The core variable in commercial charging is dwell time. An office worker occupies a bay for 8–9 hours; a shopper for 1.5–2.5. Those two numbers dictate everything, because the optimal hardware is different: DC fast charging aimed at office workers is a misallocation — the car fills in an hour and then squats on a bay all day while a unit costing ten times an AC charger idles. Our default is unapologetic: the underground garage runs on 7kW AC; the ground or street-facing zone carries a few DC units for visitors and shoppers. A bonus of the AC-led garage is that most towers absorb it without any capacity upgrade.
Capacity planning: bays first, transformer second
- Staff bays — 7kW AC at 10–20% of parking total, clustered near the cores to shorten cable runs.
- Visitor and transient bays — two to four 60–120kW DC units with explicit dwell limits and an overstay fee once charging ends.
- Retail bays — tie into membership: spend a threshold, charge free for an hour. Charging becomes a footfall tool, not a cost line.
- Non-motorised zone — 10–20 e-bike ports in the bicycle garage or an edge yard for staff who ride.
Then the arithmetic: twenty 7kW AC units draw about 140 kW simultaneous. We pull twelve months of peak load and the cooling-season curves; if headroom is thin, load scheduling — which trims charging power automatically at building peaks — costs about a tenth of a transformer upgrade.
What the property actually asks: occupancy, safety, settlement
Occupancy. A fuel car in a charging bay is a double loss in a tower. The control set has three parts — lock or plate recognition, painted markings, overstay fees — and all three must be present or management quietly fails. Safety. An underground garage is a closed volume, so the fire bar is higher: dedicated circuits, per-port RCD and overload protection, IP54+ enclosures, extinguishers on hand, integration with existing CCTV with footage retention. We write these into the construction plan and check each at acceptance. Settlement. Towers often split revenue among owner, property and operator. The platform reports by pile, by zone and by time band, and exports the flow file directly — nobody reconciles by spreadsheet archaeology.
Time-of-use pricing that lifts utilisation
Tower charging concentrates 9:00–17:00 and the garage empties at night and on weekends. Tariff design can open those idle hours: weekday standard electricity-plus-service pricing for staff and visitors; discounted service fees at night and weekends, opened to neighbourhood residents and ride-hail drivers; and employee monthly packages that lock in the anchor demand. Prices are not set-and-forget — the platform adjusts them any afternoon, and after three months of real data we send a tuning proposal.
Model, timeline and the 30–40% first phase
Commercial projects usually start from the property or owner side: self-purchase, operator-build (we fund it for a revenue share) or joint investment. Where an owners' committee exists, public-revenue procedures apply — we supply the explanatory pack and the announcement templates. Cadence: survey 3–5 working days, internal approval 1–3 weeks, construction 7–15 days scheduled nights and weekends inside the garage — about 25–35 days all-in without upgrades. On day one you get bay signage and guest-facing notices plus front-desk training; monthly you get a run-and-revenue report. And one number worth arguing about: build 30–40% of estimated demand first, reserve trays and capacity, expand on data. Real utilisation is unknowable from a desk — some towers fill ten units in a quarter, others idle half a field for six months. Hardware also iterates: buying the full field today locks in this year's modules. And bays are scarce — five pilot charging bays clear a committee far more easily than twenty.
Common questions
- Why not install DC fast chargers in the garage for staff?
- Dwell time. A staff car parks 8-9 hours; a DC unit fills it in one and the bay then blocks all day, while the unit costs about ten times an AC charger. AC in the garage, DC at ground level for short-stay visitors - that is the efficient split.
- How do we stop charging bays being occupied all day?
- Three controls together: lock or plate-recognition barrier, painted bay markings, and an overstay fee that starts when charging ends. Any one alone fails in practice.
- How many chargers should the first phase include?
- About 30-40% of estimated demand, with trays and capacity reserved. Real utilisation shows up in the platform data within a quarter, and the second phase is then sized by evidence instead of guesswork.