Solar & photovoltaic business plan: the complete guide

The business plan of a solar project (or photovoltaic plant) turns its economics into numbers: how much it generates, how much it sells, what it costs to build and operate, how it is financed, and what it returns to the shareholder. Done well, it is the document that convinces a bank or an investment committee. Here is the method, brick by brick.

1. Yield: P50, P90 and degradation

It all starts with the energy produced. You estimate an annual yield (in MWh) from the site irradiation, the installed capacity (MWp) and the performance ratio. Two scenarios stand out:

• P50: median generation (50% chance of being exceeded) — the base case of the business plan.
• P90: a prudent generation level (90% chance of being exceeded) — the one the bank uses to size the debt.

You also apply an annual degradation of the modules (often 0.4 to 0.7%/yr) over the whole life (30 to 40 years).

2. Revenue: feed-in, PPA or market (merchant)

Revenue depends on how the electricity is valued:

• Feed-in / contract for difference: a tariff awarded through a tender, indexed, over the long term — highly visible revenue.
• PPA (Power Purchase Agreement): a bilateral contract with an offtaker, at a fixed or indexed price.
• Merchant: sale at market price (spot / forward price curve) — more potential upside, more risk.

Many projects combine a contracted period (feed-in/PPA) then a merchant period at end of life. The business plan must model that switch — and that is often where spreadsheets go wrong.

3. CAPEX and OPEX

The CAPEX (upfront investment) breaks down into several items. Modelling it line by line, and staging it across construction, changes the debt drawdown schedule and therefore the equity required.

CAPEX is often expressed in €/kWp to compare projects, and has fallen sharply for ground-mount PV. The OPEX (annual operating costs) covers operation & maintenance (O&M), insurance, land lease, administration and inverter replacement. It is expressed in €/kWp/yr and grows with inflation: an underestimated OPEX inflates the margin over 30 years.

4. Financing: gearing and sculpted debt

A solar project is financed with senior debt + equity. Two sizing logics coexist:

• By gearing: a fixed percentage of CAPEX (e.g. 80%).
• By DSCR (sculpted debt): debt is calibrated to meet a target coverage ratio every year.

The DSCR (Debt Service Coverage Ratio) is the metric the bank watches: it measures the ability of cash flow to cover debt service.

5. Taxes

A credible solar BP includes the applicable corporate and production taxes for the jurisdiction (in France, corporate income tax, plus local and grid taxes such as CVAE and IFER). Forgetting a production tax, for example, overstates the returns.

6. Return metrics

From there you derive EBITDA, cash flows, then the key metrics: IRR (project and equity), NPV, DSCR and LCOE. They are detailed in our guide on IRR, NPV, DSCR, LCOE.

7. Common mistakes

• Using P50 to size the debt (the bank thinks in P90).
• Forgetting module degradation or the end of contracts (merchant switch).
• Neglecting taxes and working capital.
• A "non-auditable" spreadsheet where one wrong cell breaks the whole result.

8. Sensitivity analysis and scenarios

A business plan is never a single number, but a range. The variables that move a solar project's returns the most are usually: the power price over the merchant period, the yield (P50 vs P90), the debt rate and the CAPEX. Testing each one in isolation (sensitivity), then in combination (optimistic / base / stress scenarios), reveals the project's real robustness — exactly what a credit committee examines.

9. Estimate returns quickly

For a first order of magnitude before building the full model, use our solar ROI calculator: it estimates IRR, NPV, LCOE and DSCR live from capacity, price, CAPEX, OPEX and debt structure. For a bankable, consolidated business plan, see the solar business plan software.

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