Storage tanks for solar systems

[Mikey]

I just spent some quality time huddled up with the tank that was installed along with my solar DHW system, and was a little upset to discover it only carries a 6 year warranty. Did a little Web searching, and found that they all have a 6 year warranty, but compensate for that by charging 3 or 4 times as much as a standard 12-year unit.

Does anyone have any experience/recommendation for what I should consider when this one starts to fail? It's an attractive idea to try to combine the solar in/out connections with an anode rod and stick the combination into the anode rod hole in a standard WH, or use a 2nd WH somehow along with the one supplying the house.

Maybe I should just wait and see what's out there in 6 years...

[hj]

My experience has been that they usually outlast a standard electric water heater. Essentially ALL tanks are 6 year units. You just pay for an insurance policy when you buy 8, 9, 10, or 12 years heaters. With one company you install the 6 year heater then pay about $200.00, depending on the size, for a sticker to make it a 10 year unit. You pay more for the solar tank, even though it only has a single heating element, because of the added openings and the smaller production run for those units.

[Bob NH]

I would figure out how to use a standard electric water heater. With inlet, outlet, dip tube, drain, and availability of one of the heater element ports it should be possible to make an effective heater.

The "Solar system" label adds a big markup to the cost of any product. If you do a bit of creative engineering you should be able to avoid the problem you anticipate. You have some time now to figure it out before it fails.

[jadnashua]

Buderus makes a tank with two sets of heat exchangers...one for solar and one for an indirect. Probably not what you want, but you can get it in SS, and should last a very long time. Unfortuneately, it does not support direct gas or electric for the alternate heating mode, only indirect. It would work great if you had a boiler or other hot water generation in your system, though.

[Mikey]

With inlet, outlet, dip tube, drain, and availability of one of the heater element ports it should be possible to make an effective heater.

Great suggestion; I wasn't thinking far enough out of the box. Lots of openings indeed.

[hj]

Don' forget you also need a way to fasten the lower temperature sensing thermistor to the tank.

[Mikey]

Right now my officially-pro-installed system don't have no steenking sensors. The circulating pump runs on sunshine, there are no valves, etc., anywhere. I have no idea what, if anything, keeps the temperature under control. I do know it gets mighty hot. The lack of any "dobs and knials" offends my engineer sensibilities, but it's a) dirt-simple, and b) puts out hot water.

Edit: Made a crude measurement of the temperature of the "cold" water being sent to the solar panel today (a moderately "good" solar day) -- it was 101F at 3PM. Return was about 125, but that was pretty late in the day. Think maybe I'll invest in a couple of temperature dataloggers just for the helluvit.

[jadnashua]

I've said this before, but when I lived in Kuwait, we had water storage tanks on the roof. It was too hot to bath in, so we turned the WH off in the a/c apartment, and waited until the water cooled off then used that for cold. God forbid it was recently filled and you wanted to shower...hot and hot and nothing to do about it. Kind of annoying in those inbetween seasons when you had to make the decision to turn the WH back on, and then retrain yourself which knob was hot!

[Mikey]

We have a similar problem since re-plumbing the house overhead following an under-slab leak. "Cold" water will start out at 110-120F on a bad day, and eventually cool down to ambient (above-ground chlorination tank) of maybe 85.

[Mikey]

In case others are interested -- turns out there are several products out there designed to convert/augment a standard WH tank to work with solar collectors. Some connect via the normal cold-in/hot-out ports, others use the drain port for the cold side. Prices are reasonable. www.solarroofs.com is a good place to start.