If his winter heating need is that large he may live in an area where solar does not produce that much electricity during winter. I myself live in an area that has 0 (yes zero) sunlight for one winter month because of the polar night and just 1-4 hours of very low intensity sunlight for the rest of the 5 month long winter. In summer when we have midnight sun, literally 24 hour sunlight, the electricity is almost free so whatever the solar panel produces then is near useless. Also you simply don’t use that much in that season. For me at least it’s not really a worthwhile investment.