Quick answer
Yes. Model the site load, solar and battery together in the same half-hourly model because solar changes what is left for the battery to do. Then show the client the solar-only saving, the extra saving added by the battery and the total project saving, without counting the same electricity twice.
Yes. Run the solar, site load and battery together through the same half-hourly model. Solar changes what the site imports and exports, and that changes what remains for the battery to do. Then split the figures in the proposal so the client can see the solar-only saving, what the battery adds and the total saving from the full project.
Why separate models can count the same saving twice
Solar changes the load the battery sees. During each half-hour, the PV may supply the site directly, charge the battery, export to the grid or be cut back because the site has reached its export limit.
The battery then works on what remains. It may store spare solar, discharge after generation drops or reduce a peak that solar alone cannot cover.
If you run solar and battery separately and add the two savings figures together, both calculations can end up claiming the same imported electricity or the same peak reduction.
Say the site would normally import 100 kWh during one period. The solar-only calculation may show that PV avoids 60 kWh. A separate battery calculation based on the original load may show another 50 kWh avoided. Add them together and you get 110 kWh, even though the site would only have imported 100 kWh.
Remember that spare solar already has a value if the client can export it. A kWh sent into the battery is not free if the client could have sold it. Ofgem confirms that SEG payments depend on metered exports and that suppliers set their own rates and contract terms.
What to show in the proposal
Run the same half-hourly load, tariff and solar figures through at least three cases:
- the existing bill with no new equipment
- solar only
- solar and battery together
Add a battery-only case if the client is seriously considering that option.
Show the results as:
- Solar-only saving: Existing bill minus solar-only bill
- Battery’s added saving: Solar-only bill minus combined bill
- Total project saving: Existing bill minus combined bill
Also show where the solar and battery energy goes:
- solar used directly on site
- solar sent into the battery
- grid electricity used to charge the battery
- battery discharge supplied to the site
- exported and curtailed solar
- the highest grid import
- the client’s actual export rate
- any battery reserve kept for backup, trading or another agreed use
Only include shared switchgear, cabling, civils, controls and commissioning once in the combined project cost.
GridVolt’s simulator runs the solar array, half-hourly site load, tariff, export rate and battery together. That lets you show the client exactly how much extra the battery adds to the solar proposal.
Related questions
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