Heating the water - solar panels vs. photovoltaic

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Hello,

maybe someone has any experience or knowledge in this area… We currently have old solar panels (thermal ones) and a new heat pump (installed 3 years ago), which should work in tandem to heat our water. To be honest I have no idea how good this setup is and how much we saved on electricity…

Soon we will have also photovoltaic panels installed. Unfortunately, I’ve learned today, that one of the tubes is broken plus that the root cause is somewhere where they don’t have replacement parts for anymore. So the guy told me that I should contact the installers and change all the tubes to more recent panels (no idea what exactly).

I don’t have any more details yet (especially pricing…), but from purely technical point of view - do you think it makes sense? Or I may rather should forget about solar ones and just disassemble them and rely 100% on the heat pump + photovoltaic?

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My own tendency would be to junk the thermal solar panels and go full PV.

Thermal panels were OK when PV systems costed a lot and had an efficiency of ~10%, today they just complicate the setup and are just a liability

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Hi, I’ve recently arranged to have a heat pump installed in our ~170m2 EFH this year. In the process I read fairly deeply regarding the topic, as I wasn’t convinced by a lot of the installers and I have a technical background.

My view: Thermal solar panels rely on a large water storage tank where different systems contribute to provide hot water year round (heat pump, thermal panels, electric backup element). So you are taking the energy from the sun and storing it as hot water. Now, the heat pump can work at an average efficiency of 350-550% over the year and up to 600% when the sun is shining and the compressor can work efficiently.

This means your options are:

  • You can use xm^2 of space to generate hot water (which can only be used for sanitary purposes).
  • You use xm2 to get electrical energy which can either run your appliances or run the heat pump which then gets you up to 5x what you put in as electrical energy as thermal energy

It’s a no brainer really. Not to mention if you throw in batteries, given the very low prices, this electricity can be used during the evening peak.

Heat pumps really are amazing combined with PV. On a sunny, cold winters day you can really heat your house and probably charge up the batteries just from the sun.

I should add when sizing the battery, in purely ROI terms, summer evening use rather than storing in winter should be used to determine the number of kwhs.

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I would say the same, maybe thermal might have some theoretical higher efficiency per unit area, I don’t think it makes sense to maintain 2 different systems. You can free up the space to add more PV if required and can use the electricity to heat or for other household uses.

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Thanks a lot for amazing and very helpful answers… I’m already organising decommissioning of thermal ones, in order to try keeping installation date for photovoltaic in 2 weeks :crossed_fingers:

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good choice.

edit://

I imagine you have a buffer tank where hot water streams from heatpump and thermal solar are merging? You wont need that buffer tank anymore. It causes a higher heating flow temperature (up to 5K) which is bad for efficiency. Also you can eliminate the second circulation pump, which consumes also energy.

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This depends on a lot of different factors.