Are you thinking about installing a photovoltaic (PV) system on your house? Do you think to yourself, “It will be great to have my meter run backwards and have the electric company pay me for a change”? “And I’ll be doing something to save our environment.”
The statement above that really bothers me is the part about doing something to save our environment. My problem with it is the number of resources required: you’re going to have to give something up to buy that PV system, and the thing you are giving up could easily do a whole heck of a lot more good for the environment.
Suppose you buy a PV system for $20,000 (rebates may halve the price of this, but you’ll see that that won’t make much difference in my argument.) There’s a lot of argument over the precise numbers, but that system will produce 3,000 kWh (price $9/watt installed, 15% capacity factor) to 4,500 kWh a year ($7 per watt, 18% capacity factor.) For electricity prices at a balmy Hawaiian $.24 per kWh, that system will then pay for itself (before maintenance) in a minimum of 18.5 years, and generate 83 MWh over that time, or around 150 MWh over the life of the system (30 years.)
Before anyone starts arguing about rising energy prices, let’s compare that PV system to something else we can do with the same money, at the same electricity prices. Suppose we take that same $20,000 and invest it in a 1 year CD at 5%. After a year, we will get $1,000 in interest, which we will use to buy 500 25watt compact fluorescent light bulbs (in bulk) at $2 each. We give these away to people who are currently using 100w incandescents. Over the next several years, those CFLs will save a total of 300,000 kWh (8000h bulb life x 75w per hour saved x 500 bulbs).
After only a year, we still have $20,000 so we can still buy a PV system if we want to (and take advantage of any rebates we missed out on the year before), we have avoided someone using over 300 MWh of electricity, which is about twice as much as the PV system will generate in its rated 30 year life (and don’t forget the cost of maintenance.) Plus, most of the energy savings from the CFLs will happen over the next 8 years, rather than the 30 years it will take the PV system to generate half as much. Most importantly, we have our initial investment of $20,000 back after one year, even though we are giving the CFLs away, while it will take over 18 years to get our money back from the PV system.
Because I believe in putting my money where my mouth is, anyone who mails me a receipt for the purchase of CFLs, I will PayPal them up to $5 or $2 per bulb, whichever is less (no more than once per person.) Household LED bulbs also qualify for the same rebate. I’ve uploaded a form to fill out, and plan to keep track of the number of bulbs, and the Negawatts generated on my website (as soon as my web guys get to it.) This will be good for up to $1000 of total payments, or until December 31, 2006 (postmark), whichever comes first.
Please note: I have withdrawn this offer as of 7/16/07. I have given out about $1,500 worth of rebates for over 750 CFLs, saving approximately 44 kWh per day.
For comparison, a PV system to offset the same amount of power on a daily basis would have to be over 7.5 kW, and would cost about $67,500, or 45 times as much (although it would last about 6 times as long as the CFLs, and it might only cost 20 times as much after rebates.)