First ask what the percentage is divided by
A report showing 90% solar self-consumption can coexist with substantial grid purchases. It may mean that the home uses almost all the solar electricity produced, rather than that solar supplies 90% of everything the home consumes. Start by separating generation, solar electricity used in the home and total household consumption over the same period.
IEA PVPS distinguishes self-consumption from self-sufficiency. The example here uses a system without a battery and measurements on the AC side to make the denominators clear. It is not an estimate of savings or an assessment of any project’s right to sell electricity.
Calculate both ratios from one set of readings
In a hypothetical month, solar generates 500 kWh, the home immediately uses 450 kWh of it, and total household consumption is 1,000 kWh. Self-consumption is 450 ÷ 500 = 90%, while self-sufficiency is 450 ÷ 1,000 = 45%. Assuming complete data and no other generation, grid purchases are 550 kWh and exports are 50 kWh. These are teaching figures, not typical household benchmarks.
If a smaller system produces only 200 kWh and all of it is used, self-consumption reaches 100%. With household consumption still at 1,000 kWh, however, self-sufficiency is only 20%. Maximising the self-consumption percentage alone is therefore an incomplete sizing objective; useful energy displaced and cost also matter.
Match measurement boundaries and periods
Ask the system provider for field definitions, meter locations and report start and end dates. Inverter generation alone does not identify self-consumption. Export readings may support a generation-minus-export balance for a simple system like the example, but meter boundaries and losses between meters must be reconciled. Do not combine monthly totals from different reporting periods.
Battery systems also require the origin of charging energy, discharge and losses to be identified. Counting both charging and discharge as separate solar use would double count energy. If an app uses a different definition, put that definition beside the report before comparing systems.
Use the ratios to choose the next investigation
High self-consumption with low self-sufficiency calls for checking whether generation is small relative to demand or whether substantial demand occurs at night. Low self-consumption calls for examining actual daytime surplus and whether flexible tasks can move without disrupting operations. Trial a suitable load shift and track purchased and self-used energy; do not create unnecessary demand just to improve a percentage.
Before adding panels or storage, bring interval data, space and connection constraints, and costs to the responsible Kintury Energy team for an options assessment. Neither ratio alone establishes investment returns, outage backup capability or export purchasing terms. The useful outcome is a clear list of missing measurements and options worth examining.
