Battery bank /backup sizing

[Greenbeast]

I feel like we could do with a sticky on this.
Along  with a dream of an EV conversion I have a slightly more achievable goal of a battery genny for the farm. Like the bosch GEN230-1500. I'm thinking an old genny frame with a weather sealed box mounted within, containing a lithium battery bank, inverter and charger.

But once again I'm not sure where to start with sizing the bank.
I know there'll be losses and that I want about 2000W of power and an hours run time at that level (initial use is the corded chainsaw)

[biff]

Hi GG,
      You could consider a small petrol lawn mower engine with the horizontal shaft mated by belt to a 2,000watt pmg that delivers its best performance @ say 400rpm.
   Rectify it in 48volt into a bank of 4x 12volt x 100ah batteries, stack an old 48 volt UPS on top and you will have an inverter generator. Run for a while to charge and then run on the batteries. It is quite cost effective fuel wise but you need a decent bank. I have the diesel version of the same idea and it can bring running costs down to approx 10cents and hour.
                                                          Biff
 

[Greenbeast]

Thanks biff, not quite what i was aiming at 
Looking to move away from small ICEs and with the abundance of good value Li-ion 18650s on the second hand market though it might be a cool little project. Who knows if i'll actually get to do it, but it's certainly more likely than an EV.

If i'm looking for 2kWh at 240V, and taking into account inverter losses, what size of battery do i need and at what voltage would be best?

[dan_b]

These cells caught your eye?

http://www.ebay.co.uk/itm/tesla-18650-battery-cells-3300-mah-Panasonic-3-7v-NCA-NCR-e-bike-electric-car-/172751274652?epid=7004173727&hash=item2838c7429c:g:fscAAOSw8GtZUqQj

[Greenbeast]

yeah i did see them. i really really wish i had the time and disposable income to faff about building things. Unfortunately the pigs keep me too busy!

[Fionn]

48V is most commonly used as it's the highest voltage that  has a wide variety of inverters available for it. It's also still relatively safe to work with while reducing conductor sizes to a manageable level.
You'll want 3kWh at least if you want 2kWh usable capacity in order to limit discharge depth somewhat.
I have an 8kWh Golf GTE lithium pack if you are interested, I will be breaking it up but not sure if postage to the UK would be an issue.
They're 25Ah IIRC so a lot less faffing than 18650 cells.
You would need a BMS and a low / high voltage disconnect also.

[Greenbeast]

48V is most commonly used as it's the highest voltage that  has a wide variety of inverters available for it. It's also still relatively safe to work with while reducing conductor sizes to a manageable level.
You'll want 3kWh at least if you want 2kWh usable capacity in order to limit discharge depth somewhat.
I have an 8kWh Golf GTE lithium pack if you are interested, I will be breaking it up but not sure if postage to the UK would be an issue.
They're 25Ah IIRC so a lot less faffing than 18650 cells.
You would need a BMS and a low / high voltage disconnect also.

Thanks for the advice.
Currently not in the market for parts, as much as i wish i were. Trying to work out how viable it would be, and how much i might use it, that sort of thing