Methodology.

1. The ownership cost model

Every storage decision begins with the full cost of owning the system over the selected analysis period. Installed cost is reduced by rebates and tax benefits, then adjusted for financing, maintenance, degradation, augmentation or replacement, and the value streams the battery can realistically capture.

Installed cost is the largest initial data gap because it depends on equipment, electrical upgrades, labor, permitting, interconnection, controls, fire-safety requirements, and site conditions. Every calculator distinguishes sourced equipment prices, benchmarked installed-cost ranges, and user-entered contractor quotes rather than presenting an estimate as a firm price.

2. VPP and time-of-use revenue modeling

A home battery can earn money in two structurally different ways, and we model them separately rather than blending them into one number:

VPP programs pay a battery owner for letting the utility draw down (or avoid charging) their battery during grid stress events — a fixed per-kW/per-season payment (Vermont's GMP, most East Coast programs) or a per-event/per-kWh payment (California's SGIP equity structure, Texas retail VPP plans). Enrollment caps and waitlists are real constraints on several programs and are disclosed as "waitlisted" status rather than folded into an average payment.

Time-of-use savings depend entirely on the spread between your utility's peak and off-peak rates, which the Utility Rates page currently reports only as a flat state average — the planned TOU Battery Savings Calculator will require an actual TOU rate schedule input rather than estimating one from the average.

3. Runtime and sizing modeling

Runtime and sizing begin with the same relationship for every customer: usable energy divided by the load the battery is serving.

The model then tests whether the battery's power rating can start and sustain the selected loads, applies reserve and efficiency assumptions, and separates backup sizing from economic dispatch. The working Backup Runtime Calculator and Battery Size Calculator expose those inputs directly.

4. Incentive and rebate rules

Federal incentive policy changed materially heading into 2026, and every calculator and comparison on this site reflects the current rules rather than legacy program terms:

State, utility, and VPP program figures — California's SGIP, Massachusetts's ConnectedSolutions and SMART storage adder, New York's NYSERDA rebate and Con Edison BYOB, Vermont's GMP Bring Your Own Device, and others tracked in the Incentives calculator — are sourced directly from each program's published rate sheet and cross-checked periodically, since several of these programs adjust rebate amounts, income eligibility, or enrollment caps during the year.

5. Rate, spec, and program data sourcing

Electricity

U.S. EIA electricity retail-sales API, residential sector (sectorid=RES), monthly, by state — EIA API v2 documentation.

Battery specifications

Manufacturer datasheets for Tesla Powerwall 3/2, Enphase IQ Battery 5P, Generac PWRcell 2, FranklinWH aPower 2, and LG Enblock S. Where a spec was only available on a regional (e.g. India) datasheet or was not published at all, that gap is flagged directly next to the figure on the Battery vs. Generator page rather than estimated.

Generator specifications

Manufacturer documentation and published MSRP for Generac (7.5–22kW tiers), Kohler 20RCAL, and Briggs & Stratton 20kW units — output, noise rating at 23 feet, and warranty terms.

Installed-cost benchmarks

Lawrence Berkeley National Laboratory residential storage market research, NREL system cost benchmarks for paired solar-plus-storage systems, and CPUC SGIP program filings — used to triangulate a plausible installed-cost range in the absence of manufacturer-published installed pricing.

Federal tax policy

One Big Beautiful Bill Act (Public Law 119-21) and IRS guidance on the Residential Clean Energy Credit's repeal for battery storage.

State, utility & VPP programs

Program documents and rate sheets from CPUC/SGIP, Massachusetts DPU/ConnectedSolutions, NYSERDA, Con Edison, Green Mountain Power, Hawaiian Electric, and other issuing agencies and utilities, verified directly against each program's current published terms.

6. Case study assumptions

The case studies in development will apply the cost, VPP/TOU, solar, resilience, and runtime models above to representative ownership decisions:

• Residential TOU savings — when daily peak-to-off-peak spreads justify cycling a home battery.
• Residential solar self-consumption — when storing exported solar creates more value than sending it to the grid.
• Residential VPP participation — how recurring program revenue changes payback without assuming maximum dispatch.
• Commercial demand-charge management — battery power and duration sized against short monthly peaks.
• Commercial resilience — assigning a transparent value to avoided downtime rather than treating resilience as free.
• Industrial value stacking — combining demand response, capacity or grid services, on-site generation, and project finance.

Home sizing, critical-load lists, and specific product configurations in each case study will be representative constructs chosen to reflect realistic households in that market — not measurements of an actual specific home or installation quote.

7. Limitations

No manufacturer publishes a fully-installed cost that applies to every site. Installed-cost figures are triangulated from third-party research, program filings, and market benchmarks, then presented as ranges or editable assumptions rather than quotes. Obtain contractor or developer pricing for the actual site before making a purchase decision.

VPP program payments depend on program-specific participation factors, event frequency, and enrollment caps that vary year to year and are, in several cases, currently waitlisted. Modeled VPP income should be treated as an illustrative estimate of program structure, not a guaranteed annual payment. Similarly, generator annual maintenance cost and expected service life are not consistently published by manufacturers and are treated as a disclosed data gap rather than backfilled with an assumption.

Incentive programs, tax policy, and equipment lineups are point-in-time snapshots refreshed on the schedule each source publishes. Battery Economics is independent analysis, not financial or engineering advice; consult a licensed electrician or installer and a tax professional before making a purchase decision.