Monday, November 07, 2005

Solar Heating Lowers Construction Costs

Solar Energy is a grim business. Usually, folks who decide to buy a solar system make some sort of projection about their fuel or electricity costs and then figure out how much the solar system is going to cost. The trouble is, these comparisons take thought, and are dependent on unknowns like the rising future cost of power, effective interest rates in the future, and structure depreciation. No wonder solar systems are a hard sell.

Well, things are changing in sunny California. Our Title 24 law sets energy efficiency standards for most buildings. A new revision of this law has come into effect as of October. Among other things, the law sets standards for window thermal resistance.

Essentially, California has mandated that you are going to save energy, relative costs be damned, but at least you get to pick how to do it. I could write a blog entry on how I feel about this kind of regulation versus simply changing the price of energy... but no. Today I want to talk about the solar industry.

The big news for the solar industry is that instead of comparing solar collectors to just burning fuel, people now get to compare solar collectors to better insulating windows. It's a much easier comparison, since you pay for both things when you build the house, and solar collectors come off looking very good in comparison. When the tract home developers figure this out, they're going to slap solar panels on any place they'll fit.

How's that? Well, consider a standard 4.5 foot by 3.5 foot sliding glass window.

A good aluminum-framed version will cost a few hundred dollars, and have a U-value of 0.61, which means that it leaks 0.61 BTUs an hour, per square foot, per degree F temperature difference. In San Francisco, where we have 3458 degree-days of heating each year, that's 797,345 BTUs a year -- about ten bucks.

As of October 1, California requires a U-value of 0.38 on most windows. These are pretty nice windows. To get that U value, you need double panes of low-E glass with argon fill, wood or vinyl frames, or high-end aluminum frames with thermal breaks. This window will cost a couple of hundred dollars more than the aluminum-framed window, and it'll leak about 300,000 BTUs a year less than the aluminum-framed version.

So here's the thing. A rooftop solar thermal system can supply those 300,000 BTUs a year for about $120. (That $4068 kit with 2 Gobi 408 collectors will pull down 80 to 120 therms a year.) And California will let you use inexpensive aluminum windows if you have a solar thermal collector to supply the extra heat.

Now some people are going to want the wood-framed window look, and so for those people this comparison doesn't much matter. But developers are the kind of folks (cheapskates, and I use that word endearingly) that will save a couple of bucks per house by using skinnier electrical wire. Saving $100 a window while being able to sell the resulting house as "green" is a fad they can embrace with enthusiasm.

But developers are also the kind of folks that prefer to suceed doing things they've seen other people succeed at. So, if you live in California and are building a new house, do your part and stick on a solar thermal collector. It won't take long to get the fad going.