Stirling engines are woefully inefficient tho, PV panels are better unless you’re intending to supplement heat source with biomass or such. In a climate where most of energy is used for heating and little to none on AC, it just makes more sense to use solar collectors instead of PV because most of energy use will be in form of heat anyway, and per square meter collector will deliver much more. If you can couple excess heat production to seasonal energy storage, this gets you most or all of heat needs year round covered by solar, if you don’t there’s still free hot water in the summer and seriously lowered gas bill through the year. Small PV panel might make sense to keep pumps running or cover some of the rest of needs but won’t shift balance heavily either way. In a place where major use of energy is AC this approach makes no sense and PV panels with daily or a bit longer lasting storage of energy, be it in batteries or thermal (tanks of cold glycol or ice or whatever) would be the way to go, because the most sunny day is also the day when you need AC the most and this way you get most of your energy needs covered