Start with the load profile, not the roof
A warehouse and a machining plant can have identical roofs and completely different solar economics. The difference is when and how the plant uses power. Before we lay out a single module, we pull twelve months of 15-minute interval data from the utility and separate the load into shift-driven base, process peaks, and weekend and holiday idle.
| Operating pattern | What solar does well | What to watch |
|---|---|---|
| One shift, weekdays | Weekday output lines up with production almost hour for hour, so self-consumption on production days is high. | Weekends and shutdown weeks. Output then exceeds load and its value depends on your net metering or export tariff. |
| Two shifts | Solar covers the first shift and part of the second; nearly all output is used on site. | Late-afternoon and evening peaks are not touched by solar. Storage becomes the demand tool. |
| Three shifts, 24/5 or 24/7 | Every kilowatt-hour is consumed behind the meter at full retail value, even on a very large array. | Solar offsets a smaller percentage of total annual consumption, so set expectations in dollars, not percent. |
| Batch or seasonal production | Useful where heavy runs fall in spring and summer. | Long idle periods mean export valuation dominates the model. |
The three-shift case surprises owners in a good way. With constant load, there is no export risk, so the array can be sized to the maximum the roof, carport, or adjacent land allows. The one-shift case is the opposite: the optimal size is often smaller than the roof, unless the state's net metering rules value exports close to retail.
Demand charges, motors, and compressed air
On many manufacturing bills the demand line, billed on the highest 15 or 30 minute interval in the month, is a large share of total cost. Solar reduces it only when the peak happens to fall under strong sun. In production facilities the peak is usually set by something else:
- Motor starts. Large induction motors can draw several times running current at start. A single simultaneous start of a chiller, dust collector, and main compressor at shift change can set the month's demand.
- Compressed air. Compressed air is often among the largest single electrical loads in a plant and runs whenever the plant runs, including leaks on idle shifts. It is a steady base load that solar offsets well, and a leak survey often pays back faster than any generation project.
- Thermal processes. Electric ovens, induction heating, and injection molding barrels ramp hard at startup.
- HVAC coincidence. A July afternoon with full production and full cooling is the classic peak, and solar is already falling off by then.
How we handle it. We model energy savings and demand savings as separate lines. Where the interval data shows sharp, short peaks, a battery sized for peak shaving, sometimes combined with staggered start sequencing in the plant controls, usually beats adding modules. We cover the method in how to reduce peak demand charges and the storage economics in commercial battery storage cost and ROI.