A grid impact study is a technical assessment that evaluates how a new electrical connection will affect the local electricity network. For EV charging projects, it analyzes whether planned chargers can be connected without causing issues such as overloaded transformers, feeder congestion, voltage drop, or power quality problems, and it identifies any required network reinforcement or operational limits.
What Is a Grid Impact Study?
A grid impact study is typically carried out by a Distribution Network Operator (DNO/DSO) or an authorized engineering partner as part of the grid connection application process.
– Evaluates the proposed site’s maximum demand (kW/kVA) and load profile
– Checks network constraints at substations, transformers, and feeders
– Assesses voltage compliance, fault levels, and protection coordination impacts
– Determines whether the network can support the connection as proposed or only with constraints
Why Grid Impact Studies Matter for EV Charging
EV charging can introduce high, coincident loads, especially for depots, distribution centres, and charging hubs. A grid impact study helps avoid unsafe or underperforming installations.
– Confirms whether sufficient grid capacity exists for the planned rollout
– Identifies upgrade scope early, reducing project delays and redesign risk
– Defines any connection conditions such as import limits or phased capacity increases
– Protects network stability and reduces the risk of repeated undervoltage and nuisance trips
– Supports reliable scaling and future load reservation planning
What a Grid Impact Study Typically Assesses
A typical study evaluates the site against multiple technical criteria.
– Thermal loading of transformers and feeders under peak conditions
– Voltage drop and voltage regulation compliance at the point of connection and downstream nodes
– Fault level impact and whether switchgear and protection ratings remain adequate
– Protection coordination and selectivity implications (disconnection behavior)
– Power quality impacts such as harmonics, flicker, and phase unbalance (site dependent)
– Interaction with other loads and planned developments in the same network area
EV Charging Factors That Influence the Result
Grid impact outcomes depend strongly on how charging demand is modeled.
– Charger type and power level (AC charging vs DC charging)
– Expected simultaneity and diversity factor, especially for fleet return peaks
– Duty cycle assumptions for fleets (arrival times, dwell windows, departure deadlines)
– Use of dynamic load management to cap site import and reduce peaks
– Co-located DER (PV, BESS, V2G) that may change net import/export behavior
Typical Outputs and Deliverables
A grid impact study usually leads to a decision and a set of technical conditions.
– Confirmation of available connection capacity (or constrained capacity)
– Required network reinforcement scope (transformer upgrade, feeder upgrade, substation work)
– Connection conditions such as maximum import cap and monitoring requirements
– Recommended phasing approach for capacity increases
– Technical requirements for metering, protection settings, and commissioning evidence
– Input to the formal connection offer and grid connection agreement
Common Pitfalls
– Submitting unrealistic peak demand assumptions without validated fleet schedules
– Overestimating diversity at depots without enforceable load management controls
– Ignoring internal site constraints (DB capacity, feeder limits) while focusing only on DNO capacity
– Not disclosing future phases, leading to repeated studies and re-applications
– Treating the study as a formality and not aligning design and commissioning with the study conditions
Related Glossary Terms
Grid capacity analysis
Grid capacity assessment
Grid connection application
Connection offer
Grid connection agreement
Network reinforcement
Dynamic load management
Grid congestion
Distribution Network Operator (DNO)