Two tough questions came up in the breakroom on Friday:
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...
Within an hour, my comment was deleted.
Yesh. You would think just leaving it unanswered would be a sign of ignorance.
Deleting it is going the extra mile.
Posted by: cyanbane at October 21, 2007 02:40 AMAnd it wasn't like I was criticizing them. Just asking for more info on a subject they seemed knowledgeable about. Maybe I accidentally typed “pen1s” in my comment... ?
Posted by: sstrader at October 21, 2007 11:58 AMOn the economics of solar PV, we need to measure cost in kilowatt-hours because we can compare energy on a common matrix. The production cost of solar PV devices can be estimated from the PV supplier's income statements cost of goods sold line item. On the average, the leader thin-film and PV panel suppliers are producing at $1.62/watt, which ($1.62/20 year PV life) equates to $0.08/KWH.
Secondly I didn't dog your comment. It is still posted http://greenecon.net/understanding-the-cost-of-solar-energy/energy_economics.html - comment # 3. I do sometimes find some strange comments.
Lastly, I even set you an email detailing why it is important to measure energy in KWH. Please see http://greenecon.net/solar-and-hydrogen-energy-economics/energy_economics.html for follow up on the economics of solar and hydrogen.
Posted by: michael davies at December 3, 2007 07:54 PMMichael: I apologize for the snark, but I went back several times and didn't see my message reappear after it disappeared. Usually, messages are held and then published. I've never seen them published and then removed for later re-publishing, so I'm sure you can understand my response.
As for the email: it must have gotten lost in the spam filter or deleted by me because it looked generic. Either way, I appreciate the response.
My original question doesn't concern the lifespan of the constructed solar panel but instead the construction of it. Your measurements detail the cost of the completed material in relation to the energy it produces. This shows the relative benefit to the consumer compared to if they purchased other forms of energy. I'm interested in how much energy it takes to produce the material that a consumer uses for each form of energy.
For solar panels, this would include the energy to construct, ship, and install the panels. For coal, this would include the energy to build and maintain coal power plants and to mine the coal itself. That could be more or less; it would be a useful metric.
This is related to the issue of oil dependency in farming (see "The oil we eat" from Harper's http://www.harpers.org/archive/2004/02/0079915).
I see were your going with the measurement. From the solar PV perspective, the materials (sand and several elements that are rather abundant) are not that costly, but some are by-products of mining that would incur shared costs. The benefit of solar is the electric generation is free for the life of the PV device. I’ll see what I can find.
Posted by: michael at December 4, 2007 12:59 PM