What about the house itself affects a quote
Roof size, shape, pitch and direction matter. So does roof condition—if the roof needs repair first, that shows up on the quote. Shade from trees or nearby buildings reduces expected production and can require smaller arrays or microinverters. Your home's electrical panel, attic access and the ease of installer access affect labor time. Finally, local permitting and inspection rules can add to cost and timeline. All of these are specific to a property and explain why two nearby homes can get very different estimates.
Why financing changes the monthly cost story
The way you pay affects what you owe each month. Paying cash means you own the system outright and don’t have a loan payment, but that’s not realistic for every homeowner. Loans spread the cost over time; a longer loan usually lowers the monthly payment but increases interest paid over the life of the loan. Leases or power-purchase agreements transfer some ownership and can change who gets incentives, which changes the financial picture. Incentives, the portion you finance, down payments, interest rate and loan term all matter. When you compare quotes, ask for the same financing assumptions or get a breakdown that shows the up-front price, financed amount, monthly payment and who claims any tax credits or rebates.
The checklist: what to compare in each quote
Compare apples to apples by asking for clear line items: system size and estimated annual production; brand and model of panels and inverters; a simple explanation of performance assumptions (orientation, tilt, shading); a breakdown of equipment, labor, permits and any extra fees; financing terms — loan length, interest or whether it’s a lease/PPA and who owns the system; expected timeline and who handles permits and interconnection; and what the company promises for repairs, service or production monitoring. If one quote assumes a longer loan or a lease, convert those terms into a monthly cost so you can compare like with like.
Questions to ask installers before requesting a quote
Ask these questions to surface the big differences: Will I own the system or is this a lease/PPA? What financing choices do you offer and how will each change my monthly payment? What assumptions drive your production estimate? Is my roof in good enough condition or will repairs be needed first? Who handles permits, inspections and the utility interconnection? What are the service or maintenance responsibilities and response time? Can you provide recent local references and examples of completed projects? These answers help you evaluate quotes beyond the headline price.