> For example Haber process used for ammonia production, requires a temperature of at least 400 °C to be efficient.

I should note that this process doesn't require external heat input (except at startup). The reaction is exothermic and the excess heat is used to make steam that either is used to make power or to provide steam to other processes. It does require pressurization, but that's an input of work, not heat.

It would be nice if the process could be run at lower temperature, but we just don't have the catalysts for that.

> Electric resistance heating generated from PV will supply energy only for few hours each day.

Electric resistance heat is very storable and can provide heat 24/7, possibly even 24/7/365 at high latitude with PV.