Solar Payback Assumptions

Solar payback is simple to read but easy to distort. A few assumptions usually drive most of the result.

System cost

Lower EPC cost shortens payback, but very low cost may hide missing scope. Check whether the quote includes design, permits, grid connection, monitoring, racking, protection devices, installation, and after-sales support.

Self-consumption

Self-consumed energy is often worth more than exported energy. A home that uses electricity during daylight hours may recover cost faster than a home that exports most production at a low feed-in tariff. For businesses, load profile can be more important than roof size.

Tariffs

Retail electricity price, export price, time-of-use periods, and tariff escalation can change payback. Do not use a national average tariff when a project is billed under a specific utility contract.

Generation and losses

Shading, soiling, high temperature, wiring loss, inverter loss, and downtime reduce generation. A small percentage difference in annual output compounds over a 20-25 year project life.

Financing and tax

Debt can reduce upfront cash required but may reduce early cashflow through repayments. Tax treatment can change project economics materially, especially for business owners who may have depreciation, VAT, income tax, or incentive considerations.

A reliable payback estimate should include a conservative case. If the project only works in the optimistic case, it deserves deeper review.