If you have adequate battery storage and inverter capacity then the Cosy price works out at around 50% of the standard tariff and the heat pump can be used 24 hours per day throughout the coldest months, which is a good deal better than indicated by the summary statement above. My system has 25.6kWh of storage and a 7kW inverter as well as a useful amount of solar generation. I find that even in NW England the solar actually provides surprisingly useful returns on many winter days and, on average, I can get around 15% of the running daily consumption in December and January from solar. Clearly, some days are virtually zero but the mid-winter average is about 15% of demand. The months of November and February are significantly better as they benefit from the slightly longer daylight hours and higher sun elevations. I find that I can power my heat pump using the low-rate Cosy grid supply (8 hours each day) and also charge the batteries during these periods such that there is virtually never any need to use either the intermediate or the high premium Cosy rates. Having a 7kW charge rate is critical here but you need a G99 approval. The charging of the batteries whilst simultaneously running the HP 24 hours a day works on even the coldest days. Inverter conversion losses do erode the savings but after allowance for losses I reckon that Cosy will save me about 40% over the standard tariff on the coldest of winter days. The inverter inefficiency also creates a warm area within the house so all is not lost here either. 

@howardp99 yes, would agree.

I tried to say saving might be 20% but batteries will definitely improve matters. And as you say charge/discharge rates also matter... a lot!

Your detailed info helps with a deeper dive. Similarly all tariffs may benefit from deep dive. 

Hopefully the base comparison is a useful starting point.

I'm on Intelligent Go . Only since start of Feb. Before that Agile... and before that Tracker.

Imports so far this year are under 8p/kWh and I've exported more by filling batteries at night and maximised solar exports. 

High user with ashp & ev so likely imports for a full year may be 13000kWh. If I can keep near to 8p that will cost around £1000.

Exporting say 6000kWh @ 15p/kWh =£900

Perhaps a whole year heating, lighting, ev etc will cost around £100 - transforms the economics of the various bits of tech.

Tracker in 2022/23 saved me over 20% vs Flexible rates

Agile in 2023/24 saved circa 50% vs Flexible rates.

Intelligent Go in 2024/25 is on track to save 75% on imports alone vs Flexible rates. But with the extra savings by increasing exports its probably saving over 90%!! All depends how you slice & dice the calculations.

Without IOG I would probably import a lower 10000kWh on Flexible rates 26p ~ £2600.

Exports would be lower at say 3000kWh = £450

Net cost say £2150

Reminder..

✅ All smart/time-of-use tariffs require a smart meter.

CORRECTION

Octopus Go has 5 hours cheap 00:30 - 05:30 every night

Intelligent Go is 6 hours (minimum) cheap rate 23:30 - 05:30 every night. Extra slots may be added day by day.

Posted by: @tim441

↑

 

Intelligent Flux

• Same as Flux but fully automated for GivEnergy battery users.

  

GivEnergy, Enphase, SolarEdge and Tesla batteries are now supported. It's a net metering tariff where import and export cost the same. Octopus control the battery so no automation or monitoring/management required. Great for large net exporters in summer.

Interesting comparison!

Another good angle is the differences between seasons. Octopus Agile is relatively more attractive in shoulder months and summer than in winter (typically).  

For our set-up, Octopus GO has been the best option from March to October. But, from November to February, Cosy is likely to be the better option, as the batteries can be topped up during the day time. We also run the dishwasher during the 1 pm to 4 pm cycle. Yes, the EV charging costs a bit more, but probably negated on very cold days when the battery might run out by late afternoon on Go. With Cosy option, we can totally avoid using the grid during the peak period.

I'm on Tracker at the moment and intend to remain on it for the first year of ASHP running so I have the best idea of cost comparison.

To me Cosy seems like it would be more expensive unless you have a battery that can at least let you hop the 3 hour evening peak rate.

@scalextrix yes, battery is vital to maximise TOU tariffs...

@tim441 I’d agree wholeheartedly with that, with 2 x Powerwalls, we have a capacity of 27 kWh and have never needed to stray outside the ‘Cosy Hours’ (3 + 3 +2 hours per day). Not having an EV, I think this is probably pretty well optimum for us with a small contribution from our 8.1 kWp. solar array during the heating required months. We can import from the grid at up to 10 kW’s to charge so can recharge to full well within the 3 hour slots - no sweat. Main power draw = ASHP, Induction Hob, DHW plus washing, drying and wishdosher, the incidentals account for a further ~200-300 Watts per hour. Regards, Toodles.