PV Sizing

Step 1's load profile put annual consumption at roughly 3.2 million kWh with an 850 kW peak. This step sizes the rooftop PV array against the available roof area and that annual usage target.

With 100,000 sq ft of usable roof area, this project's array is constrained more by available space than by financial appetite — a realistic commercial rooftop layout, accounting for setbacks, fire access pathways, rooftop equipment, and row spacing to avoid inter-row shading, typically achieves roughly 6-8 W of DC array capacity per usable sq ft of roof. At the midpoint of that range, 100,000 sq ft of roof supports approximately a 500 kW DC array — the sizing target this series uses, built from roughly 1,250 modules at 400W each.

Checking that array against the annual load: a well-oriented, unshaded 500 kW DC rooftop array in a typical U.S. climate produces somewhere in the range of 1.1-1.4 million kWh annually (production factor depends heavily on climate zone and roof orientation) — against this facility's 3.2 million kWh annual usage, that's roughly 35-40% of annual energy offset from solar alone. That's a realistic, roof-area-constrained outcome for a facility this size, not a design failure — it's exactly why Step 4's battery sizing focuses on demand-charge reduction rather than trying to push solar toward 100% offset on a roof that physically can't support the array size that would require.

Module and racking selection at this stage also has to account for the roof's structural capacity (a ballasted racking system's dead load has to be checked against the existing roof structure's live load rating — a real coordination point with a structural engineer that's easy to skip past when focused purely on the electrical sizing) and the roof's remaining service life (installing a 25+ year PV system on a roof membrane with 10 years of life left is a common and expensive mistake worth flagging even at this early sizing stage).