Solar hot water—replacing tanks
Hello, I have a ~15 year old solar hot water system (pressurized glycol system with two Gobi collectors) that runs to a 119g storage tank. That tank feeds into a Stiebel Eltron Accelera 300l electric heat pump. I didn’t design the system and as I understand this is overkill. The heat pump has died and the 119g preheat tank is on its last legs too. I am hoping for advice on how to update the system.
I could replace the 119g tank with something with a built in electric heater as some seem to think that would be sufficient. I could also replace the 119g tank and put in a smaller electric resistance water heater to replace the heat pump. Does anyone have experience here or other ideas?
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We installed a solar thermal heater last year. It has a built in heating element as well for back up purposes. We haven't used the resistance heat as we have the tank set as preheat for a rinnai tankless gas heater. The solar tank is stainless steel and has a built in heat exchanger. It's made by HTP which is a quality brand.
This probably isn't the answer you're looking for, but solar thermal has fallen out of favor because it just doesn't make economic sense. Now, your system is a sunk cost so the economics are a little different.
There are different kinds of solar hot water systems and I'm not quite sure from your description what you have but it sounds like it's just a pre-heater for a water heater. If that's the case it will work with any heater.
I learned as much when I started researching (I bought the house so I didn’t install it) but as you say it’s a sunk cost so it makes sense to work with it. I’m just not sure if I can reduce the size of the backup heater because of the preheating or if I need to size that as if it’s a stand-alone unit
I would size it based on zero contribution from the solar. Hot water tends to be used in bursts, so water heaters are sized based on maximum one-hour draw. I would say your maximum hour is going to be one where the sun wasn't shining.