How to / DIY > Everything else
Solar water heaters.
guest22972:
I have been looking into direct solar water heaters but am getting confused.
Some people say they work well enough in winter, some say they are utterly useless. Seems the type, Flat plate or Tube has equal confusion.
A young bloke came to see me today about WVO Conversions. He's also into solar, wants to run a genny and go off grid etc so thought he hit the jackpot when he landed here and saw all the crap I have.
He has flat plate water heating and said the water is barely warm in winter. He lives in the next main town so not far away.
He did say that the tank he got was made OS and apparently don't hold the heat well due to poor insulation but also said that the water is never really hot anyway. Summer of course is no problem.
I was wondering if those that have these water heaters installed could give some feedback on their experiences.
At this point I am just curious about the things as I reckon it will always be easier for me to just put up panels than plumbing but I am always open to changing things for the better. There are a few of these heaters going SH atm and they may be worth using just as a pre heater for the main electric HWS. The water out the tap was getting down to 4oC here where as in summer it can be pushing 28 or more. That 20o Difference makes a big impact on the power required to heat the water especially when the solar yield is down so much to start with.
Bit of practical experience and feedback from people that own the things rather than trying to sell them would be interesting!
ajaffa1:
Hey Buddy, those solar water heaters can be great however they usually have a small circulation pump to drive solar heated hot water through a heat ex-changer coil in the storage tank. Generally the heating coil in the tank separates the heating system from the domestic hot water, allowing it to contain anti-freeze without poisoning anyone.
If that pump has failed no heating water will circulate to heat the water in the tank. Normally they have some sort of timer, thermostat or sunshine sensor to tell the pump when to cut in and out. Continuing to run the pump with no sun will pump the heat out just as fast as pumping it in. They also usually contain an electric immersion heater for when the sun don`t shine. If the pump is running, while the electric element is heating the tank, all you are doing is heating the atmosphere.
Bob
BruceM:
The vast majority of new designs today are drain back systems, to avoid antifreeze, and the stagnation related breakdown and corrosion problems it makes. Drain back systems are inherently freeze proof, and typically last twice as long. My system is the simplest of the drainback systems- I have a single 800 gallon, insulated drain back tank, mostly below grade. One pump runs/starts the system and if it fails, the water drains back into the tank and that's it. I use that water directly for my in floor heat, and domestic water is heated via copper coils in the tank. The tank is EPDM pond liner with 3" foam board, cement board, dirt. A 12" tall framed wall above and insulated, EPDM covered lid let me have the pump sit on the floor next to the tank (in my shop building).
Flat panels are much cheaper to build, but your maximum temperatures will be much lower. My flat panel collectors did have 20F higher temperatures in winter when they were double glazed with greenhouse polycarbonate panels, but the panels failed from mechanical stress- the difference in temperature of the inside and outside polycarbonate (very, very thin) was too great, causing a great deal of bending and buckling, especially during stagnation (tank maxed out so panel left sitting in the sun with no water flow). I replaced them after a few years with a single layer of 1/16th inch thick polycarbonate... which has performed marvelously. I do notice on the rare very cold, windy days that production is down perhaps 30%.
If you need higher water temperatures you have no choice but to use evacuated tubes. The flat panels just can't give you water temps in winter much over 110F, and often 100F. That's fine for my in floor system, which can heat the house just fine with 90F water.
The other option for larger hot water capacity at higher temperatures needed for radiators and such is parabolic trough collectors with the central tube in evacuated glass tube.
To recap: Flat panels are fabulously easy to build (see BuildItSolar.com for the copper pipe/aluminum fin designs like mine). But they are not designed to make high temperature water in winter. They work fabulously well with a well done in-floor heat system, which will work with low temperatures.
LowGear:
Solar Hart, an Australian product, is popular here in Hawaii. Passive system that sets up on the roof with an electrical element back up. I'm looking for one of their thermostats. The jerk distributor here won't sell them unless they do the service call.
BruceM:
I had a Solahart unit on my home in Gilbert AZ (near Phoenix). Good for a place with only very rare freezing temperatures.
Batch (direct glazed tank heating) heaters are also viable for mild winter climates.
As a preheat, an inexpensive flat panel approach could work. For just domestic hot water alone, you have to be careful about up front cost and maintenance cost. That's what's driving many to PV-electric hot water for just domestic hot water.
I got my money's worth for my solar hot water system here, since the solar water system does winter space heating as well. The endless hot water the rest of the year is pleasant luxury.
Even in winter I don't skimp on hot water for laundry or showers as domestic hot water is a drop in the bucket compared to space heating.
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