Why are we not seeing more solar thermal installations with heat pumps?Â
Lack of knowledgeable good suppliers? Payback too slow? Previously, more complicated RHI application? Cheaper to use photovoltaics (PV aka solar electric) to power the immersion and then put any surplus into batteries?
Fitting your own MID elec meter to the heatpump is very achievable, helps keep it all ‘honest’.
Sounds like I will have to look into this. We have a Solar wet system plumbed into the second heat exchanger of our DHW tank (you may have seen the rising tank temperature in two of the graphs I posted)
So would I need two MID meters? One for the HP and one for the immersion? It would be good to be able to isolate the savings in use of Emerson heater…
just to focus on this, we are getting 250ltres of water at 42c on a sunny January day. By March/ April we should be entirely using solar generated hot water. I’ve read from heat geek that solar thermal is 90% efficient compared to solar pv somewhere below 30%? Not sure if exact figure.
Why are we not seeing more solar thermal installations with heat pumps?Â
I think that dependent upon the type of solar thermal panel, the efficiency can be in the 80% to possibly 90%. A solar PV system is in the order of 20% efficient at the moment, though more efficient panels are being developed, up to 40%.
Probably the reason why there are more solar PV system installed, in preference to solar thermal, is the fact that solar PV is more versatile than solar thermal, for probably about the same cost. It can therefore be used for other purposes rather than just providing heat energy.
In an ideal World we would all have solar PV, solar thermal, battery storage, along with a thermal heat store, heat pump and EV. All paid for by the taxpayer. Hang on a minute, that's me. 🙄Â
For me, the limiting factor was roof space, and it didn't make sense to use any of it for solar thermal. I could simply use the PV to power a 3-4 COP heat pump to heat the hot water instead.
Hi @derek-m - you mean I could have got a free handout 😱 🤣🤣. Yes I guess the rush for car charging and battery storage does make it more versatile... and kind of put thermal solar into the background. It’s, sadly being overlooked.Â
Mine was a DIY install about 7 years ago costing £1400.Â
What I like about Solar Thermal is it avoids or reduces the less efficient DHW cylinder heating cycle of the heat pump so in the end it will improve COP and SCOP. Temperatures can get very high (75+) therefore eliminating the Legionella heating cycle.
Obviously it’s free hot water but one other thing I like is HOW it passively communicates with the Ecodan. By raising the hot water temperature the Ecodan DHW thermistor registers the water is hot so it doesn’t need to activate the reheating water cycle. No wires and no electronics.
Here's another 'feature' of Melcloud I've come across.
Below was taken around 10am this morning (i.e. 14th Feb had 'finished' some 10 hours prior).
Compare that with the same but run at 4pm (some 15% less heating time now being reported). The 4pm one is more accurate in terms of actual heating time yesterday. DHW was on for an hour and a half yesterday, so the 4.1% (1 hour) is some 50% off in terms of accuracy.
"Indicative Data" or not, it's about as useful as a chocolate tea pot. @william1066 your previous post should have included a moving target as well.
Hi @derek-m - you mean I could have got a free handout 😱 🤣🤣. Yes I guess the rush for car charging and battery storage does make it more versatile... and kind of put thermal solar into the background. It’s, sadly being overlooked.Â
Mine was a DIY install about 7 years ago costing £1400.Â
What I like about Solar Thermal is it avoids or reduces the less efficient DHW cylinder heating cycle of the heat pump so in the end it will improve COP and SCOP. Temperatures can get very high (75+) therefore eliminating the Legionella heating cycle.
Obviously it’s free hot water but one other thing I like is HOW it passively communicates with the Ecodan. By raising the hot water temperature the Ecodan DHW thermistor registers the water is hot so it doesn’t need to activate the reheating water cycle. No wires and no electronics.
Komplete karma 🤙
I recently watched a heatgeek video, where they have installed solar thermal panels and a heat store to provide heating at their offices. This not only allowed their heat pump to not be required for a lengthy period of the day, but also allowed more output from their solar PV to be used for other purposes.
If you can install a solar thermal system yourself, then obviously it is more financially viable than having one installed. Coupled with a large heat store could make solar thermal quite advantages for some.
Edit.
I forgot to mention, that I wonder if the heat pump controller actually records that the DHW has recently been high enough to cancel the need to perform a legionella cycle? Obviously it will not perform the cycle if the water temperature is above the required value, but it may not cancel the scheduled request.
was that repeatability was much more important than absolute accuracy.
This is the age old accuracy vs precision
I suppose that it is how we use and interpret the different words.
When one looks at the specification of measurement systems, accuracy will often be quoted as plus or minus a certain percentage of Full Scale Deflection (FSD) or sometimes percentage of reading. If there are two system each with a quoted accuracy of +/- 1%, and they are both measuring an actual true temperature of 50C, one may assume that both systems would provide similar readings within the limits of the accuracy. If it is now stated that one system has an FSD of 0 to 100C, whilst the second system has an FSD of 0 to 500C, then that assumption would be quite different.
The reading on system one could be expected to be somewhere between 49C and 51C, whilst the reading on the second system could now be anywhere between 45C and 55C. Both readings would be within the quoted accuracy.
So to me, accuracy would mean how close to the truth can the reading be expected to be.
Precision in the instrumentation field would be more to do with how the actual reading is measured and displayed. Should an actual reading of 50.15C be displayed as 50C (rounding down), 50.2C (rounding up), or 50.15 (precise)? Most measurement systems now use Analogue to Digital (A to D) converters to transfers values into a computer system. If the A to D converter only has a precision of 10 bits, it may provide a different result to one with a precision of 14 bits.
Repeatability, as used in my previous post, was more to highlight the fact that absolute accuracy is not so important, if the known errors are consistent, and can therefore be applied to any measurements taken. If it is known that a particular sensor always gives readings that are 0.55C low, then if a reading of 21.5C is obtained, the true value will be 22.05C, which dependent upon precision, could be displayed as 22C, 22.1C or 22.05C.
I forgot to mention, that I wonder if the heat pump controller actually records that the DHW has recently been high enough to cancel the need to perform a legionella cycle? Obviously it will not perform the cycle if the water temperature is above the required value, but it may not cancel the scheduled request.
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It looks like the Legionella routine is only calendar schedule driven with user selected options such as an adjustable 15 day cycle or less. Temperature is also adjustable and duration. Also at the front end of the menu the user can decide to un-tick the cycle altogether so that it becomes inactive. However I recall that our installer said they are obliged to leave the completed installation with a fully active Legionella routine in place.
As @cathoderay says, there’s a lot of mixed feelings about the risks especially in an unvented system with high useage. It’s fascinating how how even Heatgeek hovers on saying the risks are very low but, that it’s up to the individual to decide whether they want to switch it off altogether or run a cycle periodically. I’m planning on using thermal solar to super-heat our tank through the summer months... Then, maybe, have a hot bath once a month in the winter 🥶Â
Edit: I think it’s part of the MCS certification
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