@jamespa business case for batteries is not simple and at end of day may partly be a leap of faith! A few comments for mix. I'm on Intelligent Go import and Fixed 15p export. Cheap imports at 7p. I have solar too.

• I fill batteries at night through summer and force export during day.  In previous years i exported say 2500kWh but this year with extra forced exports it will be around 7500kWh. Income ~ £1000
• In winter i force charge at night but use that myself. Minimal exports in heating season. 
• I have a limitation due to older inverter. Max charge/discharge rate is 2600kWh. Making it harder to maximise both imports & exports. So Flux unlikely to work for me.
• This year with added imports above I'll import ~ 14500kWh. Hoping to keep the average nearer 8p. Meaning net cost is near zero.
• But my large heat pump means i will import some energy at peak rates on coldest days. Mild winter days the overnight + battery means i can use cheap rates only. 

When i installed the batteries in 2020 the installers told me it was too much with 3 x 8.2kw. In reality its been great. Most modern inverters will charge/discharge at faster rates and I'd recommend people looking at new installations consider that in the mix.

@papahuhu lithium prices have turned higher last few months. It may be that we're around cheapest battery prices? 

We will only know with hindsight!

@tim441 

im not in the industry so you may be correct, I’d heard they were now sub 100USD per kWh for domestic cells and under 80USD for industrial cells.

All I do know is I paid an awful lot more than that and I thought I had a bargain! I’d love to buy 3PW3 expansion packs but even with the current discounts they will never payback, so I won’t. My single one was necessary to get me on the VPP platform and that was added value.

Posted by: @papahuhu

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With an EV IOF doesn’t work, so no meaning to pay a premium to get a smart battery.

 

Why do you say that, surely it depends on how much you use for the EV relative to other uses, or is there something more than that?

Typo... of course Max charge/discharge rate is 2600kWh. 

Should read: Max charge/discharge rate is 2.6kWh. 

@jamespa 

It’s a nett metering tariff, so import and export are the same price. Plus the compatible batteries are generally more expensive. So you have to have very light import to make a short return on investment. 
Plus the downside is that octopus/Tesla  takes complete control of your charge and discharge cycles and whether the batteries supply your house/car loads or the grid. You can’t even drop your minimum discharge level below 20%, whereas I’d like it to be 5%. Little niggles like that are the downside, but they do pay you on average about 27p for your export vs 15p on outgoing octopus. 
I don’t know if they are still doing it, but about 6 weeks ago octopus were offering amazing prices on PW3 and expansion packs, it was something like £3500 per expansion pack if fitted at the same time as the master unit. Tesla has since dropped their prices by £375 per pack, so they could be even better value now. Octopus enphase batteries were very good value at the time too, but not checked for about about 18mths. 
The other tip is make sure you know your DNO export limit before paying for a large hybrid inverter, no point in having a 12kW PW3 inverter if your DNO is going to limit you to 3-6kW export. 

@tim441 What’s a dot and a few noughts between friends?😉.

Posted by: @tim441

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Typo... of course Max charge/discharge rate is 2600kWh. 

Should read: Max charge/discharge rate is 2.6kWh. 

Being pedantic I think it should probably read should read: Max charge/discharge rate is 2.6kW 

@papahuhu That ‘complete control’ can work against one’s interest too; I am talking about the algorithm that OE use with Intelligent Octopus Flux. My system is set up and can export at the rate of 10 kW; this results in the 27 kWh Powerwall being drained to 20% in little over two hours - then, at peak rate of the tariff (and during the hours of maximum demand!), starts to recharge. I have been in contact with Octopus about this and hope they will review the matter by the time that IOF might be an attractive tariff next spring/summer. Regards, Toodles.

Posted by: @toodles

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then, at peak rate of the tariff (and during the hours of maximum demand!), starts to recharge.

I wondered about that!  Thats a bit naughty.

Posted by: @papahuhu

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It’s a nett metering tariff, so import and export are the same price. Plus the compatible batteries are generally more expensive. So you have to have very light import to make a short return on investment.

I get that.  Summer my net import is essentially zero, but that is made up of 2.5MWh import and 2.5MWh export.  I guess your point is that I could manage this with just a battery no need for Octopus to intervene.

Before I got the heat pump and night time tarrif I had an automation running to turn on the car charger when the solar output was high.  It was only partly successful, the problem being that the car inherently has a minimum charge rate of ~2.5kW which, with a 4kWp solar, isnt a great match.  It seems mad however to charge and discharge a battery to charge a battery!

Hmm!

@toodles 

Sure, me too. The way I look at it, is providing it is acting in your best interest 99% of the time it pays off. It does some weird stuff but some of that is also Tesla.I’m on cosy at the moment but it suddenly went in to calibration mode at midnight yesterday and dumped all my battery to grid at the time I’d programmed it to charge up on super off peak. I would never use it if I had an EV or if i didn’t have a large export, this year my nett IOF export was 12mWh, nothing comes close to giving me the same level of ROI. In my case it was 3.7 years, if nothing changes. I’m one of those evil climate change agnostics (not because of ideology but because I understand math and complex data), so my renewable journey was pure economics. 

@papahuhu Yes, it seems bonkers to me that the algorithm would put the system into recharge during the three hours of peak demand! I explained all this to OE in a series of emails and pointed out it wasn’t just the higher price charging that ensued but that it made a mockery of their attempt to reduce the maximum demand during those three hours. Regards, Toodles.