S2D2

I take it export payments are not an option? I'd be tempted to ignore the issue even if not, 3kWh/day is a reasonable input and everything will change if you switch to ASHP when the gas boiler dies, I seem to remember you thought it might not last much longer in another thread?

There's also nothing to stop you switching away to a different winter tariff once the boosted export is no longer relevant, I need to do some calcs on cosy to see if it's worth having a summer/winter tariff split.

Something I didn't achieve at 26.5 as the boiling point would have still been around 50°C, whoops. Probably a complete waste of time unless you know your hand pump can hit 30 then!

Personally, I think highly of them because they are leading the industry in reducing ROI on renewables. The tariffs are complicated and massively usage dependent, but can be modelled and produce benefit for the grid (shifting usage) and the consumer (decreased bills). Assuming PV lifetime of 25 years and battery 15 years the amortized cost of my install is £383/year. In the last four months it has saved me £253, the majority of which is since moving to Flux a month ago. That is a vast improvement from a few years ago before Octopus shook up the export rate market. I do believe a small battery is financially viable for many if installing a new system (not replacing inverter etc. in an old system) and Octopus are helping make that argument. The problem I see is very rapidly diminishing returns as battery install costs increase which leads to people getting stung when installers insist they will need 5kWh+ capacity. I have 2.8kWh usable capacity, any more would have made it financially unviable. @Bosi I've had no issue with the Solax hybrid but there isn't an easy way to schedule a force discharge if that's something that matters to you. I've had to do it through a python battery control program running on a raspberry pi.

Integrated garage for mine. As above I would expect them to manage excessive heat by reducing output rather than just catch fire. Either way unwanted behaviour so anywhere the air temp won't be too high for the passive heatsink. Follow manufacturer instructions for outside if needed, though any batteries would get too cold outside imo.

You also need the DNO response letter which your installer will also provide. If there is any outstanding balance, hold it back until they've provided these as they're very valuable documents now that export pays a sensible amount.

Thanks, I think I'd seen your recommendations on those before and tried to get one but there seemed to be a complete lack of stock of the cheaper electric pumps when I checked at the time, not sure why. The hand pump was probably not worth the hassle given the manufacturer has instructions for an install without pump. It'd be interesting to know the effect on performance to know whether the electric pump is worthwhile or not but the manufacturer doesn't provide any clues.

If it's the really rigid boards you can just score with a Stanley knife as deep as you can then flex the tile along the line and it will open up the cut and snap cleanly. I only did this with straight cuts though, not a c shape. Pliers help if it's just a small piece needs snapping off depending where the score line ends up on each tile, grip the waste piece as you will damage it.

Isn't the main concern with this approach ground gasses with the missing airtight layer on retrofits?

I had considered this but it's not responsive enough without a huge buffer to avoid import - it certainly couldn't guarantee no export. The start up from cold cycle takes about 15 mins where it runs things harder to get everything up to temperature, but even a change of temperature of 1 degree whilst running takes about 30 seconds to a minute to stabilise on the power graph, here's a change from the boost temperature during Flux cheap hours to the normal temperature: Note also three minutes later the temperature sensor must have dropped a degree and it modulates back up, so very fine control is not possible. Coarse modulation between 400-800W should be possible as a function of several variables but as the CoP stayed above three and I have a small battery I've never looked into it further as everything just works. It runs 2-5am on boost, then 5-13 on the morning Flux battery charge + PV, 13-16 on boost before turning off for the 16-19 peak period and back to normal operation with the last bit of battery after that. It also plays a little jingle when you change a setting (fine for larger time periods, but every second?) so that'd need locating and removing! No problem, good luck with your unit, I'd be interested in any performance figures but maybe we're a little late in the heating season now.

Yes I covered it in this thread: See the second page for my experiences and performance data, my aim was to offset as much gas usage as possible with a single DIY install unit. Let me know if you have any questions.

I fitted a 3.5kW unit, it will modulate down to 400W power draw before cycling (not specified on data sheet) and would be cycling an awful lot in a 12m room as that's still about 1600W heat output. One thing to remember is that the CoP will drop at the lowest temps so it will be sized for that. Often this is not specified in any detail on the datasheet either. Even still, that sounds overspecced. Ask to see their calculations and compare them to your own assumptions.

Some data on the install now that I have 32 days worth, for those interested: Modelled heat demand for that period was 1518kWh. This probably has a 10% error margin as it's just a multivariate regression of heating data before the ASHP went in Actual gas usage in that period minus estimated hot water usage was 475kWh. If anything the hot water estimate is likely to be pessimistic ASHP usage in that period was 200kWh So on average every 1kWh the ASHP used offset between 4.5 and 5.2kWh of gas 65-70% reduction in gas heating usage from the install of a single minisplit unit Assuming 90% boiler efficiency that gives a CoP estimate of 4.1-4.7, which compares well to the data sheet SCoP of 4.2 Minimum daily CoP estimate of 3.1, maximum of 6.1. There's been a good range of temperatures over this period to see behaviour over a real heating season, though obviously performance will be lower in winter months: Daily mean: 7.0°C Max: 10.9°C Min: 1.2°C. Lowest reading -4°C That's probably all the data I'll get for this heating season as we're getting into large solar gains from the conservatory which invalidates the heating model. Since moving to Octopus Flux everything the heat pump has used has effectively come from PV due to the import/export symmetry. So we've had ~1MWh of free heating from the solar panels, which sort of blows my mind. That's effectively paid back ~18% of the installed ASHP cost in one month. I couldn't be happier with the results of this little experiment, they've lined up perfectly with expectations. For balance, a few downsides of going with a cheap unit: The indoor unit housing is cheap and plasticy, but not offensively so Horizontal fan sweeping is manual only and no fancy occupier avoidance features like on the pricer brands Only the low fan speed is very quiet and the auto mode tends to have weird peaks of high fan speed when starting up etc. The outdoor unit has a slight vibration resonance in the housing, I have it well out the way so not an issue but I may add some damping pads at some point to eliminate it The Tuya wifi integration is a great little bonus and I have a control system written with the Python bindings for much finer control on scheduling which makes best use of the Flux tariff.

The usual advice is to take 10mm off the bottom of the doors otherwise the rooms with a closed door are a bit of a microclimate. This does transmit sound as it's an open path for air (exactly why you're doing it). Following with interest for an ingenious workaround as I don't see a way around it without ducting both intake and extract to each room which is not practical.

A small battery helps to make the most of this tariff, but it is entirely usage dependent as to whether it's financially worthwhile. As an update, my total billed electric cost (excluding standing charges) since switching to Flux 3 weeks ago is £0.78. Not bad at all considering I've also been running the heat pump which has offset around £63 of gas usage over the same period. As heating demand disappears I'm realistically going to have to change my direct debit to ~£0 over the summer as the export will easily cover hot water and standing charges. It's a great summer tariff.

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.