We’ve a heat pump (obviously!). I’m on Agile and my last bill for 25 days to 28 Nov used an average of 23.24p per KWH with a standing charge of 20p per day. This is far more expensive with a daily average (if my arithmetic is right) of about 44.5p and a far more expensive standing charge ( although it’s per diem rather than hourly of course). Interesting though that some attempt to recognise the higher electricity cost of an ASHP. I can’t help but feel having 2 cosy periods is a bit old school like having your gas boiler on twice a day when the received wisdom is to run your ASHP 24/7 so I don’t follow the logic of 2 cosy periods…but then I’m no expert just a consumer.

I guess the thinking is you don’t always have to run the most efficiently but instead the most cost effectively. 

Ie  our cheap period starts at 21:0 so we turn off heating from 18:30 and let it work super hard from 21:30 when it’s only 8p/kEh. Not the most efficient but costs less overall. 

Understandable if you have an electric car and can access Go but having spent £30K on solar, battery and an ASHP I have no ability to buy an EV and cannot access Go or any other EV tariff from any other supplier. I suspect I won’t be alone…

@brooster you don't need an EV for go. They don't check...

Good to know!!

I did some calculations yesterday of cosy vs normal and it would only have been 50p cheaper for us over the last week. Given the risk of needing to use power at the expensive rate for some reason, that doesn’t seem worth it to me yet. But I’m going to wait and see what it looks like over a more normal week which would also probably lend itself to shifting away from the expensive peak too.

Could be good with those with batteries that don’t have the capacity to cover the whole day’s consumption from charging at the lower cost time.

Posted by: @brooster

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having spent £30K on solar, battery and an ASHP I have no ability to buy an EV...

Even if checks were made by Octopus, the only differences between a storage battery and an EV are

• the capacity of an EV is most likely greater - typically 50kWh and above
• one of them has wheels

The latter criteria can't be detected by looking at your consumption data 😉 

Posted by: @brooster

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the received wisdom is to run your ASHP 24/7 so I don’t follow the logic of 2 cosy periods

Having looked into the source of it a while ago, and done experiments with operation time, that "received wisdom" seems to be a distortion of the advice to leave the ASHP controller on 24x7. No-one worth their salt should be telling people the actual pump unit should run 24x7: that would just be overheating the house, or possibly short-cycling, both of which are expensive, even if slowly overheating might make CoP look good.

The advice seemed primarily not to have a time switch telling it to shut off, like gas and oil burners often do. Instead, "set" the controller target temperature "back" a few degrees when you'd prefer it not to operate, but leave it "on" so it can run a little if it's unexpectedly cold, rather than have the house have to warm up slowly/expensively from stone cold later.

100% with Cosy I could come off peak power - Only on a very coldest of days would it be an issue. You get 6hrs a day to use and fill at the cheap rate

25% of the days power is on the cheap rate. Fill your boots at your max charging rate - lets say 5kw (100A) - 30kwh (theoretically)

A personal scenario for me at 4 degrees ambient:

ASHP use 53kW - house use 15kW - total use 68kW

Cheap time nominal use = 17kW

I could charge at 6.4kw (two inverters at 3.2kw) - 38kw

Total off peak = 55kW        Peak = 13kW         Super peak = 0kW (as its straight after the charging period)

flat tariff = 68kW @ 34p = £23.12

Cosy tariff = (55kw @ 34p * 60%) + (13kw @ 34p) = £11.22 + £4.42 = £15.64 (£7.48 cheaper)

Obviously my situation isn't everyone's. I could also optimise a little with set backs etc.

There is a low tariff mode on the ashp.

Has anyone used this or have any experience of it?

The function is to heat any thermal stores and DHW cylinders at a time when electricity rates are inexpensive.

300l cylinder and family of 4 I don't know if it would be beneficial. The heating set point increases for heating by the low tariff differential water set point.