Use the value of avoided grid imports minus the solar buy-back income sacrificed. Then apply battery losses and degradation before comparing cumulative savings with the installed price.
The correct daily value
If your retailer charges 33c/kWh and buys solar at 13c/kWh, storing one solar unit does not create 33 cents of value. It replaces a retail purchase but gives up export income, with further loss through the battery.
Check whether the battery cycles
The model limits charging to the lower of solar surplus and battery capacity, then limits delivered energy to evening demand. This prevents a quote from earning fictional savings on unused capacity.
- Use average exports from monitoring or bills
- Estimate evening demand conservatively
- Model the current retailer rates
- Compare payback with the warranty
- Run a lower-export winter case
What the public EECA calculator omits
EECA’s solar calculator explicitly excludes battery costs and benefits. Battery Quote X-Ray is designed to answer that narrow quote-level question while linking back to EECA’s broader independent guidance.