Multiple battery charging question

I have a GE 3.6 hybrid Gen 2 Inverter with a GE 9.5kw h battery. If I was to buy a second battery, prices seem to be dropping? Would this inverter charge both batteries simultaneously or one after another. Similarly on discharge can you set a priority for which one to run down first? Not convinced that I need a 2nd battery as our daily total household summer and winter demand is close to 9.5kwh? 5 for the house 4.5 to the Sunamp for DHW. In Winter I think we’ll need to buy at least 6-8 off peak kWh units? ( at 17p a unit) to top up the 2-3 solar units we might glean from the 4kw of panels. Ps on a sunny summers day we can get 22kwh from our south facing panels.

Bill G

The inverter will use 2 or more batteries as if one large battery - i.e. charge and disharge from both simultaneously.

You can view date for individual batteries but have no control over the use of them. In my system (2 x 8.2kW batts) the primary has done more work than the secondary - not sure if future firmware will equalise the usage.

When calculating the savings don't forget to allow approx. 20% for the loss from charging and discharging.

billG from what you've said, it's not worth you getting a second battery.

stevelewis Thanks for this. We are on an oil fuel boiler for winter space heating still. It’s aVictorian house, stone built no wall insulation just lath and plaster, no floor insulation either but double glazed and reasonable roof insulation. We can get a grant! Of £9000 !! Here in rural Scotland to install a heat pump, But due to likely heat losses and messing about with radiators in an old house I’ve decided against giving up the oil. An extra battery would have been needed to feed the heat pump with off peak units, though I’ve found it hard to find out how many units a heat pump would consume in this type of older stone house, even with a COP of 3 or 4.

Regards

Bill

Good morning,
On our system we have 2 x 5Kw batteries. The 2 batteries run in in parallel to each other and are synced together.
(I suppose the Battery Management System takes care of that.)
They charge together and discharge together. There is a slight discrepancy in percentage between them but they don’t seam to have any problem providing energy through-out the day and night and well into the following morning when they start to charge all cover again.
All in all a really great investment.

One thing to consider is max output. I had an AC 3.0 into a 8.2kwh battery. When i bought the 9.5kwh when it came out subsequently I was told I needed to get a second AC3.0 otherwise I was limited to a max output of 3kwh. They can also both charge at 3kwh which depending on your tariff might be important.

Graham

Better spending the money on the battery on draught proofing and insulation imho.

billG I put together a simple Google sheets spreadsheet to calculate whether it was worth me getting a third battery, if you want to use it for your own calculation, the link is https://docs.google.com/file/d/10NLAyNAWC6Aun8oTCCyG9fjfXoRTh9qf/edit?usp=docslist_api&filetype=msexcel

My conclusion was that the payback time was at least 6-7 years, and that best case was based on charging it every night in the winter to take advantage of the peak/offpeak saving, and during the summer it being charged by solar and us using the saved solar overnight.
If I just looked at winter overnight charging savings the payback was something like 22 years!

When we get our flux export tarrif I’ll probably have another hack at the calcs to see if that makes it any better, but at the moment my conclusion was that its just not worth it. The 9kW battery seems to have dropped from about £4000 to £3500 but electricity prices have dropped as well so I concluded it still wasn’t worth it.

On your other question about getting an ASHP. We’ve had one for 15 months or so after our oil tank started leaking. The current regulations for oil tank siting meant we’d have had to move our tank to the middle of the garden as it has to be 1.5m from buildings and 760cm from property boundaries. The previous location next to sheds and the garden fence wasn’t acceptable.
We were just in time to get the RHI grant which required that the house energy rating be no worse than D.
For our house which is fairly well insulated band D, rough figures for running the ASHP are 4kW a day from April to October and 27kW a day from November through to March. So circa £1 a day in summer, about £10 a day in winter, but in extremely cold weather (e.g. mid December last year) it can be £15-25 a day.
It sounds like your property isn’t going to be as well insulated as mine and as a consequence you could well find the heat pump struggles to keep the house warm, runs all the time and costs a fortune to run. You really do need a well insulated house to be able to use a heat pump effectively.

geoffreycoan 27kwh per day in colder weather seems scary to me ? Apart from our oil boiler we have an open coal fire in one living room and a log burner/multi fuel stove in the other. One for daytime, one for the evening if it gets desperately cold, only a few days a year perhaps. Fires are only on intermittently in winter , scarcely on in Autumn. Looking to get an EV next year to soak up the 1000kwh we give to the grid just now, plus save on the costs of petrol, I think I worked out we could save £1000 on motoring on 8 to 10,000 miles pa? But then you do have to fund a more expensive vehicle.

We’ve run a Tesla for 18 months now and done about 14500 miles. Works out to be about 0.048p a mile which is mainly home charging (currently 7.5p a chunk) but includes supercharging and a little other type charging. If we had kept the old diesel and got 50mpg that would have been nearly 14p a mile. So as long as you ignore the cost of the car (!) it’s a no brainer. No servicing no road tax and quicker ( previous car BMW 335d gt so not slow and really would do 50mpg but only if you drove very carefully). My point is get an EV anyway and don’t worry about using up the excess solar

Hi Simon

You are right to point out the mileage savings with an EV especially if you can get a cheap overnight charging tariff and PV in the sunnier months if you have spare KWh. Like you I reckon we could save £1000 on motoring mileage costs on our more modest 8000 miles. But can I part with my COTY rebuilt Triumph TR3A to fund a “new” MG4?😊😊😊 plus possibly also have to sell the wife’s Panda!!!

billG electrify the TR!

SimonClarke would likely cost more to electrify 😊plus this car sits so close to the road siting the batteries might be problematic. I’m too
Old to start such projects now anyway! Though electrifying my 1925 Gordon England 2 seater Cup model might be easier?😊😊😊

billG had to look that up! Don’t think you’d get many batteries in but probably wouldn’t need many. Watched them do a Gordon Keeble on youtube. Seemed like an improvement.

SimonClarke try looking up my blog on Friends of Austin 7, search for AllAlloyCup, it’s had nearly 240,000 views!!!