Current solar systems are always bivalent, as they can never be solely responsible, at least not year-round, for supplying heating energy. They are therefore connected upstream with conventional systems and function as “fuel savers” by transporting more or less preheated water to the downstream heating system.

To consider the economics of a solar thermal system, the investment costs are applied to the lifetime of the system, taking into account simple interest and an amount for maintenance and operating costs. In relation to the annual heating amounts supplied, this gives the heating price in cents/kWh. The heating price for a kilowatt hour generated by solar energy is of the same order as the generation of hot water from electrical current, now considerably lower for larger systems.

This development will also enable and intensify the use of solar thermal systems in medium-rise housebuilds in the coming years. The money saved from the oncosts of burning fossil fuels is not included here. However, the slightly higher heating energy bills are becoming accepted by many tenants today as a result of an improved social image and a considerable improvement to residential surroundings with the visibly ecological “advertisement”.