EV Solar Charging Calculator

The EV Solar Charging Calculator determines how much daily solar production is allocated to EV charging, how much energy reaches the vehicle after charging losses, the estimated driving miles supported by that energy, and the remaining Grid energy needed to meet the daily charging target.

The primary planning result is Grid energy needed. It identifies the daily EV energy shortfall after solar allocation and charging efficiency are applied. That number can be carried into an EV charging energy plan, PV production review, battery-storage evaluation, or utility-energy estimate. It does not establish EVSE branch-circuit ampacity, conductor AWG or kcmil size, raceway fill, voltage drop, service capacity, or PV system design.

Solar Energy Allocation

Available solar energy is the daily solar energy available for allocation, expressed in kWh/day. It represents energy available to the planning calculation, not PV module nameplate rating, inverter output rating, or a guaranteed daily production value.

Solar allocation to EV is the percentage of Available solar energy assigned to EV charging. The calculator first applies this percentage to determine Allocated solar energy:

\(\displaystyle \text{Allocated solar energy} = \text{Available solar energy} \times \frac{\text{Solar allocation to EV}}{100}\)

A 50% allocation means half of the entered daily solar energy is reserved for the EV charging plan. The remaining solar energy is outside this calculation and may serve other loads, storage, export, or another planned use.

Charging Efficiency and Delivered Energy

Energy allocated from solar is not necessarily identical to energy delivered to the vehicle. Charging efficiency applies the entered percentage to Allocated solar energy:

\(\displaystyle \text{EV delivered energy} = \text{Allocated solar energy} \times \frac{\text{Charging efficiency}}{100}\)

The result, EV delivered energy, is the daily energy available at the vehicle for the mileage estimate and comparison against the charging target.

Vehicle efficiency converts delivered energy into estimated range. Enter vehicle consumption as mi/kWh, then calculate:

\(\displaystyle \text{Estimated EV miles} = \text{EV delivered energy} \times \text{Vehicle efficiency}\)

This is an energy-based range estimate. It is not an EVSE output test, charging-current calculation, battery-state-of-charge measurement, or trip-range guarantee.

Grid Energy Requirement

Target EV energy is the desired daily EV charging energy in kWh/day. The calculator compares that target with EV delivered energy:

\(\displaystyle \text{Grid energy needed} = \max(0,\ \text{Target EV energy} - \text{EV delivered energy})\)

The maximum-of-zero rule prevents a negative grid-energy result. If solar-delivered energy equals or exceeds Target EV energy, Grid energy needed is shown as 0 kWh. Excess solar energy is not credited, stored, exported, or otherwise modeled by this calculation.

For an electrical load review, Grid energy needed is a daily energy quantity, not an instantaneous demand in amperes. Converting a daily energy plan into EVSE load, branch-circuit conductor ampacity, feeder capacity, or service-load decisions requires the actual charging equipment rating, charging schedule, voltage, circuit configuration, and applicable project requirements.

Calculation Example

Using the entered values below:

Input	Value
Available solar energy	30 kWh/day
Solar allocation to EV	50%
Charging efficiency	90%
Vehicle efficiency	3.5 mi/kWh
Target EV energy	20 kWh/day

The calculation proceeds as follows:

\(\displaystyle \text{Allocated solar energy} = 30 \times \frac{50}{100} = \text{15 kWh}\)

\(\displaystyle \text{EV delivered energy} = 15 \times \frac{90}{100} = \text{13.5 kWh}\)

\(\displaystyle \text{Estimated EV miles} = 13.5 \times 3.5 = \text{47.25 mi}\)

\(\displaystyle \text{Grid energy needed} = \max(0,\ 20 - 13.5) = \text{6.5 kWh}\)

The entered daily solar energy allocates 15 kWh to EV charging. After the entered charging-efficiency value is applied, 13.5 kWh reaches the EV energy plan, supporting an estimated 47.25 miles at the entered Vehicle efficiency. The 20 kWh/day target remains short by 6.5 kWh, which is the calculated Grid energy needed.

Electrical Planning Boundary

This EV solar charging calculation is limited to daily energy allocation. It does not perform PV array sizing, inverter selection, battery-storage analysis, utility export calculations, interconnection review, or time-of-use scheduling.

It also does not size an EVSE branch circuit or feeder. Field design must separately verify the charging equipment’s electrical rating, conductor ampacity, terminal rating, insulation temperature rating, adjustment factor, correction factor, current-carrying conductors, voltage drop, raceway routing, available capacity, overcurrent protection, and the AHJ-approved installation requirements.