BESS Project Financial Model – Battery Energy Storage

Two IRRs on the same project. The difference is the wear cost the seller’s model never charges you.

A professional Excel and Google Sheets financial model for battery energy storage (BESS) projects. Underwrite the project, size the debt against a real DSCR, and see what degradation actually costs before you commit equity.

What makes it different. Most BESS models draw capacity as a flat line and let you cycle the asset as hard as you like. The industry spent 2026 discovering that this is not how batteries behave: field data from operators running storage at scale has compressed expected asset life from fifteen years toward five, and multi-market revenue stacking – which maximises revenue – is precisely what accelerates the wear.

This model prints the optimistic view and the bankable view side by side. The developer view assumes flat capacity, unconstrained cycling and no augmentation. The bankable view applies cycle-linked degradation, caps throughput at the warranty envelope, and schedules augmentation capex as a dated event that restores nameplate capacity.

Proof, not assertion. Set both degradation inputs to zero and the two IRRs become numerically identical. The gap is the wear, not a modelling artefact – and the quality suite checks exactly that.

The result we did not expect, and kept. We built this model to show that cycling harder lowers the bankable return. It does not: aggressive stacking earns the highest IRR. We changed the thesis rather than bend the parameters until they agreed with us. What cycling harder really does is move risk onto you – it exhausts the guaranteed throughput years early and leaves cell replacement with no supplier cover. That exposure is quantified in dollars, separately, and deliberately not hidden inside the IRR through an invented risk premium.

Inside – 10 sheets, 600 formulas: Dashboard; Inputs with every assumption sourced or declared with a band; Revenue Stack (arbitrage, capacity payments, ancillary services); Cycle and Throughput against the warranty envelope; Degradation and Augmentation; two cash-flow views; the Two-IRR Bridge with the uncovered exposure; a three-way operating strategy comparison; and sensitivity.

Quality. 36 automated checks across three independent engines: a structural pass, a full Excel recalculation on every strategy and stress case with zero error cells, and a Google Sheets compatibility scan. Four are logic proofs.

Sources. Capex from NREL’s Cost Projections for Utility-Scale Battery Storage 2025 Update; degradation and asset-life from 2026 industry field reporting; ITC per the Inflation Reduction Act 2022. Inputs without a public source are marked as declared model inputs with a band.

Works in Microsoft Excel and Google Sheets. Yellow cells are inputs; everything else is formula-driven.

Educational and planning tool. Not financial, tax or legal advice.