In my shed, I've got a 12V 120AH leisure battery and 30A MPPT solar charge controller, on the shed roof there are three 100w 12V solar panels.
Do I need to ground any of those?
If yes, what is the best way of doing it?
There is no way to connect to house earth cable and there are no metal parts outside of the shed.
For 12V equipment you don’t need an earth connection as there’s no danger of electrocution at that kind of voltage. Leaving the whole system floating (not earthed) has the potential benefit that a short of any one part of the system to earth won’t cause a problem. As Erin has pointed out, a lightning conductor is something you might consider, but a strike is arguably less likely if the system isn’t earthed, but more likely if you erect elevated spikes; for tall structures where strikes are more or less inevitable they are worthwhile but if you get a strike close to your installation then it’s likely to be toast anyway.
I would say it depends on your height vs surroundings. If you are up on a hill and are likely to draw lightning, I would recommend grounding.
More importantly, you should place spikes slightly away from the panels and slightly above them so that they draw charges from the air and attract a lightning before it hits the panels.
Those spikes should be connected with a very thick wire, but usually the rails made for that purpose. The panel frames should be connected together with thick wires, but you should know that having a contact between 2 different metals causes galvanic reaction when there is any moisture, and one metal gets spent.
It depends where you are at and what do you have available.
I would suggest reading up on lightning protection and lightning arresters/surge protectors. You will give yourself the best protection hen you know a little more about those subjects and understand how (and why) they work.
Local electric codes may mandate protective earthing, but it is good practice anyway. Yes, earthing is needed for lightning protection. You’ll need to drive a ground rod or two into the earth. Do not use random structural metal as earth connection unless you verify that the structure is earthed. I have seen plenty of metal sheds that are not earthed.
