JohnMo

There are two ways to heat water with electricity, heat pump or direct to immersion. Neither are as straightforward forward as they first seem. But breaking down practicality Heat pumps when you need them most they have the biggest power need (lowest CoP) and you are likely to have least PV available. So likely no heat pump running most of Dec-Jan. Looking at my PV today, which was quite overcast I did 17kWh, but the useful window for driving a heat pump off-grid was about 3 to 4 hrs. The other alternative would be direct DC to immersion heaters. You need to match the output of the panels very closely to the the power rating of the immersion to get them to perform as they should. You get a CoP of one, but you get useful energy whenever the sun's out. Panels from city plumbing are cheaper than ebay. Watch this and the spreadsheet mentioned is attached https://www.google.co.uk/url?sa=t&source=web&rct=j&opi=89978449&url=https://m.youtube.com/watch%3Fv%3DkVaxAfXQPDU&ved=2ahUKEwjZ2vnXhcqEAxXkZEEAHfX8DHkQo7QBegQIDhAG&usg=AOvVaw2ys-gKyKBdBX1Ku7fZDZ-M Solar PV Calculator.xlsx

Ideal just rebadge cylinders so not likely to make one off. Try these https://www.cylinders2go.co.uk/

I tried twice and they said no. Have DNO sign off, structural engineer certification etc, even have an MCS cert for the battery, but not for the PV.

I thought he meant take all his roof off... Now I understand with the additional photo.

I was in a garden centre the other day they were selling calor gas internal gas heaters, like the old gas fires, but on wheels. That would be cheaper than electric heater to run.

Not sure why you need smart for UFH, but the Computherm RF range are good. I have Computherm Q20RF in my hall (£60 from Amazon). Nice solid feel, easy enough to setup, can select a hysteresis of 0.1, which is great for UFH.

New MCS Guide now explicitly states that an additional DC isolator is not required with inverters that already have integrated DC isolators - but to me the inverter is the only thing likely to fail, over time. The isolation switch on the inverter is fine, but does not allow to isolate the panels from the inverter, to then allow the inverter to be safely be replaced at some point in the future. So from a practical perspective I would always install one. Plus you can place it somewhere convenient, for yourself, electrician or fireman, rather than having to go into the loft etc. What fire risk is there in an isolation switch? That just sounds like he is making it up as he goes along.

Really zero need, UFH can do all the heating you need. If you have a thick screed, circa 100mm you can charge the floor like a storage heater on mostly cheap rate (E7 or similar). This takes a hit on CoP, but the electric is cheap. You can get cylinders in just about any shape you want, or get it made to the size that suits you. Get one with a 3m2 coil.

Sorry don't believe those figures are possible with an 8kW inverter. PV panels maybe able to produce that many kWh, but an 8kW inverter will not let that energy out. Especially if a G98 approved inverter is installed. 25682/365, is 70kWh a day on average, which is a production of 8kW constantly for 9 hours every day, have you actually done any checks on this to see if they are realistic? Those figures are well out of date. Your export rate is likely to 40 to 50% lower in 5 weeks time.

Bit confused. Are you planning to change your roof on the main house? Assume you are semi detached with the green fence and what looks to be a party wall on you sketches. How are you going to tie the two roof together? I wouldn't be happy to agree, if I was living next door to you.

Why the added complications, UFH is fine on its own for heating. Can do cooling also, just flow at 15 degrees, will knock the extremes of summer heat off and cost next to nothing to do. Everything else sounds good.

Your pump should set to match the flow rates required. Turn it down until you see the flow meters drop, then set it one speed higher. 2l/min isn't a high flow rate, tweek the flow rates up where the area served by the loop is too cool. Thermostat should be away from any outside influences so by the front door may not be the best place. Don't see that as an issue, if you have a modulating boiler the boiler modulates to match demand, if the boiler was perfectly sized and flow temp was set correctly the boiler would/should run all the time.

Have a look at bumblesolar, they do packaged with decent descriptions. https://www.bimblesolar.com/offgrid/complete-packages?utm_source=Google&gad_source=1&gclid=Cj0KCQiA5-uuBhDzARIsAAa21T_pBfVYnZg6RQ-C1fytSoJzP7IIHhN1WXUWTLpcdoWkxqSsrT8pzWQaAqdBEALw_wcB

Something like this, would assume setting in the solar controller or inverter would stop drain down.

May be good way around things. For a simple heat pump I quite like these (on paper at least). https://eco-outlet.co.uk/products/activair-3kw-indoor-air-source-heat-pump They don't modulate, but you don't need that. They only pull 0.75kW and 5.2 Amps you could configure the ducts to do cooling in the summer also. Small off grid inverter and almost a caravan battery to act as a buffer.

I would look from a slight different direction. PV will get utilised before your demand takes from the grid. Any short falls are then taken from the grid. So if your generating 2kW and your heat pump is the only thing online and is drawing 2kW, all good, no import. If it does a stop-start cycle and the inrush current is higher than you are generating, the shortfall will be grabbed from the grid.

Now you have mortgage, why not look for an alternative mortgage supplier, that will mortgage without mains electricity. You have £32k to save. Or at least look at different ways of getting electric from A to B. We employed our own digger driver for a couple of days, cost a £1 000, saved £10 000+

So about 73,000kWh required to be exported to break even difference between option 1 and 2. So about 15 years with an average 15kWh exported 365 days of the year. That's at 15p per kWh and I would assume that price will drop in April by at least 20%, so then 18 years to break even.

Why pay a supplement to have PV installed, so you can export? As much as Octopus says they accept non MCS installs it's only a trial and you have to pay a fee, and jump through hoops. Plenty on here don't have heat for bedrooms at all, when they are upstairs. I have found the cheapest way to run my heating is. UFH run at a fixed 35 Deg demand flow temp, mostly on E7. The floor is 100mm concrete so a big lump to heat, flow temp never really exceeds 33 degs before a thermostat switches it off. Run time depends on outside temp etc. sometimes it goes off at 7am other times it runs until lunch time, controlled by thermostat. Then it's off until 0.30am. We have a GivEnergy All in one battery. We automate the charge % via home assistant based on solar forecast, so last night it charged to 64% on E7. Sunny day today, but only 4 degs currently and -4 last night. Total import 20kWh (UFH and battery from 38 to 64%) home usage so far 24kWh. Heat pump is off and battery being charged at 3.5kW. Unlikely to use much, if any high rate electric. Our typical running cost for all electricity at the moment (Feb) averaging at about £4, in Dec nearly twice that.

That's really impressive. My roof panels get lots of shade in the morning so very short productive day.

I am heating 195m2 bungalow (3kW max) and a summer house (1kW max). Why does a new build need 12kW? Unless 500m2? If it does you should really concentrate on insulation and airtightness, moderate PV and battery. When the sun isn't out no matter how much PV you have, the production is rubbish. Plus Dec and Jan when heat demand is highest you have the lowest yields from PV and shortest production time.

I would really look again at the heat pump set up your are considering. Sounds like overkill just install fan coils in the bedroom and run from a single heat pump. I'm using a 6kW one for heat, DHW and heating a summer house and it spends half its time off. PV winter yield was most important for me, so I did vertical panels and they are working out to be good. I don't export on purpose and as it's all self installed, so get zero money when I do. Why that high, look at a ToU tariff.

My output at this time last year with just 45 deg panels, wasn't worth talking about.

Octopus will have or need to have a charger they can control. At a time of their choosing they will suck energy out of the car. Later they will refill to a full charge.

Think that may be stretching. Better CoP possibly but not high CoP. The fundamental issue with phase change is it requires the the heat source to always be above phase change temperature, CoP can never be that good. So if phase change temp is 50 the heat source needs to be over 50 plus the dT, so about 58-60 throughout the heating cycle Cylinder heating, the heat source only needs to be hotter than the cylinder temperature, so heat temp ramps up slowly with the cylinder temperature, only when the cylinder is at full temp does the heat pump output get in to 58-60 range. So CoP will always be better with a cylinder. PV doesn't need to be integrated, if it's available it is is utilised if the heat pump is running. Just time DHW for the muddle if the day when PV is likely to be available. The heat losses is also a red hearing, most losses come from poorly installed and badly insulated piping on a cylinder or a phase change store for that matter, not the vessel it self. Measuring the shell temp of my C rated cylinder it's 21 degrees (50 degs inside) in a 21 deg room, so heat loss is next to zero. Even if it's loosing heat the MVHR extract captures it and it's distributed around the house.