sharpener

ATM it is exceptionally cold esp as it is still only November. Normally you would have a lot of spare heating capacity for most of the year. You can use this in different ways, for instance to limit the output during the evening peak by using noise reduction mode or setback. The difference between the 3 Cosy rates is I think much larger than the reduction in CoP from restricting the output in this way part of the time.

Original FIT scheme we signed up to cost £14k for just 3.7 kW but the rates on offer were so high the actual payback was under 7 years - which sounded good then and is still the gift that keeps on giving. I.e. it has paid for another 3.2 kW capacity plus the battery inverter system, and is now making a contribution to the cost of the HP. Well in a sense you can bc you can do all the laundry and run the dishwasher on cheap rates, which with e.g. Cosy is under 15p for 8 hours in every 24. It took some negotiating but the DNO finally agreed last year to an unlimited export capacity. So with a nameplate capacity of 6.9 kW we have exported about 5.3 MWh in the last 12 months and imported about 5.5 so we are more or less in that postition. That is the fly in our ointment, the Pylontecs stop discharging when the SoC gets down to 10% so effectively we only have 90% of the capacity we paid for. Then there is the little matter of the inverter/charger efficiency. When the battery current is at 70 amps everything gets quite warm and this accounts for losses which are possibly another 5% in each direction.

Housing Associations seem to be very active in putting in HPs for their tenants. Accounts for a large proportion of my installers business. And to judge by what is written on the Arotherm plus FB forum their contractors are amongst the worst for bodged installations, poor configuration and abysmal handovers (luckily was all OK in my case though).

Loans/2nd mortgages for home improvements are long established (think double glazing and conservatories). There are also dedicated finance schemes for solar panels (we receive the junk mail as they seem to be able to get our details from some public register). And for HPs as well, IIRC some installers have links on their web sites. So you don't actually have to have the capital. And plenty of ppl seem to blow what they do have on expensive holidays and weddings, it's largely a matter of personal choice.

Battery is now a sunk cost and depreciation not a consideration as it will probably outlast me! I cannot be doing with chopping and changing e.g. to milk Octopus Agile (even though I have an EV). So am on Cosy and charge battery to 100% every cheap period. This means I do not have to guess what the next day's PV will bring in order to leave enough room for it. (Havenwise might do a better job of this but is not compatible.) Also means we can do laundry/dishwasher at any time without penalty. With a buy price now 14.xx p and sell price at 15.00 I am still probably losing a bit bc of the round trip inefficiency but it is totally set and forget.

Don't quite understand where your 5p comes from, 125 - 75 - 20 = 30 not 5 which is an appreciable saving. But in the real world you might need to sacrifice more like 6 or 7 kWh in exports to get 5 kWh out of the battery again which is starting to make it a very close run thing.

Yes I get the depreciation calc which is often forgotten, but to arrive at the true cost of night-time usage you still have to add the cost of exports foregone which (with Octopus) is 15p/unit, and also divide that by the charge/discharge efficiency which might be as low as 0.8.

It's still not a costless option. If you can sell all you generate at 15p/unit then that is what it is costing you for domestic consumption of every kind.

Don't know why this is still a problem. When I worked in the wind turbine business 20 yrs ago it was already being introduced into the German Grid Code. I think there is a lot of good old mechanical inertia in a 10MW wind turbine. Yes but not practical for a whole-house system, we looked at this and the duct cross section was ?5x larger than just for MVHR so not practical if you want it to be virtually inaudible.

Yes, a few pence only. I elected to move off the deemed export regime when Octopus finally installed a smart meter as it was better to move to metered exports. (Including switching to Cosy and opening an export account they treated this as four separate transactions which took months. I raised a formal complaint about the time it was taking on 14 July 2024 and it was resolved - with £125 compensation - on 14 Nov.)

News of the scheme's death seem to have been greatly exaggerated - business as usual for the Grauniad. New press release says "residents will benefit from cool homes during a long, hot summer, without burning harmful fossil fuels" Well while there is still gas in the mix they cannot prevent AC from using fossil fuels so I am not sure encouraging its use is a good idea. Blocks of flats will be ruined by higgledy-piggledy installation of different AC units like they are in Korea. And the resulting heat put into the atmosphere will make it worse for everyone else, leading to an arms race. Nor should we be encouraging the use of resistive heating (Fischer should be banned from operating in the UK). Other than that the extension of the scheme is a good thing.

That would be a nightmare. I read enough posts where the original installer no longer wants to deal with a particular installation (or customer), or they have ceased trading, or the customer just wants to try someone else. If the HP is locked to a particular remote professional account what would happen then?

I have tried Havenwise and admire them for offering interfaces to a whole range of HPs. But I don't understand their business model as £50 p.a. per subscriber is not very much (but probably as much as the market will bear) and from my experience they seem to be willing to devote hours to potential customers who then drop out. (They always knew I had a multi-zone system and initially said they could support it, but couldn't.) On the subject of constancy, I found Zap-map useful but their latest upgrade isn't compatible with the latest OS on my phone. To judge by the (lack of) penetration of OpenTherm in domestic settings I wouldn't hold your breath... Have deliberately stayed away from eBusd and home automation, I fear it would become all-consuming. There are things I keep putting off fixing in the Node-Red routines in my Victron inverter bc there is quite a steep re-learning curve.

I fear it is not as simple as that. Yes with your Vaillant HP you can set the Room Temp Mod to Expanded and the Adaptive Heat Curve to Active then it will over time adapt the WC to the lowest effective value. But these are (a) not the factory defaults and (b) not even in the same part of the menu. This also presupposes that the "thermostat" aka SensoComfort controller is sited somewhere sensible and the installer has configured a whole host of other settings correctly. Some default settings e.g. min OAT shut-off temp are stupid, others like HW offset have no meaning at all for an HP. The dreadful manual assumes a lot of prior knowledge, and is not much better in the original German which I occasionally resort to. Hence the busy Arotherm plus FB forum has a small number of interesting queries but most are from ppl in housing association homes who have had little or no explanation at any level of how HP heating is meant to work or how to control it. And it is clear that HA installation contracts are awarded to the lowest bidder who has no more idea.

We have a 190 m^2 barn conversion on two floors. Original panels are 16 x 230W Upsolar with a wonderful pre-Dec 2011 indexed FIT price. Second tranche is 8 x 405W Longi for which we only get the 15p Octopus export rate. Eventually got DNO to allow unlimited inverter output and unlimited export capacity. Facing due South and with a total nameplate capacity of 6.9 kW we get over 7MWh/year (Devon). Of which 5MWh is exported and almost exactly matches total imports (house is not occupied full time.) Original panels have had no maintenance and the rain in Devon keeps them clean, no significant deterioration in output over 14 years. Battery was originally 2 x 3.55 kWh of Pylontech, quickly increased to 10.65 by adding an extra module. Would ideally add a fourth now that we have a 12kW HP but would mean moving entire stack. Is in rear lobby, not concerned about fire risk beyond getting an "all fires" extinguisher and putting it on the kitchen side of the dividing door. If you are worried then garage would be fine, self-heating will keep the batts warm in winter (we see peak cell temps about 8C above ambient), I would not put them outside in UK climate. @JohnMo's sizing guide is theoretically correct but I think the economics of guaranteeing no import at all during peak tariff periods are questionable, we can achieve this in autumn/spring but not depth of winter. Certainly not worth trying to average over more than 24 hours. We have Victron Multiplus 5kVA/4kW battery inverter (which is excellent if a little bit small, though it does give us whole-house backup) plus a 48V 60A MPPT for the newer panels, and for the others a Solax string inverter (also excellent) replacing the original 2011 Stecagrid one which failed earlier this year. If I were doing it all now I think GivEnergy AIO is worth considering and would go for a 6kW inverter with 15 kWh of batteries and as much solar PV as I could fit.