04 Mar 2026
Study reveals unexpected long-term decline in energy use in small off-grid solar home systems
Collaborative research shows most households reduce electricity consumption after the first year, even when payments are not missed
Understanding how energy use evolves over time is critical to designing sustainable off-grid power systems. A new study led by researchers at the University of Oxford, in collaboration with UCL and BBOXX, has uncovered an unexpected trend in small pay-as-you-go off-grid solar home systems across sub-Saharan Africa: after an initial increase, energy consumption declines significantly over time.
Published in Energy for Sustainable Development, the paper, “Understanding long-term energy use in off-grid solar home systems in sub-Saharan Africa” analyses load demand data from 1,000 solar home systems to examine how daily usage patterns change over the lifetime of the systems.
Using dynamic time warping clustering, the researchers identified five characteristic daily load profiles and tracked how they evolved in time. The results show that 77% of households reduce their average daily electricity consumption beyond the first year of ownership, with mean demand falling by approximately one third by the end of year two.
Crucially, this decline persists even among households that did not experience missed payments, indicating that reduced long-term energy use cannot be explained solely by financial constraints. This challenges common assumptions about energy access and highlights the importance of long-term behavioural and system-level analysis.
The findings are significant for engineers and policymakers designing off-grid systems. If long-term reductions in demand are not accounted for, systems may be oversized, leading to under-use of solar generation capacity, sub-optimal battery cycling that could shorten system lifetime, and higher levelised costs for customers. The study demonstrates the value of long-term demand data for improving system design, financial modelling, and sustainable energy access strategies.
The research was conducted in collaboration with The Bartlett School of Sustainable Construction at UCL and industry partner BBOXX, with partial funding from the Royal Academy of Engineering.
The lead author Professor David Howey said: ‘‘Our research shows that access to electricity is not a static event but an evolving process. Long-term demand data is essential if we are to design off-grid systems that remain efficient, affordable and sustainable throughout their lifetime.’’
