things that go drip in the night, or the economics of a solar water heater

[Nate Nagel]

Hi all,

this has been discussed here before, mostly because I expected this thing to crap the bed years ago, but every time I got close to replacing it suddenly my floor was dry for another year or so. I have an indirect solar water heater in my basement, and I think it has, for real this time, reached the end of its useful life. My inner greenie says, of course, to replace it, but I'm not thinking that that is really an economically good idea... my gas bills even in the winter are never over $200 a month; in the summer it's practically nothing. Even on a sunny summer day the output temp. of the solar never seems to get over

85-90F (very shady lot) in the winter I wonder if it even helps at all. There's no controller on the thing just a time switch running a pump so I wonder if on a cold, overcast day if the darn thing isn't sucking heat out of my water supply and dumping it into the atmosphere :/

I remember doing research into this a year or two ago and found that the tank alone would run me over a kilobuck. For that price, when you figure in installation as well (I could probably handle it, if I knew how to charge the loop between the tank and the collector, but I doubt I actually *would*) as well as an electronic controller with tank and collector thermocouples (seems the only way to really make it work efficiently) I don't see a reasonable payoff period... probably by the time it'd paid itself off the tank would again be 20 years old and near death.

Am I wrong...?

I'm tempted to rip it out, take the tank to the dump, and put the rest of the setup on craigslist as "haul it away! Use it for whatever the hell you want, I don't care!"

(the extra floor space in the basement would be nice, too...)

nate

[Nate Nagel]

Forgot to mention my other idea:

1) buy new 40-gallon electric water heater appx. the same size as solar one (which is obviously just a modified electric anyway)

2) remove shell from old one, save copper coil wrapped around tank, discard rest

3) disassemble new tank, slip coil over tank, reinstall shell, fill space between with lots of Great Stuff(tm) (or just stuff old fiberglass back in there) Laugh maniacally at having just spent $400+ on something and immediately voided the warranty.

4) install my "new" indirect solar tank

what do you think the odds are that a brand new Rheem 40 gal. tank (the internal tank, that is) is the exact same size as a 20 year old one?

seems a lot of mucking about for not much benefit, still...

nate

[Pete C.]

Solar DHW heating is one of the most cost effective solar things you can do. There are various federal tax credits you can take advantage of as well as usually local credits as well.

[Nate Nagel]

Please elaborate on how this is cost effective...? I'd handwave $3K minimum to replace this thing (like I said, the tank alone, without installation and delivery, seems to run around $1400;) even if my gas bills went up 50% (which I doubt that they would, I don't think it's really doing that much) I'd still be money ahead to just demo it and be done with it.

Seriously, I'm not trying to be argumentative, I just am trying to run the numbers here, but AFAICT the benefit is not there.

I suppose I could bypass it and watch my gas bill for a couple months and compare it to last year's bill before making any final decisions, but I'm guessing I will only see an incremental increase if anything.

nate

[Pete C.]

That last bit would be a good real world test of the current (failing, obsolete) system, but wouldn't tell you much about how a new current generation system would perform.

On the links I provided:

homepower.com - Download their sample issue to look at the ads for some current systems and the manufacturers web sites

nrel.gov - Look for links to the solar resource maps for your area which will tell you how viable it is in your area

energystar.gov - Look for info on current federal tax credits available

There is another site I can't remember at the moment (probably a link from NREL) that has a database of state / local incentives.

[ransley]

Why not make it work right, a aqua stat could keep the pump from running until pipe is hot, so it would not pump on cloudy days. I use a cheap unit bolted to a pipe on a recirculator system. Find the leaks. Going electric is more expensive than gas for maybe 98% of the US. For single use I use a Bosch ng tankless that is more efficent than about 98% of tanks made, Solar and cheap Tankless would likely work for two people easily. I would not junk a solar set up. alt.energyhomepower is where you will get answers from people off grid.

[Nate Nagel]

Where do you find a "cheap" one...? I'm seeing prices of $3-400 for a simple controller with two thermocouples.

I know where the leak *isn't* - anywhere I can fix. There's water coming out the bottom of the tank, and it's not coming from any of the fittings.

I've got the solar feeding a conventional 40 gal. gas tank, which I suspect is doing most of the work. Incoming water is about 60F; have not seen output of solar tank over 90ish... ever. Got a nice big collector too...

nate

[Bob F]

Just out of curiousity, did you replace the anode in the tank every several years. As I understand it, this can significantly extend the life.

[ransley]

de quoted text -

Cheap is maybe 40$, its used for hw recirculator systems, mine clamos onto a hw pipe and I set the temp for it to kick out, im sure you could engineer it to shut off when temp is low.

[N8N]

Just bought the house a little over 2 years ago. I did replace the anode in the tank and it appeared to be used up but not so much that I suspected that the tank had been left unprotected, but it seems to have been "too little too late." PO's apparently didn't understand the necessity of checking it every couple years and also regular flushing, you should have seen the crap that came out when I flushed it for the first time. Also I suspect that the bottom of the tank was getting wet externally - lots of little things were leaking in the house before I moved in and I've been picking away at them one by one. Yes, the tank is sitting directly on the floor, which I'm not nuts about.

I ended up having to replace the water heater in the garage as it failed shortly after purchase of the house (making a lovely mess of the ceiling below;) the gas water heater in the basement however appears to still be going strong. (just gave it the same treatment as the solar one - replaced drain valve so I could flush it, replaced anode) that one seems to be sitting on a high spot on the floor so the bottom never got damp.

nate

[Pete C.]

Stumbling over some stuff I printed out the last time I looked, it appears you can get a federal tax credit of 30% of the cost, up to $2,000 on solar hot water heaters currently. There are often state credits as well and some states offer low interest financing (as low as

0%) for energy efficient home improvements.

[Bob F]

You could also just use a regular tank, and add an exterior heat exchanger with piping between the top and the bottom of the tank for convection flow.

[trader4]

I think Nate has the right idea. Just because some manufacturer's website says you can save money or there happens to be a tax credit doesn't mean it's going to cost justify itself. A lot of it is going to depend on how much hot water you use and the cost of conventional fuels. In summer, my gas bill for heating water is less than $20 a month. At that rate, it would take a hell of a long time to recover the upfront cost of a solar unit. If you factor in the cost of money, it probably will never pay for itself. Plus you have the risk of the expensive solar thing crapping out long before you recover the cost.