How Should Multi-Storey Car Parks Deploy Autonomous Mobile Energy-Storage Charging Equipment When EV Charging Demand Is Spread Across Different Floors?

As electric vehicle adoption grows, parking facilities are becoming part of the energy infrastructure rather than simply places where vehicles wait. In multi-storey car parks, however, charging demand is rarely concentrated in one predictable location. An EV that needs energy may be parked on B2 in the morning, on Level 3 at noon, and on Level 6 later in the day. The result is a planning problem that is as much about movement, dispatching and power management as it is about charger quantity.

According to the International Energy Agency (IEA), global electric car sales reached about 21 million in 2025, roughly one in every four new cars sold worldwide. The IEA also reports that the global stock of electric light-duty vehicles reached around 76 million, while the number of public charging points exceeded 7 million by the end of 2025. Private light-duty vehicle charging points exceeded 43 million. These figures indicate that offices, shopping centres, airports, hotels, residential complexes and municipal parking facilities will face steadily increasing charging demand.

For a flat car park, adding charging spaces may be relatively straightforward. In a six- or eight-level parking structure, the design question is different: should operators install high-power fixed charging infrastructure on every floor, create a dedicated charging floor, or move stored energy to the vehicle only when a charging request appears?

An autonomous Mobile EV Charger introduces a third option. Instead of requiring the driver to find a dedicated charging bay, the energy-storage charging unit can receive a task, locate the parking space, travel to the vehicle, deliver energy and then move to the next task or return to a replenishment point. For facilities with distributed and variable demand, that operating model can add a flexible layer of charging capacity without positioning every kilowatt permanently at a fixed parking space.

I. Charging Demand in Multi-Storey Car Parks Is Becoming Dynamic and Distributed

EV growth changes the function of the parking space

Historically, a car park was designed around traffic flow, bay dimensions, ventilation, lighting, fire safety and payment systems. Electrification adds a new constraint: energy must now reach a large number of stationary vehicles whose location, arrival time, departure time and required state of charge are all different.

This creates a mismatch between traditional infrastructure and real operating behaviour. Fixed charging equipment is tied to a specific bay, while vehicles are assigned according to availability. A charger can therefore be idle even when another EV on the same floor needs energy. The problem becomes more visible as EV penetration increases.

Parking spaces alone do not determine charging demand

A common mistake is to calculate charging infrastructure only from the number of parking bays. A 600-space garage does not automatically need 150 high-power chargers simply because 25% of parked vehicles may be electric. Operators should first estimate how many of those EVs will actually request energy during a typical day and how much energy each session requires.

Using this model, 600 × 80% × 25% × 35% produces approximately 42 charging requests per day. At an average of 25 kWh per session, the site must deliver about 1,050 kWh per day. This is a more useful planning number than the simple statement that the building has 600 parking spaces.

The key question therefore shifts from “How many chargers should we install?” to “How many charging tasks and how many kilowatt-hours must we deliver before vehicles leave?” That change in perspective is fundamental when evaluating autonomous charging equipment.

II. Why Fixed Chargers Alone May Not Solve Distributed Multi-Floor Demand

Electrical infrastructure grows quickly when chargers are repeated on every floor

Fixed AC and DC chargers remain essential infrastructure, especially for long-dwell vehicles and predictable daily users. The challenge appears when a facility tries to reproduce the same charging density on every level regardless of demand patterns.

Consider a six-level structure with 100 parking spaces per floor. If each floor contains twenty 11 kW AC charging points, the theoretical connected charging capacity is 1,320 kW. Managed charging can reduce simultaneous load, but the building must still plan for distribution boards, feeder capacity, cable routes, network communications, civil works, protection equipment, fire zoning and future maintenance.

The U.S. Department of Energy has documented a parking-garage managed-charging project with 108 Level 2 charging ports rated at up to 6.7 kW each. If every port operated at maximum power simultaneously, the total demand would be about 720 kW. The project illustrates why software-based load coordination can be as important as the number of installed charging ports.

Charger occupancy and parking occupancy are not the same thing

A fixed charging bay creates value only when a vehicle that needs charging is parked there. In practice, a space can be occupied by a non-EV, an EV that does not need energy, or a vehicle that has already completed charging. Meanwhile, another EV may be parked several floors away. This is an utilisation problem rather than a hardware problem.

A mobile energy-storage unit changes the utilisation model because the charging asset can be dispatched to the demand. If Level 2 is quiet in the morning but Level 5 receives a group of fleet vehicles in the afternoon, the same unit can serve both areas instead of remaining permanently assigned to one floor.

Future EV penetration is uncertain

The second challenge is timing. A building may have a 10% EV share today, 25% in several years and a much larger share over the life of the property. Building the final-state fixed network immediately can create underused capital expenditure in the early years. Building only for today can create repeated construction and electrical upgrades later.

For this reason, a Mobile EV Charger is most useful when it is treated as flexible charging capacity rather than a universal replacement for fixed chargers. Fixed infrastructure serves stable, high-frequency demand; mobile equipment can absorb overflow, serve irregular floors, support priority vehicles and bridge periods when the fixed network is still being expanded.

III. Deployment Architecture for Autonomous Mobile Energy-Storage Charging Equipment

Use an energy hub, mobile charging fleet and floor service zones

For most multi-storey car parks, the most practical architecture is not “one robot per floor.” A better model is a central or zoned energy hub connected to a fleet of autonomous charging units. The hub replenishes the devices, while the mobile fleet serves charging requests across mapped parking zones.

This creates three functional layers: the Energy Hub, where devices recharge and wait; the Autonomous Charging Fleet, which moves stored energy through the car park; and Floor Service Zones, which define the bays, traffic routes, speed limits and priority rules on each level.

When a single hub is enough

A single hub can work well when the car park has four to six levels, travel distances are moderate, ramps are wide enough for the equipment, communication coverage is stable and the number of charging requests is not heavily concentrated in one distant zone. In that configuration, devices return to one controlled area for replenishment, inspection and standby.

When two service zones become more efficient

Larger structures may benefit from a lower-zone hub and an upper-zone hub. For example, Hub A could serve B3 through Level 2, while Hub B serves Levels 3 through 7. Dividing the service territory reduces empty travel and improves the proportion of operating time spent actually delivering energy.

Suppose a unit needs eight minutes to travel from Level 6 to a hub on B1. A round trip can consume sixteen minutes of non-charging time. If the device performs fifteen tasks in a day and repeatedly returns to the same distant hub, empty travel could theoretically total 240 minutes. This example shows why Travel Time Ratio should be included in the deployment model.

Door Energy autonomous charging equipment for mapped parking environments

Door Energy has developed a 100 kW Autonomous Car Charging Station designed for mapped, controlled parking environments. The current product specification lists a 105 kWh battery, up to 100 kW EV charging power, 200-1,000 V DC range, CCS1/CCS2 compatibility, OCPP 1.6J communication, liquid cooling, IP55 protection, Level 4 autonomous operation, maximum travel speed of 10 km/h and gradeability above 20%.

The device dimensions are 1,950 × 1,000 × 1,650 mm. Those dimensions, together with ramp geometry and turning space, must be checked against the actual garage layout before deployment. A strong climbing specification does not by itself guarantee successful operation in every building; the entire path must be validated.

IV. Capacity Planning: How Many Mobile Units Does a Multi-Storey Car Park Need?

Start with daily energy demand, not a fixed ratio of devices to parking spaces

There is no universal rule such as one autonomous unit for every 100 parking spaces. The correct number depends on energy demand, task duration, peak concurrency, travel time, device replenishment time and the operating window before vehicles depart.

A useful first-stage formula is: Daily Charging Energy = Parking Spaces × Occupancy × EV Share × Charging Request Rate × Average Energy per Session.

This table demonstrates an important effect: parking capacity increases only 2.25 times from the first to the third scenario, yet estimated daily charging energy rises by more than seventeen times. The reason is that occupancy, EV share, request rate and energy per session all rise together. Equipment quantity must therefore be linked to workload rather than real-estate size alone.

Distinguish battery capacity from dispatchable energy

Door Energy lists 105 kWh of battery capacity for its autonomous parking-lot charging product. Project planners should not assume that the full 105 kWh is always available for vehicle delivery in every operating cycle. A realistic dispatch model should include the reserved state-of-charge window, conversion efficiency, thermal management, auxiliary consumption, movement energy, battery-life strategy and the minimum energy required to return safely to a replenishment point.

For illustration only, if an operator models 80 kWh as the dispatchable energy available between replenishment cycles, the number of sessions varies with the average top-up requirement:

These values are a planning example, not a guaranteed service count. Actual output depends on system configuration, state of charge, conversion losses, vehicle acceptance power and the operator’s reserve policy.

Charging power and vehicle charging power are different numbers

A 100 kW charger does not mean that every vehicle will continuously receive 100 kW. The vehicle battery management system determines accepted charging power according to voltage architecture, SOC, battery temperature, charging curve and safety limits. Consequently, a capacity model should use measured or estimated energy per session and average service time rather than dividing battery size by 100 kW.

Add peak concurrency and service deadlines

Daily energy alone is not enough. A garage may need 1,000 kWh per day but still require more devices if most requests occur between 16:00 and 18:00. Conversely, a similar energy volume spread across twelve hours may be handled by a smaller fleet. Departure deadlines, VIP or fleet priorities and guaranteed service levels should therefore be included in the dispatch model.

V. Autonomous Charging Workflow: From Driver Request to Task Completion

Step 1: A charging request enters the dispatch platform

When a parked vehicle needs energy, the driver, fleet system or parking-management platform sends a charging request. The request should contain enough information for the scheduler to estimate urgency and workload rather than simply stating “charge this car.”

Step 2: The system locates the vehicle

The robot uses the parking map and sensor system to identify the target position. A structured parking-space naming scheme such as B2-A-001 or L5-C-126 improves dispatch accuracy. The more precisely the management system knows where the vehicle is located, the less non-productive search movement is required.

Step 3: The scheduler selects the best available device

The nearest unit is not always the best unit. The dispatch engine can consider current device position, stored energy, floor, route availability, task priority, expected departure time and the queue of future requests.

For example, Device A may be only 120 metres away but have 18% SOC, while Device B is 240 metres away with 75% SOC. The system may dispatch Device B to avoid an interrupted task or unnecessary return to the energy hub. This is why autonomous charging should be designed as a dispatch system rather than merely a charger placed on a mobile chassis.

Step 4: The equipment travels to the vehicle and charging begins

After route planning, the device travels to the target bay. Depending on project configuration, a mechanical connection system can complete the connection automatically, or a staff member can insert the charging connector. Charging then starts under the relevant power, voltage, temperature and safety limits.

The Door Energy autonomous product supports CCS1 and CCS2 interfaces and uses a 200-1,000 V DC range. OCPP 1.6J communication allows the charging asset to be incorporated into a broader management platform for session data, remote status and dispatch logic.

Step 5: Monitor the charging session

A well-designed platform should track output power, energy delivered, equipment SOC, temperatures, task duration, alarms and charging status. These data points are also valuable for long-term capacity planning because they show the difference between theoretical demand and actual user behaviour.

Step 6: Complete, continue or return

After the task is completed, the device can take the next request if sufficient energy remains, return to the hub when its SOC reaches a defined threshold, or move to a standby area if the request queue is empty. The operating loop becomes Request → Dispatch → Travel → Charge → Next Task / Replenish / Standby.

VI. FAQ: Deploying a Mobile EV Charger in Multi-Storey Car Parks

Q1. Does every floor need its own autonomous charging unit?

No. Device quantity should be determined by daily task volume, total kWh demand, travel distance, replenishment time and peak concurrent requests. A four- to six-level structure may be served by one central hub, while very large facilities can use separate upper and lower service zones.

Q2. Can a 100 kW unit charge every EV at 100 kW?

No. The charger provides a maximum available power level, but the vehicle controls how much power it accepts. Actual charging power changes with vehicle model, battery voltage, SOC, temperature and the vehicle’s charging curve. For planning, average kWh per session and average task duration are usually more reliable than maximum charger power alone.

Q3. What are the main specifications of the Door Energy autonomous parking-lot charging product?

The current Door Energy product specification lists 105 kWh battery capacity, up to 100 kW EV charging power, 200-1,000 V DC output range, CCS1/CCS2 connectors, OCPP 1.6J communication, IP55 protection, liquid cooling, Level 4 autonomous operation, maximum speed of 10 km/h, gradeability above 20%, operating temperature from -20°C to 65°C, and dimensions of 1,950 × 1,000 × 1,650 mm.

Q4. If the car park already has fixed chargers, is mobile charging still useful?

Potentially, yes. Fixed chargers can handle predictable daily charging, while mobile equipment can support temporary overflow, irregular demand on upper or lower floors, fleet priority tasks and periods when the fixed charging network is being expanded. The two approaches are usually complementary rather than mutually exclusive.

Q5. How does the system know which vehicle needs charging?

The parking or fleet platform provides the vehicle location and charging request. The dispatch system then links the request to a mapped parking space, selects an available unit and plans a safe route to the vehicle. Accurate parking-space IDs and reliable communications reduce unnecessary travel.

Q6. Which KPI is especially important in a multi-storey garage?

Travel Time Ratio is one of the most useful indicators because it shows how much of the device’s operating time is spent moving rather than delivering energy. A high ratio may indicate that the hub location, service zones, task sequencing or fleet size should be changed.

Q7. How should the system scale as EV penetration increases?

A phased approach is usually more practical. In the early stage, the operator may combine a limited number of fixed chargers with a small mobile fleet. As EV share grows, more fixed charging can be installed for routine demand while autonomous units increasingly focus on overflow, cross-floor demand, priority service and temporary capacity.

Q8. Is Door Energy focused only on parking-garage charging?

No. Door Energy develops and manufactures mobile energy-storage and charging solutions for multiple vehicle and industrial scenarios. The wider product range includes high-power DC charging for roadside rescue and commercial vehicles, as well as stored-energy solutions that can support construction equipment, pumps, lighting and other AC loads. Door Energy’s broader mobile charging portfolio supports up to 420 kW DC output on selected configurations, with OCPP and CCS1/CCS2 support.

Q9. How is the mobile charging equipment replenished?

Door Energy mobile energy-storage systems can be configured for rapid DC replenishment or AC replenishment depending on the product and site. For the broader Door Energy mobile charging platform, DC replenishment can restore the system from low SOC in roughly one hour under suitable conditions, while AC electrical-box replenishment may take roughly two hours. Actual times depend on equipment configuration, available input power, temperature and battery-management limits.

Q10. What maintenance strategy is suitable for a mobile charging fleet?

A modular design is valuable because operators can inspect and service functional modules more efficiently and reduce downtime. Preventive maintenance should include battery-health monitoring, thermal-management checks, connector inspection, autonomous-driving sensors, brakes, tyres or running gear, communication modules and software logs. Door Energy positions modular maintenance as an important part of keeping mobile storage-and-charging equipment practical for repeated commercial operation.

VII. Conclusion: Move Energy to the Vehicle Instead of Building Every Future Kilowatt Into Every Parking Bay

The expansion of EVs is changing the economics and operating logic of parking infrastructure. By the end of 2025, the world had more than 7 million public charging points and approximately 76 million electric light-duty vehicles, while global electric car sales reached about 21 million during the year. Multi-storey parking facilities therefore need to plan not only for today’s EV population, but also for a future in which charging demand is more frequent, more distributed and more time-sensitive.

For long-dwell users with predictable parking behaviour, fixed charging remains the most efficient foundation. For irregular visitors, upper-floor overflow, fleet-priority requests, temporary charging shortages and buildings where electrical upgrades are being phased, mobile storage-and-charging equipment can provide a flexible second layer.

Door Energy’s approach is to treat mobile charging as a movable energy node. Its autonomous parking-lot solution combines energy storage, up to 100 kW EV charging, Level 4 autonomous driving and intelligent dispatch functions so that the charging resource can travel to the parked vehicle. The broader Door Energy portfolio also covers high-power emergency and industrial applications, including selected Mobile EV Charger configurations with DC output up to 420 kW, OCPP communication and CCS1/CCS2 charging standards.

This does not eliminate the need for fixed charging infrastructure or local code compliance. Instead, it gives parking operators another design variable: charging capacity no longer has to be permanently tied to the same physical bay. The operator can decide how much capacity should be fixed, how much should remain mobile and how software should move energy through the building.

The most useful planning question is therefore not simply “How many chargers can fit in this car park?” A better question is: “How many vehicles need how many kilowatt-hours, on which floors, within what service window, and what combination of fixed and mobile assets can deliver that energy with acceptable infrastructure cost and utilisation?”

When the project is designed around that question, a Mobile EV Charger becomes more than a charger with wheels. It becomes part of a flexible, software-dispatched energy system for the parking facility.

Door Energy resources

Explore the Door Energy website for mobile energy-storage charging solutions, product information and application guidance.

View the Door Energy Mobile EV Charger product range for available charging and energy-storage configurations.

For the parking-garage application discussed in this guide, review the 100 kW Autonomous Car Charging Station / Mobile Charging Robot.

For common connector, customisation and ordering questions, see the Door Energy FAQ.

Note: Parking-space, EV-share, charging-request and dispatch-cycle calculations in this article are planning examples created to demonstrate methodology. They are not presented as customer operating data. Product specifications are based on Door Energy’s published product information and should be confirmed against the final project configuration before procurement or engineering design.