Many of the composting toilets need some ventilation to work at their best. I know of one installation on a rocky island where there is no possible way to get hydro power so they use a composting toilet which has a solar panel to power the ventilation fans. Works fine in summer but its questionable if it is suitable for year round use with low temps and cloudy weather plus snow covering the solar panel. Somehow heat would need to be added to maintain the decompostion process. Incinerating toilets might be the way to go. Judging from the number of cottages on that side of the lake is there no power utility feed at that point?