John Snow

Winter is coming……my installation was completed I April and I have been on Flux happily but am looking to the future.

I try and maximise my solar and only charge my batteries overnight when the forecast is for our typical summer weather using Settings, Timed Charge which raises my SoC% and with cloud cover I get through the 24 hours with minimal grid input. I have a strong feeling this will not work in the dark days ahead, ideally Cosy looks good for me but no Heat Pump.
So it occurred that if I stay with Flux would it be possible to ‘reserve’ my battery power for the ‘high’ grid rate for 4-7pm? Maybe by Settings, Battery Options and set reserve to 50,60,70% or whatever until 15.45 then raise it back to Usable 96%? Anyone any experience?

As an aside I have just set up HA on Pie and got it running GivEnergy but no Octopus integration (this is all very new to me I am a know nothing but Google it type of person), this may be an alternative way forward?

Thanks for your time in answering.

I'm planning to switch back to Agile late September, top up any meagre PV generation when agile rates are low and live off the batteries.

These integrations in Homeassistant should help.
https://github.com/BottlecapDave/HomeAssistant-OctopusEnergy/ - links to Octopus API to pull rates and can determine the best rate windows within a time range. Eg tell it you want 3 hours of charge between 8pm and 8am and it will determine the 6 cheapest slots that can then be used to trigger grid charge on the inverter.

https://github.com/oziee/ha-solcast-solar - gives a PV generation forecast for tomorrow, helps you determine how much grid top up is required.

https://github.com/britkat1980/giv_tcp - assume you have this already, integration to the inverter.

This one is more advanced
https://github.com/springfall2008/batpred - uses above to automate charge and discharge based on forecasted consumption, uses historic usage to predict forward.

Finally got my flux export in place (only waited 2 months for it…), so been pretty much running grid free for most of the summer. I’ve got a 10.4kW array East/West so am able to fully charge my batteries pretty much every day from solar. Not done any grid charging of the battery at all.

For the winter I was thinking about Cosy as we have an ASHP but am now thinking more of going onto Octopus Tracker. Cheaper rates and it enables me to run the heat pump 24x7 without worrying about incurring peak rate charges when the batteries run out. Been looking at the historical graphs and even though Tracker rates can go up, on average they’re cheaper than Agile or Cosy.

I think it all depends on how much you use in a day. If you have an EV then go or intelligent are a given in the months you’re not generating excess.

Thanks for the replies, can anyone comment on Paragraph 3 ‘reserving battery’ …. charge up on night rate and preserve to evening high rate rather than letting battery power deplete before 16:00?

Like Geoffreycoan above I've only just got Flux export (4 months after installation!). Apart from the initial battery set up/calibration (x2 as we had a firmware update shortly after) we've barely used any grid; maybe 2-3 kWh a month. That's a 5.5kW array facing SSE and no shading.

Having only just got on Flux export I'm just hoping we manage to 'bank' enough to top up our shortfall this winter. I'd need about 400kWh between now and end of October to achieve this. Perhaps that's optimistic, as I've done some calculations based on a friend's smaller system and he gave me his 7 year average figures month by month. Even so 300kWh+ seems feasible and very much worst case would be 200kWh.

We are low users at around 200kWh per month so maybe it's not worth us changing tariff, especially as we're only just on it now? I figure that once we get to a stage where I need to charge the battery during cheap rate then I may as well just set this up and if it's a good solar day then that will just mean we export more at a pretty much similar p/kWh (ignoring losses). Worst case I reckon we'd be about 200kWh short over the winter which will cost about £40 using the cheap Flux rate to charge overnight. Once we're into March we'll be exporting more than we use again, based on my friend's system.

I'm never sure if I just over simplify the whole thing, or whether some just enjoy the 'hobby' of changing tariffs/settings on a daily basis? Is is just because we have a large system compared to our low usage needs as it doesn't seem worth the bother? Next year I expect to be well in profit based on what we've generated in under 4 months (exported nearly 80% of our annual usage and run the house for free), I just need Flux, or something similar to remain available for the foreseeable future.

i have a very simple model, correct me if it's wrong. When on flux, it's very evident that the day time export gives you more than the lowest import + VAT of 5% .

So, i charge my battery full 80% between 2 and 5 and then let the export run upto 40% battery level between 4 and 7. This way i don't have to worry about solar forecast or any unexpected early morning high usage like using oven to bake something for bfast !

deepanshus I guess that's close enough though it does assume 100% efficiency of charging the battery and releasing the energy which isn't the case in practice. I don't know what the figures are though, but I suspect overall you'll be slightly down due to them. We're exporting during peak rate at the moment as the battery is usually full by mid morning, but I just treat it as 1:1 in terms of kWh cost (so we'll get more than my simple maths works out based on the whole day's export kWh figure).

In winter I plan to charge to 100% during cheap rate and that would get us through until the next 2am cheap rate except on very rare days (9.5kWh battery, 7kWh daily use typically). On rare 'heavy use' days we might start to draw from the grid in the evening, but that will be at the standard rate. If it's a good solar day then we'll export some during the standard rate period once the battery has topped back up after any drop from 5am until sunrise/generation starts again. Kind of 'fit and forget' for me. I think drawing anything at peak rate will be so rare that it's not worth worrying about (maybe Christmas Day judging by last year's highest daily use).

Spencers in your personal case of a battery being more than your daily use, flux or anything else with a cheap overnight rate that you can fill the battery in is perfect. I have gen 1 inverters so max charge rate is 2.6kw so on the 9.5 battery it's tight if it's completely empty.

But we go through about 10kW a day in summer and another 10-20 a day in winter when the heat pump is on. For us we will have to grid draw in the day in winter and want to avoid the peak rate premium.

deepanshus Your model doesn't take account of the energy conversion power loss which can be 5-20% depending on who you read. I personally don't think it's worth it to charge overnight to export earlier in the day on flux. If you can preserve it to the peak rate (eg very little draw in the day) then yes, but otherwise I think the benefit of flux cheap rate charge and day rate discharge is marginal / likely to be negative

Spencers can I ask what size (kw)is your PV array? Also the size of your heat pump and is it an older house. I’ve got a 9.5kwh GE battery fed by 4kw array (Gen 2 3.68 inv) and we use about 9-10 kWh in summer for the house and to charge our Sunamp heat battery. Considering ASHP as we can get a £9k grant herein Scottish Borders but worried how much EXTRA winter electricity we’d need . It’s a 4 bed Victorian end terrace cottage( no easy way of insulating the wall cavities ( lath and plaster) Currently on oil space heating ( colder months only now as the Sunamp cut out our water heating by oil since May when it was installed.
All the best

Bill G

billG Sorry we don't have a heat pump, we have a gas powered combi boiler (I've replaced every radiator over the years and properly balanced it all). Maybe mixed me up with Geoffreycoan?

Our system is 5.5kW array, Gen 2 5kW inverter and 9.5kWh battery.

geoffreycoan I can understand yours being tight with a 3 hour window and a Gen 1 inverter. We nearly got a Gen 1, but someone told me the difference just before it was ordered so I made the change for Gen 2. It helps with not drawing from the grid too if a few appliances are on at the same time. My wife has been known to put the kettle, microwave and oven on at the same time though...at least usually only for a short time!

Spencers yeah the gen 1 inverters are a bit annoying, at least they're the 5kW ones (we have two as there's a 10.4kW array). It wasn't specified on the bill of materials and I only realised there was a gen 2 after installation. I guess the installers were using up their stock. In practice it hasn't really been an issue to date. We were on a fixed rate tariff for the end of last winter and we've not needed to charge the battery overnight at all. It's only really a consideration as we look towards next winter and what our strategy and tariff will be. I have a 9.5 and a 5.2 battery (one on each inverter) but they only last the summer nights so won't be at all sufficient for winter.

billG you need to get a proper heat loss survey done on the house and from there the company can I give you an estimate of what the system design would be, radiators to change (usually need bigger rads as the ASHP flow temperature is lower) and the running costs.

We have a fairly large house that was reasonably well insulated, nothing special. We had oil fired boiler and radiators throughout but the oil tank started leaking and we couldn't site the replacement in the same place due to the latest building regulations - 1.5m from buildings and sheds, 760mm from boundary fences. At the time we got the RHI grant which over the 7 years it means the system will have only cost about £2500, the cost of the new oil tank.
In terms of running costs, just on electricity it costs about same as the oil to run over the last year. Of course some of that electricity now comes from solar whereas I can't make my own oil!

billG
Maybe get a crude estimate based on how much oil you use?
Although after we installed a couple of aircon units to do the bulk of our heating be warned that going from oil use would most likely overestimate it.

PV forecast for the next 7 days is below my threshold for export < 20kWh. Getting close to switching back to agile with a "charge to 100% when import < 17p" approach.

Anyone switched from flux, or do you think we still have some export days before winter comes?

geoffreycoan , yes i agree, the slight negative margin is always possible but thats the one to have peace of mind :-) that whatever happens, by 4PM i will have 100% so that i can export upto 40% SOC.

Arg0t Anyone switched from flux, or do you think we still have some export days before winter comes?

I’ve got a decent sized (10.4kW) array so am still seeing 20-45kW a day generation over the last couple of weeks. I’m using about 13-18kW a day so still a net exporter and (up to yesterday when one of my batteries stopped working) was still doing a force export in the Flux peak period.

Looking at my spreadsheet I didn’t put the ASHP heating on until 21st November last year, so I’ve probably got a couple more months to go. Will need to re-run the numbers about what tariff to change to (Daily tracker or Cosy) or remain on Flux and charge the battery in the overnight offpeak and afternoon to avoid any Flux peak period import.

geoffreycoan

I'm trending under 20kWh on a 6.2kW array, we use 15 to 21 kW a day. With flux I'm limited to 12.3kW a day on the overnight low rate due to the 3.6kW battery charge limit (3.6 + 0.5 base load = 4.1 x 3 hours).

I could hold on flux until solar drops below 9kWh a day, and cover all import at the lower rate, but the benefit of the high flux export rate starts to reduce. Do not see many remaining opportunities to export in my situation, cosy is out as no ASHP, leaving return to Agile or Tracker.
Agile is trending around 2p a unit lower than tracker but potential I will not cover get that rate over 5 hours a day, to cover the top end of our usage.
Tracker would effectively remove the need to charge from grid, live off grid and not expect PV to generate more than current usage. No losses from charge/discharge as batteries are pretty much idle. Downside is tracker has a 9-month cool off, use it this year and then locked out for next winter.

Think I've just talked myself into waiting two weeks, see if PV is trending near to my 9kWh a day threshold and switch to tracker.

I'm planning on moving back to Go Tariff as I don't export anything during the winter. It's all about shifting my battery charge and high drain items to overnight and then let the battery take the load during the cloudy days. Worked very well for me last year.

We're generating high 20s (5.5kW array) and exporting 18-20kWh a day at the moment. I think I'll just stay on Flux as worst case in winter I'll just charge the 9.5kWh battery during cheap rate and that's enough to see us through to the next day (7kWh typical daily use in winter). If it's sunny, then we might top the battery up or even export a bit.

No EV so I don't think any other tariffs worth switching to, plus we've only just got on Flux/export so I'm hoping to 'bank' about 300-350kWh to cover the estimated shortfall in Dec/January. We might just about break even during November and February according to the PGIS estimated (which we've exceeded every month since our May installation).

Arg0t Do not see many remaining opportunities to export in my situation, cosy is out as no ASHP, leaving return to Agile or Tracker.
Agile is trending around 2p a unit lower than tracker but potential I will not cover get that rate over 5 hours a day, to cover the top end of our usage.
Tracker would effectively remove the need to charge from grid, live off grid and not expect PV to generate more than current usage. No losses from charge/discharge as batteries are pretty much idle. Downside is tracker has a 9-month cool off, use it this year and then locked out for next winter.

I have an ASHP so Cosy is an option for me, but no EV so I can’t have Go. I too don’t see much opportunities for export during the winter; our system was installed 7th Jan this year and I think it was something like April before the battery first reached 100% full ☹️

The heat pump runs at a lower flow temperature than oil or gas central heating so I need to run it for most of the day, or all afternoon and evening at a minimum. Although Cosy gives some cheap periods and I could charge the batteries up during those periods to avoid paying premium rate, I’m undecided about the practicality of being able to do this.
Agile for me would just make the charge & discharge scheduling an order of magnitude more complex and it just seems likely that I would end up frequently having to run the heating in the peak price periods. So although Tracker is more expensive, when I last looked tracker was cheaper than the agile average rate so it takes away the risk of high price periods. If the electricity is particularly cheap one day I could charge the batteries, but otherwise I’d just not bother to do so.

The 9 month lock-out for tracker is a pain, agree. Looking at my heat pump meter readings for the last year the peak I need to get through is December, January and February, and ideally March as well. So could go onto Tracker for December-February each year and Flux or Cosy for March.
More spreadsheet stuff!

geoffreycoan I don't have an EV but spent all of last winter on Go, charging up the battery overnight and using any solar (what little there was) in the day. Octopus didn't check if I actually had an EV when signing up, just had to declare I had one...

Any of you good people know if a 6kw air2air heat pump (or air conditioner) would be eligible for the Cosy tariff. It kept our open plan 2 bed bungalow nice and cosy last winter - keeping us nice and cool now! I haven't contacted Octopus yet as I'm waiting for the sun to make the flux tariff less economical. Come October/November, when the air2air heating needs to go on, I could do with 2 bites of the cherry from Cosy as the gen1 inverter will only charge 75% of the 9.5kw battery in the night time window.
Thanks in advance.

TimHutchings According to the Cosy website it says you must have a heat pump, ground or air, and you may have to supply the MCS certificate https://octopus.energy/smart/cosy-octopus/

Doesn’t seem to distinguish between water or air heat pumps, so yes, you can apply for it

geoffreycoan Thanks for that. I'll look into Cosy more in a month or so as the sun reduces and it gets colder. I don't have an MCS certificate, though it was fitted by an authorised Mitsubishi Electric installer. If they won't les me have Cosy I'll probably stick with Flux.
Flux for me has been great this year. I've been paid over £650 since I went on flux early April, and I'm rather hoping with this and the remaining exporting this year, I'll not only cover all electric import use and standing charge, but also my gas (combi boiler - now hot water only) and standing charge.
Energy neutral was the plan, and it's looking like I may even turn a small profit too.

TimHutchings Great result. It says you “may” have to provide an MCS certificate, other proof of installation would probably be OK you’d think.

Sounds like a great result on flux for you. I only got my export setup on 10th August so my earnings are lower, about £140 to date which’ll help but not get me through the winter. I was aiming for energy neutral in the summer but Flux is definitely improving on that.
I’m not sure even with the Cosy double-dip that I’ll be able to fill my batteries sufficient to get through every winters day with the ASHP. Was looking at some of the daily usage figures and remembering the £20 a day ouch. We’ll see

geoffreycoan I had my panels fitted in October 22 and was waiting for a gen2 5kw to come into the country. Because of the Chinese lockdowns, the delivery date for the gen2 kept getting delayed and in November was told it was delayed again till February, so I bit the bullet and had them install a gen1. I know you have 2 x gen1 inverters and like you find the 2.6kw annoying on the charge and discharge rates, but not a deal breaker.
Remainder of November and December I was testing the gas heating usage and costs against the air conditioner heating costs. Because it has a COP of 4.07 and an SCOP of 4.6 in the uk, it definitely worked out cheaper to use the air conditioner for heating, rather than gas, and that was without any help from solar!
Overall very pleased with the setup apart from my wife complaining that the air blowing around creates more dust! 😂

We're still exporting over 20 kWh per day although Sept so far has been exceptional. Within the next few weeks we'll be looking at switching to Intelligent Octopus as we have an EV and can use low off-peak rate for charging the house batteries (19kwh) - we don't use the car regularly but even so, we can still take advantage of the IO rates.

We've also had A2A fitted and estimate anything from 10-15 kWh per day through winter. Even in the worst days we get around 4kwh from solar, so that plus the batteries should keep us going most of the time without dipping into peak rates. We've exported just over 3.5MW so far this year and Flux rates have paid very nicely - if we can make IO work over winter as planned, we might actually be energy cost neutral, or even a small profit. It took a chunk of investment but currently payback is decent at around 8 years. I guess it all depends on how long tariffs like Flux and IO remain available, but so far so good.

sponev Do you have a split system? We have a single 6kw A2A pump which because we have open plan lounge, dining and kitchen, works pretty well. The position it's sited, also blows air through to the hallway and into the bathroom (as long as we leave the door open a bit). Both bedrooms also are warmed sufficiently although a little cooler than the living area, and occasionally on those really cold nights supplemented with a low wattage heater for half an hour before bed.
Generally in the summer we consume around 5kw a day of electric and around 7kw a day in the winter being in doors more, with longer nights and more lights. The A2A heating added a further 7kw per day through January. We averaged 5.35kw pd solar generation through Jan, from a 5.46kw solar array, 7 panels facing south and 6 on the east roof. We have some shading from a couple of trees in others gardens in the winter too, so fairly pleased with the generation.
Overall, the solar system has worked without fault since installation 🤞, and the A2A heat pump means we now only use around 5kw of gas per day summer and winter.

TimHutchings We have 5 indoor units and two external units (Daikin) - split systems with some spare ports, although looking like we won't need those. It was a bit more capital cost but two units allowed us to eliminate any internal trunking, no condensate pumps and better flexibility for localised heating/cooling. We haven't used them in earnest for heating yet but they've been excellent for cooling on days like today. Also seem to be very efficient on the cooling cycle. Certainly very happy so far.

sponev You'll be pleased with the heating too! I've found that without temperatures dropping much below freezing, our 6kw Mitsubishi runs at about 400-500w once the area is up to temperature. Took a bit of getting used to as A2A don't switch off and on like normal central heating but constantly ebb and flow to keep the right temperature. They also use quite a bit more power when outside temperatures drop well below freezing as the condenser unit outside keeps defrosting every half hour or so.
Overall though, really pleased with it!

TimHutchings sponev

Thanks for your input. I was really interested in your A2A info and am contemplating doing the same.

Perhaps you could share and update how your systems are performing now we are into Oct/Nov & Dec, usability, kWh use, comfort, pros & cons?

Thanks again.

I switched back to Agile late September, decided that move to tracker was not required.

Averages to 10.8p a kWh for import over the 3 months, factoring in the export income plus the Octoplus income nets out to below 0. Install in March to date, even with export MPAN being delayed to June, I'm ahead by £94. System returning £1573 on the £18800 invest, kWh consumed at the Octopus Flexible rate + credit generated.

Flux Mid March to Mid Sept
Agile with Fixed export Mid Sept to Mid March

Watcher we have some decent experience with the units now and overall very pleased. They are very responsive and heat quickly. Also flexible in that you can spot heat rather than wasting a lot of energy heating rooms which are not in use.

They are comfortable although there is air movement initially when heating a room from cold. However ours also have a quiet setting which is hardly noticeable. We've been running at anything between 10 - 20kwh per day depending on the outside temp, actually less than this before it started getting colder.

One thing to note is that there is a point where temps drop to freezing or below and COP drops away when our gas boiler is actually cheaper to run. This is when the batteries are depleted and we have to use grid at peak rates. So there have been five days so far this year when we've run the boiler for the last few hours of the day. I stress that this is purely financial and not that the A2A won't handle it. This type of (infrequent) hybrid running is least cost if you've retained your boiler.

If you have good battery storage (we have 19kwh) and a cheap overnight tariff, A2A is a very good option. You will also have to make provision for hot water - we still use gas but researching a heat pump cylinder. We also changed our energy sapping tumble dryer for s heat pump model which has been very well worthwhile.

Very helpful feedback, thank you.
We bought and renovated our 2 bed semi-bungalow, we just swopped an ancient oil system (off main gas grid) with 47kg calor bottles and a combi boiler and installed 4.75 solar with 2 x 5.2 batteries. Working and combining well together. I don’t feel I am ready to go solely down the heat pump route just yet so the A2A hybrid system seems a good halfway house utilising the scop factors during ‘shoulder’ periods of the year (minimising gas) along with cooling availability in the summer.
At the sub zero times when using gas to heat your house does the A2A then substantially reduce its electric use as it does not have to contribute as much heat or does the defrosting period hold costs higher regardless?
Cheers.

Watcher with a 2 bed you may manage with just a couple of units, so lower installation and running costs. When we do use the boiler (infrequent) we just switch the A2A off, one of the advantages is the ability to do this unlike with A2W which typically needs to be kept running. One of the key factors is being able to charge the batteries on a cheap overnight EV tariff; without that, the savings are much less pronounced.

Watcher we've been using it since constantly since January for heating all this year when needed. When we moved into this 2 bed bungalow 2 years ago, I put in a new combi boiler, for heating and hot water. Before we moved I had thought about putting in solar and battery, and after moving in April 22, decided rather than have money sitting in the bank earning nothing, we would go for solar and battery, especially since energy prices started shooting up - this was June or July. I had a local company quote, and they suggested a 3.5kw inverter and 5.6kw battery. However, I decided to go with as many solar panels as I could get on my east and south roof (13 - 5.46kw array) and a 5kw inverter and a 9.5kw battery. I was told it was oversized for our needs but went with it anyway at £10,300.
While we were waiting for it to be installed, I then started looking at A2A as a way of using some of the surplus electric or maybe an EV. EVs were just too expensive for the mileage we now do, so A2A looked interesting. On reading more and with the open plan layout we now have after taking a kitchen wall down, one decent unit seemed like it would work and heat the whole bungalow. Got several quotes and chose a Mitsubishi 6kw AP A2A at £1,875 which again I was told was oversize as a 5kw would probably do, but chose the 6kw so as no to overstress the 5kw and it was only £100 more. Of course it would also give us the benefit of nice cool air in the summer when needed.
Anyhow, both the solar and battery and the air con unit were fitted in November last year, and I spent the next 6 weeks till the end of the year testing the gas heating against the A2A to see which worked out the most economical and most comfortable. Hot water is still provided by the combi which covers showers, basins and sinks, but all cooking is electric.
The magic of the A2A with an SCOP of 4.6, pumping out 4.6kw of heat for every 1kw of energy used, meant that as long as the price of gas was no more than 4.6 times cheaper than lecky, A2A had to be cheaper. And of course any solar produced in the winter was an added bonus! So from January we just used A2A for heating, and the gas combi for hot water.
Then in March, Octopus introduced flux and we moved onto that tariff. Fortunately my oversized solar system then became a bonus.
We've made around £770 exporting this year after covering all our electric from solar. This has covered all standing charges, both gas and electric, and all our gas usage, and any electric imports we've imported during the 4 dark months. There's a very good chance we'll be £100 or so in profit by year end.
Energy neutral is a lovely feeling, and even better to know that the distressed purchase of Energy is no more! 😂🍾