In terms of efficiently using sun's energy. Let's not forget passive solar.
With no mechanical parts to break, a sufficiently heavy or phase change thermal mass can go a long way when the house is properly insulated. 4 m2 of windows (40 sq ft) is close toe 4 kW. (circa 12 000 BTU )
There's an interesting summary of the situation in the UK here.
In short, the most widespread option is likely to be heat pumps, despite some significant disadvantages, such as cost, and that fact that they don't always work well with existing heating infrastructure.
It may be that hydrogen, generated by renewable power, will also play a significant role - ...