Where the money is on an industrial bill
An industrial electricity bill has two large components, and solar treats them very differently.
The energy charge, in dollars per kilowatt-hour, is what solar attacks directly. Every kilowatt-hour generated and consumed on site is a kilowatt-hour not purchased. For a facility running production shifts through daylight hours, the match between generation and load is excellent, and nearly all output is consumed behind the meter at full retail value.
The demand charge, in dollars per kilowatt, is billed against the single highest 15 or 30 minute interval in the billing period. This is where many industrial hosts are surprised. A plant can cut 30 percent of its kilowatt-hours with solar and see a much smaller reduction in the demand line, because the monthly peak may be set by a compressor start, a furnace cycle, or a late-afternoon summer coincidence when generation is already declining.
Practical implication. For industrial sites we model the demand charge separately from the energy charge using twelve months of interval data. In facilities with high load factor volatility, storage sized for peak shaving frequently produces a better return per dollar than adding more modules.
Massachusetts adds a third layer: utility demand response programs pay commercial and industrial hosts for dispatchable reduction during system peak events, which turns a battery from a cost-avoidance asset into a revenue asset. SMART 3.0 also pays an Energy Storage Multiplier of $0.04 per kWh for qualifying paired systems. We break both down in battery revenue from demand response and reducing peak demand charges.
Structural capacity is the first real constraint
Warehouse and distribution roofs are engineered to a snow load, not to a snow load plus a photovoltaic array. In Massachusetts and northern New England, ground snow loads are high enough that the margin on an older steel-joist roof can be thin.
- Ballasted versus attached racking. Ballasted systems avoid penetrations but concentrate dead load. Mechanically attached systems distribute load into structure but require penetrations coordinated with the membrane warranty.
- Joist and deck capacity. We obtain or commission a structural review before design is finalized. On pre-1990 buildings this frequently changes the racking approach or the layout.
- Drift and obstruction loading. Parapets, mechanical screens, and adjacent higher roofs create snow drift zones where added dead load is least welcome.
- Skylights and smoke vents. Layout must preserve required venting and daylighting, and fall protection around skylights is a construction planning item, not an afterthought.
- Sprinkler and fire code access. Setbacks and pathway requirements reduce usable area and belong in the layout from the first iteration.
- Membrane condition and age. A roof with under 10 years of remaining life should be replaced first. Removing and reinstalling a megawatt array later is a substantial cost.