Replace a solar hot water tank without replacing the flat plate collectors?

[hotwaterman]

Our house was built 8 years ago and was fitted with a solar hot water system (make: Solarpower), which apparently has gone out of the market. The overflow valve started leaking water (constant drip) and we called a plumber. He replaced the valve, but didn't help. We are told we need to replace the whole system, 2 solar flat panels and the tank.

Question: is it really not possible to just replace the tank and use the same panels?

I would really appreciate your help. It's a big difference in price.

[J.P.M.]

Without knowing the particulars, but depending on what you mean by overflow valve (Relief valve ? - they weep 1X in awhile, ~ $10 - $20 and a service call, or easy DIY). My guess is either you misunderstood what was said or the vendor is full of road apples. It may take a system drainage, but most every component of a plumbing system can be replaced with equally fit for purpose equipment. To scrap an entire system because of a valve is simply ludicrous.

Call a reputable solar thermal vendor or simply a good and established plumber and have the system checked out.

[LucMan]

I'm going to assume that it is your T&P safety relief valve (Temperature & Pressure) that is leaking. They tend to weep after a few years, but since it has been replaced the main reason that it could be leaking is because the expansion tank bladder has gone bad. Water expands when heated, the expansion tank absorbs the additional pressure.
I suggest you quickly hire another knowledgeable contractor before this guy screws you.

[hotwaterman]

Thanks! I appreciate your quick answers. I will get a second opinion.

[peakbagger]

Unfortunately finding someone good with flat plate SHW systems is tough, its dated technology that has fallen out of favor due to high initial cost. Its heyday was 20 years ago with a resurgence about 10 years ago when evacuated tube type collectors rose up and quickly went away when they started to fail prematurely That doesn't mean flat plates are not good, its just cheap PV panels in conjunction with heat pump hot water heaters are far lower cost to install new.

Unless the system was totally abused there is no reason to replace it. If its glycol based system and was abused because the circulating pumps were left off for a long period the glycol could have gone acidic and corroded the piping and panels but that's highly unlikely with flat plates.

My guess is that you probably have an expansion tank on the glycol loop, it will be a small cylinder about the size of basketball that is plumbed into tee on the piping usually downstream of the circulating pump. The tank has rubber diaphragm inside and its not unknown for them to break when used on SHW systems. A SHW system needs a place to expand and contract as the temperature of the fluid varies a lot. When the diaphragm fails, the tank fills up with glycol and it no longer will do its job. For a short time it sort of works as there could be an air bubble in the tank but eventually that goes away and next thing you know, your relief valve starts seeping. There is usually a rubber cap on the end of the expansion tank with a bicycle tire type fitting on the end of it. If you quickly press down on the stem for a second, if any liquid sprays out, that means the expansion tank is shot. It happened to me after about 10 years of operation so I got first hand experience with this.

Replacing the expansion tank is easy but what is not so easy is refilling and re-pressurizing the system. It requires a charge pump kit and someone who knows how to use it. A homeowner can assemble a kit but its about $200. Anyone with SHW experience is going to have one and can do it in minutes. DIY it takes a bit of learning and inevitably plan on getting wet with glycol and have plenty of rags and buckets to sop up the spills. I did my own install so I bought the charge pump and the other fittings when I installed the system and had it on hand 10 years later when I had to replace the tank. While you are at it, its probably a good time to change the glycol (make sure it polypropylene glycol instead of ethylene glycol which is toxic). At minimum go to a gardening store and buy pH test kit. You want to test the glycol and make sure its neutral pH, if its acid then you need to replace it, if its neutral you could get away with reusing it.

These systems will run for long time as they are pretty simple, usually what stops them from running is something minor like a bad thermistor, a blown expansion tank or a controller that died. All are easy fixes but since there aren't a lot of folks who understand the basics a lot of the get ripped off for scrap when someone is haven't a roof replaced. My friend has a system that has been running for about 37 years. The key is he installed it and understands it so when it acts up he fixes it. He installed his with several other families under a group buy and the other systems are now dead or removed as the original owners sold to new owners that don't understand the fundamentals..

I think I have posted how to assemble a charge kit and how to recharge a SHW system at some point on this website. If you want search my old posts you probably can get lucky if you want to DIY it.