Relying entirely on solar water heaters may not be enough in winter. It would be more economical to install both. Of course, the height of the floor should not exceed six floors. On the 6th floor, the cold water from the hose can be collected and put into the washing machine without wasting much.
Air water heaters are suitable for areas south of the Yangtze River, where the temperature is low and cannot achieve energy saving effects. Additionally, they are larger and only suitable for. the top or first floor.
If you value environmental protection, just use solar water heaters, but I personally think that air-to-energy water heaters are not as efficient as electric water heaters because the Electric water heaters have fewer restrictions.