The short answer
Compare the export payment you would give up with the later import purchase the stored energy would avoid. Battery losses, demand, capacity and tariff terms can change the answer.
Compare one unit at the same starting point
Suppose 1 kWh of surplus solar could be exported for 15p. If it is stored with an assumed 90% round-trip efficiency, it delivers 0.9 kWh later.
At an illustrative avoided import price of 28p/kWh, that delivery is worth 25.2p. The extra gross value over immediate export is 10.2p, before wear and other costs. These are example rates.
Change the assumption and the result changes
If immediate export instead earned an illustrative 30p, the same 25.2p avoided purchase would be 4.8p less valuable than export. Storage is therefore not automatically the highest-value use of every surplus unit.
The comparison also needs a real later demand. Stored energy left unused at the end of the assessment should not receive an invented saving.
Consider competing uses
The car, hot-water system, household loads and battery may compete for the same surplus. Compare the useful alternative each would replace, rather than counting the same solar unit several times.
Ask how the installed controls set priorities and what happens when a device reaches its limit. Comfort, driving readiness and outage reserve may matter alongside cost.
Check payment conditions
Ofgem explains that SEG suppliers set their tariff terms and pay using export readings. Check the chosen supplier’s eligibility and treatment of stored or grid-charged energy.
SolarIQ models solar export under the entered assumptions. It does not simulate trading stored battery energy back to the grid.
Before your assessment
Bring these questions with you.
- Export credit forgone at the time of storage.
- Import price actually avoided later.
- Losses and useful later demand.
- Supplier rules and competing uses of surplus.