Firewood does not constitute a "substantial amount", by any industrial measure. It will continue being used, in decreasing amounts as very cheap efficient stove designs gradually penetrate the tropics.

Growing algae occupies >10x the area of floating solar panels producing the same usable energy. Harvesting and processing algae costs >>1 orders of magnitude more than delivering electrical power via wire.

The reasonable expectation is that transitions will be toward cheaper alternatives, with societal inertia acting to delay transition well beyond the point of obvious benefit. Thus, existing nukes will continue operating well after building solar + storage and then switching to that would be cheaper.