To try to answer the original question : my guesses : Electric aircraft are going to be propeller driven *( at least for the foreseeable future ) = slow.
For unmanned or cargo aircraft ; I would guess 10.000 ft max. ( or above FL600 is solar rechargeable for long missions , like television relays for events, , observations, etc..)
For passengers carrying aircraft : electric pressurization cost energy, so why fly high? , but turbulence is an issue , so above weather , my guess will be between FL240 and 280 max.