In this guide
The short answer
To check monthly affordability, subtract your loan payment and remaining utility spending from what you would otherwise spend on electricity. A lower utility bill can still leave you paying more overall. Include other costs and compare a full year, not just the first month.
Start with twelve months of electricity costs
Add the electricity portion of your last twelve bills and divide by twelve for a monthly average. Exclude gas and unrelated services. If you are expecting a major usage change, make a separate scenario rather than quietly adding it to the baseline.
Compare that baseline with estimated post-solar utility spending over the same period. A summer production surplus should not be used to represent every month of the year.
Use the full monthly equation
Monthly cash-flow difference = baseline electricity expense − remaining utility expense − solar payment − other ongoing costs. A positive number leaves room in the budget; a negative number means more spending under those assumptions.
If utility charges are settled annually, set money aside for them. The average is useful for planning but does not mean your actual invoices will be equal each month. Maintenance, insurance changes and equipment replacement reserves may also affect the budget.
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Separate the system price from the loan
Request a cash price and financed principal for identical work. Then compare APR, term, any upfront costs and the total of scheduled payments. A longer term may reduce the monthly payment while increasing total interest.
The CFPB’s 2024 report describes solar loan markups and structures with payment increases tied to prepayment assumptions. Read your actual offer; these features should be checked, not assumed to exist in every loan.
Ask what happens after the introductory period
Get the complete payment schedule, including the payment if you do not make an expected lump-sum contribution. Identify any balloon payment, variable rate or prepayment conditions before comparing offers.
Do not fund a planned prepayment with a tax credit you are ineligible to receive. The IRS ended the residential clean energy credit for property placed in service after December 31, 2025. A new 2026 installation should not be modeled with that homeowner credit.
Monthly affordability and lifetime value are different
A purchase can have a long-term benefit while tightening your budget during the loan. Conversely, a small first-year payment does not establish a good lifetime deal. Compare both the annual cash flow and the full repayment commitment.
Run a less favorable case: lower production, more remaining grid usage or no utility-rate growth. If a modest change erases the projected benefit, get the assumptions verified before taking on the obligation.
Get a written illustration you can check
Ask for a year-by-year schedule separating utility expenses, loan payments and other costs. Keep claimed home-value increases out of the monthly budget: they are not cash available to pay a bill.
Our estimate shows a starting purchase scenario, not loan approval or lender comparisons. An installer can verify the site assumptions and provide an actual price; any financing illustration should identify the lender and complete terms.
Same $300 baseline, three different outcomes
| Monthly average | Lower spending | Break-even | Higher spending |
|---|---|---|---|
| Electricity before solar | $300 | $300 | $300 |
| Remaining utility expense | $60 | $80 | $90 |
| Solar loan payment | $220 | $220 | $240 |
| Combined spending | $280 | $300 | $330 |
| Difference before other costs | $20 less | $0 | $30 more |
| Annual difference | $240 less | $0 | $360 more |
What to request in writing
- Twelve-month electricity baseline and remaining annual utility estimate.
- Cash price, financed principal, APR and full loan term.
- Payment schedule with and without any planned prepayment.
- Total of payments and any fees paid outside the loan.
- Maintenance and other costs kept separate from utility savings.
Ready to check your own numbers?
Start with your home’s estimate. If you want a closer look, ask us to find an installer to verify the results and provide a written recommendation, price or savings illustration by email first. No sales call is required to request the introduction.
See my estimateContact details, including a phone number, are required only when you request an introduction. You can attach an electricity bill to help the installer verify usage. The bill is optional.
Related guides
Sources and assumptions
Examples on this page illustrate the comparison method; they are not installation quotes, financing offers or guaranteed savings. Use your current tariff and written proposal for a personal decision.
- CFPB: Solar Financing, August 2024 — fees and payment structures
- IRS: Residential Clean Energy Credit — current installation deadline
Read our estimate methodology and how this site makes money.