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15kw Solar System with Solar Hot Water?
- Thread starter Racerx22b
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- Energy Environment Policy
nwdiver
Well-Known Member
Rough estimate of the energy required to reheat the tank. The range is probably 2-6kWh depending on tank size and ambient temperature...
I really like the new Rheem HPWH. They can be connected via wifi. You can use the app to decide when you want the tank to heat.
Resurrecting this thread because I'm too lazy to dive deeply through TMC's very awkward search engine to look for a more specific thread, so -
...regarding hot water via heat pumps versus through solar collectors:
I've zero experience in the former but an enormous amount in the latter. At 63ºN, we have a whole lot of goose-eggs in the solar insolation basket, but even so....
the seven flat panels (about 7' x 5') we installed facing south atop our newest roof, with the system shielded from our -50º winter temperatures via a glycol/water heat exchange barrier and a "Go Home" gravity drain system after -20ºF provided more blisteringly hot water than we could use. In our case, we stored it in a dedicated highly insulated 3,000 gallon tank* but the reason I bring up the topic again is because....
we have a friend at 47º in a locale that rarely sees temps below +20ºF, who has an indoor pool and a massive, sunny, south-facing roof. We've told him he should ditch that propane-fired water heater and install panels similar to what we installed.
I've no idea of the current costs of hardware or installation, but I think it's a perfect choice for his setup. Any comments, particularly specifics as to why a heat pump still is a better option, will be received with an open mind.
*In our case, it was the crushingly poor design of this storage system that led to the entire project earning a D-, and our dismantling it and selling the panels after 7 years. But we sure miss those panels!
...regarding hot water via heat pumps versus through solar collectors:
I've zero experience in the former but an enormous amount in the latter. At 63ºN, we have a whole lot of goose-eggs in the solar insolation basket, but even so....
the seven flat panels (about 7' x 5') we installed facing south atop our newest roof, with the system shielded from our -50º winter temperatures via a glycol/water heat exchange barrier and a "Go Home" gravity drain system after -20ºF provided more blisteringly hot water than we could use. In our case, we stored it in a dedicated highly insulated 3,000 gallon tank* but the reason I bring up the topic again is because....
we have a friend at 47º in a locale that rarely sees temps below +20ºF, who has an indoor pool and a massive, sunny, south-facing roof. We've told him he should ditch that propane-fired water heater and install panels similar to what we installed.
I've no idea of the current costs of hardware or installation, but I think it's a perfect choice for his setup. Any comments, particularly specifics as to why a heat pump still is a better option, will be received with an open mind.
*In our case, it was the crushingly poor design of this storage system that led to the entire project earning a D-, and our dismantling it and selling the panels after 7 years. But we sure miss those panels!
SageBrush
REJECT Fascism
I live in a neighborhood that was Eco minded back when a lot of it was built in the 1970s, and many houses still have thermal panels on the ground or on the roof. I have yet to speak with one person who says they are still working. All the systems failed from plumbing problems *, and the cost to repair them was considered not worth it.
This is not a direct answer to your question, except to say that the heat pump solution is modular enough and reliable enough to to probably not suffer the same fate. And NOT specific to your friend, heat pumps win for all those cases where self-generated electricity is not only used for hot water year round.
* It's probably germane to point out that we all use well water that has high mineral content. But even so, plumbing problems is the #1 issue I read about for thermal solar.
Mmm. Now, I completely agree that heat pumps are efficient ways to extract heat and, from experience, are superb at supplying heat for a house.
But heat pumps, too, can be cantankerous. Atmospheric pumps have those fans that ice up and have to go through a defrost cycle (wasteful!); u/g heat pumps can fall prey to scaling, as well as the same kind of pipe/tube failures you mention for solar heaters. Good - in that any such failure isn’t on or through a roof; bad - in that they’re underground and hugely expensive to repair.
The virtue of solar hot water is, I believe, in that the simplicity of the system easily is modularity multipliable to provide the immense amount of calories needed to supply a swimming pool. I do know one should never use direct transfer - either pool fluids or consumable water almost always has dissolved solids that, sooner or later, will cause the panels’ tubes to become scaled (or worse, corroded), and fail. Rather, a glycol fluid of appropriate strength for one’s winter temps, passed through a high-quality plate heat exchanger, is the way to go.
And roof penetrations? These are not difficult to design properly for decades of leakproof use. We’re still using ours after thirteen years - now as conduits for PV electric lines - with zero issues. It is absolutely incumbent to use the highest quality pipe insulation on all tubing, both supply and return lines; such will assist in making negligible expansion/contraction problems as well as keeping the system efficient.
But heat pumps, too, can be cantankerous. Atmospheric pumps have those fans that ice up and have to go through a defrost cycle (wasteful!); u/g heat pumps can fall prey to scaling, as well as the same kind of pipe/tube failures you mention for solar heaters. Good - in that any such failure isn’t on or through a roof; bad - in that they’re underground and hugely expensive to repair.
The virtue of solar hot water is, I believe, in that the simplicity of the system easily is modularity multipliable to provide the immense amount of calories needed to supply a swimming pool. I do know one should never use direct transfer - either pool fluids or consumable water almost always has dissolved solids that, sooner or later, will cause the panels’ tubes to become scaled (or worse, corroded), and fail. Rather, a glycol fluid of appropriate strength for one’s winter temps, passed through a high-quality plate heat exchanger, is the way to go.
And roof penetrations? These are not difficult to design properly for decades of leakproof use. We’re still using ours after thirteen years - now as conduits for PV electric lines - with zero issues. It is absolutely incumbent to use the highest quality pipe insulation on all tubing, both supply and return lines; such will assist in making negligible expansion/contraction problems as well as keeping the system efficient.
SageBrush
REJECT Fascism
I've read that solar thermal can collect 70% of solar insolation, although I don't know how much is lost in the heat exchange. Since PV is about 20% it follows that all else being equal, heat pump COP has to average 2.5 - 3.0 year round to match the solar thermal collection. I wonder if AK is a test case for CO2 heat pumps.
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