Self-consumption measures the share of your generation used at home. Self-sufficiency measures the share of your demand supplied by your own generation.
Use the right denominator
Imagine a home generating 4,000 kWh, using 1,600 kWh of that directly, and consuming 5,000 kWh overall. Its direct self-consumption is 40%; its direct self-sufficiency is 32%. These are illustrative numbers, not typical results.
Keep the seasons in view
A yearly balance does not mean you can disconnect from the grid. Surplus on a bright summer day does not automatically cover a cold winter evening. Storage usually shifts energy over much shorter periods than the seasons.
Ask what improves the outcome
Flexible demand can use generation as it arrives, while a battery may move some use to later. Neither creates extra solar energy. Compare the cost and practicality of each option, and check how losses and exported electricity are treated in any calculation.
Turn the percentages into an energy balance
Using the earlier example, 4,000 kWh generated minus 1,600 kWh used directly leaves 2,400 kWh for export when there is no storage or other diversion. Household demand of 5,000 kWh minus that same 1,600 kWh leaves 3,400 kWh of grid imports. These four quantities make the two percentages easier to audit. Ask for this balance whenever a proposal presents a headline independence figure without showing the flows behind it.
Measure the value of changing the schedule
Imagine shifting 300 kWh of existing demand into hours when solar surplus is available. With a purchase price of €0.30/kWh and export payment of €0.08/kWh, the extra annual value is 300 × (€0.30 − €0.08), or €66. The example excludes any cost of automation. The household has changed the timing of necessary use, not increased consumption merely to improve a percentage.
Keep the accounting consistent when adding storage
With a battery, distinguish direct solar use from electricity delivered after storage and from storage losses. Ask whether the displayed self-consumption figure includes energy lost in charging. Check that grid-charged energy is not counted as solar generation. A useful report shows energy into and out of storage as well as imports and exports, so the performance can be understood without relying on one large percentage.
Your planning checklist
- Annual generation, direct use, exports and grid imports.
- A clear denominator beside every percentage.
- Separate battery charging, delivered energy and losses.
- Savings calculated from necessary demand shifted in time.
Common questions
Is 100% self-consumption always the best result?
No. A small array can have a high percentage while supplying little of the home’s total demand. Judge the useful energy, installation cost and overall result together, rather than trying to maximise one ratio.
Will doubling the panels double my direct use?
Not automatically. If daytime demand stays the same, much of the extra generation may become export. Compare the larger array’s total additional value with its additional cost using a realistic consumption profile.