Adoption and spatial distribution disparities of residential plug-in and rooftop photovoltaic systems in Germany

In contrast to residential rooftop photovoltaic systems, plug-in photovoltaic systems offer a significantly lower barrier to entry in terms of upfront costs, installation complexity, and the need for roof space. These attributes make them appealing to a wider demographic and position them as transformative tools in the energy transition, opening opportunities for broader participation in renewable energy and aligning with the growing emphasis on energy justice and inclusivity. Nevertheless, adoption patterns for plug-in PV systems are not well understood, especially given their unique characteristics, which limit the applicability of insights derived from residential rooftop systems. This study addresses this research gap by applying spatial econometric models to investigate plug-in PV system adoption, revealing pronounced disparities. Our findings show that income support recipients are less negatively associated with plug-in PV adoption compared to larger rooftop systems, indicating that the lower upfront costs of plug-in PV systems may reduce financial barriers. Furthermore, the influence of household income on adoption is weaker for plug-in systems, suggesting that these systems may be more accessible to lower-income households. Contrary to expectations, solar radiation plays a less significant role in the adoption of plug-in PV. Additionally, the negative effect of the proportion of rented apartments on adoption is less pronounced for plug-in systems, highlighting their suitability for renters. Regional subsidies have demonstrated a positive impact on plug-in PV adoption, further emphasizing the potential of targeted support programs. Our findings can equip policymakers with the necessary insights to formulate strategies promoting the uptake of plug-in PV systems.