If you have enough solar, mini-splits are fantastic at heating or cooling. Even on-grid, they are generally much better than almost any other heating source, with the only better (more economical) sources being geothermal or cord wood, with pellets in the running depending on price paid. After factoring in the labor and mess of wood or pellets, and the capital costs of geothermal, mini splits are about as good as it gets. We live in Maine and have at least two sources of heat in our buildings, and our mini splits have been the primary heat source for the past two winters. They have performed well to below zero, and we've switched over to propane when it gets that cold primarily to give the propane boiler or Rinnai unit a "workout" to keep them running and make sure they're functioning if we do ever need them. We've yet to see a situation in which the heat pumps wouldn't perform well at heating.