Solar Bill of Materials Generator
List the parts a system needs, with quantities worked out from standard rules, and download it as a PDF.
A parts list is easy to get nine-tenths right and hard to get all the way right. Miss a box of end clamps or a length of conduit and the crew waits on a supply run. This generator counts the parts from the size of the array and the way it’s wired.
It’s for installers, DIY builders and system designers. Enter the panel count and size, how the panels sit in rows, the inverter type, the wire runs and the mounting. You get a parts list with quantities that you can edit, add prices to and download as a PDF. Nothing is uploaded, and there’s no account.
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Quantities come from standard counting rules and are a starting point. Check them against the maker manuals, your design and local code before you order. Data as of October 2026.
How this tool works
The counting rules
The panels are split into rows of the length you set. Each row gets two rails, and each rail run is the row’s width plus a few inches at the ends. Rails are cut from the stock length you choose, with a splice at each join. Roof attachments go along each rail at the spacing you enter, plus one more. Each row gets four end clamps, and every joint between two panels in a row gets two mid clamps, one on each rail. Strings are the panel count divided by the panels per string, rounded up. Each string needs two conductors of PV wire for the full one-way run, and two connector pairs, plus two spare pairs for the job.
The electrical side
The AC breaker is sized at 125% of the inverter’s output current, then rounded up to the next standard breaker size. The AC wire is the smallest copper size whose rating covers that breaker, using the 75 °C column of the National Electrical Code ampacity table and its 15, 20 and 30 amp limits for the three smallest sizes. Take a 7.6 kW inverter on 240 volts. Its output is 31.7 amps, times 1.25 is 39.6 amps, so the breaker is 40 amps and the wire is 8 AWG. Wire quantities include the waste allowance you set.
Tip: edit the quantities in the table before you download. The rules give a clean count, and your crew knows what’s already on the truck. Prices are optional. Type them in and the PDF adds a parts total.
The Solar Panel String Calculator gives the panels-per-string limits for your inverter, and the Voltage Drop and Wire Size Calculator checks the wire runs.
What it doesn’t do
- It isn’t a design. The counts are a starting point. Check them against the mount maker’s manual, your layout and local code before you order.
- Wire sizes are minimums. They don’t include voltage drop or the heat and conduit-fill derating that some runs need.
- Ground mounts get rails and clamps only. Posts, piers and bracing come from the mount maker’s design for your soil and wind.
- Microinverter cabling is maker-specific. The tool counts trunk cable length, end caps and branch breakers. Order the cable and connectors to the maker’s parts list.
Where the numbers come from
- NFPA 70, the National Electrical Code. The 125% rule for continuous current, the wire ampacity table (Table 310.16), standard breaker sizes (Section 240.6(A)) and the small-wire limits (Section 240.4(D)). Use the edition your area has adopted.
- Racking, clamp and attachment counts differ by maker. The counts here follow general practice, so follow the installation manual for your mount.
Questions
Can I change the quantities?
Yes. The parts list is a table you can edit. Change a quantity, rename a part, add lines or remove one. If you change the answers above it, press the build button again to refresh the counts. Prices you typed stay with parts that keep the same name.
Why is the breaker 125% of the inverter output?
A solar system can run at full output for hours, which the electrical code treats as a continuous load. It asks for breakers and wire rated for 125% of that current.
Does it handle microinverters and optimizers?
Yes. Pick the inverter type. Microinverters give one unit per panel or per group, the branch circuits and breakers, trunk cable and end caps. Power optimizers add one per panel to a string inverter system.
Why are rapid shutdown devices on the list?
Rooftop systems need rapid shutdown under the electrical code. A string inverter system with no shutdown built into its panels or inverter needs a device at each panel. Tick the box if yours already has it. Microinverters and most optimizers handle it themselves, so they add no line.
What panel size should I enter?
The long and short sides in inches, from the panel’s data sheet. A 400 W panel is often about 68 by 44 inches, but sizes vary by model, so use yours.
Can I download the list as a spreadsheet?
No. The PDF is the only download. Your last list stays in this browser so you can come back and update it.
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