V2G Architecture and Grid Services
Vehicle-to-Grid (V2G) technology enables EV batteries to discharge power back to the electrical grid, transforming parked vehicles from passive electricity consumers into distributed energy storage resources. A V2G-capable system requires: a bidirectional onboard charger (OBC) that can operate as both an AC-DC converter (charging) and a DC-AC inverter (discharging back to the grid); a bidirectional EVSE that supports two-way power flow (standard Level 2 EVSE only supports unidirectional charging); communication protocols (ISO 15118, which defines the Power Delivery Message Set for V2G communication between vehicle and charger, including energy service offers, pricing signals, and grid operator commands); and utility/aggregator agreements that define the terms for grid services provision. Grid services that EV fleets can provide through V2G include: Frequency Regulation — the grid must maintain 60 Hz frequency; EVs with V2G capability can inject or absorb power in seconds in response to automatic frequency regulation signals from grid operators, earning payment at $15–$40/MW-hour. Peak Demand Response — discharging during high-demand periods (5–8 PM) when wholesale electricity prices spike, earning arbitrage revenue. Capacity Market participation — guaranteeing availability of battery capacity during grid stress events for longer-term payments. A fleet of 100 EVs each with 75 kWh usable V2G capacity = 7.5 MWh of total grid-connected storage. At an average frequency regulation revenue of $30/MW-hour for 4 hours per day: 7.5 MW × $30 × 4 hours = $900/day potential revenue, shared between the aggregator and fleet operator.