Hi All

Charenteman in France here.
I have been busying myself during the respective lockdowns in framing and insulating barn roofs and walls in readiness for 1st fix plumbing and electric works prior to plaster boarding the lot.

During this time I have been trying to firm up a heating and hot water scheme using a heat pump solution.
Earlier thread discussions had suggested that integrating pv panels would be a good idea - connected straight into the Hot Water Cylinder with any excess electricity (when HW is at desired temperature) stored in back up batteries to power the heat pump?).
The trouble is that when I explain this objective to local plumbers I get glazed looks. They all propose heat pump packs (Hitachi, De Dietrich, Mitsubishi) with outdoor unit and indoor unit (with HW storage) serving both central heating and hot water demands from a single tall unit.
Connecting PV panels is not an option they say.
Can anyone out there set me straight on this and suggest some tried and tested component combinations that I could refer them to?
Any help appreciated!

Thanks

Ed, I am totally with you on batteries , we are swimming against the tide though

Re Solar PV, big problem is that there is the least amount of solar PV when it is needed the most

Excess solar pv can be diverted via a black box to make hot water - better would be divert to a heat pump and for that to make hot water, uneconomic unless you have heat pump already

Heat pumps often have very high start up currents and solar pv cant cope with that so need to be grid connected

Posted By: tonyHeat pumps often have very high start up currents and solar pv cant cope with that so need to be grid connected

That used to be the case but is nothing like as much of a problem as it used to be with modern inverter heat pumps.

Posted By: tonyRe Solar PV, big problem is that there is the least amount of solar PV when it is needed the most

Indeed, but what can be missed is that the angle of the panels makes a big difference. If the panels are near vertical then there's a small reduction of overall annual production but a substantial increase in winter generation.

However, being as far south as the Charente makes this a bit moot. For a point at the western end of the main runway of Angouleme-Cognac airport [¹] (45.731, 0.207) PVGIS reckons the “optimum” angle of the panels is 38° with annual production of 1234 hours (i.e., kWh per kW peak) with January production of 55.48 h whereas increasing the angle to 70° only increases the January production to 61.14 h while knocking back the annual production to 1091 h (and also significantly reducing the July production to the point that it's less than in some of the shoulder months).

At this location, though, the difference between summer and winter is less marked than further north. For 38° panels the January production, as noted above, is 55.48 h whereas the July production is 136.77 h so only a 1:2.47 difference.

[¹] I like to use airports for this sort of thing as they often have relatively clear horizons for some reason.

Ive no experience with heat pumps but Id be very surprised if you cant find a standalone heat pump to connect to your own cylinder. Cylinders can be built to your spec with as many immersions and indirect input coils as you want to cover boiler, heat pump, woodburner, solar thermal etc. Obviously youd need a pretty big cylinder to get them all in. Newark copper cylinders built a custom cylinder for us and well worth discussing what you want with them. Other suppliers are available, probably!

If you find local plumbers a bit resistant to something they are not familiar with, it may be worth tracking down a French custom cylinder supplier as that may help get your plumbers on side if they are installing something home grown. Alternatively get a Newark cylinder and stick some French labels on it:)

Charenteman,

sometimes people think that using PV to heat water means that you have to feed from the PV directly. It's much simpler than that. PV doesn't know or care what it's feeding, it all goes to your dist board, and then to what ever happens to be running, or back to the grid. (sorry if you already knew all that).

Point being, you need to be able to switch things on, when PV is generating adequately. So a little black box which confirms that you are making excess PV, will then feed power to the piece of kit that black box is connected in line with.

Here's one I often fit (I have no other link to this company apart from being a satisfied customer).

www.earthwiseproducts.co.uk/shop/

You simply insert this in-line in the power feed from your dist board to the immersion in your cylinder, near to the dist board, so you can clip the sensors onto the main incomer, so it can determine if you are starting to export.

No idea if this can be used in France, thought I suppose you can just fit it yourself after everyone else has left


The second question is...does it make sense to use this direct electricity user, when you can utilise a heatpump and get a COP of say 3. The points have been made by others above about trying to coincide PV excess generation with running a complex kit, rather than a dumb immersion (which can take the varied voltage to give power inputs of down to about 200W).

To add a little complexity, it may not matter whether you use the PV, or send it to the grid (financially), since you'll get 5p /kWh from the grid, but if you buy that back later at say 15p/kWh, using it to run your heatpump will drop that actual cost to 5p/kWh due to the CoP.

So, you might as well just run the heat pump, and if it coincides with excess PV generation, each kWh will cost you say 2p, (opportunity cost of not exporting it 5p divided by CoP). If it doesn't coincide, then it's costing you 5p/kWh.

That may be moot, however, if you go for air-air heat pump, and have no "wet" element to that system, in which case the use of immersion and excess PV diverter would be ideal.

Confused? You have been.

Posted By: GreenPaddyrather than a dumb immersion (which can take the varied voltage to give power inputs of down to about 200W).

Just to note that whilst it is true that an immersion can handle reduced voltages, which heat pumps etc can't, that isn't actually the situation with the power supplied by one of these devices (known as 'diverters'). They supply power at mains voltage but continually interrupt it so that the average power supplied matches that available rather than the normal situation where the power supplied through an ordinary switch matches that demanded by the immersion.

Posted By: Ed Davieslikely sunshine over the rest of the day and the next day or two

Good luck with getting that info

Has charenteman said he's off-grid?

Also, I'm not convinced that the start-up current is a problem with reasonably modern inverter-driven heat pumps. A while ago I had a look at the specifications for some and they seemed well within the capabilities of standard off-grid inverters to deal with short overloads. You'd probably not want the HP to start (or run) while you're cooking but that shouldn't be difficult to arrange.

if [ "sunny" != "`wget --retr-symlinks -q -O - https://weather-broker-cdn.api.bbci.co.uk/en/forecast/rss/3day/kt1 | awk '/<title>.*emperature/ { if(++count==2) {if($0 ~ /[Ss]unny/){printf("sunny");}exit;} } '`" ] ; then rm -f /var/run/FORECAST_PV_GEN_GOOD.flag; else touch /var/run/FORECAST_PV_GEN_GOOD.flag; fi