Three solar installers visit your home and send three proposals. One quotes $24,000, another $31,000, a third offers a lease with “no money down.” The documents use different layouts, different equipment and different savings projections. Comparing them seems impossible until you pull out the handful of numbers that actually determine value.
Key Takeaways
- Compare quotes by cost per watt (total price ÷ system size in watts) before incentives.
- Check the estimated annual production in kilowatt-hours and how it compares with your yearly electricity use.
- Savings projections depend on assumptions about utility rate increases and export compensation; ask to see them.
- Look at three warranties separately: panel product, panel performance and workmanship, plus inverter coverage.
System size and cost per watt
System size is listed in kilowatts (kW) DC — for example, 8.4 kW. To compare prices:
Cost per watt = total price ÷ (system size in kW × 1,000)
A $25,200 quote for an 8.4 kW system works out to $3.00 per watt. A $29,400 quote for the same size is $3.50 per watt.
Cost per watt varies by region, roof complexity and equipment, so a higher price is not automatically a bad deal — but it should come with a reason, such as premium panels or a complex roof.
Estimated annual production
Proposals should estimate how many kilowatt-hours (kWh) the system will produce in a year. This depends on:
- Your location and sunlight
- Roof orientation and tilt
- Shading from trees and nearby buildings
- System size and equipment
Compare the estimate with your annual electricity use from your utility bills. A system producing 10,000 kWh a year for a home that uses 11,000 kWh offsets roughly 90%.
Ask how the estimate was calculated. Reputable installers use shading analysis and standard modelling tools.
Savings projections
Savings estimates depend on:
- Your current electricity rate
- Assumed annual rate increases
- How your utility compensates exported power (net metering vs net billing)
- Panel degradation over time
- Financing costs
Small changes in assumptions — for example, a 5% annual rate increase versus 2% — can change 25-year savings dramatically. Ask installers to show the numbers with a conservative rate increase.
Incentives
Federal, state and utility incentives have changed significantly. The federal residential clean energy tax credit for homeowner-owned systems was ended for systems placed in service after 2025 under legislation passed in 2025. Some states and utilities still offer rebates or performance payments. Ask installers to separate the price before and after incentives, and verify incentives with official sources.
Equipment
- Panels: efficiency, wattage, brand and warranty
- Inverters: string inverters, microinverters or power optimisers. Microinverters and optimisers can perform better with partial shading.
- Monitoring: apps that show production and performance
Warranties
- Panel product warranty: defects in materials, often 12 to 25 years
- Panel performance warranty: guaranteed minimum output over time, commonly 25 years
- Inverter warranty: varies widely; microinverters often have longer warranties than string inverters
- Workmanship warranty: installation quality and roof penetrations, ranging from a few years to 25 years
Ask who honours each warranty if the installer goes out of business.
Ownership options
- Cash purchase: highest long-term savings if you stay in the home.
- Loan: you own the system; compare interest rates and fees.
- Lease or power purchase agreement (PPA): a third party owns the system; you pay a monthly fee or per-kWh rate. Check escalators and what happens if you sell the house.
Questions to ask every installer
- What is the cost per watt before incentives?
- What production estimate did you use, and how was shading modelled?
- What rate escalation did you assume?
- How will my utility compensate exported power?
- Who handles permits and interconnection?
- What do the warranties cover, and who backs them?
Frequently Asked Questions
Is a bigger system always better? Not if your utility pays little for exported power. Sizing to your usage is often best.
Should I replace my roof first? If your roof needs replacement within several years, consider doing it before installing solar.
How long does installation take? Physical installation often takes a few days; permits and utility approval can take weeks.
Do panels work on cloudy days? They produce less but still generate electricity.
The bottom line
Reduce every quote to cost per watt, annual production, realistic savings assumptions and warranties. Those numbers reveal which proposal is actually the best value.
