Self-consumption vs self-sufficiency
Two different ratios and what each measures.
Reviewed
What this is for
Two percentages that are routinely swapped, and they answer opposite questions.
Self-consumption is of what the array made: the share of production that did not leave the site and was not dumped. Export and curtailment take it down. Charging the bank from the array raises it - that energy stayed on site.
Self-sufficiency is of what the site used: the share of load served without the grid. Import takes it down. A large array on a small load can look like perfect self-consumption and still leave the night uncovered.
They are not complements and they do not add to 100%.
Steps
- Open Storage and press Save and compute on a model. The strip leads with self-sufficiency, because that is the figure the screen exists to move. A dash is nothing computed yet.
- On the result, both tiles sit together: self-consumption of what the array made, self-sufficiency of what the site used. Read the captions. The same two words on a proposal without those captions are how a customer is shown the friendlier number.
- Strategy changes which of the two moves. Self-consumption dispatch keeps production on site. Backup-only holds the bank for interruptions and will look worse on both until the grid goes away. Time-of-use arbitrage needs a tariff; without one it behaves as backup.
- Financials' year-one self-consumption is from the bill. When a matching storage model exists, that cash flow prices the dispatched flows. Name the same run and the same consumption profile on both screens if you want the two sentences to describe one site; a storage model on another profile is not the one the bill reads.
Until a model has been computed, neither ratio is stored.
Tips and common mistakes
- Do not quote self-consumption as "the site is 80% off-grid". That is self-sufficiency, and it is usually smaller.
- A battery that charges from the grid can raise self-sufficiency while lowering self-consumption (the bank is already full from the grid, so PV exports). Both can be true.
- Unserved load is kilowatt-hours the site asked for and did not get. It is not 100% minus self-sufficiency; dump loads and export sit elsewhere.