It's about £200/kWh savings on a powerwall.

What have you got @batalto?

@chris-in-kemnay when mine went in I paid £1600 for 7kwh of storage, so £228/kWh; this was at 5% VAT. If you just bought off eBay today it would be around £280/kWh.

From your previous post yours looks like around £460/kWh of storage.

@batalto what sort of batteries do you have? The salt water batteries can discharge to zero without harm whereas all the others have to have some sort of safety buffer, so the 5kWh isn't really 5Kwh it's only 3.5 or 4 usable.

@chris-in-kemnay I'm running pylontech batteries at 80% DoD which gives me 80% after 10 years. You can run them higher but the guarantee DoD life is lowered. Looks to me the salt water batteries don't have the cycle lives as the NiFe batteries

Are the salt water batteries more environmentally-friendly when it comes to disposing of them?

@editorYes Mars, Just aluminium plastic steel and some cotton and of course salt and water.

Thats what attracted me to them initially that and the ability to drain them completely without  damage and also they're stackable so once I had 4 I could stack the next row on top if needed. I can see they've got  your interest 😏

@batalto I'm no expert on batteries.. I made my choice because I wanted to be green and had plenty of space available and for the reasons above.

The benefits of solar and batteries on a cloudy day!

Just joined forum so only just picked up on discussion.

I installed 2 Tesla Powerwalls in July 2017, this was in part a lifestyle choice and in part because I was fed up giving most of my spring / summer Solar PV production to Electric Co for a pittance, only to be charge top wack for evening and night consumption. Another annoying issue was that the FIT payments were fixed at only 50% of Solar PV production so, although I was giving Electric supplier around 80% of my production I was only getting payment for little more than half of what I fed back in. They said I would have to pay for a FIT meter.

I have nearly 4 years of data now so I can give some idea of payback. Batteries cost £15,800 including installation and adaptation to already installed 6 Kw Solaredge PV. I chose Tesla Powerwalls as they can also be charged from Economy 7 half price off peak energy. Tesla have a great energy management app (who needs a smart meter) which also allows you to look back over past house demand, solar Kwh generation, battery Kwh (in and out and where it came from, eg solar charging or mains charging) and mains Kwh consumption and compare data, and even download it for analysis in Excel. The app also allows you to set off peak times so you can charge batteries and run household equipment at off peak rates and conserve battery power for avoiding peak rate electricity consumption (useful in spring and autumn), or you can click to go totally off grid and run your house solely off the batteries.

The cost benefit calculations get complex as in the winter months most solar PV production is being used as it is generated so benefits are from charging the batteries at half price off peak mains electricity. In the summer for three to four months the batteries enable me to go totally off grid. The spring and autumn months its a combination depending on the sunshine hours so maximum benefits require daily monitoring of battery capacity and the weather forecast (not something I always do).

Based on a saving of 11p per Kwh on consumption (based on current charges) and allowing for low general consumption in the summer months (I would not be using all 26Kwhs available from the batteries in the summer) and an estimated mixed consumption in spring and autumn, I have estimated around £800 average savings per annum. I still get the 50% FIT on Solar PV production although I now export around 25% or less, so this means I am getting paid a better net rate for my FIT, estimated benefit of around £400 per annum (this would be less for someone with a standard 4Kw Solar PV system.

My repayment on two Tesla Batteries is therefore estimated at 13 to 14 years.

@hmk 

Do you have a power diverter to produce hot water from your solar PV system rather than running your ASHP? It is another good way to use your excess solar generation and also reduce importing energy from the grid.

No but this may be a good idea, I will check the costs involved. Thanks

@hmk a cheapest devices are around £200 to buy. With an electrician I imagine you are looking at £300-£400 installed (depending on the complexity of the install). Several suppliers exist, Solic, Immersun, MyEddi etc with various price points.