Bidirectional charging during grid outages
Bidirectional charging that lets electric vehicles power homes during grid outages is attracting interest, but commenters highlight practical limits and trade‑offs. Many argue EV batteries can easily handle occasional backup use and short‑term load shifting, yet long multi‑day outages, heavy HVAC loads, and regional climate risks still favor traditional generators or combined solar‑battery‑generator setups. Technical standards, regulatory requirements for safely islanding a home, lack of interoperable hardware, and cautious automakers and utilities are seen as major barriers to making vehicle‑to‑home systems simple and widely available.
Battery Wear, Economics & TOU Arbitrage
- Extra charge/discharge cycles from outages are seen as negligible for EV lifespan; using an 80+ kWh pack a few times a year barely adds cycles.
- Daily time-of-use (TOU) arbitrage with V2H increases cycling but still modest if only ~10 kWh/day is used; some see this as minor, others worry about noticeable degradation over time.
- In-home batteries are cheaper per replacement than EV packs but add separate capex.
- Regulatory battery-warranty rules (e.g., minimum capacity after 8 years) make manufacturers cautious about officially supporting bidirectional use.
- Utilities might “lose” on arbitrage, but several comments argue dynamic tariffs are explicitly for this kind of load shifting; in some markets, retailer/distributor incentives are aligned with customer-side storage.
Generators vs Batteries/Solar/EVs for Outages
- For long, hot, humid post-hurricane outages and running 5+ ton HVAC full-time, commenters argue batteries alone are not economical; generators plus large fuel stores win on cost and practicality.
- Others note this is a minority scenario; most people face shorter outages where modest batteries/EV backup (for fridge, lights, internet, furnace blower) are sufficient.
- Several describe hybrid systems: solar + batteries as first line, EV via V2L as secondary, and small gasoline/propane/diesel generators as last resort “charger of batteries.”
- There is debate over “comfort vs survival”: some call full-house AC after a disaster entitled, others stress mold and dehumidification are real health and structural concerns.
Technical & Standards Barriers
- Islanding (safely disconnecting from the grid) is mandatory; microgrid interconnect devices and transfer switches are needed, but control protocols are not standardized.
- Lack of interoperable specs between EVs, inverters, chargers, and home energy systems makes V2H hard; vendors push vertically integrated stacks (e.g., Tesla Powershare, Enphase).
- CHAdeMO historically supported V2H; new standards (SAE J3400/2, ISO 15118-20, SAE J2847) are mentioned but not yet widely realized in products.
- Many report it’s easier to enroll in V2G programs via utilities than to do home-only V2H.
Practical Workarounds & Current Capabilities
- Some use EVs’ 120V/240V outlets (V2L) plus extension cords or furnace-only transfer switches to run critical loads.
- Manual transfer + V2L is seen as simple, cheap, and “good enough” for rare outages, even if it falls short of whole-home automatic backup.
- EV–home integration remains finicky; people struggle to find installers willing to implement nonstandard or DIY-style solutions.
Battery Chemistries & Future Home Storage
- LiFePO4 is favored for home storage: safer, cheaper materials, good cycle life, but lower energy density and can’t charge below 0°C.
- Sodium-ion is discussed as a promising, safer, colder-tolerant and potentially cheaper chemistry for stationary use, but widespread, consumer-available products are seen as several years away.