A group of researchers at the University of Oxford in the United Kingdom has investigated the consumption behavior of 1,000 households relying on off-grid solar home systems (SHSs) across sub-Saharan Africa and has found that their vast majority tend to significantly reduce power consumption, after an initial increase, from the start of operations.
“Our analysis shows 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,” the research's lead author, David A. Howey, told pv magazine. “This decline persists even in households that do not experience missed payments, indicating that reduced long-term energy use is not solely driven by financial constraints.”
“Our findings demonstrate the value of long-term demand data for understanding how electricity access evolves,” said co-author Priti Parikh. “Long-term reductions in consumption can leave systems oversized, leading to under-utilisation of available solar generation, sub-optimal battery cycling that may shorten lifetime, and higher levelised costs for customers.”
In the study “Understanding long-term energy use in off-grid solar home systems in sub-Saharan Africa,” published in Energy for Sustainable Development, the research team explained that its analysis considered the daily SHS load-demand profiles of the households and patterns in real-world data, as well as payment and energy data under the pay-as-you-go (PAYG) model.
PAYG solar across Africa enables low-income families to obtain solar home systems through affordable, incremental payments rather than large upfront fees. Users generally make payments through mobile money platforms, which activate or extend their electricity access.
The model has drawn digital and telecommunications companies into the energy market, but its success hinges on consistent repayments in economically vulnerable settings marked by irregular incomes and inflation. It also faces a structural constraint: many households have limited ability to increase their electricity spending, and in areas where the grid exists, off-grid solar power often ends up costing more than grid-supplied electricity.
“The PAYG approach allows users to top-up usage when they desire, in their local currency, and enables them to stop paying on certain days if they wish. However, when payment stops, electricity supply is also stopped,” the scientists emphasized.
For their analysis, they used a dataset provided by London-based off-grid solar company Bboxx, which generally offers packages including a 50 W solar panel, a 12 V, 17 Ah lead–acid battery, and various DC loads. It comprises data from solar systems deployed mostly in Kenya, Togo, the Democratic Republic of the Congo and Rwanda between September 2018 and December 2020, with consumption data until January 2022.
The analysis led to the identification of 647,021 daily load profiles and 5 archetypal daily load profiles, which the scientists called low use, moderate use, nighttime use, single peak and double peak, in order of increasing mean energy use.
Stratified sampling grouped the data by daily energy consumption to preserve the overall distribution in a representative subset. Ten representative days per household were initially selected, yielding 10,000 time series, and this set was then reduced to 2,000 using the same approach to maintain diversity while enabling efficient clustering.
Cluster centres were subsequently identified, and all 647,021 daily load profiles were assigned to their nearest cluster. Each household was ultimately represented as a chronological sequence of days, labelled according to its closest load-profile cluster.
The analysis showed that most of the solar systems utilized under the PAYG scheme are only fully utilized and provide basic supply, covering moderate daytime use and limited nighttime consumption.
It also demonstrated that household energy use is highly variable, with day-to-day behaviour showing only 55% cluster homogeneity on average, and that over periods of up to 1,200 days, energy consumption trends reveal a gradual decline across both high- and low-consuming households. “While economic outages are not uncommon under the PAYG scheme, they are not the sole reason for decreasing energy consumption, indicating that changes in energy behaviour extend beyond financial considerations. The decrease in energy consumption when not in the economic outage state is characterised by a decrease in nighttime energy use, and reduction of days with large evening peaks,” the scientists explained.
Households with predominantly single- or double-peak profiles were found to show slightly higher utilisation, yet even these systems experience economic outages.
“Overall, the systems are often underused and therefore oversized, leading to knock-on effects on costs for households and suppliers,” the academics concluded. “The significant proportion of economic outages suggests that costs remain a limitation for many households, warranting further investigation into how to maximise energy provision from each solar system in order to reduce the overall cost of energy. There is a need for solar system designs and pricing structures to better align with the actual energy requirements of households.
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