20 October 2007

Water and sun

Two tough questions came up in the breakroom on Friday:

  1. What percent of the water sent out from reservoirs is returned and reused via water treatment plants?
  2. What percent of the energy it takes to create a solar panel is returned by that solar panel?

Either of these would probably be worth a book-full of research just to get close to the truth. I, however, have only a bored hour-or-so of surfing to offer.

On the first question, I had guessed that 60-70% of water was recycled. A coworker was much more optimistic at 95-98%. The only usable link I could find was for Australian treatment plants where the recycled water use of six cities in 2001-2002 averaged ~5%. Yipes. Not a lot to go on, but still not good numbers. The question is probably more complex: recycled water is maybe never used for drinking, and so it's uses are limited.

On the second question, the website green econometrics got completely on my shit list. Here's the deal: they had the only useful page I could find, unfortunately it discussed the consumer's economic cost for using solar compared to coal, oil, and gas. In that regard, solar costs more per KWH because you have to pay more for solar panels that produce the equivalent energy. E.g. solar costs $0.38/KWH, where coal costs $0.006/KWH, oil $0.05/KWH, and gas $0.03/KWH.

The problem is that this doesn't tell us society's energy cost to produce a KWH of each. The fuel to produce and maintain digging equipment could be greater than the fuel to produce and maintain solar panel factories. Or it could be less. So, I posted a quick comment with my question in the section below the article with the friendly imperative: "Leave a comment." Within an hour, my comment was deleted. So much for the dynamism of web 2.0 sites.

I'll still pick around for the answer. My search fu could be a little weak, so maybe I missed an obvious article or encyclopedia entry. Until then, item 2 remains a mystery...

[ posted by sstrader on 20 October 2007 at 9:02:11 PM in Science & Technology ]