After transport, building materials are a large energy consumer. Coming up with alternatives to concrete, steel, aluminium, and similar materials, possibly though biologics, whether low-tech like wood, or self-forming biocrete and biobrick.

Paving, especially.

and a TED talk https://www.ted.com/talks/michael_green_why_we_should_build_...

What I'm pointing out is that energy is a means to some service goal, and in the case of construction, alternate means to ends may well obviate much the need for new energy supplies.

Or taking an alternate formulation: rather than tap energy and convert and store and transform it multiple times to accomplish some goal, employ biological means to achieve the same end with far fewer (loss-entailing) energy transforms.

Trees, plants, algae, and/or microbes, operating over a large area, accomplish a very large net throughput. The questions are whether we can manage that, what outputs are possible, at what rates, and what subsequent changes in capabilities result. I suspect no biologic will have, say, the capabilities of steel. If we're limited to masonry or ceramic-based structures, the age of the 100-storey supertower is gone, but there are a many 10-20 storey towers which might be possible, resulting in high urban densities, if that's what we want.