Most Spanish rooftops can host cost-effective solar — no perfect tilt required

New research shows that 3–5 kW coplanar rooftop PV systems deliver nearly the same returns as “optimized” setups — but at much lower cost.

A research team from the Polytechnic University of Cartagena and the University of Castilla–La Mancha analyzed 2,640 real-world rooftop PV profiles (3–5 kW systems) over a full year. Their study challenges the long-held belief that solar panels must be installed at the “ideal” tilt and orientation to be economically viable.

While many installers chase optimal angles, these non-coplanar setups add structural complexity, higher costs, and heavier roof loads. In contrast, coplanar designs — flush with the roof surface — deliver almost equivalent generation at far lower cost.

The findings show that payback periods remain competitive across most roof orientations, provided systems are sized to match household demand and Spain’s self-consumption with surplus compensation schemes. Only north-facing roofs present notable performance drawbacks.

The authors argue that economic performance, not just maximum energy yield, should guide small PV design. They also call on policymakers to reward prosumers based on the local and temporal value of their generation — through measures such as dynamic tariffs, smart-meter incentives, or capacity-based subsidies.

For grid planners, the study underscores the role of distributed, demand-synchronized PV in stabilizing networks and easing load management.