We can already capture solar energy at a much better energy efficiency than living beings. Making hydrocarbons with hydrogen extracted from water by electrolysis and concentrated carbon dioxide has acceptable efficiency and already almost one century ago it was possible to do this at a large scale where fossil oil was not available.

The step that has the least efficiency for now is concentrating the dilute carbon dioxide from air, which plants do much better.

There is no doubt that the global efficiency of such a process could have been greatly improved if only a small fraction of the resources allocated to much more frivolous goals had been allocated to this purpose.

While other alternatives are speculative, it is enough to look outside to see plenty of PoCs that this is feasible.

But the concept of “base load” is outdated. As I mentioned in another comment - Because actually “base load” nuclear is terrible in a grid increasingly full of nearly-free variable sources (solar&wind). The nukes need to stay at 100% all the time selling their power at a high fixed price to have any remote chance of being economical. Cheap variables push nuke's expensive power off the grid during the day, and increasingly into the evenings with batteries. This is unavoidable in an open energy market, and is fatal to the economics of nuclear.

The only way you can make it work is state subsidies and/or forcing people to buy the more expensive nuke power. Which will be unpopular. But maybe you can sell it as a “grid backup fee” or something.