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The cost of reliability in decentralized solar power systems in sub-Saharan Africa


Although there is consensus that both grid extensions and decentralized projects are necessary to approach universal electricity access, existing electrification planning models that assess the costs of decentralized solar energy systems do not include metrics of reliability or quantify the impact of reliability on costs. We focus on stand-alone household solar systems with battery storage in sub-Saharan Africa using the fraction of demand served to measure reliability, and develop a multistep optimization to compute efficiently the least-cost system with the fraction of demand served as a design constraint, and take into account the daily variation in solar resources and costs of solar and storage. We show that the cost of energy is minimized at approximately a 90% fraction of demand served, that current costs increase, on average, by US$0.11 kWh–1 for each additional ‘9’ of reliability, and that this reliability premium could be as low as US$0.03 kWh–1 in a plausible future price scenario.

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Fig. 1: ASAI for countries in SSA.
Fig. 2: LCOE of Tier 5 decentralized systems in the present and future scenarios.
Fig. 3: Statistical relationship of LCOE and FDS in SSA.
Fig. 4: Spatial distribution of reliability premium.
Fig. 5: Predictive power of mean insolation on the LCOE.
Fig. 6: Cost difference between decentralized solar LCOE and grid tariffs.

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Data availability

All of the data used in this study, with the exception of the sample microgrid load profile from Uganda, is publicly available and referenced here. The sample microgrid load profile is owned by New Sun Road, P.B.C., and can be made available upon reasonable request. Tables on national electrification rates35, grid reliability28 and electricity tariffs34 used to generate Figs. 1 and 6 are included in Supplementary Table 1 for convenience. Solar insolation data are available from the US National Aeronautics and Space Administration38, and the code to download and analyse this data is available at the repositories listed above.


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We thank the US National Science Foundation for supporting this work through the CyberSEES program (award no. 1539585) and are grateful to J. P. Carvallo, R. Shirley, D. Kammen and I. Ferrall for their advice and comments. We also thank J. Sager and New Sun Road, P.B.C., for sharing their insights into decentralized system designs and sample data from their systems.

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J.T.L. contributed the primary development of the optimization program, methods and computer modelling. D.S.C. supervised the research effort. The authors jointly developed the research questions, analysis, conclusions and manuscript.

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Correspondence to Duncan S. Callaway.

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Supplementary Information

Supplementary Notes 1–4, Supplementary Figures 1–5, Supplementary Tables 1–4, Supplementary References

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Lee, J.T., Callaway, D.S. The cost of reliability in decentralized solar power systems in sub-Saharan Africa. Nat Energy 3, 960–968 (2018).

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