Been told that the maximum power I can put into my proposed solax battery is 2 kw in and out is this the same with all batteries ? what is the restriction? still awaiting decision from network company for 18 panels ,supplier says I may be asked to buy a larger transformer any one else had this ?

All batteries have an upper limit on the power which can be put in or taken out. 2 kW is on the low side for a home energy storage system but is not atypical. The Tesla Powerwall is limited to 5 kW continuous, 7 kW peak but that's quite large (13.5 kWh capacity) whereas many systems intended to mostly just carry one day's PV into the evening peak and maybe a bit overnight will have capacities of around 3 to 5 kWh and so correspondingly lower power ratings.

Also, the inverter/charger attached to the battery will have a power limit.

Similarly, there's an upper limit on the amount of power you and your neighbours can put into the local distribution network before that'll reach too high a voltage. By rights you can put in 16 amps per phase (which corresponds to 3.68 kW at 230 V), if you and your neighbours all putting in that amount results in the voltage getting too high then it is the distribution network operator's (DNO's) responsibility to modify the network at their expense. They can tell you to stop feeding in while they do it but that's only temporary.

If you want to put in more than 16 A then the DNO needs to check if that'll be alright before hand. They have to bear in mind that if they give you permission to put in more then all your neighbours get PV or wind turbines or whatever and also put in their 16 amps then they'll be met with the expense to upgrade the network so it's only in their interest to give you permission if there's plenty of headroom available.

Two other approaches if you have more than 3.68 kW of panels:

1) Have a smaller inverter or configure the inverter to not output more than 3.68 kW thereby ensuring that the 16 A limit is met. Given that the panels only produce around their peak output for a very small part of the time (and usually when there's less need for energy anyway) this is a quite sane and common approach.

2) Have the inverter wired up with gubbins which the DNO is happy with to make sure that the export is limited to 16 A even though the panels are generating more because the difference is being used in the house to charge the batteries or for other useful purposes like normal domestic use, heating hot water or charging an EV.

Posted By: jhsigmaBeen told that the maximum power I can put into my proposed solax battery is 2 kw in and out is this the same with all batteries ? what is the restriction? still awaiting decision from network company for 18 panels ,supplier says I may be asked to buy a larger transformer any one else had this ?

Were just in the throws of adding a second 16A limited system to give us 2x16A output to grid. Informal discussion with DNO so far reveals that our pole mounted transformer is undersized by their current standards so is getting upgraded from 5KVA to 25KVA at the DNOs expense. I think this is part of grid reinforcement for future EV/heat pump loads. The existing 5KVA transformer sounds a bit light on capacity but thats what the DNO says is there.

To keep us under the max voltage limit of 253V the transformer is being tapped down by 2.5% so that when the PV is generating it wont push the voltage over the 253V limit. All at no cost us! Only thing that we have to do is provide a disclaimer that we take reponsibilty for the reduced voltage which is still well above the UK standard of 230V.

Might be worth some subtle discussion about existing transformer capacity for future heat pump/EV loads. Im guessing all DNOs have a degree of gov funding for bolstering network capacity for much larger future electric loads??