Fostering investments in green technologies through social norms is a cost-effective alternative to financial incentives. The success of energy efficiency programmes incorporating social influence methods depends on the extent to which individuals in a social system consider peer behaviour in their decisions. This study investigates the impact of geographical concentrations of personality traits on peer effects for solar photovoltaic (PV) systems. Using data on the Big Five personality traits of 375,000 individuals and adoptions of solar PV systems across 2600 postcode districts in the UK, a first-difference fixed effect regression model is estimated to analyse the link between the personality traits and the peer effects. The results suggest that districts with spatial concentrations of Openness to Experience and Conscientiousness exhibit stronger peer effects, but only under settings of low financial subsidies for solar PV systems.