Literature has established many social, economic, residential and environmental factors affecting photovoltaics (PV) adoption in developed countries. However in developing countries, only limited research has been conducted on the viability of micro-generation PV as a main stream clean energy source for greening the electricity grid. This study provides an insight into how residential PV adoption operates in a small developing country. Using a zero-inflated negative binomial regression model (ZINBM), this study compares the influencing factors of PV adoption in the Colombo district of Sri Lanka, a lower-middle income country, against the well-established factors of PV adoption in developed countries. The results suggest that highly educated middle-aged persons and retirees in the Colombo district are more likely to adopt PV. In addition, early adopters reside in larger houses of average, or above average, housing quality. In the short term, policies focused on expanding the knowledge base on PV technology, as well as incentivising the initial costs of installation, could increase the adoption rate of PV systems in Sri Lanka. In the longer term, increasing opportunities for tertiary education could accelerate the diffusion of innovations, as well as narrow socioeconomic gaps by even distribution of benefits of technological innovations.