> Less than 100% reliability is essential for the sustainability of an off-the-grid solar system, because above a certain threshold the fossil fuel energy used for producing and replacing the batteries is higher than the fossil fuel energy saved by the solar panels.

I wonder if whoever wrote this has actually done the calculations. These days it's not really difficult to provide fairly reliable solar power by overgenerating while still beating fossil fuels - perhaps not beating them as much as with zero overgeneration, but beating them anyway. So I'd take the quoted text with a considerably large grain of salt.