whenever one turns a device on. You can gets some sense of that from the following diagram, also drawn from Morgan's essay.
As we move up the pyramid, the blue changes to yellow , recognising the shift from firm measurements to estimates. You can see that to run a hospital in Australia we need an EROEI of around 12. It can't be done on solar and wind and biomass. Not on these figures.
So let me end with the corrective that these two papers, interesting and persuasive as they are, are by no means the end of it all. Morgan's essay comes with dozens of objections from commenters, and it contains a vigorous and well-argued debate. Yet the EROEI template seems to me a great start, and in time we will have some agreed figures for the estimates. For my part, the objectors were niggling at the margins: the general picture seems to me to be that there is a basic insufficiency in alternative energy that means these forms, as suppliers of grid power, can only operate usefully within a fossil fuel electricity grid system.
They cannot, at least with our present understanding, replace such a system.