Solar and Battery Storage: Which Electricity Plan Costs Less? A Four-Offer Demo Comparison
Compare four Origin offers using one demo home’s August 2026 data, and see why the lowest modeled cost changes when solar and battery supply are removed.
One demo home, four electricity offers
Does a lower electricity rate always mean a lower bill? For a home with solar and battery storage, it may not. When the system supplies most household consumption and exports far more than the home imports, daily supply charges and feed-in credits can matter more than the import rate.
This case study uses Solar PV System in the IAMMETER demo account: a residential solar system with a battery-storage inverter, not a real customer bill case study. We compare Origin Go TOU, Weekday Shift, Night Shift and Solar Boost TOU using its August 2026 grid energy data.
The selected offers are Ausgrid residential versions. This is a fixed-price scenario using the same 31-day load under each version, not evidence that the demo site is eligible for these offers or a reconstruction of an actual retailer invoice. The Shift versions became effective on August 13; their selected prices are held constant across the full month for this experiment. All amounts are AUD. No controlled-load, demand or optional GreenPower charges are modeled.
Most household energy comes from the inverter side
Household consumption is inferred as grid import minus grid export plus inverter output minus inverter reverse input, assuming consistent AC measurement boundaries and no omitted sources. The separately monitored special-load channel is not added to this balance.
In the 22:00–06:00 observation window, net inverter supply covers approximately 80.6% of inferred load. Continued nighttime output is consistent with the identified battery-storage system. These figures do not separate direct solar use from battery discharge or establish battery efficiency, capacity or state of charge.
- Inverter AC output: 749.20 kWh. This includes solar and battery discharge; it is not a separately measured PV-generation total.
- Inferred household consumption: 210.36 kWh, about 6.79 kWh per day.
- Grid imports: 19.10 kWh. Grid exports: 557.94 kWh.
- Net inverter-side contribution to the inferred load: 191.26 kWh, about 90.9%. Grid imports account for the other 9.1%.
August bills with the existing solar and battery system
BillSave calculations were independently checked. Solar Boost TOU has the lowest modeled cost among these four selected offers for this profile. Feed-in income is shown as a positive credit: net cost = supply charge + import cost − feed-in income.
| Offer | Fixed supply charge | Grid import cost | Feed-in income (credit) | Net cost |
|---|---|---|---|---|
| Go TOU | 49.20 | 6.03 | 16.74 | 38.49 |
| Weekday Shift | 49.21 | 5.93 | 16.74 | 38.39 |
| Night Shift | 49.21 | 4.72 | 16.74 | 37.19 |
| Solar Boost TOU | 54.66 | 6.70 | 29.14 | 32.22 |
Why the higher import-price offer wins here
Only 19.10 kWh is bought from the grid. Consequently, differences in import prices affect a small volume. The 557.94 kWh exported makes the feed-in structure much more important.
In these selected versions, Go, Weekday Shift and Night Shift credit exports at A$0.03/kWh. Solar Boost credits the first 248 kWh at A$0.08/kWh and the remainder at A$0.03/kWh: A$29.1382 in total. The 248 kWh allowance is 8 kWh multiplied by the 31 billing days, applied as a billing-period allowance—not an independent daily reset.
Compared with Go, Solar Boost adds about A$5.47 in fixed charges and A$0.67 in import charges, but adds A$12.40 in export credits. The net modeled bill is approximately A$6.26 lower. Buying electricity cheaply is not the only consideration for a household that imports little and exports a lot.
An interesting experiment: remove the inverter's contribution
What if exactly the same household consumption had to be supplied by the grid, with neither solar nor battery supply? This removes the whole inverter contribution, not just the battery. The inferred half-hour profile totals 210.36 kWh of imports and zero exports.
Three small negative balance residuals totaling 0.06 kWh are set to zero and offset against their preceding positive intervals. Each pair shares the same price window in all four offers, preserving monthly energy and tariff-window totals. All 1,488 half-hours are explicitly marked estimated.
Same consumption, no solar or battery supply
The no-system column contains checked modeled costs; the estimated-data quality limitation is explained below. Solar Boost without solar is an arithmetic comparison only and does not establish eligibility.
| Offer | With solar and battery | Without solar or battery supply | Same-offer cost difference |
|---|---|---|---|
| Go TOU | 38.49 | 116.26 | 77.78 |
| Weekday Shift | 38.39 | 106.38 | 67.98 |
| Night Shift | 37.19 | 110.73 | 73.54 |
| Solar Boost TOU | 32.22 | 129.18 | 96.96 |
Counterfactual results are estimates, not finalized bills
BillSave returned all four no-inverter amounts, and independent local calculations agree to the cent. In the September 26 checks, however, BillSave marked these fully estimated results as incomplete and reported missing-interval charges despite there being no time gaps. This quality-label issue remains unresolved in this analysis. These are checked modeled costs, not a platform-confirmed complete-bill ranking.
What this tells us about system value—and what it does not
The preferred price structure changes: Solar Boost has the lowest modeled existing-system bill, while Weekday Shift has the lowest modeled no-system cost. With exports removed, a generous feed-in tariff provides no benefit. Under Weekday Shift, 55.97 kWh falls in the discounted weekday 09:00–17:00 window, or about 26.6% of monthly consumption; Night Shift discounts 32.35 kWh in the 00:00–06:00 window, about 15.4%.
The same-offer differences of approximately A$68–97 illustrate one month's electricity-bill benefit of the whole solar-plus-storage supply system under unchanged demand. They are not battery-only savings, a measured return on investment, or a guaranteed annual saving.
Estimating investment payback requires installation cost, maintenance and replacement assumptions, seasonal generation and demand, battery degradation and tariff changes. Isolating the battery's value additionally requires a solar-without-battery counterfactual. One August month should not simply be multiplied by twelve.
Your own profile can produce a different result. BillSave supports IAMMETER Cloud data and independent CSV uploads; compare compatible offers using your own measured intervals and actual contract conditions.
Calculation notes
Calculations were checked on September 26, 2026 using 30-minute intervals for August 1 to September 1 exclusive, UTC+10, aligned to Sydney's August clock. Existing-system costs use BillSave's Cloud conversion: 1,486 actual and two estimated intervals. Counterfactual inference uses a separate timestamp-based Grid/Inverter conversion with six interpolated intervals before marking the whole derived series estimated. Grid monthly totals agree; seven individual allocations differ between the conversion methods. These are scenario comparisons, not exact battery-attribution measurements.
Selected catalog versions: Go gp-gstfix-cdr-ori1140595mre1-2026-07-09-725fc158ae2b; Weekday Shift cdr-ori1157109mre1-2026-08-13; Night Shift cdr-ori1157126mre1-2026-08-13; Solar Boost cdr-ori1140621mre1-2026-07-09. Rates are selected-version snapshots, not a claim about current availability. Network, meter and solar/feed-in eligibility must be checked separately. Rounded component displays may differ by one cent from displayed totals or differences calculated using unrounded amounts.
Explore more BillSave examples
Compare this solar-and-storage profile with another household offer comparison, or follow the setup guide to try your own data.