For water based systems: We propose the use of evacuated tubes with drain-back. These units are reliable, highly efficient and maintenance free, if installed properly. Smart controls do exist these days, which allow integration with existing DHW and heat- distribution systems in your house. Possible pool heating to extent the swimming season are also simple to add.
These units need to be installed on an existing, south-facing roof, with a 300/500 Ltr insulated tank, one or two small pumps and heat- exchangers located near your CV system.
A demonstration can be provided on request. These tube-panels are wind-insensitive and require no power to operate (heat-pipes) , except for the pump-unit and controller. Tank temperatures are limited to 80-85 Celcius for safety reasons, and provide ample DHW and CV support, if properly sized.