Bill of materials

Where the quantities come from

Every balance-of-system item carries the rule that turns a sizing result into a quantity, so the bill of materials falls out of the calculation instead of being typed up afterwards. The rules are:

• Per PV module - string cable, mid clamps, roof hooks.
• Per kWp of array - mounting rail, cable tray, earth cable.
• Per string - MC4 pairs, string fuses, end clamps.
• Per MPPT input - combiner boxes.
• Per inverter - DC isolator, AC breaker, surge arrester, monitoring.
• Per battery module - interconnects and BMS comms leads.
• Per kW of AC output - the AC cable run.
• Per system - one-offs: earth rod, labels, energy meter.

On top of the rule sit a waste factor for off-cuts, a minimum quantity, and a round to figure so cable is quoted in drum lengths and clamps in packs.

Size bands

An item can be limited to a range of system sizes, and this is what keeps the BOM honest across the whole 1 kW to 1 MW range. Six square millimetre AC cable is right for a 4 kW house and dangerous on a 500 kW plant, so it carries a maximum system size and a heavier cable takes over above it. The same applies to isolators, distribution boards and earthing.

When you add your own items, check the bands meet without a gap. A system size that falls between two bands will simply have no line for that item.

Optional lines

Items marked optional are priced but not counted in the system total - alternative mounting methods, for instance, where you pick one. They appear on the BOM clearly marked so nobody quotes both.

Replacing the starter catalogue

The seeded items and prices are planning placeholders. Replace them with your own suppliers' parts and prices under Settings -> Balance of system, or upload them in bulk through Product import.