Adding Battery to Solar PV

[RickH]

I have an existing solar PV install ..... all working fine.
As I had to change the Inverter due to failure, the new one (warranty) now has direct plug & play battery inputs, so considering adding a 10kWh battery.

I attach the diagram of the current set-up, and of how I assume what would need to change to add a Battery, I would need to have the existing meter chnaged to SMART as Battery installer states it's a prerequisite.

Welcome any comments ... am I understanding it correctly ?

 

[ericmark]

I note 4 kW panels, don't know inverter size, or what your back-ground use is. So the battery can do three things.
1) It smooths out the troughs and peaks. Any size battery will do that.
2) It extends how long you can use solar for.
3) It allows you to use off-peak on peak times.
In general, the battery will discharge at the same in kW as it size in kWh, and a kettle etc, is around 3 kW so with back-ground usage looking at around 3.5 kW so need around a 4 kWh battery. That assumes the inverter can handle 3.5 kW. Charging is around 2/3 of battery capacity, so to charge at 3 kW you will need around 4.5 kWh of batteries, it is rare to get total power of the solar array, so the next in battery size is how long it will last, I leave 10% unused, and use around 12 kWh per day, most in the evening, so to get from dusk until off-peak starts, need around a 6.5 kWh battery. I have two 3.2 kWh batteries. So in general, battery needs to be around ½ the size of your daily use.

If the battery is too big, and you get more for export to what you pay for off-peak, then no problem. If however you're not paid for export, or it is less than you pay for off-peak, then you end up charging a battery only to then export what you have just paid for. So the tariff matters.

I don't get FiT I get SEG, so I don't know how the rules differ. Octopus Flux is claimed to be designed for solar panels, but come December I can't be sure I will have battery left by 7 pm, so use Go which it does not matter if I run out battery, I am not paying a huge amount for peak. There are two versions of Flux and Go, can't use the other Go as don't have an EV, the Flux depends on what the inverter will allow, if you can give control to supplier or not.

 

[RickH]

I don't have an off-peak tariff. (may change in future, but unknown)
Considering a battery to store excess Solar generation I'm not using during day, and simply using that when the panels not generating.
Inverter is 3680 VA with max continuous discharge of 16A

 

[ericmark]

Inverter is big enough.

So the question is, will off-peak help? The thing one watches is state of charge.

Without the off-peak, I would not reach midnight without running out of battery. Simple using 11.1 kWh and getting 8.6 kWh, so I need the off-peak this time of year.