@tim441 I am using Cosy at present and eagerly collecting comparative costs for Agile. I am using one of the website’s daily Agile prices and wish to run them for some months more to arrive at a fair comparison; however over the two months of comparisons, Cosy is coming out a little cheaper. Like you, I have 8.1 kWp of sub-optimally sited PV panels and have 27 kWh of Powerwall storage. My ASHP is a Daikin 8 kW pump.

Cosy offers a total of 8 hours at the lowest rate each day (3 plus 3 plus 2 hours) and this enables me to ensure that I only consume during those 8 cheapest hours of grid time. I intend to take the average figures and also consider the ‘FF’ (faff factor) when using Agile so that daily selection of charging would ensure the cheapest HH’s only are used. In the past I have used Agile and as I am retired, have been able to set aside time each day to set up charging times. In due course, I’ll publish my feelings (findings sounds a little too academic!). Regards, Toodles.

@toodles

@tim441 Yes, I am fortunate in having the Tesla Gateway which allows me to import / export up to 10 kW - this allows me plenty of latitude to charge - discharge and then recharge, all in the cheapest 8 hours. So far this scheme is working for me. Regards, Toodles.

Really not convinced with that switching and upping flow temps or setbacks with a heat pump is the way to go. It spends it's whole time in recovery mode playing catch up. We did batch charging the floor mostly during cheap 7 hrs, even though cheaper than gas we used a huge amount of energy (kWh).

Did quite a bit of testing, the longer you leave the flow off the longer it takes to get back to target flow temperature. One day ran for 8 hrs and the output flow never went above 30 with a target of 35.

So this year it's going on low and slow 24/7.

With all your batteries something simple like cosy allows you charge 3 times a day on cheap electric.

Needing such a big heat pumps, your best time and effort would be insulation, max out the loft insulation (400mm plus), look at drafts and eliminate. That's going to be your biggest saving in running cost.

@johnmo thanks for thoughts.

I will keep on weather compensation as base way of managing flow temps. I will not generally change flow temps. I agree with 24x7 operation.

Setback might be used on a digital thermostat so we can tweak it to avoid/reduce heating if possible during peak periods. But I agree its not helpful to cool too much as the heating back up will use more energy than saving. Setback will be 0.5 or max 1deg. i feel worth trying. At times it should avoid peak imports completely. On cold days it should reduce imports but not allow building to cool excessively.

In same way to boost by 0.5deg or 1 deg in the 2 or 3 hours before peak might help avoid/reduce drawing peak imports. Again i feel worth trying.

As mentioned my inverter can only charge or discharge batteries at 2.6kwh which is likely to be insufficient for our 16kw ashp without some draw from grid . Having said that I would hope using WC we typically might need to draw 3 or 4kwh except on coldest days when i think it might draw closer to 6kwh if freezing weather.

So Cosy not likely to suit us but I will watch usage on Agile in coming months to see how the average goes. If I can get it somewhere under ave Tracker rates then I'll be happy. Ave in past 6 months has been under 12p so anything sub 18p would seem good and maybe 15p as an annual average? I.e. same rate as fixed exports.

I will be interested if anyone knows their average import cost on any of the time of use tariffs. Would be useful to know inverter maximum charge/discharge rate, size of batteries, ashp size, whether pv is part of setup or anything else that people have to hand that might help comparisons

Posted by: @tim441

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In same way to boost by 0.5deg or 1 deg in the 2 or 3 hours before peak might help avoid/reduce drawing peak imports.

But to do that with WC, means you are running higher temps than you really need, so generally you are bouncing off thermostats to keep room temps stable.

@johnmo I think it will become pretty obvious if the savings are outweighed by extra demands or if it takes a long time to warm up again etc. But I suspect/hope a small setback will work as intended and overall create a saving with little discernable impact on comfort or ashp.

Many people use small setbacks overnight without issue and WC by its nature is designed to cope with fluctuations. They could include solar gain, weather, woodburner etc.

But your point is valid and noted in the mix.

In my case 16kw ashp, 8kw pv, 24kwh batteries, ev. Inverter charge/discharge at max 2.6kwh

Interesting to see that imports so far in 2024 5326kwh @ ave 13.98p from Jan
Switched to Octopus Agile from about 20th Feb I think (tracker prior). Agile only is ave just under 12p since switch.

Exports 2432 @ 15p

Hopefully coming winter can keep under Tracker rates by good use of batteries as well as a bit of setback in peak periods

Ave import cost just 8.08p in Aug for 331kwh
Ashp for hot water and EV

Export 438kwh @ 15p

2023 imports were 8304kwh @ 22.2p on Tracker (not bad vs standard rates?)

Everyones usage, setup and ability to timeshift will mean its not one tariff that suits everyone. But so far I think Agile import and Fixed export is best for me.

I use WonderWatt to semi automate my charging of batteries using slots. Most days I then change a bit according to Agile prices, weather etc. Only spend a few minutes. Using WonderWatt automation to preselect slots under 13.5p (on basis pv exports are 15p it seems a good starting point)

Thought I ought to do proper analysis of Agile - So corrected info:

 Interesting to see that imports so far in 2024 5326kwh @ ave 13.98p from Jan

Switched to Octopus Agile from 23rd Mar (Tracker prior). Agile only is ave just 10.22p for 2458kwh from 23 Mar. Usage includes EV, hot tub for a month, some imports at cheapest rates to fill batteries etc.

So by way of comparison I am on E7, as we are able to do a smart tariff - with 13.5kWh battery ASHP (heat and cool) etc.

We have imported 4100kWh so far in 2024. Average cost to import is 18p kWh. So paying quite a chunk more. But taking in to consideration PV generated works out at 11p kWh. So much closer.

It all gets quite complicated making like for like comparisons! Actual imports:

Tracker 1st Jan to 22nd Mar
2818kwh @ 16.15p

Agile 23rd Mar to 31st Jul

2458kwh @ 10.22p

Agile Aug await bill but looks like 331kwh @ 8.08p

PV solar based on sub optimal orientation & pitch 8kw array

1 Jan to 31 Aug = 5475kwh 

I've exported 2432kwh @ 15p which is mostly from pv solar but some will be forced discharge of battery which I occasionally do if Agile imports are sub 5p for extended periods (sometimes negative even)

Mentally I don't treat my pv solar as "free" - I see my it as a "cost" of 15p/kwh as that's what I can get for it if exported. 

Crucial period coming up over winter once ashp in full use. If I can avoid peak Agile rates and maximise batteries I'm hoping my average import rate might be 15p/kwh or less? We shall see!

If my maths correct..

Imports 5608kwh @ 13.06p = £732.31

Exports 2432kwh @ 15p = £364.80

Net ytd cost = £367.51