Use the cash price as the project-cost baseline
Ask what the identical solar system costs without the proposed financing. That cash-equivalent price separates the underlying project from the cost of credit and is the cleanest starting point for comparing installer $/W.
If the project includes a battery, roof work, main-panel upgrade or other separately itemized non-solar scope, keep those amounts distinct when comparing the solar-only cash price.
A solar loan adds a financing layer on top of the project
For a loan, record the financed principal, APR, term and total scheduled payments in addition to the cash price. Home Solar Atlas calculates the percentage premium versus cash only for a confirmed loan because that comparison uses two prices for the same purchased project.
Do not use the same premium formula for a lease or PPA. Those contracts have different payment and ownership structures and need their own long-term review.
Dealer and program fees can make the financed principal much larger
The CFPB has reported that some solar-specific loans include substantial markups and fees embedded in the principal, with some loan amounts increasing by 30% or more above the cash price. A low advertised interest rate can therefore coexist with a large financed-price premium.
Ask whether dealer, platform, origination, finance or program fees are embedded in the principal and compare at least one financing option that shows the identical system's cash price clearly.
The old 30% homeowner federal credit is not a 2026 default
The IRS says the Section 25D Residential Clean Energy Credit is not allowed for expenditures made after December 31, 2025. A new 2026 residential solar purchase should therefore not be evaluated by automatically reducing the project or loan balance by the old 30% federal homeowner credit.
Verify any state, local, utility or other incentive separately, including eligibility and timing, before treating it as money available for a down payment or early principal reduction.
Compare total cost and liquidity, not only the monthly payment
Cash normally avoids loan interest and financing markups but uses household liquidity. A loan preserves more cash upfront but can increase total cost. Put both options on the same decision timeline and compare the cash outlay, financed principal, interest, fees, total scheduled payments and the value of retaining liquidity.
If the loan includes re-amortization or an expected early principal payment, model the higher-payment path too rather than assuming a future incentive or refund will fund the step-down.
Use the proposal tools with the actual financing structure
Quote Analyzer and Compare Solar Quotes keep solar-only $/W separate from loan math. For a confirmed loan with a financed amount, financing readiness requires APR and loan term; the original loan documents still control fees, payment changes, prepayment rules and total obligations.