Solar project finance model: generation, costs and debt

A solar project finance model turns expected electricity sales into a period-by-period cash schedule and tests whether that cash covers debt. Start with approved generation, pricing and payment assumptions, then compare the base case with a clearly labeled downside case. A project can pay its scheduled debt and still miss its required coverage ratio.

Start with the project owner's files

This is a business review for a company owning a US commercial solar project. It uses generation estimates supplied by the project team; it does not estimate equipment performance or determine tax-credit eligibility.

Collect the construction sources-and-uses workbook, approved generation schedule, power purchase agreement, operating budget and lender repayment schedule. A power purchase agreement determines how electricity sales become revenue: the EPA describes solar power purchase arrangements as purchases of the system's electricity output over an agreed period.

Keep one row per project, period and scenario. Preserve assumption owners and approval dates alongside the amounts. Record whether electricity is measured in MWh or kWh and whether prices use the same unit. Revenue should reflect delivered, billable generation after any exclusions specified in the agreement.

The broader project finance spreadsheet structure covers construction funding and operating schedules. The solar-specific task here is connecting supplied output and contract terms to debt coverage.

Lay out the assumptions before calculating

The following are illustrative management assumptions, not market benchmarks. Put the values in column B, with the labels in column A. Amounts are USD except where another unit is stated.

Sponsor equity in B4 is =B2-B3. Debt plus equity must equal total uses: $6,000,000 + $4,000,000 = $10,000,000. Initial reserve funding, fees and construction-period interest belong in those uses if applicable; the recurring reserve contribution is a separate operating-year cash movement.

The zero cash-tax input simply isolates the operating and financing arithmetic. Replace it with the approved tax schedule before an investment decision. No tax-credit receipts are included.

Calculate cash available and debt service

Use cash amounts rather than accounting depreciation. A reserve contribution consumes unrestricted cash even when it is not an expense in reported profit. Likewise, an increase in working capital consumes cash before the project can pay lenders.

Cash available for debt service = Electricity receipts − Cash operating costs − Reserve contributions − Cash taxes − Increase in operating working capital

Debt-service coverage ratio = Cash available for debt service / (Principal repayment + Interest payment)

The federal laboratory's project-finance documentation defines debt-service coverage using cash available divided by principal and interest. The exact cash deductions for a contractual test must follow the financing agreement; the cash available for debt service schedule documents that bridge.

In this first-year example, receipts equal billed revenue, the full debt balance is outstanding throughout the year and principal is paid at year-end. Label B15 through B22 as revenue, cash available, interest, debt service, coverage, cash after debt, coverage headroom and closing debt. Enter the following formulas in those cells, in order:

=B5*B6
=B15-SUM(B7:B10)
=B3*B12
=B11+B17
=B16/B18
=B16-B18
=B16-B18*B13
=B3-B11

Carry full precision; show coverage to two decimals.

Change generation and follow every dollar

For the downside, change only billable generation from 15,000 MWh to 13,500 MWh, a 10.0% reduction. All other assumptions remain as shown above.

The downside still leaves $45,000 after scheduled debt payments, but misses the supplied coverage requirement. That distinction matters when considering distributions or additional borrowing. Read the contractual debt-service coverage test separately from the bank balance.

Prove the cash and carry the schedule forward

The base case must reconcile: $180,000 + $40,000 + $0 + $20,000 + $660,000 + $150,000 = $1,050,000 of receipts. The downside gives $180,000 + $40,000 + $0 + $20,000 + $660,000 + $45,000 = $945,000. Neither case creates unexplained cash.

Closing debt is $6,000,000 − $300,000 = $5,700,000. Carry that amount into the next period's opening debt, then use the actual repayment dates for interest. Carry approved generation changes, pricing escalators, maintenance and reserve movements through the remaining periods. A favorable first year does not establish lifetime debt capacity.

Use scenario analysis to keep a single changed assumption distinct from a combined downside. Finance owns the reconciliation; operations owns generation and maintenance inputs; treasury owns debt terms and covenant interpretation. The recurring review belongs within the company's FP&A analysis, with approved assumptions carried into each reporting period.

Where it goes wrong

• Generation and price use different units. Match MWh with USD/MWh before multiplying.
• Revenue is treated as cash immediately. Add collection timing when billed sales and receipts differ.
• Principal is treated as an operating expense. Calculate cash available before principal and interest, then deduct debt service once.
• Positive residual cash is called distributable cash. Check reserve restrictions and distribution conditions in the agreement.
• Only annual averages are reviewed. Examine payment periods, low-generation months and the minimum contractual coverage result.

Compare your prepared project scenarios in Covirage

Bring your approved project cash-flow workbook; Covirage maps the columns, and its tools compute and check the scenario figures, while the external AI model explains the differences with every figure traced to its rows. Create a free Covirage account and bring a sample of your own data; creating the account takes about a minute.

See project cost control for the supporting business context.