A solar proposal is easier to judge when you compare what each line item includes, not just the final total. Use the steps below to put competing quotes on the same footing and identify differences that could affect cost, performance, or service later.
1. Make each proposal describe the same project
Before comparing equipment or price, check whether the companies are proposing the same scope. A quote for a smaller system, a different roof area, or no battery cannot be compared directly with a larger, battery-ready design.
Record these basics from every proposal:
- System size: Look for the planned direct-current (DC) capacity, usually expressed in kilowatts (kW), and the alternating-current (AC) rating if provided. These are different measures; ask the installer to explain how the quoted figures relate.
- Panel count and model: Note the number of modules and the exact manufacturer and model. Similar-looking panels may have different output ratings, dimensions, warranties, or electrical characteristics.
- Inverter arrangement: Identify whether the design uses string inverters, power optimizers, microinverters, or another setup. The equipment list should show model numbers and quantities.
- Roof and electrical work: Note roof planes, array locations, electrical-panel changes, conduit routing, trenching, and any roof repairs included or excluded.
- Storage and backup: Separate a battery system from solar-only equipment. Confirm whether backup is included, which circuits it would serve, and what additional equipment is required for operation during an outage.
- Ownership and payment: Mark whether the proposal is a cash purchase, loan, lease, or power-purchase agreement. These arrangements have different payment terms and ownership responsibilities.
Ask each provider to correct the proposal or explain the difference if these project basics do not match. A larger system may cost more overall but have a lower cost per watt; that alone does not prove it is the better fit. The appropriate size depends on the home, energy use, roof conditions, utility rules, and the homeowner’s goals.
2. Read the equipment line items closely
The equipment list should let you identify the main components, not just broad labels such as “premium panels” or “advanced inverter.” Request manufacturer names, model numbers, quantities, and data sheets for major components. This helps you check that the promised equipment is specific enough to compare and that replacement models are handled clearly if a product becomes unavailable.
| Line item | What to compare | Question to ask |
|---|---|---|
| Solar modules | Model, quantity, rated output, product and performance warranty terms | Are these exact models in the design, and what substitutions are allowed? |
| Inverter equipment | Type, model, quantity, monitoring, warranty | Which component converts the array’s power, and what happens if it fails? |
| Racking and attachments | Roof compatibility, mounting approach, included flashing or attachments | Is the mounting system specified for my roof type and layout? |
| Battery and controls | Usable capacity, power rating, compatible inverter, backup equipment | What loads can it support, and what equipment is needed for backup? |
| Monitoring and communications | Included hardware, connectivity needs, access and support | Does monitoring require home internet or a separate subscription? |
Do not compare panel wattage in isolation. The array’s output also depends on the number and placement of modules, shading, orientation, inverter limits, and local conditions. Ask how the layout handles shaded roof areas and whether the proposed inverter design has module-level monitoring or power management. These features may be useful in some layouts, but the quote should explain their role rather than relying on a marketing label.
For a battery, distinguish energy capacity from power output. Capacity describes how much energy it can store; power describes how much it can deliver at a moment. Neither figure alone tells you how long backup will last. Ask which loads are included, whether the system can start large appliances, what operating limits apply, and how the manufacturer defines usable capacity. Compatibility depends on the specific battery, inverter, controls, and system configuration, so confirm the proposed combination in equipment documentation or directly with the installer.
3. Inspect design, labor, and site-work costs
A proposal may itemize panels and inverters while grouping the work that makes the system fit the house. Look for separate descriptions of design and engineering, permitting or utility paperwork, installation labor, electrical work, roof work, inspection coordination, and commissioning. The names vary, so compare the stated scope rather than assuming two similarly named fees cover the same tasks.
Check whether the quote includes:
- A site assessment and a final design based on the actual roof and electrical service.
- Roof attachments and the labor to install them, with the roof surface and mounting approach identified.
- Electrical upgrades, such as panel work or a new disconnect, if the design requires them.
- Conduit, wiring, trenching, or other routing work, including the assumed distance and path where relevant.
- Permit applications, utility interconnection documents, inspections, and system commissioning.
- Removal and replacement of existing equipment, if applicable, and any stated limits on that work.
- Cleanup, monitoring setup, and handoff instructions.
Look for allowances, exclusions, and “subject to site inspection” notes. An allowance is an estimate for work whose final scope may not yet be known; it is not necessarily a fixed price. Ask what conditions could change it, who approves additional work, and whether you will receive a written change order before that work begins. If a quote excludes roof repairs, electrical upgrades, trenching, or service-panel changes, ask whether the installer has identified those as unnecessary or simply left them outside the quoted scope.
A low design or labor charge is not automatically a problem, and a high one is not proof of quality. The useful comparison is whether the company has described the work needed for your specific site and assigned responsibility for each part. If a line item is vague, request a plain-language scope and the assumptions behind it.
4. Compare total cost and payment terms separately
For a cash quote, compare the contract price for the same system scope and note any deposit, milestone payments, exclusions, and conditions that could change the final amount. If taxes, utility charges, or other costs are discussed, ask the provider to identify which figures are included in the contract total and which are estimates or outside charges. Do not assume that a quoted incentive or projected savings is a guaranteed reduction in what you owe.
For financing, keep the equipment price separate from the cost of borrowing. Record the amount financed, interest rate or other stated finance terms, term length, fees, payment schedule, and whether the quote assumes a later lump-sum payment or other adjustment. Ask for the cash price as well as the financed price and a payment schedule showing the full obligations under the agreement. Read the loan documents for any conditions that may change payments or require action later.
Leases and power-purchase agreements are not directly comparable with cash purchases or loans. The provider or another party may own the system, while you pay under a separate agreement. Compare the contract length, payment formula, maintenance responsibilities, transfer terms if the home is sold, and what happens at the end of the agreement. Get these terms from the contract itself; a sales summary may omit details.
Avoid deciding on a projected utility-bill reduction alone. Savings estimates rely on assumptions about energy use, future rates, system output, fees, and the agreement with the utility. Those assumptions can change, and a proposal cannot guarantee future utility bills.
5. Check production estimates against household energy use
A quote’s production estimate is a modeled projection, not a promise of a specific amount of electricity. Ask for the estimated annual production in kilowatt-hours (kWh), the design assumptions, and how shading, roof orientation, weather, equipment losses, and system downtime are represented. If the proposal shows monthly estimates, ask how seasonal variation was calculated. A simple division of annual production by twelve can conceal months when solar output is much lower or higher.
Compare the proposal with your own utility bills or account records. Use a full year if available because heating, cooling, electric vehicles, and seasonal habits can shift consumption. Check whether the quote uses actual household use or a generic estimate. If your home’s energy use is likely to change—for example, you expect to add an electric vehicle or change heating equipment—ask for a separate scenario instead of treating a larger system as automatically necessary.
Useful questions include:
- What annual consumption figure did you use, and what source did it come from?
- What annual solar production does this design estimate, and what does that estimate exclude?
- Does the estimate account for shading throughout the year and the actual roof layout?
- How might the result differ if energy use rises or falls?
- Does the utility’s billing or export arrangement affect the value of electricity sent to the grid?
Solar production and bill savings are related but not identical. The value of energy produced depends on when the home uses it and the applicable utility arrangement. If the proposal presents a bill-savings figure, ask for the assumptions and a calculation that distinguishes electricity used at home from electricity exported. Treat any future-rate or savings forecast as a scenario, not a guaranteed outcome.
6. Compare warranties and service responsibilities
A proposal can list several warranties that cover different things. Separate the equipment manufacturer’s warranty from the installer’s workmanship coverage and any roof-penetration coverage. Check the duration, what is covered, who handles a claim, and whether labor, shipping, removal, or replacement work is included. A long equipment warranty does not necessarily pay for the labor to diagnose or replace a failed component.
Ask who will monitor the system and respond to a fault alert. Find out whether monitoring is included, how you access it, whether an internet connection is needed, and whether service requires a separate fee. Confirm how to contact the company after installation and what happens if the installer stops operating. For equipment-specific maintenance or care, follow the manufacturer’s instructions; do not assume the proposal includes ongoing cleaning or repairs unless it says so.
For battery systems, clarify warranty conditions related to usage, operating temperature, cycling, or backup operation. These terms vary by product. Request the manufacturer’s written warranty for the exact model and ask the installer to identify any operating limits that matter for your intended use.
7. Resolve gaps before choosing a quote
When a proposal is unclear, send the same written questions to each provider. This makes their answers easier to compare and creates a record of what the quoted scope includes. Ask for a revised proposal when the answer changes equipment, system size, price, or responsibility for work.
Use this short checklist before signing:
- Match system capacity, panel count, inverter design, battery scope, and roof areas across proposals.
- Confirm exact equipment models or the rules for substitutions.
- Identify every included task, allowance, exclusion, and possible change-order condition.
- Compare cash price separately from borrowing or contract payments.
- Review production and savings assumptions against a year of household energy use.
- Read equipment, workmanship, and roof coverage terms separately.
- Confirm who manages permits, utility coordination, inspection, commissioning, and service.
If the numbers still do not line up
Calculate price per watt only after the proposals describe comparable system scope. Divide the relevant system price by the quoted DC system capacity in watts, and state what price you included. This can be a quick screening measure, but it does not account for batteries, electrical upgrades, roof work, financing, or differences in equipment and service. Keep those costs visible instead of forcing them into one number.
If a provider cannot explain a significant difference, ask for a drawing, equipment schedule, production assumptions, or written scope clarification. If the design depends on a roof condition or electrical issue that has not been confirmed, ask how that uncertainty will be resolved and what happens if the site assessment changes the plan. Do not rely on verbal assurances to settle a contract detail; have the final proposal or agreement state the equipment, included work, price, and change process.