In this paper, the analysis of the diffusion of photovoltaic systems is performed using the Bass model. The historical data of installed rooftop photovoltaics are not enough for the model, as the installation of photovoltaics was almost non-existent; hence data of solar water heaters are utilised to calculate the parameters for the model. The trajectory of growth for solar water heaters in the market presents a congruence for the growth of solar photovoltaics due to inherent similarities in the technologies and their application. India was used as a case study of the application of this borrowing approach in a market where PV is also used to provide electricity to local communities. Data from India's solar water heater market were used, indicating an innovator parameter of 0.00105 and an imitator parameter of 0.12219. The study is significant as it forecasts the diffusion of photovoltaics in the market, which is essential for achieving India's Intended Nationally Determined Contributions goals and Renewable Energy targets. The results indicate that residential rooftop photovoltaic diffusion will tend to present slower in India than in other markets if no additional policies are implemented to foster this market.