Solar self-consumption viable on all Spanish roofs, regardless of orientation

Spanish researchers have discovered that 3 kW to 5 kW rooftop solar self-consumption systems can deliver competitive payback across most roof orientations, with coplanar designs often matching the performance of optimized setups at lower cost.

From pv magazine Spain

A group of researchers from the Polytechnic University of Cartagena and the University of Castilla–La Mancha studied real-life self-consumption photovoltaic installations that reflect the current profiles of Spanish prosumers. They evaluated 2,640 generation profiles from rooftop systems with nominal power outputs of 3 kW to 5 kW over a full year of operation.

A common trend among installers is the search for the optimal tilt and orientation to maximize output. But it is not always possible to reach these values on all roofs, so they are artificially “targeted.” These non-coplanar installations carry notable drawbacks, including structural complexity, higher costs, and increased roof loads.

In contrast, coplanar designs, where modules are aligned with the existing building surface, deliver nearly equivalent generation at significantly lower cost.

The study, “Alternative non-optimal orientations in highly PV self-consumption integration: Exploring Spanish prosumers as a case study,” published in Renewable Energy, offers new data on the viability of residential self-consumption photovoltaic installations in a wide range of rooftop configurations.

Contrary to the widespread belief that optimal energy production requires precise orientation and tilt, the results show that most existing rooftops can achieve competitive economic performance with their natural geometry.

In fact, when system design takes into account household demand profiles and appropriate sizing of peak power, payback periods remain favorable, even comparable to or better than those of conventional optimized configurations, according to the study's authors. Only roofs with extreme, predominantly north-facing slopes present significant performance drawbacks.

Once the compensation mechanism has been established, energy prices have been set, and the consumption profile has been selected, the compensation results and the annual savings achieved for each generation profile can be calculated. The annual savings achieved for each generation profile allow for calculating the payback period, i.e., the number of years required to recover the investment cost.

The results of this study underscore the potential for wider adoption of photovoltaics without the need for structural modifications, reinforcing the feasibility of leveraging existing rooftop conditions in residential environments. This phenomenon is largely attributed to better temporal alignment between electricity production and domestic consumption during peak tariff hours, especially in time-of-use and self-consumption pricing structures with surplus compensation systems.

“These results challenge the traditional paradigm that maximizing energy production should be the primary design objective for small-scale photovoltaic systems,” the authors explain. Instead, they support a more nuanced approach that prioritizes the system's economic performance, taking into account both market price variability and the self-consumption ratio. “Furthermore, the data presented highlight the importance of evolving remuneration mechanisms to fairly compensate prosumers, not only based on the volume of energy injected into the grid, but also on the temporal and systemic value of their contribution to local distribution networks,” they add.

The scientists suggest that policymakers rethink the design of support programs and regulatory frameworks: “Traditional policies have tended to reward total energy generation, but this work shows that this approach may not be consistent with optimal grid integration or economic efficiency. Instead, policy instruments that incentivize demand-driven system design and reward local self-consumption, such as dynamic tariffs, smart metering incentives, or capacity-based subsidies, are recommended. These initiatives could accelerate PV deployment and reduce pressure on the grid,” they conclude.

Finally, for system operators and grid planners, the study highlights the role that decentralized, demand-synchronized PV systems can play in stabilizing local grids and improving load management. In this context, the methodology provides a valuable tool for assessing the potential of distributed generation—that is, when and how energy is injected into or demanded from the grid.