The Swiss energy strategy aims at increasing electricity generation from solar power by 2050, to fulfil Switzerland's commitments in the Paris Agreement. However, the market of singleand two-family houses is characterized by low return rates for excess power injected to the grid, and the installation of rooftop solar photovoltaic (PV) is sensitive to financial incentives. We assess the drivers influencing the diffusion of rooftop solar PV systems until 2050, by employing an agent-based model. An agent is a single-or two-family house, and its decision to invest depends on the economic profitability of the investment, the agent's income, environmental benefits (injunctive social norm), awareness and knowledge about the solar PV technology, and the impact of the social network (descriptive social norm). The model includes a synthetic population of agents, statistically equivalent to the true population. We also investigate the impact of different support policies, technology learning rates, electricity prices, and discount rates on the investment decision. We find that the concept of prosumer emerges, mainly via self-consumption strategies. The diffusion process of rooftop solar PV systems in single-and two-family houses gains momentum in the future. In the near-term, PV deployment is sensitive to the profitability of the investment, while after the year 2030, peer effects play an increasing role in the agents' investment decisions.Energies 2019, 12, 2460 2 of 33 comparison, the EU average is 0.21 kW per capita in the same year. Among the European countries, Germany has the highest installed solar PV capacity per inhabitant (0.51 kW), followed by Italy (0.34 kWp), Belgium (0.33 kW) and Greece (0.25 kW) [7]. Energies 2019, 12, x FOR PEER REVIEW 2 of 35 Energies 2019, 12, 2460 3 of 33Accelerating the deployment of solar PV systems on residential buildings is claimed as an effective decarbonization strategy [2]. However, the market of single-and two-family houses in Switzerland has shown a deceleration of the annual sales of solar PV systems between 2014 and 2016 ( Figure 3), mainly attributable to the revision of the policy. As there are low return rates for excess power injected to the grid, system owners dimension their PV systems as small as possible to optimize their consumption. Given that the single and two-family houses constitute more than two thirds of the residential building stock in Switzerland [8], it is crucial to increase the adoption rate of solar PV technology in this sector to meet the climate change mitigation objectives (see for example [9]). Hence, the importance of singleand two-family houses in achieving a low-carbon energy system and the dependence of this particular market segment on the level and type of policy support [10], constitutes an interesting case study to examine and understand the dynamics of the adoption (i.e., investing) of the solar PV technology.Energies 2019, 12, x FOR PEER REVIEW 3 of 35Energies 2019, 12, 2460 4 of 33 versus leasing). Installers and experts can help to lift t...