I have solar panels, and battery, and today had a smart meter fitted and while the grid supply was disconnected my central heating was running, so clearly it can run without a grid supply, (Islanding) but as to if battery fully flattened over night whether it would kick back in when the sun comes up, never tried.
The grid tie is designed to power down when grid fails to ensure no back feed, and my supply comes from a special part of the inverter and the 4 sockets and FCU are always powered from the inverter, and there is a system to auto disconnect the TN-C-S earth when the power fails.
So I have some thing like this
a small generator may work, or a second inverter, but it needs to run within the permitted voltage and frequency as it is designed to disconnect if it detects loss of supply.
I simply don't know how accurate the supply would need to be, and clearly it could not export any surplus. You are trying to make the inverter do some thing it was never designed to do.
So the system has three parts, the panels, the battery, and the inverter. My panels produce around 250 volt DC, this goes into the inverter which produces two outputs, 230 volt AC at 50 Hz and 50 volt DC, the latter is fed into the battery, but there is some software which one works out how charged the battery is, and stops it charging when full, and two works out how much power so it can charge battery at 2 kW and discharge at 3 kW and the inverter limits the charge and discharge within those limits.
Now with a lead acid battery it is easier to control, but a typical lead acid will take around 8 hours to fully charge, where my battery could be fully charged in 2 hours.
To power my sons inverter (3 kW) in his narrow boat, we had 3 x 140 Ah batteries and really not enough, and with the farm I worked on in the Falklands we had ex-bus batteries Nickel Iron. And we used them at 24 volt DC no attempt was made to get 230 volt.
Many years ago around 1958 I stopped in a caravan site where a DIY wind charger kept the toilet block lit, so I am sure there is a way, but the DIY methods are normally extra low voltage, and use panels designed for extra low voltage.
So if the club is willing to buy a new inverter to connect the panels and battery I am sure it can be done, but one is the price of the inverter, and two some one who knows how to select an inverter to do the job.