Ted Bavin is president of All Valley Solar, a solar heating contractor that does business all over pool-crazy Southern California. He's seen a lot of changes in his 35 years working with pool builders and remodelers, as edges have vanished, shapes have shifted and things like real rock and fire features have found homes in and around the backyard pool.
One thing that hasn't changed in that time is the simple science behind turning the sun's energy into warm pool water. Like pioneers in many simple-but-effective technologies, the early inventors in solar pool heating pretty much got it right from the get-go.
AQUA spoke with Bavin about the beautiful simplicity behind solar heating, the public's misunderstanding of it, and his efforts to save the earth, one solar system at a time.
What got you into the solar industry?
I started in solar in 1976. I'd just gotten a degree from UCLA in environmental science, and had fought nuclear power for a few years. I decided solar was the only way to avoid nuclear power (laughs). Sure enough, there hasn't been a nuclear plant built since.
But solar is a very necessary technology, it's very green, and now, with today's concerns, there are so many reasons to emphasize solar over fossil fuels that didn't exist back when I started. Whether it's that we subsidize potentially terrorist countries, or because of greenhouse gasses and global warming, or the ordinary environmental pollution caused by drilling for or burning oil. Any way you look at it, it just makes perfect sense.
So you have those things coupled with the fact that it's economically beneficial and that systems pay for themselves in less than 10 years, and often as little as five years. It's very cost effective.
Without solar heating, all you are doing is renting heat. You're paying every month for gas, and that's just like renting an apartment. You buy a house to invest in something, and you buy solar to avoid that "rent" — that throwaway, disposable rent where at the end of the month you have nothing to show for it but whatever swimming you got out of it or whatever hot water or electricity you got for it.
How long does a solar pool heating system take to pay for itself?
It's usually on the lower end of that range I gave. Sometimes as little as four years, but typically five to seven years, with the higher end being for highly elaborate — effective but elaborate — systems. Whereas for simpler systems it's down around four or five years, and that's without tax credits or rebates. But solar thermal doesn't need rebates and tax credits to justify itself. You can't really say that about solar electric.
Can you describe solar thermal in greater detail?
Solar is very old technology. It's like the wheel. The wheel was invented 10,000 years ago and it hasn't changed much in those 10,000 years. It's still the wheel. Even today, it's still the best way to move things around on dry land. And like wheels, solar thermal heating isn't getting any cheaper.
You don't not buy a car because the wheel might get better, or cheaper, next year. If anything, it's going to get more expensive next year. Solar thermal is that way too. Today, prices are at least four times what they were 30 years ago because labor, plastic, copper if you're using that, all of those have gone up; they never go down. So the cost of thermal solar will never get cheaper.
Again, it's old technology. It's simple. It's a black material that absorbs heat, water goes through it, and it comes back warmer. There isn't going to be a breakthrough in that because the current efficiency of solar pool heating on a halfway decent day is typically up in the 80 to 90 percent. That's how efficient it is at converting the heat of the sun into heat in the pool. That is remarkable, and there's not going to be an improvement in that.
Do people typically understand there's a difference between solar thermal and solar electric?
Most people don't know the difference. We get calls from people that say, "Oh, we have solar pool heating but we're going to get rid of it because we're getting solar electric." A lot of times that's because some solar electric contractor has put that into their minds: "Get rid of that old-fashioned thing. We're going with solar electricity now." But that "old-fashioned" thing is the best way to heat a pool, and unless pool heating is no longer important to that customer, they'd better not get rid of it.
Solar electric is less efficient, then?
You would never put in solar electricity to heat your pool. It would cost four times as much to do that same job, and that wouldn't make sense. We often have to explain the differences. Often, too, we have to share the roof with a solar electric system, which requires figuring out how to divvy it up in appropriate ways for each client.
So you wouldn't use it to heat a pool, but does solar electric have any place in the backyard?
Yes, it is often a good idea. You'd never use solar electricity to heat water, but you can use it to make light, to run motors, to do things that only electricity can do. And those technologies make sense if there are tax credits and rebates. Which there are. But without those tax credits those technologies won't pay for themselves in 10 years.
For any given square foot of sunshine, there's approximately 2,000 Btu per day that the sun provides. A solar pool heating system can convert 80 to 90 percent of that into warm pool water. A solar thermal hot water system for your shower is typically about 60 percent efficient at heating hot water. A solar electric system is about 15 percent efficient, so in that case 85 percent of the energy in that square foot of sunshine is lost and only 15 percent goes into making electricity. And the theoretical maximum is up around 25 percent, according to physicists. It's a completely different process. It's not as simple as just absorbing and conducting heat. It's actually kicking loose electrons and making a current flow.
Can you describe the difference between thermally heating water for the pool and heating it for hotter water, such as is used in the shower?
It's almost the same as heating a pool. Where in pool heating we usually take pool water and put it through the panels, and our goal is typically 80 to 85 degrees, for hot water we cover those panels with glass in order to get it up to 140 degrees. That's a lot harder to get, because the ambient air is rarely over, say, 90.
The best way to describe it is to liken it to an automobile. If you're sitting in your car on a cool, sunny day, it would be cold. But if you closed all the windows and the sun is streaming in through the windows, that car can be quite hot. Well, a glazed solar panel can reach temperatures of around 400 degrees if you let it bake in the sun, so heating water to 140 can easily be achieved. You still keep your gas backup so that on lousy, cloudy, rainy days you always have enough hot water.
The reason it's less efficient is we're raising water to a higher temperature, and that is harder.
How far north can you go and still effectively heat a pool with solar?
Solar in Canada is going gangbusters. I don't know if I need to say any more. New York is starting to get lots of solar. It's really more of a political question, which is tied to economics. I'm talking about the bigger picture of solar now, not just pools.
The season is shorter in the north, and that has an effect on the economics, but solar can be effective in those short seasons, just like here. Canada is very pro-solar, so there happens to be a lot more solar going on there. Do you know what the No. 1 country for solar in the world is? Is it the U.S.? No, it's Germany. Everything is solar is Germany. It's a huge market, and that's a much colder country than we have here.
Pools have an additional problem that solar-heated hot water doesn't have — the big surface area that's open to that cold weather. So don't think you can put in a solar system that's going to heat all year, even in Los Angeles. Here solar will help all year, but it can't do it all when the nights get down to 35 and 40 degrees. You just lose too much heat for a sensibly sized solar system to recover. So maybe we do a third of the job, maybe half the job, but not more. You have to commit to a sizeable gas expenditure if you want to swim year-round, even if you have solar. Often in L.A., solar will give you seven months of swimming with pretty much no gas. Colder areas of the country would require either more gas or even better solar to significantly extend the season.
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Out In The Cold
Don't make the common mistake of failing to factor in an occasional freeze
A builder in Bismarck, N.D., would certainly know enough about the weather to account for freezing in a solar system he installs, but what about one in Burbank?
"This is the most common mistake," Bavin says. "And the most common assumption is, 'Why worry about freezing? It doesn’t freeze here in Santa Monica, or Malibu or wherever.' The fact of the matter is that it does freeze everywhere in the continental U.S., on occasion. Add to that the fact that solar panels can reach temperatures up to 15 degrees colder than the air. Every part of the country gets temperatures down to at least 40. That means the inside of a solar panel could be as low 25, and that will freeze and crack and split and leak like crazy when it thaws in the morning.
"So systems must drain completely, by gravity, in the evening. Or else you have to fill them with an indirect fluid that drains back to another reservoir and have a heat exchanger, or you go with glycol in some areas. Here in Los Angeles, we commonly use drain-back technologies to make sure the panels are empty."
Barrett Kilmer, has been on the editorial staff of AQUA magazine since 2000. He has a B.A. in English from the University of Wisconsin - Madison, and currently lives in Madison, Wisc.