V2G Grid Risks — DSO and TSO Hazards from Bidirectional EV Charging

V2G is framed primarily as a flexibility resource — EVs as dispatchable storage that benefits grid stability. The framing is valid but incomplete. When an EV discharges into the grid, it functions as a distributed generator, and distributed generation creates DSO and TSO risks that the V2G policy discussion largely underweights. This page synthesizes those risks across five categories.

The central tension: V2G that stabilizes the TSO’s transmission network can simultaneously destabilize the DSO’s LV network. The two effects are not contradictory — they operate at different grid levels — but they will need to be coordinated before large-scale V2G deployment is viable.

1. LV network voltage rise and thermal overload

DSO risk. Quantified in the Swedish context.

V2G discharge adds generation at the distribution tail. Combined with rooftop solar — which is co-located with EV owners and correlated in time — this creates bidirectional LV power flows that standard radial networks were not designed for.

Source - FlexAbility Delrapport 3 (2025) ran Monte Carlo simulations (Plexigrid platform) of V2G + PV penetration against two real Swedish LV networks during FCR-D upregulation events (~58 activation hours per year):

The binding scenario is not winter peak demand but weekends in Q3: low residential load, high solar injection, V2G dispatch active simultaneously. All binding constraints in both networks occurred in this window. The 2.7× range in thresholds between two Swedish networks is the key result for policy: grid impact is highly network-specific, and national averages are unreliable. DSOs cannot use aggregate statistics to manage this risk — they need network-level simulation before enabling V2G at any given substation area.

The DSO implication: a blanket FCR-D activation of all connected V2G assets, issued by a TSO-level aggregator or BSP, may solve a balancing problem at the TSO level while creating voltage and thermal violations at the DSO level within the same dispatch window. This is the structural TSO-DSO coordination problem made concrete — see TSO-DSO Coordination — The Central Design Problem.

2. Unintentional islanding (oavsiktlig ö-drift)

DSO risk. Regulatory gap exists.

When a V2G charger is discharging, it functions as an inverter-based generator. If the upstream grid connection disconnects — due to a cable fault, protection trip, or planned switching — and the charger continues supplying the isolated section, an unintentional island forms. This creates risk of electric shock to field workers who assume lines are dead, impedes fault clearing, and can damage equipment on reconnection.

The fundamental detection challenge is the Non-Detection Zone (NDZ). Under Swedish grid code (implementing RfG), all generators must remain connected within 47.5–52 Hz and 0.9–1.1 Un. If, at the moment of disconnection, the island’s internal generation and load are in near-balance, frequency and voltage stay within those bounds indefinitely — passive monitoring cannot distinguish the islanded state from normal operation.

V2G chargers exacerbate the NDZ problem in two ways:

Low fault current: inverter-based sources produce 1.0–1.2× rated fault current versus 4–6 p.u. from a synchronous generator. Standard overcurrent relays set for synchronous-generator fault signatures may not detect the fault at all. The same finding appears in the Arholma and Simris protection engineering studies for BESS. (Source - Energiforsk 2023-957 Felbortkoppling i Mikronät (2023), Source - Lund Arholma Microgrid Fault Detection (2025))

Grid-forming capability: higher-quality V2G chargers designed to support grid frequency actively regulate voltage and frequency in the island, suppressing the perturbations that passive detection methods rely on.

A further complication in Swedish MV networks with high-impedance earthing: the neutral resistance is physically located outside the islanded section. Earth-fault detection becomes non-functional during the unintentional island. Mitigation requires zero-sequence voltage protection (öppet-delta VT) at each generation connection point. (Source - Energiforsk 2025-1128 Oavsiktlig ö-drift med Distribuerad Generering (2025))

Real precedent — E.ON case, September 2022

A real Swedish event illustrates the topology: a 130 kV earth fault triggered distance protection, auto-reclose caused a wrong-zone trip at 40 kV, and a 1.6 MW run-of-river hydro unit sustained an unintentional island on a 10 kV network for ~6 minutes before an operator manually intervened. The hydro’s frequency regulation capability sustained the island against passive detection. A V2G fleet in a comparable topology — with bidirectional inverters and potentially grid-forming capability — is harder to detect and may sustain the island longer before passive protection acts. (Source - Energiforsk 2025-1128 Oavsiktlig ö-drift med Distribuerad Generering (2025))

Regulatory gap

Under RfG Articles 13–14 (EU 2016/631, implemented in Sweden as EIFS 2018:2), Type C and D generators must have an islanding detection method agreed with the DSO/TSO. But V2G chargers connected at household or small commercial level do not clearly fall under the Type C/D thresholds. The IEC 62116 standard (2-second detection limit) applies to grid-connected inverters in Sweden, but it is not universally tested or enforced for consumer-grade bidirectional chargers in the current market. ACER Recommendation 03-2023 (NC RfG 2.0 / NC DC 2.0) explicitly brings V2G into scope of EU connection requirements for the first time — but this recommendation is not yet in force. Until it is, the anti-islanding compliance requirement for V2G chargers has no clear regulatory owner. (Source - ACER Recommendation 03-2023 NC RfG DC (2023), Generator Connection Requirements)

3. Protection relay coordination degradation

DSO operational risk. General inverter-based DER problem.

Beyond the islanding scenario, the proliferation of V2G chargers degrades protection performance across the network. Distribution protection systems — overcurrent relays, directional elements, reclosers — are designed for radial power flow and synchronous-generator fault currents. As V2G penetration increases:

• Phase overcurrent relays may fail to pick up faults due to low inverter fault current contribution
• Directional relays may misread power direction in networks with high bidirectional flow
• Auto-reclose sequences may be undermined if V2G chargers do not trip and ride through the dead interval

The low-voltage circuit breaker (LVCB) has emerged as a practical enabling component for managing fault detection and isolation in inverter-dominated networks — documented in the Arholma PowerFactory simulations. The principle is that local, fast-acting circuit breakers at each generation connection point provide fault isolation that relay coordination cannot. (Source - Lund Arholma Microgrid Fault Detection (2025))

4. Coordinated fleet dispatch as a systemic TSO risk

TSO risk. Scales with adoption.

Aggregated V2G creates a large synchronized dispatchable resource. The RISE cybersecurity analysis found that approximately 300,000 connected heat pumps approaches the critical mass at which a coordinated cyber attack could drive Nordic grid frequency outside the normal operating range. (Source - RISE Cyberhot mot Elsystemet (2023))

The same logic applies to V2G fleets, with higher attack surface per unit:

• V2G chargers have persistent bidirectional internet connectivity by design (OCPP 2.1 backend connection)
• Consumer-installed hardware with variable security posture
• Aggregation platforms represent a single point of control for potentially hundreds of megawatts

A software fault, misconfiguration, or attack that triggers simultaneous large-scale V2G discharge or sudden recharge would appear to the TSO as an unplanned generation or load event. At the 5,000 MW theoretical potential cited in FlexAbility, even a partial synchronised fleet event could exceed the TSO’s automatic corrective capacity. The cybersecurity risk profile increases as V2G moves from pilot scale to commercial deployment.

Mitigation requires: inverter-level rate-of-change limits, aggregation platform fail-safes, and network segmentation between charger control channels and the public internet — the same architecture Energimyndigheten recommends for heat pumps under NIS2. (Source - Energimyndigheten Cybersäkerhet Energisektorn (web, 2026))

5. Cold-load pickup on recharge

DSO and TSO risk. Not yet quantified for V2G specifically.

After a large-scale V2G activation event — for example, FCR-D upregulation across a fleet — EVs that have discharged below their preferred state-of-charge will resume charging once the activation ends. If no staggered recharge profile is enforced, a simultaneous charging surge follows every large dispatch event. On a distribution feeder with high V2G penetration, this creates a demand spike structurally similar to the cold-load pickup problem documented in island operation restoration contexts (Island Operation › Cold-load pickup). The amplitude is proportional to fleet size and depth of discharge during activation.

No Swedish source has quantified this effect specifically for V2G; it is an inferred risk from the physics of fleet dispatch. Smart charging coordination between the BSP/aggregator and individual charger schedules is the mitigation — but this requires precisely the OCPP 2.1 platform maturity and TSO-DSO coordination that are currently cited as implementation gaps. (Source - Power Circle V2X Synthesis 2024)

Risk summary and coordination implications

The common thread across all five risks is that they emerge from the grid operator’s lack of real-time visibility into mobile, distributed, aggregator-controlled assets. The datahanteringsverktyg / FIS architecture being developed by Ei and Svk is the infrastructure layer that would ultimately enable DSOs and TSOs to manage V2G activation with grid-awareness rather than blindly. Until that exists, the risks are managed either by keeping V2G at pilot scale or by individual DSO-level prequalification of specific network areas — which is the current de facto approach. (Elmarknadshubb, Network Code on Demand Response › Flexibility Information System)

Data gaps

• Harmonic distortion and power quality impacts from bidirectional V2G inverter operation on LV networks — no Swedish study covers this quantitatively
• Cold-load pickup quantification for V2G fleet recharge events — no source models the demand surge following a large FCR-D activation
• Anti-islanding compliance verification process for consumer-grade bidirectional chargers in Sweden — no known Ei or DSO guidance
• DSO operational experience with V2G in network-constrained areas — Vattenfall/Energy Bank/VW pilot (2026–2028) may produce this data