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TL;DR
Self-sufficiency measures the share of electricity consumption covered by local generation actually used. It ranges from 0 to 100 %. Annual generation above annual consumption does not prove independence at every hour.
Definition
Self-sufficiency = locally generated energy consumed on site ÷ total consumption × 100, using the same period and boundary. It differs from self-consumption rate, whose denominator is generation.
Range
0–100 %
Denominator
Total consumption
Energy in the numerator
Local generation used
Sizing
Hourly profile
Grid purchases remain necessary when local generation and available storage do not meet demand. Exported surplus does not directly increase self-sufficiency. For storage, count local energy actually delivered to loads after losses and distinguish energy charged from the grid. 100 % self-sufficiency requires all demand within the boundary to be covered during the period.
Request a seasonal hourly simulation for your roof and appliances. A home battery shifts consumption by hours; it does not store summer surplus for the whole winter. Compare the cost of additional self-sufficiency with avoided purchases instead of targeting a universal percentage.
Related guides
It depends on location, demand, generation and storage. An annual surplus is insufficient. Check hourly coverage, adverse periods, losses and backup arrangements before calling a project self-sufficient.
With 9 000 kWh generated, 5 000 kWh consumed and 4 000 kWh of local generation used on site, self-consumption is 4 000 ÷ 9 000, about 44 %, and self-sufficiency is 4 000 ÷ 5 000, or 80 %. Use consistent data for the same period.
Sources & method
Check equipment values in the offered model’s datasheet and warranty terms. Confirm grant, permit and connection requirements with the responsible programme, municipality and grid operator.
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Estimate output, avoided purchases and payback using your data. Confirm the assumptions in a quote.
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