Residential EV Group Power Sharing Calculator

A residential EV group power sharing calculation applies one fixed Shared group power cap (kW) across two or more EVSE ports or vehicle charging requests. The central result is the allocated charging power available to each active request under the selected Allocation policy.

This allocation is used during residential EV charging planning when a service, feeder, panelboard, EVEMS, or charging group has a defined power limit that cannot support every connected vehicle at its individual Requested maximum power (kW). It identifies the difference between the combined connected demand and the power actually available to the group.

The calculation supports a load review before final branch-circuit, feeder, raceway, conductor ampacity, voltage-drop, and equipment-selection decisions are made. It does not select conductors, establish ampacity, or determine NEC load-calculation compliance.

Group Power Cap and Requested Power

Each charging request has a maximum charging rate, while the group has a single upstream cap.

Shared group power cap (kW) is the total real power made available to all active ports or vehicle requests. It may represent a fixed EVSE group limit, an energy-management-system limit, an available feeder allocation, or another imposed charging-power constraint.

Requested maximum power (kW) is the maximum power requested by each individual charging port or vehicle. The sum of these requests establishes the group’s unconstrained charging demand:

\(\displaystyle P_{\text{requested,total}} = \sum_{i=1}^{n} P_{\text{requested},i}\)

When total requested power exceeds the shared cap, not every port can receive its full requested maximum power simultaneously. The calculator reports that difference as:

\(\displaystyle P_{\text{unserved}} = P_{\text{requested,total}} - P_{\text{allocated,total}}\)

where total allocated power cannot exceed the Shared group power cap (kW).

A positive Unserved requested power value does not mean charging stops. It shows the amount of simultaneous requested charging power that the group cannot supply under the entered cap and allocation policy.

Allocation Policy

The Allocation policy determines how the available group power is assigned among active ports.

Allocation policy	Allocation behavior
Equal share	Each active port receives the same initial share of the available group power
Priority share	Power is allocated in ascending Priority number (rank) order

For equal sharing, the initial per-port allocation is:

\(\displaystyle P_{\text{equal share}} = \frac{P_{\text{group cap}}}{N_{\text{active ports}}}\)

where \(N_{\text{active ports}}\) is the number of active charging requests.

For priority sharing, Priority number (rank) establishes the allocation order. A lower rank is allocated before a higher rank. The ranking itself does not describe vehicle state of charge, charging efficiency, battery condition, EVSE communications, or a manufacturer-specific load-management response. Those operating behaviors must be established by the installed EVSE or energy-management equipment.

Energy Need and Available Time

The calculator combines allocated power with each vehicle’s entered charging window.

Required energy (kWh) is the energy the vehicle request needs during the stated period. Available charging hours (h) is the time available for that request to charge. Estimated delivered energy is based on allocated charging power and available charging time:

\(\displaystyle E_{\text{delivered},i} = P_{\text{allocated},i} \times t_i\)

where:

• \(E_{\text{delivered},i}\) = estimated energy delivered to a request, in kWh
• \(P_{\text{allocated},i}\) = allocated power for that request, in kW
• \(t_i\) = Available charging hours (h) for that request

A port meets its entered energy need when:

\(\displaystyle E_{\text{delivered},i} \geq E_{\text{required},i}\)

The result Ports meeting entered energy need counts the requests that satisfy this comparison. The calculation uses the entered power and time values; it does not add losses, charging taper, EVSE efficiency, battery-management limits, or changes in vehicle demand during the charging period.

Calculation Example

Enter a Shared group power cap (kW) of 11.52 kW with the Allocation policy set to Equal share.

Input	Vehicle A	Vehicle B
Port or vehicle label	Vehicle A	Vehicle B
Requested maximum power (kW)	9.6	7.2
Required energy (kWh)	20	12
Available charging hours (h)	8	6
Priority number (rank)	1	2

The total requested power is:

\(\displaystyle 9.6\text{ kW} + 7.2\text{ kW} = 16.8\text{ kW}\)

With two active ports sharing an 11.52 kW cap equally, the initial allocation is:

\(\displaystyle \frac{11.52\text{ kW}}{2} = 5.76\text{ kW per port}\)

The calculator results are:

Result	Value
Active ports	2 ports
Total requested power	16.8 kW
Total allocated power	11.52 kW
Unserved requested power	5.28 kW
Estimated delivered energy	80.64 kWh
Ports meeting entered energy need	2 ports

Vehicle A receives an estimated:

\(\displaystyle 5.76\text{ kW} \times 8\text{ h} = 46.08\text{ kWh}\)

Vehicle B receives an estimated:

\(\displaystyle 5.76\text{ kW} \times 6\text{ h} = 34.56\text{ kWh}\)

The combined estimated delivered energy is:

\(\displaystyle 46.08\text{ kWh} + 34.56\text{ kWh} = 80.64\text{ kWh}\)

Vehicle A’s estimated 46.08 kWh exceeds its 20 kWh requirement, and Vehicle B’s estimated 34.56 kWh exceeds its 12 kWh requirement. Both ports therefore meet the entered energy need even though the group cannot supply both requested maximum charging rates at the same time.

Electrical Design Limits

The calculated kW allocation is a charging-group planning value. It must be converted and evaluated separately for the actual electrical system voltage, phase arrangement, power factor where applicable, EVSE nameplate ratings, continuous-load treatment, branch-circuit ampacity, feeder capacity, overcurrent protection, disconnecting means, and panelboard or service load calculation.

Conductor sizing requires the actual circuit current and installation conditions, including conductor material, AWG or kcmil size, insulation temperature rating, terminal rating, ambient-temperature correction factor, adjustment factor for current-carrying conductors, and applicable raceway fill. A group power cap does not by itself establish allowable conductor ampacity.

Voltage drop also requires the actual circuit configuration: voltage, one-way conductor length, conductor impedance, conductor size, and expected load current. Long residential feeder runs can require a voltage-drop review even when the allocated group power remains within the feeder’s calculated capacity.

The final installation must match the listed EVSE equipment and the implemented load-management controls. Verify the control sequence, communication-loss behavior, minimum charging output, demand-management settings, and the authority having jurisdiction (AHJ) requirements before relying on a reduced EV charging group cap for design or permitting.