Sizing a solar carport from bay count, not roof area

Key Takeaways

• A solar carport typically produces 1.2-1.5 kW per parking bay, so bay count, not an assumed roof footprint, is the starting input for sizing the array.
• A 100-bay car park under a solar carport structure generates roughly 300-500 kWp of capacity, a range wide enough that bay-by-bay design decisions matter.
• Panel tilt on carport structures is kept low, typically 5-15°, because steeper tilt disproportionately increases structural cost for columns and foundations that a rooftop system doesn't carry.
• Adding EV charging changes the sizing exercise again: Level 2 charging draws roughly 7-11 kW per port, which can materially shift how much of the carport's generation is self-consumed versus exported.

A rooftop solar system starts from a fixed, known area: the roof is already there, and you size panels to fit it. A carport has no such starting point, the structure itself is being built, so the sizing exercise runs in the opposite direction: bay count first, then structure, then array size, not the other way around.

Why bay count is the correct starting input

Solar carports typically produce 1.2-1.5 kW per parking space, and a 100-space car park under a full carport structure generates roughly 300-500 kWp of capacity (SurgePV, solar carport design guide, retrieved 2026-09-10). That per-bay figure is the practical design unit, because the carport's footprint is defined by the parking layout you're covering, not by an independently-measured roof area. Run your actual bay count through the car parking estimator to get a first-pass capacity figure before engaging a structural designer, since the per-bay range (1.2 to 1.5 kW) is wide enough to matter once you're sizing dozens or hundreds of bays.

How project scale changes the sizing conversation

Commercial carport installations range from around 50 kW for a small commercial or educational car park covering 20-50 bays, up to 5 MW+ for a large regional retail centre (SurgePV, retrieved 2026-09-10). This spread means the sizing question isn't "how big can we build," it's "how many bays are we covering, and does the structural and electrical design scale linearly with that count or does it hit efficiencies (or new complications) at a larger footprint." A 50-bay project and a 500-bay project aren't the same design scaled up, the larger one usually needs a different electrical interconnection strategy and phased construction approach.

Why carport tilt is lower than rooftop tilt, and why that's a deliberate trade-off

Panel tilt on carport structures is typically kept low, in the 5-15° range, specifically because a steeper tilt angle creates disproportionately higher wind loading, which drives up the structural cost of the columns and foundations supporting the whole canopy (SurgePV, retrieved 2026-09-10). This is a cost-driven design choice, not an oversight: a rooftop system doesn't carry this same penalty because the roof structure and building foundation are already doing the load-bearing work, whereas a carport's entire structural cost is purpose-built for the array. The lower tilt does mean slightly reduced annual yield compared to an optimally-tilted rooftop system, and that trade-off is usually worth it once the alternative's foundation cost is priced out.

What EV charging adds to the sizing exercise

If the carport is also hosting EV charging, Level 2 charging (the common commercial standard) draws roughly 7.2 kW per port at 240V/30A, with typical stall-level charging in the 7-11 kW range, and adding a port typically costs USD 1,000-3,000 on top of the base carport cost (Adhaiwell, EV charging capacity calculation, retrieved 2026-09-10; SurgePV, retrieved 2026-09-10). This changes the generation-versus-consumption balance materially: a carport sized purely for shade-and-export generation behaves differently once a meaningful share of its output is consumed on-site by charging vehicles during daylight hours, rather than exported to the grid for net-metering credit. Size the EV load explicitly, port count times draw per port, alongside the bay-count-derived generation figure, rather than treating EV charging as an add-on that doesn't affect the underlying array size decision. Once bay count and EV load are both settled, the solar carports and parking solutions overview is the practical next step for matching a structural design to that specific capacity.

Frequently asked questions

How many kW should I expect per parking bay covered by a solar carport?

Roughly 1.2-1.5 kW per bay, though the exact figure depends on panel efficiency, bay spacing, and structural layout. For a rough capacity estimate, multiply your bay count by that range rather than trying to estimate from an assumed roof-equivalent area.

Why is carport panel tilt lower than a typical rooftop installation?

Steeper tilt increases wind loading on the structure significantly, which raises the cost of the columns and foundations that support the whole carport canopy. Rooftop systems don't face this same structural cost penalty since the building itself already bears the load, so carports are deliberately built at a lower, cost-optimised tilt (typically 5-15°) even though it slightly reduces annual yield.

Does adding EV charging reduce how much solar generation I can export for net-metering credit?

Yes, potentially significantly, since charging load consumed on-site during daylight hours competes directly with the same generation window a carport is optimised for. Size EV charging load explicitly against your carport's generation profile rather than assuming exported credit stays unaffected.

The bottom line

A solar carport's design starts from the parking layout it's covering, not from an assumed roof footprint, because the structure itself doesn't exist until the project builds it. Bay count, tilt-driven structural cost, and any EV charging load all flow from that starting point, and getting the sizing right means working through them in that order rather than retrofitting a rooftop-style calculation onto a fundamentally different structure.

Figures were verified on 10 September 2026 against published solar carport design and EV charging capacity guides. Actual per-bay capacity, structural cost, and EV load requirements vary by site, structural engineer, and panel specification; confirm with a qualified solar carport designer before finalising a project budget.