This paper proposes an evaluation study of the impact of mini-grid electrification projects on SDG7 (ensure access to affordable, reliable, sustainable and modern energy for all). Questioning the effectiveness of mini-grid development programmes on electricity access is essential because we have observed many failed cases in which the mini-grids stopped delivering on their promises a few years after commissioning the equipment. Our approach is based on night-time light (NTL) data. The methodology is designed and tested using mini-grid projects precisely localised and documented in published papers. We compare NTL data for each project before and after commissioning. We show that in about half the projects, NTL detects significant positive changes after commissioning. We build a test of impact, which confirms the causal nature of the observed effects of mini-grid projects on progress being made in SDG7, based on a comparison between non-treated localities matched with treated localities. But the domain of validity of this conclusion has limitations, related in particular to remoteness, extreme initial energy poverty and insufficient inclusiveness. These factors should be considered in the design of mini-grid development programmes.