Bidirectional Charging 101: Vehicle-to-Home and Vehicle-to-Grid Explained for 2025
INTRODUCTION
Bidirectional charging lets an electric vehicle discharge stored energy to a building (vehicle-to-home, V2H) or back into the utility network (vehicle-to-grid, V2G). As 2025 models like the Ford F-150 Lightning, Nissan Leaf, and Hyundai Ioniq 5 mature, homeowners can offset peak rates and improve resilience without standalone batteries.
1. TERMINOLOGY SNAPSHOT
V2H: Supplies critical circuits during outages.
V2G: Exports power under a utility tariff for payment.
V2L: Portable 120 V or 240 V outlet from the vehicle (no fixed transfer switch).
CCS Combo 1 with ISO 15118-20: Emerging US standard for bidirectional control.
2. REQUIRED COMPONENTS
Compatible EV: Onboard inverter rated for discharge (≥5 kW).
Bidirectional EVSE: Example, Wallbox Quasar 2 (11.5 kW, UL pending).
Automatic Transfer Switch (ATS): Segregates home loads from grid during islanding.
Utility-approved inverter firmware if V2G.
Cloud aggregator for market participation (Nuvve, Fermata Energy).
3. INSTALLATION OVERVIEW
Service Upgrade: Many V2G inverters need 100 A circuit.
Load Calculation: Critical loads panel ≤9 kW to avoid depleting vehicle overnight.
ATS Placement: Within 10 ft of main panel to meet NEC conductor length limits.
4. ECONOMIC ANALYSIS
ParameterV2H BackupV2G Demand ResponseUpfront cost (inverter, ATS, labor)USD $6 000 – $9 000USD $6 500 – $10 000Annual utility savingsPeak shaving 150 $ – 300 $DR revenue 400 $ – 1 200 $*Simple payback20 – 40 years8 – 18 years*Assumes 50 discharge cycles, 10 kWh each, 0.80 round-trip efficiency, utility DR rate 0.10 $ kWh plus capacity bonus.
Battery degradation: Modern NMC packs lose ≈2 % capacity per 300 full cycles. Partial V2G cycles add <0.5 % annually.
5. REGULATIONS AND UTILITY PROGRAMS (SELECT STATES)
California: PG&E VGI export pilot pays 2.36 $ kW-month plus energy credit.
New York: Con Edison incentives cover up to USD $6 000 for interconnection costs.
Colorado: Xcel Energy Off-Peak 2024 tariff allows reverse flow at avoided cost.
ISO-NE: FERC 2222 compliance opens wholesale frequency regulation via aggregators.
6. SOFTWARE CONTROL LOGIC
Priority 1: Reserve 30 % SoC as mobility buffer.
Priority 2: Follow time-of-use schedule.
Priority 3: Participate in real-time price spikes above 0.25 $ kWh.
Cloud API failsafe: Disable export if grid frequency deviates ±0.1 Hz.
7. CASE STUDY
Homeowner: suburban NJ, 13 ¢ off-peak, 29 ¢ peak.
Hardware: Hyundai Ioniq 5, Wallbox Quasar 2, Span Smart Panel.
Outcomes for first 12 months:
Peak cost avoided: 740 kWh × 0.16 $ = USD $118.
Demand response export: 28 events, 300 kWh, payout USD $90.
Net savings: USD $208, battery cycle depth averaged 35 %.
8. LIMITATIONS
Insurance riders may exclude back-feed unless certified equipment lists.
Inverters limited to 60 Hz. Many Japanese CHAdeMO V2H units are 50 Hz only.
Tesla vehicles remain closed to external V2G in North America as of Q2-2025.
9. FREQUENTLY ASKED QUESTIONS
Does V2G void the vehicle warranty? Only if OEM prohibits discharge; Nissan and Ford explicitly allow.
Can rooftop solar and V2H coexist? Yes via hybrid inverter or separate transfer switch coordination.
How fast can the car recharge after backup use? Same EVSE, 7 – 11 kW typical, restore SoC overnight.
Will utility export credits count as taxable income? Yes on 1099-MISC above USD $600 annual.
Is DC wallbox safer than AC bidirectional? DC avoids redundant inversion but needs thicker conductors.
CONCLUSION
Bidirectional charging transforms an EV from passive load to active energy asset. Payback depends on tariffs, but resilience value and emerging DR markets make V2H and V2G viable for tech-savvy homeowners beginning in 2025.