Ill-formed question. You must put solar in context: latitude, insolation. Here in northern New Mexico, at 6000', my 7kW PV array(s) work extremely efficiently

Ill-formed question. You must put solar in context: latitude, insolation. Here in northern New Mexico, at 6000', my 7kW PV array(s) work extremely efficiently in winter, arguably slightly more efficiently than in summer because the panels prefer it cold. They collect somewhat less energy than in summer due to shorter days, but that's not a question of efficiency.