BEYOND THE 100% ASSUMPTION: ADJUSTING OnSSET TO REFLECT GRID RELIABILITY COSTS

The document introduces updates to the OnSSET tool to move beyond the assumption of 100% grid reliability. It proposes two proxies for the cost of non-supplied electricity: a parametric Cost of Non-Served Energy (CNSE) penalty and a diesel back-up system model. Testing in eastern Uganda shows that incorporating these reliability costs shifts the 'least-cost' preference from grid extension toward off-grid solutions, with the diesel back-up approach causing more significant shifts in technology mix and increasing total estimated investment by approximately 20%.

• The standard OnSSET model assumes grid extension provides 100% reliability, which is not reflected in its capital expenditure (CAPEX) or electricity cost calculations, whereas off-grid systems are sized with reliability requirements of 95-99%.
• The Cost of Non-Served Energy (CNSE) approach applies a monetary penalty for outages based on reliability indices like SAIDI; in the Uganda case study, this caused minor shifts from grid connections to solar home systems (SHS) and had limited impact on total investment because it acts as a shadow price.
• The diesel back-up system approach, which models the CAPEX and OPEX of generators to cover supply gaps, resulted in more significant shifts from grid extension to off-grid solutions and increased the total estimated investment of the least-cost scenario by approximately 20%.
• The CNSE approach is limited by its 'value-laden' nature, as there is no universal method for calculating the economic cost of outages, and it cannot currently capture sectoral differences (e.g., higher costs for hospitals versus residential users) at the settlement level.
• The diesel back-up approach relies on the assumption that all customers use generators to cover unmet demand and uses a generic average-to-peak load ratio for sizing, which may lead to undersizing critical loads or oversizing household systems.

APA

Sustainable Energy for All (n.d.). BEYOND THE 100% ASSUMPTION: ADJUSTING OnSSET TO REFLECT GRID RELIABILITY COSTS. https://www.seforall.org/system/files/2025-12/GridReliaiblityOnSSETWhiteReport.pdf

Chicago

Sustainable Energy for All. BEYOND THE 100% ASSUMPTION: ADJUSTING OnSSET TO REFLECT GRID RELIABILITY COSTS. n.d. https://www.seforall.org/system/files/2025-12/GridReliaiblityOnSSETWhiteReport.pdf.

Wikipedia

{{cite report |author=Sustainable Energy for All |title=BEYOND THE 100% ASSUMPTION: ADJUSTING OnSSET TO REFLECT GRID RELIABILITY COSTS |url=https://www.seforall.org/system/files/2025-12/GridReliaiblityOnSSETWhiteReport.pdf |access-date=17 August 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{sustainableenergyforallndbeyond, author = {{Sustainable Energy for All}}, title = {{BEYOND THE 100\% ASSUMPTION: ADJUSTING OnSSET TO REFLECT GRID RELIABILITY COSTS}}, institution = {Sustainable Energy for All}, url = {https://www.seforall.org/system/files/2025-12/GridReliaiblityOnSSETWhiteReport.pdf}, urldate = {2026-08-17}, note = {Indexed by Climate Insights Directory} }