@toodles 13.5kWh here, but no ASHP. 27kWh would be ample for me (as would 13.5kWh if Mrsmk13 didn't insist on a greenhouse heater. At least this year it's controlled via HomeAssistant).

@toodles @ianmk13 there is software available (My Energy Optimiser) that analyses your usage, solar generation, battery capacity etc and based on the tariff optimises use of the battery.  With Agile it plans all this for the next day at 1600, but checks every 30 mins to see if it needs to make adjustments.

I have been using it since last December, when I switched to Agile.  Headline results:

Total grid import: 10,491kWh

Total cost (excluding SC): £1,590

Average cost:  15.2p/kWh

Octo's Flex tariff would have cost £2,946 so savings are £1,355 over nearly 12 months.

Here's a graph showing my daily average costs, with rolling averages:

I have an EV (10,000 miles p.a.) and a 14kW Ecodan so my annual usage is higher than this, as I generated about 6,700kWh from solar this year and exported about 50% of that on the 15p fixed tariff.

@downfield I use Predbat hosted on Home Assistant which calculates every 5 minutes to optimise battery use to achieve lowest cost.  However, the times that the battery charges are wholly dependent on the tariff.  While this is (largely) well-defined on Intelligent Octopus Go, the times and prices vary throughout the day and from day to day on Agile so a complicated regression analysis is necessary if I now wish to accurately determine if I would have been better remaining on Agile.  From the complaints I see elsewhere on social media, I think I'm most likely still winning where I am at the moment (although maybe I would be better on Cosy to stop my using a couple of £ per day at high rate).

@ianmk13 I hear good things about HA /Predbat on the GivE forums, but am wary of going down the Pi rabbit-hole because of usability / maintainability should I not be around.  Or for the next owner if we sell.

My wife is already concerned about the recent improvements (ASHP/batteries/solar) to the house which she doesn't fully understand, although she is generally comfortable with computing devices and apps at the iOS level.

So I am trying to keep the HVAC systems simple whilst getting the best efficiency I can.  That means using third party software in the cloud, with a developer I can trust and who can be consulted in my absence and fix issues remotely.

@downfield Very important considerations, for sure.  My wife has been saying for years that she doesn't know what she would do without me - and that's not just for opening ketchup bottles 🤣. My PV system has an app (and a web portal), which I have never used. It just works.  Left to its own devices, the battery system would be the same - the app has 4 'quick settings' for 'Charge Now', 'Discharge Now', 'Pause' and 'Eco mode' (this being to charge from solar, IIRC). With a little digging, timed charge schedules are available. I have a lot of temperature monitoring around the heating system, which can easily be ignored or removed (unplugged). A personal weather station has its own graphical display (but is easily removeable). There are two potential problem areas. One is the intruder alarm.  I believe that it is possible to link this to a free Samsung SmartThings account. Worst case, a new control box will be required. The other is the CCTV system which saves to a NAS box. This system 'just works' along with an app.  The only maintenance required has been an occasional power-cycle. Worst case, take away the NAS and leave the non-working cameras.

One thing I have done, which I believe is essential, is to maintain a 'House Manual' on my PC which contains a record of all product manuals, all cabling (including cabling routes) added during my residence and all other 'useful' information I have gleaned (e.g central heating pipe gauges and route map).

@ianmk13 a House Manual is on my to-do list - very good idea.

Posted by: @ianmk13

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@downfield Very important considerations, for sure.  My wife has been saying for years that she doesn't know what she would do without me - and that's not just for opening ketchup bottles 🤣. My PV system has an app (and a web portal), which I have never used. It just works.  Left to its own devices, the battery system would be the same - the app has 4 'quick settings' for 'Charge Now', 'Discharge Now', 'Pause' and 'Eco mode' (this being to charge from solar, IIRC). With a little digging, timed charge schedules are available. I have a lot of temperature monitoring around the heating system, which can easily be ignored or removed (unplugged). A personal weather station has its own graphical display (but is easily removeable). There are two potential problem areas. One is the intruder alarm.  I believe that it is possible to link this to a free Samsung SmartThings account. Worst case, a new control box will be required. The other is the CCTV system which saves to a NAS box. This system 'just works' along with an app.  The only maintenance required has been an occasional power-cycle. Worst case, take away the NAS and leave the non-working cameras.

One thing I have done, which I believe is essential, is to maintain a 'House Manual' on my PC which contains a record of all product manuals, all cabling (including cabling routes) added during my residence and all other 'useful' information I have gleaned (e.g central heating pipe gauges and route map).

I don't know if you've taken a look at all, @ianmk13, but one of the addons you can install onto your HomeAssistant box is Bookstacks. That then gives you effectively your own Wiki which is absolutely superb for a "House Manual". I have four separate "books" in my installation; one for my network and all the devices on it, one for renewable energy and how all the kit is implemented, one for the garden including planting plans and so forth and one for general local information including local suppliers I want to remember, full names of neighbours and which house each lives in, links to local event calendars and other info I want to keep track of.

The fact it's pretty free-form to write allows me to link pages with other pages so I can quickly navigate to the info I want to find and wherever I want to keep any product manuals I can either link to the manufacturer's site and download path or I can simply download the manual and store it directly as a file in Bookstacks. Wherever I describe any piece of kit I have installed, I also tend to include a link to the web interface on that bit of kit if it's needed for management; that way, if I'm reading something to refresh my memory, I can jump straight to the box itself from my notes. Needless to say, I use a password manager too so that having clicked the link to the box I can fill in the credentials without having to rummage around elsewhere to find them, yet ensure each bit of kit has a separate, secure and autogenerated lengthy password.

Posted by: @majordennisbloodnok

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I don't know if you've taken a look at all, @ianmk13, but one of the addons you can install onto your HomeAssistant box is Bookstacks.

@majordennisbloodnok  No, I wasn't aware of that.  To be honest, the manual is more for someone else to use, should I inadvertantly fall under a bus or kick the bucket. Since I'm the only one in the family using HA, the manual will be more easily discovered and accessed in an area of the NAS that my family has access to (along with all the other records of everyday life that they will need if I'm no longer around). My father planned for his absence in a similar way.  He left a written list of various account and insurance details and a list of contacts and their telephone details.  Nowadays, we tend not to deal with individuals; I don't even get to see the same GP twice in a row.

@ianmk13

Agile: average import cost vs other tariffs? In this instance,

Agile vs. Cosy Tariff.

The answer is not quite as straightforward as one might wish; ‘it all depends’ you might say.

I have based my assumptions on my own situation; different circumstances might well sway the results of such comparisons.

We are an all-electric household and have an 8 kW Daikin monobloc ASHP, induction hob, microwave cookers, DHW heat battery which takes power from grid and / or solar power.  We also have a washing machine and a heat pump condensing tumble dryer.

My wife and I live in a 1930’s semi detached 97 sq. metres well insulated 3.5 bedroomed house with mainly double glazing and some triple glazed windows and have an EPC rating of C (73) assessed before the ASHP and grid / solar heated DHW systems were installed. (Notionally, our house would now have an EPC rating of B [83], as we carried out the work outlined to more than meet this requirement.)

Our solar PV is rated at 8.1 kWp. but not ideally orientated with slight shading at various times; it produced 6.5 MWh in 2023 and 6.0 MWh in 2024, most of which was during the times of lower domestic demand and exported at a rate of 15 pence per kWh to our provider Octopus Energy. We have Tesla Powerwalls providing a battery of 27kWh. capacity and are able to charge / discharge power at up to 10 kW to and from the system. (During charging times, this might well be a rate of 10kW plus domestic usage which might add a further 5 kW.)

For the purposes of simplicity [and being somewhat lazy!] I have utilised the Agile tariff half hourly rates published by agileprices.co.uk on their website which is updated daily. It has been pointed out to me that just using the daily ‘average off-peak’ rate does not necessarily equate. to the amounts paid by some Agile users. For this reason, I have based my chosen Agile daily charge requirement on the minimum time required to charge the battery and at the lowest rate half hours each day.

Our total consumption from the grid for December (I am excluding the small contribution of 71.6 kWh from the solar PV, [some 66% of which was exported] amounted to 1,253.84 kWh. (40.45 kWh per day) I am using the rounded figure of 40 kWh as the average daily grid use so that I might calculate the number of half hourly Agile slots that would be required to replenish the battery as would be required for our actual use of Cosy. I am assuming that the charge rate would be 10 kW as this is the rate at which I charge normally. Lower wattage inverters would require a longer time of course and on Agile, this may well involve using half hours at a higher price. I am therefore using the rounded figure of 1240 kWh at a rate of 12.32p. for our consumption from the grid at the then Cosy rate; this being the lowest rate that is available for a total of 8 hours per day which is adequate to supply our needs daily.

The fixed rate offered by Cosy during the 8 cheapest hours per day is used for my consumption since July 1st. 2024. Being 2 periods of 3 hours and 1 period of 2 hours with a maximum space between these cheapest slots of 7 hours. Enabling us to avail ourselves of the cheapest rate alone without needing to draw from the grid at any other time, has been possible with 27 kWh of battery capacity. We wouldn’t normally exceed ~ 4kW of drain for an extended period; on a cold day with  laundry and some cooking added to the heat pump’s consumption, 7 hours might require ~22-23 kWh so we have a small margin left at the next re-charge time. N.B. No allowance has been made in these figures for the ~ 10% loss in conversion from AC to DC and then DC back to AC., but this factor remains the same whichever tariff were used anyway.

I have decided (for good or bad) to [loosely] base my calculations on our average daily consumption for December, 2024. As our average consumption of 40.45 kWh (rounded to 40 kWh) could be imported at the rate of 10 kW in 4 hours, I have taken the 8 cheapest half hours of the Agile tariff to provide the equivalent amount of energy. I will leave it to the reader’s imagination to decide whether the additional daily check of rates, times and faff of programming their control gear to charge during these cheapest times, assuming their system will allow them to charge at the rate of 10 kW/h is a practicality.

The agileprices.co.uk site indicates individual half hourly changes and I have endeavoured to follow the negative pricing too. I decided that absorbing all 180+ days of 48 readings per day into my noggin was a little beyond the call of duty, (and beyond the capability with my limited visual acuity to read figures accurately) so I hope readers will forgive me for basing the details on just the 31 days of December; this is also perhaps the heaviest month for consumption this year and with the price varying several times over the last six months, I felt this would be more representative anyway.

Right, without further prevarication, here are the figures for Agile as against Cosy based on the case above. The weekly figure is the total of each of the 8 cheapest daily slots added together.

The Agile prices are for consuming 1.0 kWh for each of the 8 half hourly slots, thus the sum shown below has to be multiplied by 5 to obtain 40 kWh total each day.

I’ll save typing and space by taking a week at a time except where there are negative prices:

Sun. 1st. Dec. - 7th. Dec. = £6.556 x 5 =£32.78

Sun. 8th. Dec. -14th. Dec. = £9.214 x 5 =£46.07

Sun. 15th. Dec.                    =. £.394 x 5 = £1.97

Mon. 16th. Dec. (Some Negative) = - £0.01 x 5 = -£.05

Tues, 17th. Dec.  - 21st. Dec. = £2.209 x 5 = £11.05

Sun. 22nd. Dec. (All Negative) = -£07.0 x 5 = - £0.35

Mon. 23rd. Dec. - 28th. Dec. = £7.291 x 5 = £30.46

Sun. 29th. Dec. - 30th. Dec. = £2.166 x 5 = £10.83

Tues. 31st. Dec. (Some Negative) = £0.365 x 5 =£1.83 less £0.058 x 5 = £0.29 = £1.54

The sum of the above amounts to: £134.30 (If VAT is additional to this, then the cost would be £141.01

The equivalent amount of energy with the Cosy tariff amounts to: £152.77.

Were I only able to charge @ 5 kW, then the 8 hours of cheapest Cosy rate would still provide the 40 kWh required; however, though this might incur greater charges with 8 hours usage of Agile rates.

I will leave it to the reader to consider whether the saving of £18.47 (or possibly £11.76 if VAT is to be added) on the Agile tariff would be worth the additional work or ‘faff’ as I term it!

As an aside, the total annual energy consumption for our all-electric abode amounted to £1,214.31 # for 10,028.01 kWh and our solar export* returned £952.39 thus we paid a total of £261.92 for the year which, in present extremely high energy prices, represents a situation I am fairly well pleased with. Perhaps I should also mention that we were on the Agile Tariff from 1st. Jan.-31st June.

# These Cosy figures include VAT @ 5% but exclude all standing charges. I believe the Agile prices do not include VAT though. (At least we are not paying gas meter standing charges as well!

*Somewhere in these figures, there is also an amount for savings sessions returns but I am unsure just where they are shown on the Octopus summaries but, it is the ‘bottom line’ that matters!

All the above goes to show that statistics are a long way from damn lies but that it is probably easier to get away with a few lies than it is to try to provide meaningful statistics that can be extrapolated to cover different circumstances. 😉Regards, Toodles.

@toodles  I've only got 13.5kWh of battery (no ASHP) and it doesn't get me through the day - primarily because Mrs mk13 wants the heater on in the greenhouse. I'm on IOG but keeping an eye on Agile prices.  They've been quite high in recent times but I've been sorely tempted my a couple of low price periods.  I have HA automation that takes care of the Agile 'faff' but I draw the line at swapping tariffs on an almost daily basis as some people allegedly do.

@toodles regarding the actual cost of power on the Agile tariff, are you aware of the OctopusCompare app?  This gives you your actual half-hourly usage at the half-hourly Agile rates for each period, with the option to aggregate by day, the previous week and month.  Plus it calculates your average p/kWh over the same periods.  It also gives you the upcoming Agile rates, updated at 1600 each day.

see for example my usage for yesterday below (note that only a few h-h periods are shown in the s/shot - you need to scroll down in the app for more - but the daily total is correct:

you'll notice the ability to compare the cost with any other tariff - in my case I just have it set to the Octo Flexible tariff, but many others are available, including non-Octopus tariffs.

So in summary you can compare the costs of any 2 tariffs based on your actual half-hourly usage over a historical period - as long as you have the Smart meter data of course.

Octopus Compare is available as an iOS app but also as a MacOS app from the Mac app store IIRC.

@downfield octoprice also offers comparisons using own data and also allows you to play with "Load Shifting Visualizer" because most people woukd probably load shift to suit a different tariff. Making comparisons an art as much as a science!

https://www.octopriceuk.app/compare