Net Present Value

What NPV tells a solar customer

SAM’s NPV documentation describes NPV as a financial feasibility metric incorporating revenues or savings and costs. It recommends evaluating NPV alongside other financial metrics. A result is conditional on the modeled cash flows and discount rate, rather than proof that a project should be purchased.

Record currency, reference date, analysis horizon, tax treatment and investor perspective. A project-level result and an equity-investor result may include different cash flows and cannot be compared as if their boundaries were identical.

Formula with a stated timing convention

For this explanation, use an initial outlay at time zero and net cash flows at the end of each year:

NPV = -C0 + sum(Ct / (1 + r)^t), for t = 1 through N

C0 is the initial outlay, Ct is each period’s net cash flow, r is the matching discount rate and N is the number of years. Software may use a different reporting reference or timing convention; check its documentation before reconciling a displayed result with a spreadsheet.

Small worked example

Suppose an illustrative project costs 1,000 monetary units today and returns a net 600 at the end of each of two years. At a hypothetical five-percent annual discount rate:

NPV = -1,000 + 600/1.05 + 600/1.05² = 115.65.

At ten percent, the same flows give 41.32. These are arithmetic examples, not solar quotes or recommended rates. For this particular cash-flow pattern, the higher discount rate reduces NPV. Do not increase a discount rate merely to improve an investment presentation.

Build the cash flows before selecting a headline result

For a customer project, document installed costs, electricity-bill savings, export treatment, operating expenses, equipment replacements and any residual or disposal value. Enter confirmed support at its actual expected timing. Do not assume a universal tax-credit percentage, first-year receipt or fixed electricity-price escalation.

If financing is included, define whether the analysis is for the project or the owner’s equity. Avoid charging both the full project cost and debt repayments without the corresponding financing inflow. Ask the model reviewer to check the cash-flow boundary and tax basis.

A battery comparison needs the incremental purchase cost, losses, dispatch assumptions and replacement costs, alongside any changed savings. A higher self-consumption percentage alone is not a financial return calculation.

Match nominal and real assumptions

Use a discount rate consistent with the cash-flow basis. Cash flows with inflation and escalation are nominal; constant-price cash flows use a real basis. Document the investor’s selected rate rather than assigning every homeowner or business the same range.

Test plausible alternatives for generation, prices, operating expenses and rate assumptions. Show what changed in each scenario and retain the original inputs. Sensitivity is useful precisely because future cash flows are uncertain.

NPV, payback and other metrics

Simple payback asks when cumulative undiscounted flows recover an initial outlay. NPV discounts the included flows over the chosen horizon. A shorter payback and a higher NPV need not identify the same option.

Compare projects using consistent currency, timing, perspective and scope. Consider liquidity, risk and operational constraints alongside the modeled value. A negative NPV is relative to the chosen assumptions and required return; it is not necessarily a negative undiscounted cash surplus.

Practical review

Ask for the cash-flow schedule, discount convention, assumptions and scenario changes behind the result. Use solar financial modeling to understand the wider workflow, and evaluate the inputs and reports available in SurgePV’s financial workflow. This definition does not certify a product calculation or replace a customer’s financial and tax advice.

Reviewed September 29, 2026 using the linked SAM metric documentation. Example rates are hypothetical; no current return benchmark, tax eligibility or observed customer result is claimed.