Example Germany: roof solar thermal, 4–6 m² collector, 300 l tank, hydraulics complete: 1,500–2,500 € installation only (excl. components). Materials + buffer tank: additional 4,000–6,500 €. Total investment typically 6,000–10,000 €. In Poland 30–40 % below German levels.

Example Germany: PV with heat pump pays back better today (electricity is universal, longer 25+ year lifetime, clear subsidies). Solar thermal only makes sense with very high hot-water demand or in legacy heating with a buffer tank. Market shrinking 30 %+ since 2020.

Flat plate: simple, cheap, up to 75 % efficiency, up to 90 °C operating temp. Evacuated tube: 15–30 % more efficient especially at low outdoor temperatures, more expensive, higher stagnation risk. Choice depends on target use and roof orientation.

South ±20°, tilt 30–45° for hot water. Steeper 45–60° for winter heating support. East/west orientation possible but yield 15–25 % lower. Avoid shading from trees or neighbouring buildings – even partial shading halves yield.

Under heat and pump off, solar fluid in the collector evaporates. The system must be 'stagnation-proof': adequately sized expansion vessel, rising layout to the collector, heat exchanger at the tank bottom. After multiple stagnations: check glycol and replace if needed.

Wrong heating-circuit integration with lost solar gain, leaky collector unions, failed frost protection from glycol degradation (check every 5 years), too small expansion vessel with frequent pressure drops, missing vents on the collector flow.