Dillsue

OK, but that's the shower that may need a pump, not a vented cylinder. We're open vented for CH and DHW and have a pump only on an indulgent en suite shower. Rest of house incl a second first floor shower isn't pumped.

Our house has a calculated heat loss of 8.5 kw at -2 but we put in a 7kw HP on the basis that it would be more efficient as the days of sub zero temps are few and far between and we could always run a fan heater or switch over to an LPG boiler if the HP couldn't cope. The HP has done 100% of the space heating since september and through the few cold snaps we've had recently with temps getting down to a degree or 2 below freezing. It worked very hard and guzzled eleccy whilst it was freezing but I'm hoping that the undersizing will pay efficiency dividends for the rest of the year?? An MCS umbrella/HP supplier wanted to sell us a 12kw unit!!

Why do vented cylinders need pumps? Other than the circulator in the boiler/HP there's no additional pump needed because the cylinder is vented??

Yes, assuming you'd charged the battery from solar. If you've charged the battery from grid eleccy then you need to deduct the unit cost of the energy in the battery from the import your offsetting or the 15p export rate. When weighing all this up don't forget that when the ASHP is using the most energy in winter your solar will be generating at its lowest. Unless you've got a massive array its likely your solar will make only a negligible saving on your ASHP running costs. PVGIS will give you a monthly forecast so you can see what you're likely to generate in the winter and compare it to forecast ASHP demand.

I'm not certain on this but there was a long discussion on net metering a while ago and I think the upshot was the net metering only happened in real time ie you had to be importing on one phase and exporting on another at the same time for them to cancel each other out. If you imported one minute and exported the the same the next minute then you wouldn't get net metering??

That's great and thanks for the detail......all seems logical so works for me

It's not sugar coating, it's just a balanced view. Constant slagging of the company/engineer could well cost them work and be the start of a bad reputation if the OP doesn't consider the possible flip side.

Agreed. If I can do what I'm hoping to do I won't be using a single kwh of PV but letting the neighbours have it all whilst racking up export credit:)

Perfect, thanks. Like you say it's very much what fits the individual

Work out average daily consumption for each month. Put 20 units of each day or whatever the average is if its less than 20, into a battery at 8.5p=£1.70/day cost for 20 units to use during peak rate. At peak rate of 32p/unit the 20 units used during peak time would have cost £6.40 so there's £4.70/day saving. December's saving would be £4.70x31=£145.70. With my usage I'd get that Nov-Feb, a bit less Mar and Oct and quite a bit less for the summer when the HP isn't running and the PV is going full chat. Total for me is just under £1100/yr. 30kwh of Fogstar batteries and 6kw solis inverter is just under £4k. I'm also hoping to be increasing PV export by exporting most of what we currently use by using the battery and off peak eleccy rather than the PV. Not as lucrative as the peak to off peak saving but it's a bit more in the savings pot. That's a rough estimate based on current Octopus Go rates and doesn't include charge/discharge losses. With 30kwh of batteries I think I'll be able to use more than 20kwh of off peak eleccy which will hopefully offset the system losses?? Figures pan out for me so just fine tuning things before taking the plunge

Didn't the company send in a quote for remedial work together with a service report??

If you use Excel it's straight forward to do room by room heat loss calcs. Work out the area of each surface x U value x temp diff and that's your heat loss. If a surface has an element with a differing U value ie a window or door, deduct that elements area from the main surface and work out that elements loss separately, if it has a differing U value. Add all the losses for each surface of the room, 4x walls+floor+ceiling, and youve got the room loss. Repeat for each room and you've got the whole house loss. Simples:) After that you need to account for ventilation losses and I can't remember how I calculated that without opening up my laptop which I haven't got access to!! Someone else will likely guide you on that??

I believe IOG needs an Octopus approved EV charger which we don't have so we're stuck with the basic Go. Assuming you do all those calculations automatically with a bespoke system then that level of automation is beyond where I want to go with this, but....... If the battery inverter supports it, I suppose I could configure the inverter to dump what's in the battery to export after we've gone to bed?? Any suggestions for inverters that might do this??

The battery inverter will be a separate inverter to the 2 x PV inverters so that's OK. The physical layout is problematic as both PV systems connect to consumer units at the back of the house whereas the ASHP that will be the biggest battery load is fed from a CU at the front by the DNO incomer. I'd need to get a chunky cable from the back to the front to take the PV to the Henley block. That's doable if this is a solution. So PV needs to be connected nearest DNO incomer then CT connected between PV connection and house load?? Battery connected anywhere on house side of CT?? Have you done this....be awesome if thats a solution??

If I charge the battery from PV then I'm charging at 15p/unit(export rate) rather than 8.5p/unit(off peak rate). If I power the house from PV rather than drawing off peak battery charge then it's the same....15p to self use PV and 8.5p to use the battery. I appreciate your description is the normal PV/battery set up but I'm just trying to see if it's possible to force export of all PV generation and use the battery until it's empty then use any available PV followed by the grid if there's no PV.