Self-consumption and self-sufficiency are different

Name the denominator

For a simple system without storage, solar self-consumption is the share of generated solar energy used on site. Solar self-sufficiency is the share of household consumption supplied by solar. The first divides by solar generation; the second divides by household demand.

Write the words under the fraction before calculating. “Solar used here ÷ solar generated” answers one question. “Solar used here ÷ household consumption” answers another. Neither is a direct measure of equipment efficiency, and neither describes the value of the electricity without further information.

A small array can have high self-consumption

Do not describe that 100% as “the home runs entirely on solar.” It describes the destination of generation, not the source of all consumption.

A larger array can reverse the impression

The lower first percentage does not establish that this system is worse. It answers a different question about where production went. Compare systems against the goal you actually have, using the same definitions and time window.

Storage adds a boundary question

A battery can move solar energy to later hours. It may also charge from another source, and charging and discharging involve losses. If you count battery discharge as solar without knowing its source, the claimed solar share can be overstated.

The Australian government’s solar monitoring guidance identifies generation, consumption and storage as quantities to understand. In practice, your ratio needs a defined treatment of stored energy and a consistent measurement boundary. State whether you are measuring direct solar use, solar plus attributed storage, or simply non-grid supply.

Check whether the data supports the label

You need matched intervals and the relevant generation, load and import/export measurements. Missing grid power cannot safely be reconstructed as zero. An inverter serving selected circuits cannot establish a whole-property percentage unless the unmonitored circuits are accounted for.

Sunstead’s reported self-sufficiency uses matched load and AC-input observations where available; that is not automatically the same as a separately audited solar-origin fraction. Read the metric’s basis and coverage before comparing it with a vendor portal’s label.

Keep a ratio note containing the numerator, denominator, time range, coverage and storage treatment. If the denominator is zero or unknown, the percentage is undefined. A dash is an appropriate answer.