Start with a year of power bills
System size comes from usage, and usage comes from the customer's bills. Ask for twelve months of electric bills and total the kilowatt-hours. One summer month or one winter month will mislead you; the annual number is what the system has to offset.
Ask about what is changing, too. An electric vehicle on order, a heat pump conversion, or a new hot tub all raise future usage, and a system sized to yesterday's bills will disappoint. Note planned changes and size for them where the roof allows.
Walk the roof before you size anything
Production depends on the roof, and you cannot assess a roof from the kitchen table. Check orientation and tilt, and look for shading from trees, chimneys, and neighboring buildings at the times of day the array would work. Satellite tools help, but an in-person look catches what images miss.
Check the roof's condition and age while you are up there. Mounting panels on a roof that needs replacement in a few years means paying to remove and reinstall the array later. If the shingles are near end of life, tell the customer plainly: reroof first, then solar, or price the combination honestly.
Size the system and pick an equipment tier
Combine annual usage with the usable roof area and its production potential to set a system size in kilowatts. Then talk equipment in tiers, not hype: standard panels and string inverters do the job on most roofs, while higher-efficiency panels and module-level electronics earn their cost on tight or shaded roofs. Price the tier that fits the roof, from your supplier costs.
- System size in kW: annual usage against usable roof and orientation
- Panels: standard or high-efficiency tier, priced from your supplier
- Inverter: string or module-level, matched to shading and layout
- Racking and flashing: from the roof type and attachment count
- Battery storage: a separate scope with its own line items
Permits, interconnection, and the main panel
Solar jobs carry paperwork you must price: the building or electrical permit, the utility's interconnection application, and the inspection visits. Check your local requirements and your utility's process, and put the fees plus your time on the estimate as visible lines.
Older homes sometimes need main panel work to accept the system. Check panel capacity and condition on the site visit and price any upgrade separately, so it never ambushes the job on install day. Keep incentive and tax-credit math out of your price: the rules change and eligibility varies by customer, so your estimate should stand on its own numbers.
Build the price from your own costs
Equipment goes in at supplier cost including freight. Labor comes from your crew's install history: layout, racking, wiring, and commissioning each carry hours you know. Overhead and profit go on top as your markup from your own books. The contractor markup guide walks through setting that number.
| Line item | How you size it |
|---|---|
| Panels and inverter | System size and tier at supplier cost |
| Racking and flashing | Attachment count from the roof layout |
| Labor | Crew hours per install stage from your history |
| Electrical and panel work | Scoped separately, parts plus time |
| Permits and interconnection | Actual fees plus your time |
| Overhead and profit | Your markup on real costs |
Solar mistakes that burn margin
- Sizing from one or two months of bills instead of a full year
- Assessing shading from satellite images alone
- Mounting on a roof that needs replacement soon without saying so
- Folding permit and interconnection time into install labor
- Surprise main panel upgrades discovered on install day
- Building the price around incentives that may change or not apply
What goes in front of the customer
The estimate should show the system size in kilowatts, the equipment tier, what the price includes stage by stage, permits and interconnection, any panel work, and the total. State your roof-condition assumptions, note that production depends on weather and shading, and give the price a validity window.
EstimateBook can draft the estimate from the site visit: describe the job by voice or attach photos of the roof and panel, and the iOS and Android app builds itemized line items you can edit for quantities, prices, and markup before sharing a PDF. Treat the draft as a starting point and verify it against your design and supplier pricing first.