In 2001, voters in the city of San Francisco approved Propositions B and H, which directed the city to develop renewable energy resources for city-owned buildings. San Francisco now has its first results of that effort -- 30,000 square feet of photovoltaic panels on the roof of the Moscone Convention Center, across the street from the SF Museum of Modern Art. The 675 kilowatts of power the panels can produce at peak are not quite enough to meet the full electricity needs of the Moscone Center, but (coupled with efficiency improvements in the building) they're enough to help the facility save $210,000 annually.
According to Metropolis magazine, San Francisco is the first of what promises to be many cities pushing solar:
According to Adam Browning of Vote Solar, a San Francisco-based advocacy group, measures similar to San Franciscos are appearing across the country: on January 29, New Mexico passed a solar bond for its government buildings; New Jersey has what Browning calls a "perfect storm" of legislation in the works; and last December, the city of Austin, Texas unveiled a $5/watt rebate for solar energy, as well as passed legislation mandating that the city produce 20% of its energy needs from renewable sources by 2020.
There's a popular enviro-meme that nearly all of America's electrical needs could be met by installing solar on city rooftops. It will be very interesting to see the real-world result of urban solar installations. As the cost of solar continues to drop, we'll see more and more locales eager to cut their power bills in this way.
Hmmm, isn't San Francisco notoriously foggy?
Let's see: 675 peak kilowatts at about $4/Watt (not counting inverters, batteries if you're trying to reduce reliance on the grid, labor to install the thing, etc. etc.) comes to $2.7 million.
So they spent probably well over $3 million to save $210,000/year - well 7% return isn't bad - IF the thing lasts more than 14 years! But it's not cheap either.
But how much electricity would the $210,000/yr represent? At 7 cents/kW-hr that would be about 3 million kW-hrs, or over 4400 hours of full sun every year - close to 50% capacity factor! That's highly unlikely - even the best solar installations have trouble getting above 25%, and San Francisco can't possibly be the best location.
If they actually get 1000 hours/year average, that corresponds to assigning something like 30 cents/kWhr - are they really paying electric prices at that rate in San Francisco?
Something here doesn't quite add up...
SF is notoriously foggy in late summer, but is actually quite a bit sunnier than you might think.
As the article notes, the $210,000 annual savings comes from the use of solar coupled with conservation/efficiency improvements in the building itself (I fixed the wording of the post so that it doesn't sound like the entire savings comes from solar).
Electricity rates in SF -- and in California at large -- *are* fairly high, although it's unlikely the city is paying 30 cents k/Whr. I'll see if I can dig up the actual rates for SF.
Okay, according to the calculator at the National Renewable Energy Laboratory, a 675kW-peak flat (non-rotating) PV system in San Francisco, at the California average electricity rate of 10 cents/kWhr, works out to an energy value of just over $110K. But SF is more expensive than California average; calculating at 13 cents/kWhr, it's an energy value of $139K.
BTW, when figuring how much the city spent for the PV system, remember that the costs are mitigated a bit by state-level (and, if I recall correctly, some federal-level) subsidies for the installation of renewable sources of electricity.
Buck Fuller calculated that energy needs could be met by installing a wind generator on the top of every power line tower.