Why payback is the wrong first question
Most conversations about commercial solar open with a single question: how long until it pays for itself? It feels like the right place to start. It isn't.
Payback period treats a 25-year asset like a short-term purchase. It ignores what the system earns after it has paid for itself, it ignores rising grid prices, and it flattens the difference between a system sized for your actual load and one sized to look good on a brochure.
A seven-year payback on the wrong system is worse than a nine-year payback on the right one.
What actually drives the numbers
Three things move a commercial solar business case more than anything else: how much of the generation you use on site, what you pay for grid electricity today, and how those prices move over the life of the system. Get those right and the payback period takes care of itself.
The work that matters happens before a single panel is specified — in the load analysis, the tariff review, and an honest read of how your site actually uses power across a day and a year.
1. Map your real load
Pull at least twelve months of interval data and look at when you actually draw power. Self-consumption — using solar generation on site rather than exporting it — is where the value is.
2. Read the tariff, not the headline rate
Demand charges, time-of-use windows, and lines charges often matter more than the per-unit rate. A system designed against your specific tariff structure earns more than one designed against an average.
3. Model the 25-year curve, not the break-even point
Look at lifetime return, not just the year you cross zero. Rising grid prices mean the most valuable years of a solar asset are often the later ones.