Using an EV Battery as Home Solar Storage with a Hybrid Inverter

What is possible today, and what is permitted

High-voltage hybrid inverters, which combine solar, battery and grid functions in one unit, accept a battery of a few hundred volts on a dedicated DC input, and most EV packs are built in the same voltage class. With a controller between them that speaks the car's charging protocol on one side and the inverter's battery protocol on the other, an unmodified car can supply and absorb energy through its DC fast-charging port, much as it does at a public charger.

Possible and permitted are different questions. US codes require bidirectional EV equipment and energy storage systems to be listed. A custom interface between a car and an inverter is not a listed system, the utility will not approve it for parallel operation with the grid, and both the automaker and the inverter maker may decline warranty claims because of it. The compliant route today is a listed bidirectional charger that the automaker supports for the specific vehicle, described in our guide to EV backup power in New York.

Why an EV battery is attractive, for owners and for the grid

Car batteries are produced at very large scale and are already paid for as part of the vehicle. The figures below are published market data, not our prices; a pack price excludes the inverter, wiring, permits and installation included in an installed home battery price.

BNEF's 2025 survey (opens an external site) puts the average pack at $108 per kWh, Recurrent's replacement cost research (opens an external site) implies roughly $150 to $360 per kWh for automaker replacement packs, and EnergySage reports (opens an external site) a typical installed 13.5 kWh home battery near $15,600. The salvage figure is the weakest: one vendor, before derating for state of health, and without the controller, protection, enclosure and listing a stationary system needs.

Capacity is the second attraction: a common home battery holds 13.5 kWh, many EVs 60 to 100 kWh. US Department of Energy data (opens an external site) counted 5,689,100 battery EVs in the United States in 2025, 209,300 of them in New York. At an assumed average of 60 to 80 kWh, they carry roughly 340 to 455 GWh of storage, already built and parked most of the day.

A study in Nature Communications (Xu et al., 2023) (opens an external site) found that, worldwide, vehicle-to-grid capacity or retired vehicle batteries could each meet short-term grid storage demand by as early as 2030, and that participation by 12 to 43 percent of owners, depending on the country, would be enough. Brattle's analysis for Google (opens an external site) estimated that capacity from virtual power plants, which aggregate household devices, costs about 40 to 60 percent of a gas peaking plant or utility-scale battery, though it covers household flexibility generally, not vehicles. Further benefits are resilience in outages, use of solar that would otherwise be curtailed, and lower peak demand that can defer grid upgrades. China selected 9 cities and 30 projects for national vehicle-to-grid pilots in April 2025, and European energy suppliers and automakers offer bidirectional tariffs.

The counterpoints are real: battery wear, larger losses than a stationary battery, warranty exclusions, and programs that need cars plugged in for long hours. A 2017 California pilot with the Department of Defense found revenues below administration costs, and we found no residential V2G compensation from Con Edison or PSEG Long Island. Our position is that the benefits arrive through standards, listed products and open interfaces that make vehicle storage safe and routine, not through improvised installations.

Vehicles that can export energy, and how

In DC export, the pack's current leaves through the DC charging port and an external unit converts it to household AC; in AC export, the car's onboard inverter produces AC. Only DC export is relevant to a hybrid inverter's battery input. The DC protocols are CHAdeMO (opens an external site), the Japanese standard that supported bidirectional power early, and the Combined Charging System (CCS) (opens an external site), whose bidirectional functions are defined in ISO 15118 (opens an external site)-20 (April 2022). Developers of the open-source EVerest charging software reported in 2025 that no publicly known vehicle fully implemented it.

No source we found states which protocol the EV9 and Quasar 2 use. Nichicon's VSG3 sold for ¥1,280,000 before tax and installation in 2024, and Nichicon reported about 90 percent of Japan's V2H market in 2023. Tesla has announced no DC export. Our guides on why automakers restrict V2H and on GB/T, CCS and NACS cover the hardware and protocols in more depth.

Matching pack voltage to the inverter

A typical “400 V” pack with nickel-based cells has 96 cells, or groups of parallel cells, in series, which places it at about 288 to 403 V between the usual cell limits of 3.0 and 4.2 V, and the car's battery management system keeps the usable range narrower. GM gives 350 V nominal for the Chevrolet Bolt. US residential hybrid inverters with high-voltage inputs accept roughly 120 to 500 V: the Solis S6 US hybrid datasheet (opens an external site) gives 120 to 500 V, and Deye's US models 160 to 500 V. A 400 V-class pack therefore fits across most of its charge range.

An “800 V” pack, such as the Hyundai Ioniq 5 77.4 kWh at 697 V nominal, spans roughly 576 to 806 V. No US residential split-phase or 120/208 V hybrid inverter we found accepts an 800 V-class battery; their battery ports top out around 500 V. Some international three-phase residential hybrids accept up to 800 V, commercial hybrids reach 950 to 1,000 V, and the listed Wallbox Quasar 2 home charger accepts 200 to 920 V DC according to its datasheet (opens an external site). The ceiling appears to reflect grid voltage, each market's battery products and certification, more than any fixed limit of insulation technology.

• 800 V-class cars charge on 400 V chargers by adapting inside the vehicle. Kia states (opens an external site) that the EV9 uses the motor's internal coil to boost the voltage to 800 V; the Tesla Cybertruck and GM's 800 V trucks are reported to switch two pack halves between series and parallel.
• That adaptation serves charging. We found no sourced case of a car exporting DC at 400 V through its port.
• Voltage moves with state of charge and temperature, so the whole operating range must fit the inverter's window, not only the nominal figure.
• A bridge must verify the voltage the car actually presents before it closes its own contactors, and stop if the voltage leaves the agreed range.

Voltage is rarely the deciding limit. Every inverter maker we reviewed requires a battery from its approved list, speaking its own battery protocol; an EV pack speaks the vehicle maker's.

What a bridge controller must do

A bridge controller sits between the car's DC port and the inverter's battery input. Toward the car it must behave as a legitimate DC charging station; toward the inverter, as the battery management system (BMS) (opens an external site) of an approved battery, the electronics that report a battery's limits and condition. The description below is conceptual; message contents and sequences are deliberately left out, because this work belongs with qualified engineers and listed equipment.

• Car side: CHAdeMO runs over a CAN bus (opens an external site), the wired controller network used in vehicles, and the vehicle controls the current. CCS runs over HomePlug (opens an external site) Green PHY, power-line communication on the control pilot wire. A step called SLAC (signal level attenuation characterization, ISO 15118-3) measures signal strength so that the car pairs with the charger it is physically plugged into rather than a neighboring one, and the charging messages then follow DIN 70121, ISO 15118-2 or, for bidirectional power transfer, ISO 15118-20. China's GB/T 27930 also uses CAN.
• Certificates: ISO 15118-2 uses TLS 1.2 encryption only for Plug and Charge, the automatic certificate-based sign-in at public chargers, while ISO 15118-20 requires TLS 1.3 with mutual authentication. The certificates are issued within industry public key infrastructures; they are a security measure, and they also mean that an independent bridge cannot simply join the system.
• Inverter side: the bridge reports voltage and current limits, state of charge, temperatures and alarms over CAN or RS485, in the protocol of a battery the inverter supports. Emulating a supported battery does not make the combination approved.
• Precharge (opens an external site): before contactors close, the side about to be connected, such as a charger's output or an inverter's input capacitors, is brought close to the pack voltage, preventing a damaging inrush of current.
• Insulation monitoring (opens an external site): the high-voltage system floats, isolated from ground, and is tested before energy flows and watched during operation, because a first fault to the chassis is not dangerous by itself but leaves the frame one further fault away from becoming live.
• Contactor and welding checks: contactors are heavy relays that can weld shut after an overload, so a check after each session confirms they opened; an open-source project reports welding in some Leafs used with other V2X equipment.
• Emergency stop: a hardware path that opens the circuit regardless of software state.

Timing matters as much as logic: an insulation failure or overcurrent must open the circuit within a fixed, short time whatever else the controller is doing. A deterministic microcontroller, with hardware interrupts that react to fault signals directly and a real-time operating system (RTOS) (opens an external site) that guarantees when each task runs, provides that bound; a general-purpose operating system does not guarantee one.

The car remains in charge throughout. It closes its contactors only inside a charging session it recognizes, and exports only if its firmware allows it; open-source testers report cars ending unexpected sessions. Because this behavior is set in software, an automaker can change or disable it with an update.

Our own engineering test

To understand the limits first-hand, we connected an unmodified, road-legal vehicle capable of battery swapping to a residential hybrid inverter configured for Con Edison's 208 V service, common in New York City network areas. The connection used the car's own DC fast-charging port, with every vehicle-side safety layer left intact. The pack operated at about 380 V, inside the inverter's battery window. The bridge controller was our own design, built on a RISC-V microcontroller running an RTOS with hardware interrupts for deterministic fault response, using RS485 or CAN toward the inverter and the vehicle's charging protocol toward the car.

We parked the car outdoors, away from the house, so that a thermal event could cause minimal damage and never endanger anyone. The test showed that the electrical and protocol problems can be solved when each safety layer is taken seriously. It did not make the arrangement a listed or permitted installation: it was an engineering test of what is possible, not a service we offer.

Warranty, battery wear and reputation

Tesla's US New Vehicle Limited Warranty (opens an external site), effective September 1, 2026, excludes “using the vehicle as a stationary power source” outside supported Powershare setups, and long-term use “with signs of unreasonably high energy throughput that may be inconsistent with mileage driven” outside a Tesla-supported grid program. Nissan said its approved bidirectional charger would not affect the Leaf battery warranty (opens an external site), an approval for that charger only. Hyundai Australia said in August 2026, as reported by The Canberra Times, that damage from third-party bidirectional setups is not covered. The Solis approved battery list (opens an external site), dated May 2024, states that batteries not on the list void the inverter warranty.

Battery wear has two parts. Cycle aging grows with throughput, depth of discharge and current; calendar aging proceeds with time, fastest when a pack sits hot at a high state of charge. A Geotab study of more than 22,700 vehicles (opens an external site) (January 2026) found average capacity loss of 2.3 percent a year, up to about 3.0 percent with heavy DC fast charging. Research on bidirectional use ranges from measurable extra wear under frequent deep cycling to little added wear when state of charge, depth and temperature are controlled, as our guide on why automakers restrict V2H summarizes. We found no automaker document stating whether the pack's cooling runs while a parked car exports to an unapproved device.

A further reason for caution goes beyond warranty cost. A battery fire is reported under the car's brand, whether or not the car was in warranty and whatever equipment was attached, so automakers have a fair interest in approving only tested equipment.

Safety and where the car is parked

Leave the battery in the car. There the pack keeps its cooling, structure, crash protection and supervising controller, engineered and tested together by the manufacturer. Removing a pack is a different matter, covered in our guide to second-life EV batteries as home storage; in New York City, 1 RCNY 3616-07 (opens an external site) §4.2.10.1 prohibits reusing or repurposing batteries previously used for electric vehicle propulsion.

EV fires appear uncommon, but they are hard to extinguish, so a car used as storage should be sited for the worst case.

• Re-ignition: the NTSB's 2020 safety report (opens an external site) documents a damaged pack that re-ignited 5 days after a crash, and repeats manufacturer guidance to keep a damaged EV 50 feet from structures, noting this may be infeasible in some places.
• Burn time: in UL FSRI tests of six EVs (opens an external site) without suppression, vehicles typically burned out within about an hour.
• Toxic gases: lithium-ion fires release hydrogen fluoride (opens an external site), measured at 20 to 200 mg per Wh of capacity, with the greatest risk in confined, occupied spaces.
• Siting: where the equipment allows, park the car outdoors or under an open carport, at the full reach of the cable from the house and clear of windows, eaves and exit paths.

No code requires outdoor parking, and product instructions can limit the distance. Kia specifies a garage or carport with shade and ventilation for its V2H equipment, and the Quasar 2 installation guide (opens an external site) asks for a location out of direct sunlight, with cables of 16 or 25 feet and no extensions.

Round-trip efficiency and when it is worthwhile

Measured round-trip efficiency for vehicle-to-home and vehicle-to-grid in good conditions is about 80 to 88 percent. Schram and colleagues (2020) (opens an external site) measured an average of 87 percent, from 79.1 to 87.8 percent between 25 and 75 percent state of charge, lower at low temperature and current; an EU Joint Research Centre test found about 80 percent. Manufacturers rate stationary home batteries at about 89 to 90 percent.

A parked car adds overheads. A University of Delaware dissertation (opens an external site) measured a fixed loss of about 0.6 kW in the vehicle tested, plus a loss that grows with power, so light loads such as a home at night are served least efficiently; in cold weather the car also spends energy warming its battery. As an illustration, a 1 kW overnight load with 0.3 kW of fixed overhead and 18 percent proportional loss draws about 1.5 kW from the pack, and with charging losses the round trip falls to roughly 55 to 65 percent. In our own testing, under unfavorable conditions, losses approached about half of the energy, a worst case rather than a typical figure.

• Worthwhile: solar that would otherwise be curtailed, in a zero-export or export-limited system or during a grid outage once household loads are met.
• Worthwhile: outage backup, where keeping power on outweighs the losses.
• Usually not worthwhile: routine daily cycling in New York, where exported solar is credited under net metering or the Value Stack, so storing it at 60 percent efficiency costs more than exporting it.

Codes, listings and the limits of what is permitted

The New York State Standardized Interconnection Requirements (opens an external site), in effect since October 1, 2026, require equipment tested to UL 1741 including Supplement B, and allow the utility to disconnect a system that operates in parallel before approval. In New York City, electrical work falls under the 2025 NYC Electrical Code, based on the 2020 NEC, and requires a licensed master electrician and a DOB permit.

Technically possible is not the same as permitted. A custom or unlisted interface between a vehicle, a battery and an inverter is generally not a listed or approved system under US codes, UL listing requirements, utility interconnection rules or, in New York City, the Fire Code and FDNY requirements, and it is often not permitted. It can void vehicle, battery and inverter warranties and affect insurance; check your policy and tell your insurer before installing any battery system. High-voltage DC can kill, and lithium-ion batteries can burn. Consult the authority having jurisdiction, your utility, the manufacturers and licensed professionals. This article explains the technology; it is not installation guidance.

The compliant options today are a listed bidirectional charger approved for your vehicle, a hybrid inverter with a battery listed with it, and, for homes with microinverters, AC coupling the array to a hybrid inverter. Related guides cover adding a battery to existing solar, inverter protection functions such as insulation monitoring, and open monitoring over RS485 and Modbus.