The maintenance comments are a "red herring",as the system proposed by the OP would need similar levels of maintenance.
After all,the storage tank doesn't know where the hot water came from,& needs most of the same facilities.
The system proposed by the OP uses your existing electric hot water tank, adds a couple solar panels, some wire and a cheap circuit board. It's as simple as mounting a couple solar panels to the shed with some 2x4 treated lumber, running a wire and having a cool beverage.
The system proposed by the OP..
- Does not add pipes, tanks, PTC valves, check valves, directional control valves, elaborate insulation, closed loop 'refrigerants', mixing valves, expansion tanks, heat exchangers, pumps, electronic controllers, temp sensors or even a single additional joint.
- It does not use an inverter, grid tie solution, or batteries.
- There are no massive temperature fluctuations in the pipes/fittings causing expansion/contraction stresses.
- There is no worry of extra cold days causing freeze induced leaks, excessively hot days causing scaling, vapor lock, absorber fade, etc.
- There is no worry of equipment failure causing massive water/refrigerant leaking damage.
- There's no need to replace glazing, or refrigerants, recaulk seals, de-scale/drain the lines, or inspect for corrosion.
Maintenance of the OP's proposed system amounts to keeping snow off the panel.
Actually, in the spirit of this concept, you shouldn't even do that.. because it would unnecessarily push out the ROI.