Right. A useful sink for surplus energy could be something like surplus heat or electricity to synthesize carbon-neutral fuels. We're not likely to get large electric aircraft anytime soon.
Bitcoin mining is commonly promoted as this kind of ideal electricity consumer. Hydrogen production could be another.
However, I think more interesting for this community would be to build some kind of demand response general computing datacenter. Basically, sell computing resources with poor availability guarantees, but at a cheaper rate than standard datacenters.
i.e. we'll run your batch jobs very cheaply, but we can't give you strong guarantees about how long it will take because we have to wait for excess grid electricity to have the energy to run them. Best case that's every night. Worst case we won't be able to run anything for weeks because Texas is going through another freak winter storm.
I think you misunderstood. The parent comment implied that excess electricity could be use to produce synthetic fuels (via carbon capture) to power conventional airplanes, ships or other machinery.