Savings and payback model
We first estimate how much exported solar can be charged and later used after sunset. Delivered energy is limited by the usable capacity, stated solar exports, stated evening use and round-trip efficiency.
Charge energy is the lower of daily solar export and usable capacity.
Delivered energy applies round-trip efficiency and cannot exceed evening use.
Daily value is avoided grid imports minus the feed-in tariff sacrificed.
Payback accumulates yearly savings with 2% annual degradation until the price is recovered.
Default efficiency is 90%. The user can change it. We show warranty recovery because “eventually pays back” is not enough if eventually comes after the warranted life.
Federal certificate model
For batteries installed May–December 2026, we use the official factor of 6.8 and the legislated capacity taper: 100% for 0–14 kWh, 60% for 14–28 kWh and 15% for 28–50 kWh. We round down the final certificate count.
Dollar support is displayed as a range of $35–$40 per certificate. That is not a promise of the retail discount: the certificate market, retailer contract and administration affect what appears on a quote.
What this first version does not model
- Half-hour interval data, seasonal solar generation or weather.
- Time-of-use tariff windows or wholesale energy plans.
- VPP payments, curtailment, demand tariffs or grid charging.
- Finance interest, maintenance, replacement parts or residual value.
- Switchboard, metering or site-specific installation complexity.
- State incentives, which can change independently of the federal scheme.
Those omissions make the result a decision screen, not a bankable engineering forecast. Interval-data analysis is not currently available.
Inputs, screening bands and editorial responsibility
Battery Quote X-Ray publishes and maintains this model. Prefilled values are illustrative examples, not measured facts about your home. Edited inputs are not independently verified. Price-per-kWh thresholds are heuristic screening prompts—not live market averages or product-quality rankings. No installer can pay to change the result.
Useful solar-shifting capacity is the lower of exported solar and evening demand divided by efficiency, rounded to 0.5 kWh. If either energy input is zero, there is no solar-shifting case in this model; it does not recommend buying a minimum 5 kWh battery. Read the worked quote comparisons for examples of what this screening can and cannot establish.
Suggestions or a correction? Use our contact and correction form. We do not claim an independent electrical-engineering review.
Primary sources and verification
Federal factor and eligibility source rechecked. Added on-page sizing/rebate calculators, illustrative quote comparisons and clearer price-screening limitations. The $35–$40 range remains an assumption, not a current market quote.