It comes down to a cost-benefit analysis

When a potential utility-scale solar project is proposed in a rural community, many residents ask, “Why can’t we just use existing parking lots or rooftops for solar power instead of using farmable land?”

While rooftops are often suggested as an alternative to converting farmland into solar fields, they are not a viable substitute for meeting large-scale energy needs. The main challenge is the sheer scale of energy production required. Utility-scale solar farms can span hundreds of acres, generating enough power to supply entire cities. Rooftop solar, on the other hand, is inherently limited by the size, structure, and orientation of available rooftops. Even if every building in a region were equipped with solar panels, the output would fall short of the capacity needed to replace fossil fuels on a significant scale.

Another key issue is efficiency and cost. Utility-scale solar farms are designed to maximize sunlight exposure, with arrays oriented at optimal angles to capture energy throughout the day. Rooftops, however, vary in slope, direction, and shading, leading to inconsistent energy generation. Retrofitting rooftops for solar panels often involves additional costs, including structural reinforcement and maintenance, making rooftop solar less cost-effective for large-scale deployment. Moreover, the logistical challenge of managing energy generated from thousands of small rooftop installations complicates grid integration, especially compared to centralized utility-scale systems that deliver consistent output.

Lastly, rooftop solar fails to address the broader land-use strategy that utility-scale solar fields can support. Many solar farms are designed with dual-use strategies, such as incorporating pollinator habitats, sheep grazing, or other forms of agrovoltaics. This allows solar fields to coexist with agricultural and ecological functions, maintaining some of the land’s original purpose. Rooftops, by contrast, lack such multifunctional potential. While rooftop solar can be a good solution for individual households and businesses to reduce their electric bills, it cannot replace the efficiency, scale, and versatility of utility-scale solar farms.

Sources: Grist