Solar Export Energy Calculator

A solar export energy calculator determines how photovoltaic production is divided among on-site use, battery charging, and exported energy during the same measured interval. Its primary result, Grid export, is the solar energy remaining after direct site consumption and the entered battery charging allocation.

Grid-export kWh is used when reviewing inverter production records, utility net-metering data, energy-management performance, battery charging strategy, and the relationship between PV output and building demand. It also helps identify intervals where excess solar generation may create export, reverse-power-flow, or interconnection-control considerations.

The calculation is an energy-balance screen. It uses kilowatt-hours, not instantaneous amperes, conductor ampacity, inverter output current, or utility interconnection limits.

Input Energy Values

Enter all values for the same interval or billing period. A 15-minute production interval, a daily total, and a monthly utility total cannot be combined because the energy balance would not represent one common operating period.

Input	Electrical meaning
Solar generation (kWh)	Total AC-side solar energy generated during the selected interval or period.
Site load (kWh)	Total energy consumed by the site during that same interval or period.
Direct self-consumption (kWh)	Solar energy used directly by the site load before energy is exported or allocated to battery charging.
Solar energy to battery (kWh)	Solar energy allocated to battery charging before battery losses.

Direct self-consumption is the portion of PV generation that serves load without first being treated as exported energy. Solar energy to battery is entered before battery conversion, charging, state-of-charge, and round-trip efficiency losses. The calculator does not calculate those losses.

Export and Import Calculation

Solar generation is allocated first to direct site use, then to the entered battery charge request. The remaining solar energy is calculated as grid export.

\(\displaystyle \text{Grid export} = \max(\text{Solar generation} - \text{Direct self-consumption} - \text{Solar energy to battery}, 0)\)

Grid import is the site load not supplied by direct solar self-consumption.

\(\displaystyle \text{Grid import} = \max(\text{Site load} - \text{Direct self-consumption}, 0)\)

Self-consumption is the percentage of solar generation retained on site through direct use and battery allocation.

\(\displaystyle Self-consumption = \frac{ \text{Direct self-consumption} + \text{Solar energy to battery} }{ \text{Solar generation} } \times 100\)

Export share is the percentage of solar generation sent to the grid.

\(\displaystyle \text{Export share} = \frac{ \text{Grid export} }{ \text{Solar generation} } \times 100\)

For a balanced result, solar generation equals the sum of direct self-consumption, solar energy to battery, and grid export:

\(\displaystyle \text{Solar generation} = \text{Direct self-consumption} + \text{Solar energy to battery} + \text{Grid export}\)

Calculation Example

Use the following same-period energy values:

Field	Entered value
Solar generation	20 kWh
Site load	14 kWh
Direct self-consumption	10 kWh
Solar energy to battery	4 kWh

The solar allocation is:

\(\displaystyle \text{Grid export} = 20 - 10 - 4 = \text{6 kWh}\)

The remaining site demand is supplied by the grid:

\(\displaystyle \text{Grid import} = 14 - 10 = \text{4 kWh}\)

The on-site solar retention percentage is:

\(\displaystyle \text{Self-consumption} = \frac{10 + 4}{20} \times 100 = \text{70\%}\)

The exported portion of PV generation is:

\(\displaystyle \text{Export share} = \frac{6}{20} \times 100 = \text{30\%}\)

The resulting energy balance is:

Result	Value
Direct self-consumption	10 kWh
Solar energy to battery	4 kWh
Grid export	6 kWh
Grid import	4 kWh
Self-consumption	70%
Export share	30%

The site used 10 kWh of solar energy directly, allocated 4 kWh to battery charging, exported 6 kWh, and imported 4 kWh to satisfy the portion of the 14 kWh site load not served directly by PV.

Electrical Planning Use

Grid export and import results support energy review, but they do not directly establish branch-circuit or feeder design values. A 6 kWh export result identifies accumulated exported energy over the selected interval; it does not identify the maximum instantaneous AC output current from the inverter.

For electrical design and field verification, inverter output circuits, AC disconnects, feeders, overcurrent protective devices, conductors, terminals, raceway fill, voltage drop, and equipment ratings must be evaluated from actual electrical characteristics such as:

• Inverter nameplate AC output rating and continuous-current requirements.
• PV and energy-storage system equipment listing and manufacturer installation instructions.
• Conductor ampacity after applicable adjustment factor and correction factor requirements.
• Terminal rating, insulation temperature rating, conductor material, AWG or kcmil size, and installation conditions.
• Point-of-interconnection configuration, backfeed conditions, service equipment limitations, and utility export-control requirements.
• Battery charging and discharge controls, including actual battery state of charge and conversion efficiency.
• AHJ requirements, utility approval, and applicable NEC provisions for the installed system.

A period with modest net export can still include high instantaneous inverter current. Conversely, a period with zero net export can include substantial PV output that is absorbed by site load or battery charging. Use interval data alongside inverter ratings and electrical drawings when evaluating conductor sizing, voltage drop, switchgear loading, or utility interconnection conditions.

Field Boundary

The calculation treats entered energy values as an arithmetic allocation: direct site use first, then the stated battery charging allocation, with remaining solar energy shown as export. It does not model battery state of charge, battery efficiency, charging limits, discharge behavior, tariffs, demand charges, export curtailment, inverter clipping, utility approval, export controls, or interconnection compliance.