Apartment Parking Lots Can't Achieve "One Charging Station Per Unit"? Door Energy Shared Mobile Charging May Offer an Alternative Solution

The number of electric vehicles is constantly growing, but many older apartments still cannot install an individual charging station for each fixed parking space. The problem isn't just "insufficient number of charging stations," but also involves transformer capacity, underground garage wiring distance, parking space ownership, fire safety approvals, cost sharing, and subsequent maintenance.

According to global electric vehicle data released by the International Energy Agency, global electric vehicle sales exceeded 17 million units in 2024, a year-on-year increase of over 25%, accounting for more than 20% of global new car sales. Meanwhile, approximately 43.9 million homes in the United States are multi-family homes, accounting for about 31.4% of the total housing stock. This means that a large number of electric vehicle users do not have independent garages and cannot easily install private charging facilities.

Therefore, apartment managers need to rethink a question: Is it really necessary for every parking space to have a fixed charging station?

For some existing residential, commercial apartment, serviced apartment, and mixed-use buildings, Door Energy's shared mobile EV charger may offer another technological path. The equipment no longer requires vehicles to search for charging stations; instead, it autonomously moves to the vehicle's parking space based on orders, providing on-demand charging.

I. Key Conclusion: Apartment charging doesn't need "one charging station per car," but rather available power.

From Equipment Coverage to Service Coverage

Traditional planning typically follows the approach of "building as many charging spaces as there are electric vehicles." However, what residents truly need is not long-term occupancy of a charging station, but sufficient range before setting off the next day.

Assuming a resident drives 40–60 kilometers daily, with a vehicle energy consumption of 15–22 kWh/100km, then typically only about 6–13 kWh of electricity needs to be replenished daily. Even considering low winter temperatures, air conditioning use, and charging losses, the actual demand each night may not reach the full battery capacity.

Therefore, whether a parking lot can support electric vehicles cannot be judged solely by the number of charging ports. More important indicators include the nightly deliverable energy, order completion rate, equipment arrival time, charging success rate, and vehicle availability for the next day.

The Core Value of Door Energy Mobile EV Chargers

Door Energy's shared mobile EV chargers integrate the battery, charging module, mobile chassis, and dispatch system into a single device. It can move between multiple parking spaces and schedule charging based on appointment times, vehicle remaining battery power, and resident departure times.

This doesn't mean fixed charging stations are worthless. For newly built apartments or residences with sufficient power distribution capacity, low-power fixed AC chargers are still suitable for extended overnight charging. Door Energy mobile devices are better suited for parking lots where fixed infrastructure is difficult to expand quickly, serving as a supplement, transition, or coverage for dispersed demand.

II. Why is it difficult to truly achieve "one charging station per unit" in apartment parking lots?

Power Distribution Capacity Often Reaches Its Limits Before the Number of Parking Spaces

Existing apartment power distribution systems are typically designed for lighting, elevators, ventilation, air conditioning, and general resident loads. Adding a large number of charging devices simultaneously can cause a rapid increase in peak building load.

For example, in an apartment building with 200 parking spaces, if 50 of them simultaneously use a 7kW AC charger, the theoretical additional load could reach 350kW. If 100 spaces are charging at the same time, the theoretical load would reach 700kW. Even with dynamic power distribution, the distribution cabinet, cabling, transformers, and fire protection system may still require upgrades.

The loads in the table are theoretical values and do not represent that all equipment will necessarily operate at full power simultaneously. However, it is sufficient to illustrate that as the number of electric vehicles increases, the problem may evolve from "how to install a few charging piles" to "how to reconfigure the power supply for the entire building".

Underground Garage Cabling Costs Are Not Asymmetrical

Parking spaces near the electrical substation may require shorter cables, while those further away may need to traverse multiple fire compartments, walls, or floors. Construction also impacts garage access and involves trenching, cable trays, restoration, signage, and acceptance.

Furthermore, assigned parking spaces may not be perfectly matched to electric vehicle (EV) users. A resident who has a charging station installed today may move out, while the next EV user's parking space might be located at the other end of the garage. Thus, there is a risk of spatial mismatch in infrastructure.

Property Rights, Billing, and Management Responsibilities Are More Complex

Multi-family homes typically involve owners, tenants, property management companies, homeowners associations, and electricity providers. Who bears the initial investment, who pays for maintenance, how electricity is metered, and who is responsible for equipment failures all need to be determined in advance.

The U.S. Department of Energy's guidance on charging in multi-family homes also lists electricity access, installation costs, billing, property rights, and legal liability as major challenges.

Therefore, "one charging station per household" is not simply an equipment procurement project, but a comprehensive renovation project involving building, electrical, property rights, and operations.

III. How Does Door Energy's Shared Mobile EV Charger Change Parking Lot Charging Logic?

From "Vehicle Finds Charging Station" to "Equipment Finds Car"

The fixed charging model requires drivers to park in designated charging spots. If the charging spot is occupied by a gasoline vehicle, the previous vehicle hasn't left in time, or the resident's designated parking space isn't in the charging area, the equipment may be unusable even if it's idle.

Door Energy's mobile charging uses the opposite logic. Residents still park in their designated parking spaces and then submit a charging request through the management platform. The dispatch system, based on the parking space map, dispatches the Mobile EV Charger to the vicinity of the vehicle.

This way, property management doesn't need to convert a large number of ordinary parking spaces into dedicated charging spots, and can still provide service to vehicles distributed across different areas.

One Device Can Serve Multiple Parking Spaces

The value of the sharing model lies not in having one device simultaneously cover an unlimited number of vehicles, but in utilizing the differences in residents' parking times for dispatching.

European official data indicates that cars are parked for an average of approximately 23 hours per day, and it is projected that by 2030, 60%–85% of charging will likely occur at private charging stations. This extended parking period creates opportunities for scheduled charging, off-peak charging, and mobile charging.

For example, resident A requests to top up 20 kWh before 10 PM, resident B only needs to top up 15 kWh before 6 AM, and resident C plans to leave in the early morning. The system can prioritize vehicles with earlier departure times, rather than simply queuing them according to the order of submission.

Shared Dispatch Requires Four Basic Data Items

Without this data, equipment may be mobile, but it cannot form a highly efficient shared service. Therefore, the Door Energy Mobile EV Charger project is not only a hardware deployment but also an energy dispatch and parking lot operation system.

IV. How Does Door Energy's Autonomous Mobile Charging Solution Complete a Task?

Step 1: Resident Sends a Charging Request

After parking, users can submit an order through the property management platform, parking management system, or dispatch backend. The request should include at least the parking space number, estimated departure time, and target battery replenishment.

In more mature systems, three types of orders can be set: regular, scheduled, and emergency. Regular orders are executed at the system's recommended time; scheduled orders must be completed before the specified time; and emergency orders prioritize replenishing enough battery power to support the next leg of the journey.

Step Two: System Vehicle Location

The dispatch platform identifies the target area based on the parking space map, while simultaneously checking for obstacles, closed passages, or construction zones between the equipment and the vehicle.

To reduce error rates, parking space numbers, map coordinates, and sensor recognition results should be cross-verified. If the vehicle's parking position deviates from the parking space boundary, the system can pause the task and notify the administrator.

Step Three: Autonomous Equipment Movement

The Door Energy Mobile EV Charger uses an L4 level autonomous movement system with a maximum movement speed of 10 km/h and the ability to adapt to garage ramps. Product data shows that its climbing ability is greater than 20%, suitable for most common underground garage ramp environments.

However, speed is not the primary indicator for parking lot operation. In areas with high pedestrian, vehicle, and corner traffic, the equipment should be set to a lower operating speed according to the project risk assessment, and electronic fences should be installed for blind spots, ramps, and fire lanes.

Step 4: Connect and Begin Charging

After the equipment arrives near the target vehicle, it can be automatically connected using a robotic arm or manually by staff, depending on the configuration. Automated connection is suitable for projects with high standardization and easily identifiable vehicle interface locations; manual connection is easier to adapt to different vehicle models but requires configuring on-site operational procedures.

After completing handshake, safety checks, and insulation checks, the equipment begins outputting DC power. The charging power will not always remain at the nominal maximum value but is determined by the vehicle's BMS, SOC, temperature, charging curve, and equipment status.

Step 5: End Task and Return to Standby Area

Upon reaching the target charge level, order energy, or stopping condition, the system ends charging and records the order data. The equipment then proceeds to the next vehicle, returns to the standby area, or enters its own recharging process.

The entire process should record arrival time, connection result, delivered electricity, charging duration, error code, and SOC termination, providing a basis for billing, maintenance, and subsequent capacity planning.

Door Energy Key Technical Parameters

It should be noted that product configuration, interface type, and bidirectional functionality should be confirmed based on the project location, vehicle type, and certification requirements. Bidirectional charging and discharging capability does not mean the equipment can directly supply power to the building or grid without approval.

V. How many vehicles can 105kWh serve? Building a capacity model with data

Don't use "battery capacity ÷ vehicle battery capacity" for calculations

If a vehicle is equipped with a 75kWh battery, it doesn't mean that 75kWh needs to be delivered for every service. In apartment scenarios, the more common need is to replenish the electricity consumed that day, rather than charging from 0 to 100%.

Furthermore, the equipment itself needs to retain a safety margin, and there are losses due to conversion, cabling, temperature control, and charging processes. Therefore, the entire 105kWh should not be considered as deliverable capacity during planning.

The following examples are calculated based on 80% net dispatchable capacity, or approximately 84 kWh per round. This percentage is a project assumption used to illustrate the methodology and is not a fixed result that can be directly achieved in all scenarios.

In actual operation, a minimum return capacity should also be set. For example, when the equipment's SOC drops to 20% or 25%, the system can stop accepting regular orders and return to the standby area for recharging to prevent the equipment from losing operational capability en route.

100kW Doesn't Mean All Vehicles Can Be Charged at 100kW

Theoretically, delivering 20kWh at a constant 100kW power output takes only 12 minutes. However, vehicles may limit their maximum input power, and charging speed typically decreases as battery SOC rises.

The above times do not include equipment movement, location, connection, and task completion operations. Project owners can add 5–10 minutes of non-charging time to each order to establish a more realistic scheduling model.

How many orders can be completed in one night?

Assuming an apartment's operational hours are from 6:00 PM to 8:00 AM the following day, a total of 14 hours; each vehicle delivers an average of 20 kWh; the average effective power is 60 kW; and the entire process of moving, connecting, and ending takes 7 minutes. Therefore, a single task takes approximately 27 minutes.

Theoretically, based solely on time, one device can complete approximately 31 tasks. However, considering energy capacity, if the net dispatchable power per round is 84 kWh, only about four 20 kWh orders can be completed per round. Therefore, nighttime throughput ultimately depends on the device's ability to quickly recharge between tasks.

Under matched DC recharging conditions, the Door Energy device can be fully recharged from a low battery state in approximately 1 hour; with approximately 50 kW AC input recharging, the theoretical time is approximately 2 hours. Actual time will also be affected by initial SOC, input power, temperature, charging curve, and safety margins.

Example Model for a 200-Parking Apartment

This case demonstrates that device selection cannot solely rely on 100kW power. Property management also needs to verify device battery capacity, replenishment window, order time distribution, and resident needs simultaneously.

VI. Shared Mobile Charging vs. Fixed Charging: How to Choose?

Comprehensive Comparison of Three Modes

Therefore, mobile solutions are not the only answer for all apartments. A more reasonable approach might be a hybrid deployment: install some fixed AC chargers for high-frequency users, and then use mobile EV chargers to cover remote parking spaces, temporary demand, visitor vehicles, and peak orders.

Comparing Total Cost of Ownership (TCO) Instead of Unit Price of Equipment

The total cost of a fixed charging solution typically includes charging piles, cabling, cable trays, trenching construction, distribution cabinets, transformer capacity upgrades, network fees, platform fees, and maintenance costs. A mobile solution includes equipment, standby charging areas, dispatching systems, fire protection and security upgrades, maintenance, insurance, and potential manual connection costs.

The following formulas can be used for comparison:

Fixed Solution TCO = Equipment Cost + Line Construction + Distribution Upgrade + Software & Network + O&M Costs

Mobile Solution TCO = Mobile Equipment + Charging Facilities + Dispatch Platform + Security Upgrades + O&M Costs

If remote cabling costs are high, user growth is uncertain, or parking space ownership is complex, a mobile solution may offer better long-term investment value. Conversely, if almost every vehicle requires 40–60 kWh per day, and the parking lot has sufficient power, fixed charging infrastructure is generally more reliable.

An 8–12 week pilot program is recommended.

During the pilot phase, it's not enough to simply record the amount of electricity charged; it's also important to observe whether orders are completed on time, whether the equipment can be accessed smoothly, and whether residents are willing to use the reservation system.

After completing the pilot, the property management can decide based on actual order data to add mobile devices, build more fixed charging points, or adopt a combination of both.

Security Boundaries Must Be Clearly Defined Before Deployment

Underground parking lots are controlled but complex environments. Prior to project implementation, fire safety, electrical, accessibility, insurance, and local certification reviews are required, and the following must be clearly defined:

* Fire lanes, accessible parking spaces, and vehicle exits must not be obstructed;

* Speed limits and electronic fences must be installed at ramps, corners, and pedestrian walkways;

* Battery temperature, insulation, smoke, and abnormal collision monitoring must be established;

* Emergency stop, manual takeover, and fault isolation mechanisms must be implemented;

* Compatibility of CCS1 or CCS2 with the target vehicle must be verified;

* The boundaries of responsibility for automatic connection and manual plug-in must be clearly defined;

* Backup procedures must be developed for network outages, map errors, and charging failures;

* Modular maintenance should allow for rapid location and replacement of faulty modules.

Door Energy employs a modular design, reducing the complexity of troubleshooting and maintenance. However, any energy storage mobile EV charger should be integrated into the parking lot's fire safety and energy management system, rather than operating as a regular mobile device.

Long-Term Value: Upgrading from Charging Equipment to Dispatchable Energy Assets

As the number of electric vehicles increases, apartments may initially deploy one device to cover low-density demand, then increase the number of devices based on orders. The dispatch platform can also allocate different devices to different floors or parking areas, reducing unnecessary travel distances.

If the project is equipped with bidirectional charging and discharging and completes local grid connection, protection, and metering approvals, the equipment may also participate in building emergency power supply or load management in the future. Door Energy products can also be configured with AC output to power loads such as lighting and water pumps. However, these functions need to be designed independently and cannot be enabled simultaneously with vehicle charging by default.

Therefore, the long-term value of Door Energy shared mobile charging is not just "installing fewer charging piles." It changes the way electricity is delivered in parking lots: electricity is centrally stored and then distributed to different vehicles according to time, location, and demand.

VII. Frequently Asked Questions about Apartment Mobile EV Chargers

Q1: How many electric vehicles can one 105kWh device charge?

A1: It depends on the amount of electricity each vehicle needs to replenish. Assuming 80% net dispatchable capacity, approximately 84kWh can be delivered per round. Replenishing 10kWh per vehicle can serve approximately 8 vehicles; replenishing 20kWh per vehicle can serve approximately 4 vehicles. Actual results should also deduct safety reserves and system losses.

Q2: Can a 100kW charger fully charge all vehicles in one hour?

A2: That's not the correct understanding. 100kW is the device's maximum DC charging power; the actual power is determined by the vehicle's BMS, battery temperature, SOC, and charging curve. Shared parking lots are better suited for on-demand charging rather than a commitment to fully charge vehicles every time.

Q3: Do residents need to move their cars to the public charging area?

A3: Usually not. Residents park in their designated spaces and submit an order; the Door Energy Mobile EV Charger can then move to the vicinity of the vehicle. This is the main difference between mobile charging and shared fixed charging spots.

Q4: Is the vehicle connection process fully automated?

A4: Yes, it can be automated with a robotic arm or manually plugged in, depending on the project configuration.

Q5: How does the device recharge itself?

A5: The device can return to the centralized standby area for recharging. Under matched DC input conditions, it takes approximately 1 hour to fully charge from low to high; with approximately 50kW AC input, it takes about 2 hours. Actual time depends on initial SOC, input conditions, and temperature.

Q6: What is the function of OCPP 1.6J?

A6: OCPP 1.6J can be used for device status monitoring, order management, charging records, remote control, and platform integration. Projects still require interface development and compatibility testing; one cannot determine direct connection to all systems solely based on protocol names.

Q7: Is this solution suitable for all apartment parking lots?

A7: No. Fixed charging infrastructure may be more suitable if garage routes are narrow and chronically occupied, fire safety approvals are not possible, vehicles require significant daily power, or there are no suitable charging areas. Projects should first assess route, power, and order requirements.

Q8: Can the equipment operate in rain, snow, or low-temperature environments?

A8: Door Energy equipment has a nominal operating temperature range of -20°C to 65°C, an IP55 protection rating, and uses liquid cooling thermal management. However, specific projects still need to assess water accumulation, icing, ramp friction, salt spray, and local climate conditions.

Q9: How are residents charged?

A9: Common methods include charging by electricity delivered, by order, by service duration, or a membership package. Billing rules need to clearly define electricity costs, service fees, reservation cancellation fees, and overtime handling methods, and comply with local metering and consumer protection requirements.

Q10: Can Door Energy shared mobile charging completely replace fixed charging stations?

A10: A more accurate positioning is supplementary and optimization. For existing apartments, it can reduce extensive upfront wiring and verify actual demand; as the number of electric vehicles increases, properties can still build some fixed charging points, forming a hybrid system combining fixed and mobile charging.

Conclusion

The real goal of apartment charging is not to make every parking space appear to have a charging station, but to ensure residents have sufficient, reliable, and billable electricity when they need to go out.

Fixed charging is suitable for new projects with stable demand and sufficient power distribution; shared fixed charging spaces are suitable for buildings that can accept vehicle relocation management; autonomous mobile Door Energy Mobile EV Chargers are more suitable for existing apartments with scattered fixed parking spaces, difficult wiring, and still growing demand.

Door Energy integrates 105kWh of mobile energy storage, up to 100kW DC charging, OCPP 1.6J, CCS1/CCS2, and L4 autonomous mobility into a single system, enabling charging equipment to proactively locate vehicles based on orders. For parking lots where a "one charging station per household" system is not yet feasible, this shared mobile charging is not simply an emergency alternative, but a new energy service model that can be deployed in phases and continuously expanded using data.