Guides
Solar installer inventory write-offs and job costing for tax season
Year-end solar installer inventory write-offs, physical counts, and job costing methods that turn leftover panels, racking, and inverter stock into defensible COGS.
What to take away
- Inventory is a tax accounting method, not only a shelf count. Leftover modules, racking, and inverter stock stay on the books at cost until sold, installed, or written off.
- Damaged or obsolete material comes off the books at cost, and the deduction belongs to the year you document the loss.
- Cost of goods sold is beginning inventory plus purchases minus ending inventory, and that number drives every job margin you report.
- Serial numbers, pallet labels, and photos make the count and the write-off defensible.
- Job costing built on real inventory cost exposes margin leaks before your accountant finds them.
Inventory is a tax method before it is a shelf
Under IRS rules, a business that carries inventory generally reports cost of goods sold and uses an accrual method. The small business taxpayer exception, with a gross receipts threshold indexed for inflation, lets many contractors use the cash method and treat stock as non-incidental materials and supplies.
The Tax Cuts and Jobs Act also ended the lower of cost or market method for most taxpayers with tax years beginning after 2017. Your leftover pallets are therefore valued at cost, not at what a used equipment dealer would pay.
Form 1125-A carries the calculation for corporations and partnerships. Schedule C, Part III does the same work for sole proprietors.
What each pile of stock is worth
| Stock type | Year end treatment | Job cost line |
|---|---|---|
| Unopened module pallets | Ending inventory at invoice cost plus inbound freight | Material, allocated per watt installed |
| Leftover racking, rails, and clamps | Ending inventory at cost, counted by piece or length | Material, allocated per roof plane |
| Inverter and battery stock | Serialized inventory at cost, with warranty start date logged | Equipment, charged per unit installed |
| Damaged or obsolete modules | Written off at cost when scrapped, with documentation | Variance, charged to the job that caused it |
| Consumables under a small taxpayer method | Deducted as non-incidental materials and supplies | Consumable line, per job |
Capture the manufacturer, model, and listing mark for every inverter at receiving. That data ties to the equipment standards your interconnection paperwork cites, and the IEEE standards portal is where the underlying documents live.
Stocked inverters also carry a warranty clock. Log the serial number and sale date so a failed unit becomes a warranty claim instead of dead stock, since warranty terms usually hinge on documented purchase and install dates.
Counting and writing off in six steps
- Freeze the warehouse and every truck on one date, and write that date on each count sheet.
- Count by SKU, and record serial numbers for inverters, batteries, and any module that carries warranty value.
- Price the count at invoice cost plus inbound freight, because freight is part of inventory cost.
- Compare the physical count to the perpetual record, and investigate any variance above your threshold.
- Post ending inventory, then compute cost of goods sold with the beginning inventory formula.
- Move damaged or obsolete stock to a write-off log with photos, serial numbers, and the approver's name.
A count you cannot rebuild on paper is a count an examiner will rebuild for you.
Scrapped modules still need handling beyond the ledger. Recyclers sort them under e-waste categories rather than general construction debris, and the electronic waste overview explains those categories. Your crew also needs the pickup, labeling, and manifest side, which the equipment disposal and recycling rules set out step by step.
Example: a two crew shop at year end
Say a shop runs two crews and keeps four module pallets, a rack of rails, and six inverters as buffer stock. That buffer sits at cost all year. If nobody counts it, the material cost of every finished job looks higher than it is, and the shop pays tax on phantom profit.
At year end the count finds two modules cracked in a fall from a truck. Those units move to the write-off log and come out of ending inventory. Next year's beginning inventory then matches what is physically on the rack.
Feeding the count into job costing
Per job costing starts with the bill of materials you priced during the count. Standard cost per job comes from that bill, and actual cost comes from the invoice plus the count variance. The gap between them is your real margin.
Labor belongs in the same sheet. Sales commissions paid per kilowatt affect job cost, and the sales commission structure benchmarks show how US shops set per kW rates, draws, and recovery.
Damage and rework should land on the job that caused them, not spread across the year. A written change order process keeps that cost on the right job when a scope change grows the array or moves the conduit run.
Planning next year's purchases is the other half. Inventory ties up cash, and the trends that move demand tell you which stock to carry and which to order per job.
