S2D2

It can be clearer to think about it in terms of price if you have a reasonable export tariff. If you can export 1kWh solar for 15p and add 1kWh of heat to the tank with an ASHP for ~11p (33p/CoP of 3) then worst case (no solar) you are still 4p/kWh better off. That only gets better if you happen to have excess solar during the ASHP schedule, as the ASHP will then add 1kWh of heat for 5p (15p missed export/CoP of 3). No need to change the schedule regularly, just set it for when you're most likely to have excess. Different export rates will change the calculations, it's a fine balance at the moment with actual reasonable export rates starting to tip the balance. I hope that's clear!

Yes, the rates are essentially symmetric once losses are factored in. That's the main attraction of this tariff I think, the 2-5am charge at 19p is essentially shifted export which you got 21p for some other day (it doesn't matter which, so true seasonal shifting). It's been working perfectly for me so far, the battery ticks along from 5am and lasts until it starts being charged by the solar again. Export covers that initial charge and the very small amount of other import. This includes running the heat pump so the PV is covering ~70% of the heating demand too with the improved weather. Credit to Octopus for this tariff, it really incentivises renewables. As the heating demand reduces the forced discharge will probably become more important, the one thing to avoid is charging up 15:00-16:00 at 32p then having charge left in the battery at 2am meaning you can't charge at 19p. I've had one day where there was a tiny bit left over so may look again at the forced discharge. Though losses are a smidge higher it's still essentially symmetrical to force discharge at 35p then just import at 32p if needed.

Forecasting and control systems are indeed the reasons to be gathering house data. I started logging internal climate and smart meter data a long time ago. When I came to make an investment decision on PV and A2A ASHP, the data was already available to calculate the real life ROI bespoke to my house and installed system. It also provides the required data for evaluating the performance of a time of use tariff. Now I've bundled that historic climate data into a heating demand forecast model which coupled with live smart meter and climate data drives the ASHP control system. That will never be a fad, it will continue, year on year, to increase the yield of the investment by 75%. Priorities for me are ease of use, minimal boilerplate and active maintenance. I haven't seen better than a Raspberry Pi running InfluxDB with Grafana. InfluxDB's Python bindings mean you can easily connect pretty much any data sources up to it with a few lines of Python then configure what you want to see with a few clicks in Grafana. There are caveats to any of the proposed solutions including mine, but Python is there to pick up the slack if you need something not supported, e.g. average time of day binned data. Finally, storage for this sort of data is cheap. Log it all, often.

Thanks @Nick Thomas @Ronski, I just wondered if a phone chase was required but I've just checked and the export has gone over now too so all good. I've also gone for two charge periods for the battery, that gives the PV a chance to charge it for effectively 21p/kWh (missed export) rather than the fall back 32p standard rate. I've skipped the force discharge for now as I only have a small battery so it gets used between 7pm and 2am.

Any luck with the export for either of you? I was also switched over the same day as applying but export still showing as outgoing. I guess it'll be backdated anyway as it's a linked tariff? Battery happily running the house since 5am on cheap energy, I just need to play around with my ASHP control system to see if I can shift demand into this period too. Turning it off in the peak period worked okay, though the Octopus saver session pushed it to half 7 so the gas kicked in.

Having just done exactly this, I have to agree it's an easy win. <£700 for DIY unit and ancilliaries, installed in a day and currently offsetting ~60% of my gas heating use at a CoP of around 3.7. Gas boiler kicking in for HW and the parts of the house it doesn't reach. Heat pump technology doesn't need to be expensive to have a massive impact.

How daft they haven't done existing customers that have already submitted their forms and registered interest but oh well, I'll apply tomorrow. Thanks for the update.

Strange that they've opened up sign ups, I registered interest weeks ago and have heard nothing!

Yes it was put in as an experiment really in ASHP's in general and A2W vs A2A. Some early notes: The product delivered was actually eiQ-12WMINV-V4, though the user guide linked on the store page is V3. I can't see any obvious differences other than a couple I came across installing. The V4 manual states 100mm clearance is needed above the internal unit whereas the V3 manual states 250mm. Also the V4 data sheet shows a minimum room size which the V3 does not. I've uploaded the V3 installation manual for interest as it's not available on the site I used a 65mm diamond tip core drill with an SDS plus drill with safety clutch. The clutch kicked in when the brick core separated along a mortar join as i reached the internal hole from outside, up a ladder, so I wouldn't recommend drilling without a safety clutch. The pipes, wire and drain actually fit through a 50mm drainpipe which I used as a sleeve inside the 65mm hole, packed externally with strips of pipe insulation and siliconed in. The manual mentions the sleeve and packing but none are supplied with the unit There is very little space behind the internal unit for the pipes, drain and wire so avoiding a tight bend on the coolant pipes means the bottom of my unit sits several mm proud of the wall. It may be possible to improve this by trimming insulation as the unit can be pushed flush with force or it may just be the design of the bracket, I'm not sure. The internal unit is charged, I presume with nitrogen, so once the internal work is complete you can be confident there isn't a leak as there is a release of pressure when the plastic pipe caps are removed You have to use the supplied 3m pipe extension even if not required as it has two female ends, converting the internal unit's male end I used a hand vacuum pump as per this video: https://www.youtube.com/watch?v=2RDfAkmDId0 - The unit can be installed without a vacuum pump and my hand pump only reached -26.5 rather than -30 so I did one flush of coolant as described in the installation manual. I have no idea how much better this is than just doing the three flushes without vacuuming at all as per the instructions so it can probably be skipped The unit seems to be able to modulate down to 400W input from it's nominal 1.2kW then starts cycling on/off to reach lower gains. I've been running it between 400-800W so far The wifi module uses the Tuya smart app, which has a Python library here: https://pypi.org/project/tinytuya/ - Some customisation is needed for the data registers which I can upload if required but this allows control of the unit via Python, so I intend to put together a more intelligent control system using this. The input power seems to be some function of set temperature and difference between set temperature and current temperature so combined with tracking power draw via a smart plug this could be adjusted to divert solar export without any expensive hardware and with a high CoP. This needs to be coupled with heat requirement modelling to prevent overheating. Hopefully that helps those interested. Installation Manual V3.pdf

I have now fitted this unit so if anyone has any queries drop them in here and I'll try to provide answers. I'll do an update once I have some usage figures too.

It is oddly vague, but based on how SCOP is calculated and the balance point being specified as -7 I would expect 4.2 (stated in manual, 4.1 on product page...) to be pretty close to the average performance short of them straight up making up figures. All heat pumps have reduced COP as the temperature differential increases so I guess it's just referencing that? It's not like A2W where there are lots of variables affecting this, it's a closed system so should perform as expected? I believe @Radian's have a SCOP of 5.15 so the real life performance staying close to this at low temperatures is encouraging. I was almost convinced, then Octopus went and added 50% to export rates with Flux so a bit more thinking needed.

Early modelling suggests I'd have a 31% higher financial yield from my system per year on this tariff compared to standard variable and outgoing export, a nice little upgrade. Based on 30 min smart meter and PVGIS data, maybe 25% in reality based on the limited data I have so far. Nice to see a PV+Battery targeted tariff at last. Massively system and usage dependent of course, most of the benefit for me comes from the increased export rate.

The FAQs say prices change when the standard variable prices change, so presumably it's like Cosy where it's +/-some percent of the standard variable but the numbers didn't come out nicely enough to say it. I've been put off cheap overnight tariffs due to losing the outgoing export rate, so this looks well suited to my setup where the battery isn't large enough to shift everything to overnight charging but could get us through the peak rate window.

Looks good, it removes the need to forecast PV generation when charging battery overnight as the daytime export rate is matched. Time to run some calcs on how much it could save.

I notice the old versions of this model used to have higher power options (with an f-gas coolant) so 400g is presumably the upper limit set by some regulation. Payback if as advertised is around one year with the PV, I'm tempted.

400g charge apparently, so bigger than a fridge freezer. No joins allowed internally, but still not worth the risk you reckon?

I did get confused by all the other units that were easy fit but required an fgas engineer. As far as I can tell the difference with this one is the use of R290 which is not covered by fgas. Indeed having seen the installation manual now the install without a vacuum pump just floods the pipe with a bit of coolant which you then bleed out to the atmosphere. Apparently it's not much worse than CO2, none of the fgas nasties. Still highly flammable mind. Would the flushing install method reduce the CoP due to a tiny bit of air still in the system or would it just limit peak power output a bit?

I was assuming based on this being sold as "including everything you need" that one side is pre-gassed and one side is evacuated then the two mix when you lock the connector in. I'm struggling to find the install instructions for V3 though so I could be way off the mark. Thanks for the feedback both, it sounds like it lines up with expectations which is encouraging!

Thanks both, I read this blog with great interest at the time and now that you don't even need a vacuum pump with the DIY model I'm considering jumping in. I guess the newer electriQ models still don't give you any sort of CoP estimate @Jenki? Do the Daikens @Radian? I have a load of smart meter data so could estimate it once installed, I just wondered if anyone else had done the same before I trust their claim of 4.1 CoP when there's so many A2W installs falling short of the manufacturer's claim atm, albeit not all the manufacturer's fault.

I think current installs are Daikin, based on the prize draw t&C's: > The prize will be the installation of a Daikin heat pump (model EDLA-e or EDLA HP)

Does anyone have any experience/thoughts on the electriQ heat pump which claims to be suitable for DIY install: https://www.electriq.co.uk/p/eiq-12wminv/electriq-12000-btu-panasonic-powered-smart-wall-mounted-split-air-conditioner-with-heat-pump-5-meters-pipe-kit-and >Does not require installation by an F-Gas registered engineer or specialist equipment for typical installation – everything you need is supplied. With a SCoP of 4.1 it's a tempting alternative to just exporting the excess solar and burning gas to heat the house. Provided the SCoP stays above 3 in reality that is, I'm unsure how much the data sheets can be trusted on this?

Is it? I thought it was around 15p/kWh? https://www.energy-stats.uk/wholesale-energy-pricing/ https://www.epexspot.com/en/market-data?market_area=GB&trading_date=2023-02-09&delivery_date=2023-02-10&underlying_year=&modality=Auction&sub_modality=DayAhead&product=30&data_mode=table&period=

This is the max, it's mostly the old usb external 2.5" HDD, 5W total when this is spinning and about 2W the majority of the time just for the Pi.

I've probably just been lucky, and I don't go near any sort of video storage on the card that would really hammer it. It was swapped for a larger capacity after six years but until that point had managed it's own failures very well, nothing I log ever had an I/o error. Any data I actually care about is covered by Syncthing, the rest just isn't important. Couple of hours to recover everything makes setting up anything more robust a bit pointless as it wouldn't repay itself. If the failures were annual though yes, a better system would be needed. I agree it's a price to performance trade off, if you get to the point where your system needs an i5 you're not going to be spending £35 on the finished article and drawing 5W. The laptop is a good step up price/performance wise if required, but personally I still wouldn't touch anything mission-critical with it, depending on your definition of that.

Rpi3 here going seven years without skipping a beat, never had an SD card failure. Does everything I ask of it and all for <5W. Now if only the zero w's were in stock more often...