If two solar proposals use the same headline capacity, comparing their totals is only a starting point. One may exclude supporting work; another may show a financed payment rather than a cash price. A production forecast can also use different assumptions from the neighboring quote.
The useful first result is a matched comparison with named unknowns. This article gives a free checklist and one hypothetical price example. It does not estimate your home's production or recommend a contract or loan.
Check what the number measures
Keep DC array capacity, inverter AC rating, annual kWh and dollars in separate columns. For example, 20 modules rated at 400 W total 8,000 W, or 8 kW DC. That is a nameplate check, not a forecast of 8 kWh in every hour or a household bill reduction.
PVWatts estimates photovoltaic energy production using inputs such as DC size, array type, losses, tilt and azimuth. Its own cautions describe assumptions and uncertainty. Ask providers for the input record behind each forecast; this article has not run a model for your address.
Use this free matched-offer checklist
Copy these lines into a document with columns for Offer A, Offer B, evidence and the next question. Keep actual quotes beside your analysis adjustments.
- Document: installer, equipment owner, lender, revision date and complete attachments.
- Equipment: DC capacity, AC inverter rating, exact models and any storage listed separately.
- Scope: roof review, supporting electrical work, access, applications, monitoring and exclusions.
- Energy: model inputs, monthly kWh and the exact contractual guarantee if any.
- Bill: self-use/export assumptions, utility tariff, remaining fixed charges and excluded effects.
- Payments: cash price, financed obligation, lease or PPA, full schedule and escalation basis.
- Future events: maintenance, roof work, transfer, early end and end-of-term options.
A lower headline cash price can reverse
Original invented USD example: both offers list 8 kW DC. Offer A quotes $22,400, with an assessed $1,800 supporting-work package and $600 of application costs excluded. Offer B quotes $24,000 including those same tasks. Assume all other scope is matched:
| Comparison line | A | B |
|---|---|---|
| Actual headline cash price | $22,400 | $24,000 |
| Matched analysis additions | $2,400 | $0; included |
| Complete comparison total | $24,800 | $24,000 |
| Comparison dollars per DC watt | $3.10/W | $3.00/W |
A's original $2.80/W headline becomes $3.10/W on this basis. The $800 comparison difference favors B only under the stated assumptions. It is not a national price benchmark, quality ranking or promised saving. Ask for written inclusion confirmation and a revised offer; an owner spreadsheet does not amend a proposal.
Ownership changes what you are comparing
The FTC solar consumer guide distinguishes buying a system, leasing it and buying its power through a PPA. Equipment ownership and the payment basis matter. Keep the remaining utility bill alongside the solar obligation, and check what the agreement says about maintenance and a future home sale.
A monthly lease amount and a PPA rate per kWh are different units. Ask for billable quantities and escalation terms before comparing annual costs. Do not assume an advertised annual generation figure has the same financial value as that many kWh avoided at a retail import rate.
Put the cash price beside financing
Ask for the identical installation's cash price and full lender disclosures. Record every payment period, any expected lump sum and any later payment reset. The CFPB's August 7, 2024 report describes embedded financing markups and risks associated with assumed prepayments. It is historical consumer-risk context; its market and tax discussion is not current 2026 guidance.
For a simple schedule with no other payments, monthly amount multiplied by payment count gives its nominal total. This does not establish APR, affordability or the best option. Reconcile it with the lender's actual disclosures and use qualified independent advice for unclear obligations.
Do not automatically subtract a federal credit
As checked October 27, 2026, the IRS Residential Clean Energy Credit page explicitly says the credit is unavailable for property placed in service after December 31, 2025. Our new-installation examples therefore assume no new homeowner federal credit. Older passages or sales materials describing a 30% benefit should not silently become a 2026 household cash assumption.
For any other claimed benefit, record the program, source date, eligible recipient and timing. A benefit to the equipment owner is not automatically money payable to the homeowner. Confirm current terms with the administering authority and a qualified adviser as appropriate; this is not individual tax advice.
End with the missing answer
Write which exact difference prevents a fair comparison, who must answer and what document will resolve it. A scope clarification or qualified assessment can be a better next step than ranking incomplete offers.
The free contractor quote comparison tool helps with general scope comparisons. The Solar Quote Comparison Workbook adds the eight-sheet solar-specific packet, four complete worked cases and 40 fillable fields across 25 pages for £9.99 GBP. This free checklist remains usable without a purchase. Existing energy and contractor books overlap on general budget concepts; another purchase is optional.
Primary links checked October 27, 2026. Examples and checklist are original teaching material. No source endorses this publication. There are no verified reader outcomes, purchase-demand findings or guaranteed savings. Qualified local providers must resolve technical, tariff and contractual details.