Plug it in and attach a plastic bag over it as a temporary measure. If the bag gets blown of by the wind and it rains your rcd may trip. Not really recommended though.

Suer hot and 80% efficient must mean its also super insulated. For reference lithium batteries can be up to 99% efficient. I guess efficiency becomes less important if the power comes from renewable sources and the batteries are cheap. When excess renewable energy is available it makes absolute sense to use it rather than waste it.

New wallpaper, thanks wezzy!