Compensation for delayed and ultimately wrong product (solar battery) delivered?

SAIL

I had solar panels and a 5kWh battery installed a couple of years ago with a view to expanding the battery capacity when I had the funds (this was a fundamental selling point). Last June, after a lot of research and quotes from the few supplies who could actually source the correct (they assured me) batteries, I paid a £500 deposit (of a £2000 quote) to double the battery storage capacity, including delivery and installation. 

Since then it has been an utter shambles (with people at the company concerned admitting this). Nearly 6 months later, I am left with no new batteries and (1) have lost a summer's worth of using off peak stored electricity and (2) selling excess solar back to the grid when they need it at peak times (instead having to pay the day rate, which is three times the overnight rate, for all use over what my panels can generate). In the last couple of months as solar generation has declined dramatically and I would have been relying on battery power even more, it has cost me considerably more.

One of the main reasons I am upset though is that (3) for my system (FoxESS cubes) when adding new batteries, they are only ever as good as the most degraded battery in the stack. In the last 6 months, my original batteries are considerably more degraded that they were in June, devaluing any new batteries added. 

I started asking for my deposit back around 10 weeks ago and was assured that it would be returned on Saturday, when they collected the batteries they had sent with the wrong connector (I ask asked them a number of times about this - soo frustrating).

The main, main reason for this post however, is that the correct batteries were hard to source 6 months ago, and now, it would seem almost impossible, leaving the only option for a larger system being to replace the whole lot. I suggest the company in question could do that for me but I don't think they took me seriously! Obviously I'm expecting my deposit back but do I have any legal basis for asking for compensation beyond that, given the points mentioned above?

Sorry for the long post, but any insights into what I should/could ask for would be most welcome.

Thanks,
Sally

the_lunatic_is_in_my_head

If they breach the contract you may generally claim any damages that are foreseeable and stem directly from the breach. 

In principle you are entitled to be in the position you would have had been in had the breach not occurred. 

If there was a timeframe for install then you could probably claim the cost of buying electricity minus what you got for exporting into the grid based on what the batteries would have held. 

If you have to spend more to get the same batteries then you can claim the addition cost. 

Not sure on the batteries being depleted, I appreciate they may have done to some extent but presumably it’s not that much? I guess if you can quantify it then you could claim it. 

If you add all that up and ask them for it they might offer you something, if they don’t, or you aren’t happy with their offer, you can send a letter before action and file through small claims. 

I would advise some professional advice, or at least running it by CAB, before starting small claims based solely on my advice 🙂