How to decommission an old solar water system?

[JoshH]

I have a 1980s vintage Suncatcher solar hot water heater system, installed by the original owners of the house to heat a hot tub that is no longer present. It feeds the domestic hot water, supplemented by a normal natural gas water heater. The system was high-end for its time - copper pipe, silicone heat transfer fluid - and has worked pretty reliably for decades. However, the economics of it are getting marginal. The monthly savings in natural gas are modest after accounting for the electricity to run the pumps, and the next time it needs a repair or servicing it's not going to make sense to invest in such old hardware. So it will soon be time to decommission it. My question is how? Does anyone on the forum have experience with the end-of-life phase of a solar water system?

In Colorado, solar water systems used to be fairly common and so there were several companies to service them. But these days it seems like both the systems and the service companies are nearly extinct in this area. So, if I can't get a specialist, do I hire a plumber to remove it, who presumably knows pipes and fluids but may not be equipped to get heavy stuff off a roof? Do roofing companies handle this and I should get one of them to remove it next time I have new shingles put on? Do I need to coordinate both?

If I shut down the system myself but leave it in place until the next time I get the roof replaced, is there anything special I need to do to safe the system for the long term? I think the combination of copper and silicone is pretty robust against overheating or corrosion, but do I need to do something like drain the system or cover up the panels?

Are there any particular issues to consider with disposal, such as something that's valuable as scrap (the copper, anything else?) or requires special handling for disposal (silicone?)

Thanks in advance

[brycenesbitt]

The scrap value is there, but minimal compared to the labor costs.

Hopefully you can track down exactly the brand of heat transfer fluid involved, to see what the disposal implications are.
Here's one such fluid https://www.ecousarecycling.com/recycling-duratherm-s/

Your pump costs appear to be be the issue. Consider instead a high efficiency modern circulation pump like the Grundfos Alpha
.

There are certainly still people servicing such systems. Yours does not seem to need much re-thinking, so really any plumber --- warned of the silicon transfer fluid -- ought to be able to do it for you.

Reroofing is the time to deal with this: and to consider a lifetime roof rather than disposable shingles. (e.g. Metal, tile). You roofer can definitely do the solar moving.

===================

Can you share numbers on the electric cost and the gas offset cost?
What pump model do you have, what's the height it has to pump, and does it have a variable speed circulator you can lower?
Is there a high cutoff, so you're not heating water too hot to use?

[brycenesbitt]

Ok, replace the pump with a model that's direct current, and powered directly from a solar PV panel.

[peakbagger]

I have a 20 plus year old system running on a DC pump and solar panel with a very basic controller that cycles the pump whenever the collector is warmer than the tank. It works quite well but I installed the system and know the design and its low friction loss system. IMO before I made the switch I would need to know a lot more about the system that the OP has. Many systems used heat exchangers between the working fluid and the domestic hot water and they were high pressure loss and would not be suitable for a typical DC pump. A new AC ECM pump like the Grunfos is a far better substitution. A properly designed and operated SHW system can be quite reliable and I would be hard pressed to understand why the current economics would make them unattractive to run unless major components need to be replaced. The reason most systems stop being used is no one locally works on them as it is a dying art. They do need minimal service and on many they did not get it and the result is stagnant glycol turning acidic and corroding a hole in the panels. Once that happens in one spot its not worth trying to fix the panel.

There is some demand for old panels as many are mostly copper inside a aluminum outer housing. They can either be reused or scrapped as the price for copper is over $3 a pound. The downside is a pro with insurance is not going to be interested unless you pay him so it means some well meaning amateurs are going to show up and try to remove them from your roof "for free". There are various mounting brackets and piping that will need to be removed from the roof and patched. If they get hurt they may sue you and good luck if they do any damage. Roofers frequently rip them off when replacing a roof as they are equipped to patch a roof but odds are its an old roof and they will take the work in hopes of convincing your to eventually replace the roof. Its likely that if the system is removed, the piping in the basement will need to modified to get rid of the old complexity of SHW..

[J.P.M.]

Chances are the system needs at least servicing (different than an upgrade). After 35 or so years however, I'd suggest the system may be nearing the end of its useful life. Before that however, I'd check the system performance and see how much the system is producing. While doing so, know that glycol, or "indirect" systems all have heat exchangers of one type or another to transfer the collected heat from the glycol to the potable H2O. Heat exchangers foul (get dirty) over time and usually are the first cause of system performance degradation, but also the least understood, and for many reasons also the most difficult to address.

If it's not leaking and still producing useful heat, I'd then think about getting it serviced including at least checking the glycol and changing it out. I would however, be careful about doing too much servicing/upgrading. For one thing, older mechanical systems of any type tend to "get set in their ways" and don't take kindly to system changes. So, one change causes other things to fail when life changes for them and you often wind up chasing a series of self induced system failures.

In changing out the glycol, be careful of how you dispose of it. For one thing, there are regulations covering disposal. For another, if you have a cat, know that they love the stuff and it's fatal to them if they ingest any of it.

I've got a self designed SDHW system with an oversized pump. The pump draws ~ 40 running watts and runs ~ 3,500 - 3,800 hrs./yr. Even in CO, I kind of doubt your system runs much more than.

That means unless your system is totally non productive, and/or your nat. gas cost is really dirt cheap, I also doubt the cost of the ~ 150-200 kWh/yr. your system's pump uses surpasses the nat. gas cost savings the system is realizing. What do you pay for a kWh of electricity ?

Also, until the pump fails, replacing it may not be worth the cost (and maybe/probably not even then unless the pump and labor to install it is free). Unless/until the pump fails, a new pump will not improve system performance in any way you'll be able to measure or realize in greater heat production, much less get any payback period less than your remaining time on this planet. If it ain' broke, don't fix it.

Get a grip on what the existing pump draws, how much it runs, what the system currently generates in a year and what those thing are worth. Your assumptions are based on an ignorance of realities and probably leading you astray.

With regard to perhaps replacing the pump with a PV powered DC pump, I think that is a waste of money and an all around bad idea. Too much $$, too much of a system upset, and with the age of the system, simply too much hassle, even if you can find someone to correctly size it and design also do any piping and control system changes the rest of the system will require.

[LucMan]

I have a 1980s vintage Suncatcher solar hot water heater system, installed by the original owners of the house to heat a hot tub that is no longer present. It feeds the domestic hot water, supplemented by a normal natural gas water heater. The system was high-end for its time - copper pipe, silicone heat transfer fluid - and has worked pretty reliably for decades. However, the economics of it are getting marginal. The monthly savings in natural gas are modest after accounting for the electricity to run the pumps, and the next time it needs a repair or servicing it's not going to make sense to invest in such old hardware. So it will soon be time to decommission it. My question is how? Does anyone on the forum have experience with the end-of-life phase of a solar water system?

In Colorado, solar water systems used to be fairly common and so there were several companies to service them. But these days it seems like both the systems and the service companies are nearly extinct in this area. So, if I can't get a specialist, do I hire a plumber to remove it, who presumably knows pipes and fluids but may not be equipped to get heavy stuff off a roof? Do roofing companies handle this and I should get one of them to remove it next time I have new shingles put on? Do I need to coordinate both?

If I shut down the system myself but leave it in place until the next time I get the roof replaced, is there anything special I need to do to safe the system for the long term? I think the combination of copper and silicone is pretty robust against overheating or corrosion, but do I need to do something like drain the system or cover up the panels?

Are there any particular issues to consider with disposal, such as something that's valuable as scrap (the copper, anything else?) or requires special handling for disposal (silicone?)

Thanks in advance

Silicon fluid ( liquid gold) I can't imagine what a gallon of that goes for today. It can be recycled, check on the internet for companies . Used it back in the 70's at I think $150 a gallon. Silicon fluid complicates a pump change out unless there's still a gallon left over at the job site because the system will need to be purged and additional fluid will be required . The good thing is that it's not supposed to break down or degrade so no replacement ever required, also should be fine with out covering and deactivating the system. The original fluid had an extremely low expansion rate at higher temps.
Do not hire a plumber for any repairs or modifications, you need a solar pro preferably a really good one. I see no reason for not using the system if the panels are functioning, maybe the glass panels just need a cleaning inside and out to remove oxidation from the glass to increase the performance. The impeller and volute on the pump are possibly worn after 30 years so a pump changeout would improve performance.
Keep it going especially in CO where sunshine is plentiful.

[JoshH]

Thanks to all who responded.

Answers to some of the questions folks raised follow:

Can you share numbers on the electric cost and the gas offset cost?
I measured the energy draw with a meter over several days in February and September and measured 3.2 - 4.0 kWh per day. If I had been smarter I would have measured in summer and winter. (Tip - in many places you can check out a power meter from the library. ) I turned off the system for a few months last year and the difference in the power bill vs prior years was roughly consistent with that (though hard to tell precisely given normal fluctuations plus who knows what usage change due to COVID). Electricity cost ranges from 11.8 cents /kWh average cost in winter to 16 cents/kWh marginal cost in summer. So I'm paying something in the range of $11-19 a month to run the pump.
Much harder to judge how much gas I'm offsetting. My best estimate is 4 therms per month during the summer. Definitely less than 10, possibly as little as 2 therms/month. The gas water heater still runs. Much less clear what the difference is in the winter. Maybe more. Gas cost is around $.6 / therm. So, I'm saving about $2-3/month in gas. Not a good deal.

Now, I'm sure there are ways to improve the payoff. I should clean the panels, or optimize how much I bypass the hot water heater. I could imagine replacing the pump with a more efficient one. But my utility says folks in my neighborhood (i.e. similar houses without solar water) are using something like 10-15 therms a month in the summer. So, best case I could save something like $6 a month. Hard to see any investment paying off.

(Interestingly, I have the original sales brochures from 1983, which were heavily emphasizing the fact that utility prices had been increasing rapidly and projecting that they would continue to do so. But in fact they didn't.)

If anyone else has run the financial numbers on their system, I'd be curious to see comparable data. I assume these systems can pay for themselves when heating a pool or other big demand, but hard to see how it's worth it for basic domestic hot water at current natural gas prices.

What pump model do you have,
Based on the documentation, I believe I probably have a Grundfos UP26-624F. The specs for that pump are online here UP 26-64 F - 52722330 | Grundfos. It looks like it draws 185 W max, which is not consistent with the power draw I'm seeing. Sounds like I should take the system casing apart and see what's really in there.

What's the height it has to pump,
Roughly 20 ft of head from a basement to the roof of a garage.

and does it have a variable speed circulator you can lower?
Not that I know of.

Is there a high cutoff, so you're not heating water too hot to use?
I believe not.

Before that however, I'd check the system performance and see how much the system is producing.
How does one measure that?

... heat exchangers ...
Yes, it's a silicone system, so it does have a heat exchanger.

[LucMan]

Here's what my drain back system uses. 190 watts x 5 hrs. per day=950 watts /1000=.95 KWH x .21 per KWH delivered= $0.1995 cost per day, lets call it $6.00 per month.
I heat my water with oil no gas available, oil is $2.54 a gallon now. MY boiler has been off since april (and will stay off until the middle of october) so no oil has been used. I have 160 gallons of storage that I use in the summer, in the winter I only use 80 gallons of storage. In Jan / Feb I can only preheat my water to about 90 degrees F. My Hi limit is set at 150 degrees. I can go 3 days with out sunshine and still have HW in the summer.

Performance.
To calculate BTU's. Determine delta T from switch on in the a.m until switch off, times the pounds of water in storage (1 gal weighs 8.34 lbs.). It takes 1 BTU to heat 1 pound of water 1 degree.

[brycenesbitt]

Grundfos UP26-624F.

Get yourself a $15 clamp on recording Watt meter, slip the coil over the hot wire going to the pump.
Likely, the Grundfos is using far less power than the nameplate rating.

I have a 180 Watt nameplate Grundfos pump that most of the time cruises at 110 Watts.


Watt Meter.PNG