Solar Import and Export Meter Readings Explained

Four numbers that are easy to confuse

A grid-connected solar property can expose several measurements:

• Grid import: energy taken from the grid.
• Grid export: surplus energy sent to the grid.
• Solar generation: energy produced by the inverter/system.
• On-site consumption: energy used by the property, whether supplied by solar or grid.

One register cannot always describe all four.

Read the register label, not just the digits

Bidirectional meters rotate through import and export registers, often identified by provider- or meter-specific codes. Inverter apps may report generation using a different clock, sampling method or timezone.

Record import and export as distinct cumulative series. Never subtract today's export register from yesterday's import register.

Basic interval calculations

For each register:

Imported energy = current import − previous import

Exported energy = current export − previous export

If compatible inverter generation data covers the same interval, an approximate relationship may be:

On-site solar use = generation − export

and total site consumption may be estimated as on-site solar use plus grid import. Timing gaps, battery charging, inverter losses and different measurement points can prevent exact agreement, so label derived values honestly.

Net billing is not a meter subtraction rule

The provider decides how imported and exported units affect the bill under the applicable agreement and tariff. A simple “import minus export” unit total does not necessarily reproduce the payable amount. Rates, carry-forward rules, taxes and settlement periods can differ.

Organize the records

At one property, create clearly named records such as “Grid import”, “Grid export” and “Solar generation” only when the app supports their distinct roles. Preserve native units, register labels and source.

MeterPilot's general meter ledger can retain readings, but official net-metering interpretation must remain provider-specific. Do not combine registers into a standard household contribution chart unless the calculation explains exactly what it represents.

Troubleshooting disagreement

Compare identical intervals and timezones. Confirm whether the inverter reports AC output, DC production or household load. Check for meter replacement and register rollover. If official export credit appears wrong, preserve dated meter observations and contact the provider rather than editing readings to match the bill.

The US Department of Energy notes that net-metering arrangements and export compensation depend on local utility policy and are rarely as simple as an old meter running backward; see the Homeowner's Guide to Solar. Use your connection agreement and issued bill for the applicable settlement method.

A register example

These are three separate measurements. The simple energy relationship suggests about 225 kWh of solar was not exported during the interval, but batteries, conversion losses, different timestamps and measurement locations can prevent exact reconciliation.

Battery systems need another boundary

Battery charge, discharge and state-of-charge are not interchangeable with cumulative solar generation. A home can import while charging, export after on-site loads fall, or discharge without new generation. Do not infer battery behaviour from one net meter register.