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Solar Loan APR Unmask Calculator

Enter your solar loan offer and the cash price of the system — see the real APR hidden behind the low advertised rate and the dealer fee markup.

Your solar loan details
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%
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True cost of your solar loan
Real APR: 6.35% (advertised: 2.99%)
Hidden dealer fee$13,000 (40.6% markup)
Advertised monthly payment$213.16/mo
Total interest paid (loan)$18,948
HELOC at 7% monthly (cash price)$226.17/mo
Total HELOC interest (same term)$35,851
Cash buyer advantage over loan$31,948
Break-even vs HELOCNever yrs
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How to Use This Calculator

Enter your loan offer details

Start with the financed system cost — the number on your solar loan agreement. This is almost always significantly higher than what a cash buyer would pay for the same system, because the installer has added a "dealer fee" (also called a finance fee) to cover the cost of offering you the loan. Next, enter the advertised APR from your loan offer and the loan term.

Enter the cash price — the key input

Ask your installer what a cash buyer would pay for the exact same system. This number should be 20-30% lower than the financed price. Some installers refuse to disclose this — which is itself a red flag. If you can't get it, use 75-80% of the financed price as a reasonable estimate. This "cash price" is the true market value of the solar system.

Read your real APR

The calculator solves for the true interest rate you're paying based on the actual cash value of the system and your monthly payment. A 2.99% advertised loan on a $45,000 financed system where the real system costs $32,000 cash works out to a ~7-8% real APR — comparable to a standard home equity line of credit.

The Formula

Monthly Payment = Financed Amount × (r / (1 - (1+r)^-n)) where r = monthly rate (APR/12), n = months Real APR: solve for rate where PV = Cash Price, PMT = Monthly Payment, n = months (binary search / IRR calculation) Hidden Dealer Fee = Financed Amount − Cash Price Dealer Fee % = (Financed − Cash) ÷ Cash × 100 Total Interest (loan) = Monthly Payment × Months − Financed Amount Total HELOC Interest = HELOC Monthly × Months − Cash Price Cash Buyer Advantage = Total Loan Paid − Cash Price

The real APR calculation is an internal rate of return (IRR) solve: given that you're making payments of X per month for N months, what interest rate makes the present value of those payments equal to the true cost of the asset (cash price)? This is the rate that honestly represents the cost of your financing — not the rate applied to an artificially inflated principal.

Example

Sarah — Evaluating a "2.99% solar loan" offer

Sarah is offered a solar system for $45,000 financed at 2.99% APR for 25 years. She discovers that a cash buyer could get the same system for $32,000. She wants to understand what she's really paying.

Financed amount$45,000
Advertised APR2.99%
Loan term25 years (300 months)
Cash price$32,000

Result

Hidden dealer fee$13,000 (40.6% markup)
Monthly payment$213/mo
Total interest paid~$18,900
Real APR~7.4%
HELOC monthly (7%, cash price)$226/mo
Cash buyer advantage~$31,900 total cost savings

Sarah's "2.99%" loan is actually costing her ~7.4% in real financing terms because she's borrowing $13,000 more than the system is worth in cash. Over 25 years, she'll pay $63,900 total ($45,000 principal + $18,900 interest) for a system a cash buyer gets for $32,000. The HELOC would be nearly identical in monthly cost but on the true system value.

FAQ

The advertised APR is technically accurate — it's the interest rate applied to the financed amount. But the financed amount includes a "dealer fee" that inflates the loan principal 20-40% above the system's actual market value. Your monthly payment is calculated on this inflated principal, meaning you're paying interest on money that went directly to the lender as a fee — not into your solar system. The real APR accounts for this by measuring the cost of financing relative to what the system actually costs a cash buyer.
Yes — in specific situations. If your alternative to the loan is leaving cash in a savings account earning 2-3%, a 7-8% real APR solar loan still provides net positive returns from solar electricity savings. If you don't have $30,000+ in liquid cash, financing is the only option. And for the 26% federal tax credit: if you can't pay cash but can still claim the full ITC on a financed system, the credit substantially improves the economics. The problem is when buyers assume the advertised low rate means the financing is free — it isn't.
A dealer fee (also called a finance charge, origination fee, or back-end fee) is the cost a solar lending company charges the installer for providing loan products to their customers. The lender fronts the low-APR loan to the customer but charges the installer 15-30% of the loan value upfront. The installer recovers this cost by inflating the financed price. For example: a system that costs $32,000 in cash becomes a $42,000 loan — the extra $10,000 is the dealer fee flowing from you to the lender. This structure allows lenders to offer low headline rates while maintaining profitability.
If you have sufficient home equity, a HELOC often provides better economics for solar financing. Key advantages: (1) You borrow the actual cash price — no dealer fee markup. (2) HELOC interest may be tax-deductible if the loan improves your home (consult a tax advisor). (3) HELOCs are typically flexible — pay down principal faster without penalties. The main drawbacks: HELOCs have variable rates (rising rate risk), and you're securing the debt against your home. A home equity loan offers the same cash-price borrowing with a fixed rate — often the best of both worlds.
Ask the installer directly: "What would this exact system cost if I paid cash today?" A reputable installer will tell you. Red flags include refusing to answer, claiming "the price is the same either way" (it never is), or showing you only monthly payment comparisons. You can also get 2-3 competing cash quotes for similar-sized systems from other local installers — this gives you the market reference price. EnergySage's marketplace shows installer cash prices side-by-side, making it easy to benchmark.

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  width="100%" height="620" frameborder="0"
  title="Solar Loan APR Unmask Calculator"></iframe>