Solar Export vs Battery Storage: Break-Even Worksheet

Storing surplus solar has an opportunity cost: you give up the export credit on the electricity sent into the battery. You also get back less electricity than you put in. To compare storage with export, value the electricity delivered later, then subtract the credit you would have received for exporting the input energy.

This worksheet isolates that marginal energy value. It does not estimate a battery’s installed price or promise a payback period. All dollar rates, energy quantities and efficiencies below are hypothetical inputs, not current utility offers or measured household results. Source guidance checked 31 October 2026.

The break-even rule

For each eligible surplus input kWh, the incremental energy value of storage is η × r − x. Here η is round-trip efficiency as a fraction, r is the marginal import price avoided when the battery discharges, and x is the marginal export credit forgone when it charges. Positive means storage beats export on variable energy value for that kWh. Zero means a tie before equipment and operating costs. Negative means exporting has greater energy value.

The break-even export credit is x = η × r. At a hypothetical 90% efficiency and $0.30/kWh avoided import price, the threshold is $0.27 per input kWh. An export credit below $0.27 leaves a positive energy margin; a higher credit does not. This is an energy comparison, not an investment recommendation.

Use one measurement boundary

Use surplus AC electricity available at the household connection as the input and AC electricity delivered back to household loads as the output. Select an efficiency measured across that same path. A battery cell’s DC efficiency alone does not account for every conversion or standby load in a complete installed system.

The Australian Government’s battery guidance explains storage, export limits and conversion losses. Those physical distinctions are useful here; Australian incentive programmes and tariffs should not be applied to another jurisdiction. For the equipment definition, see our round-trip efficiency guide.

Worked example: 1,000 surplus input kWh

Assume 1,000 kWh that would otherwise be exported, 90% AC round-trip efficiency, an avoided evening import price of $0.30/kWh and a forgone daytime export credit of $0.05/kWh. Assume every delivered kWh replaces a purchase and that the same tariff treatment applies to all of them.

1. Delivered electricity: 1,000 × 0.90 = 900 kWh.
2. Avoided imports: 900 × $0.30 = $270.
3. Forgone export credit: 1,000 × $0.05 = $50.
4. Incremental variable energy value: $270 − $50 = $220.

Calling the full $270 a storage benefit would omit $50 of export value. Calling all 1,000 input kWh delivered electricity would omit 100 kWh of losses. The $220 result is before battery purchase, installation, financing, maintenance, degradation and any changes to fixed or demand charges.

Sensitivity table for editorial reference

The zero-export row can represent electricity that would otherwise be curtailed, but only if the battery can actually capture it. Do not label all solar surplus curtailed simply because a connection has an export limit. The equal-rate row shows why storing instead of exporting can reduce variable energy value when every exported kWh earns an equally usable retail-rate credit and losses are positive.

Fill in your own household worksheet

1. Choose a billing period and obtain interval generation, household import/export and battery monitoring records where available. Annual generation alone cannot show whether surplus and later demand coincide.
2. Identify the surplus actually available for charging after direct household consumption. Bound it by battery capacity, charge power, reserve settings, operating rules and later household demand.
3. Record the export credit that each captured kWh would otherwise earn. Distinguish usable bill credits from credits that expire or cannot offset the relevant bill component.
4. Match battery output to the import rate it actually displaces. Under time-of-use pricing, a daily average can misstate the evening benefit.
5. Calculate input kWh × (η × r − x) for each group with comparable rates and operating conditions, then sum the groups. Use observed input/output if available rather than imposing a constant efficiency.

For example, if only 600 of the proposed 1,000 input kWh can be shifted usefully under the first row’s assumptions, the energy value is 600 × $0.22 = $132, not $220. Remaining solar may still be exported; it is not an additional storage benefit. Keep the original export baseline for those unshifted kWh.

Where the shortcut stops working

This formula assumes a linear, usable per-kWh export credit and a known marginal avoided import price. Minimum bills, tiered rates, annual netting, true-up rules, non-bypassable charges, demand charges, export caps and negative prices require the actual tariff calculation. A fixed monthly charge usually remains even when imports fall. A battery dispatch that creates a new demand peak may change the bill beyond its energy value.

State-of-charge at the start and end also matters. Do not count energy left in the battery as electricity already delivered to loads. Grid charging and virtual-power-plant payments require separate baselines and contract terms. Backup power has a separate household value; outage readiness may reserve capacity that cannot also earn the modeled daily savings.

Our net-metering guide explains the billing distinction. The Australian Government’s solar bill-savings guidance distinguishes self-consumption, export and demand effects. Use your own utility’s approved tariff and connection agreement for the numbers.

From an energy margin to an investment decision

A positive margin is necessary for this particular bill-saving strategy, but it does not establish that a battery pays for itself. Compare the discounted stream of incremental benefits with incremental equipment and operating costs; account for changing usable capacity, replacement risk and contract terms. Do not multiply one favorable day’s result by every day of a warranty.

No federal tax credit is deducted in this worksheet. For a new US residential project, the IRS Residential Clean Energy Credit page states that property placed in service after 31 December 2025 is ineligible for that credit. Separately confirmed local programmes need their own eligibility check. Our solar payback calculator addresses a different, whole-system question.

Method, limitations and citation

The arithmetic and table are original illustrative calculations by SolarSunLabs. They are not a household survey, a tariff database or manufacturer test data. Rates are nominal dollars per kWh in one consistent currency, efficiency is dimensionless, and results are rounded only for display. The same algebra works with another currency if all rates use that currency consistently.

To reference the example, identify the 1,000 input kWh boundary, 90% efficiency, $0.30 avoided import rate and $0.05 forgone export rate, and link to the worked example or sensitivity table. Cite the official sources for their underlying guidance. This page adds no redistribution licence to any third-party source.