PhilT

Or maybe there's a forum member who can help if nearby, in which area are you?

There are also 2 of us and the domestic hot water takes 30 minutes each day to heat up for everything we need, that's it. I don't think you have a problem.

21kW ??? You could try one of these in each room! https://www.hotspotenergy.com/DC-air-conditioner/#:~:text=An all-DC system means,for many years without maintenance.

I would also very much like to get rid of ghastly tank in loft. I have a heat pump but the 2nd video in the original post specifically refers to a gas boiler application at 09:00

Banning R32 seems like a sledgehammer to crack a nut, because there are well established processes to recover the miniscule amounts of refrigerant. I worry that it will screw the already fragile UK heat pump market unless the site location regs for R290 are relaxed.

The base Cosy calc at the moment uses the % hour split but it matters not - it's just another scenario. Interesting to play around with the numbers

Cosy 2 is a no brainer for me, at least for the room heating months anyway. I used Cosy 1 when it was launched but that extra 22:00-00:00 low rate makes a useful difference. Re the spreadsheet I reckon I will still export around 50% of my solar, without the battery, at 15p/kWh, but obviously most of that will be in the summer months.

One other thing I just noticed is that Cosy cheap rate hours I think are 8, not 7? Definitely useful as a directional steer, obviously you can debate the assumptions till the cows come home but that's where the "modelling" bit comes in based on your own particular circumstances. O

Ah, VisiCalc, the first commercial spreadsheet. I used it on an Apple IIe. Cue jokes about 5" floppy drives.

Good effort. Cosy "normal" rate = 25.81

Take a lot of time and care in working out the justification for a battery. With no export it is marginal at best so why go through all the hassle to install a potential fire bomb in your house. With export I would say impossible to justify on purely financial grounds. If someone has a spreadsheet which proves otherwise, more than happy to concede

I beg to disagree. If you already have a heat pump then Cosy makes financial sense without a battery. Getting a battery by itself just for Cosy would not be financially justifiable. For a heat pump consuming say 3,000kWh pa there would be a potential maximum saving of (3,000 x 12p) = £360 pa, with no up front investment, having already bought the heat pump. For a battery only, for an average consumption of 3,000kWh pa, the potential maximum saving would be the same at £360pa, but with a big up front investment. Considering the alternative use of your money at a few % interest on a fixed deposit account for 10 years after which you get all your money back, I would not consider getting a battery just for Cosy. Happy to be challenged on this.

is this what your controller looks like?

It still does that at warmer outside temps, say 12 - 15, but not at around the 10 or lower that we had over a week ago. Looking at the power draw curve, the behaviour suggests that AA manages the compressor to run as near as possible to its efficiency sweet spot around 40% of maximum capacity, and if it can't, then if the run has been long enough (never less than 20 minutes), AA allows the compressor to ramp up and either switch off while keeping the flow pumps running, or when target room temp +1 is reached.

So includes the electricity standing charges and 5% VAT, or not?