Integrating EV Charging With Solar PV: Export Limiting, Divert Modes and Smart Scheduler Settings

Quick Answer: Solar-integrated EV charging uses a CT clamp on the solar generation or grid connection to detect excess solar export and redirect it to the EV rather than exporting to the grid at a low rate. The Myenergi Zappi is the most widely used solar-divert chargepoint in the UK. Three modes are common: "eco" (divert solar excess only, minimum 6A), "eco+" (top up from grid to maintain a minimum charge rate), and "fast" (ignore solar, charge at full grid rate). The chargepoint must be configured with the correct CT clamp position and mode to work properly.

Summary

UK domestic solar PV installations export power to the grid when generation exceeds household demand. Under the Smart Export Guarantee (SEG), households earn 5–15p per kWh exported. However, charging an EV from excess solar is often worth 25–35p per kWh avoided import cost — two to three times more valuable than export payments.

Solar-integrated EV charging maximises self-consumption: the chargepoint detects when the property is exporting and diverts that excess to the vehicle instead. This requires a chargepoint capable of variable current output (ramping between 6A and 32A in real time) and a CT clamp measuring export/import on the grid connection or solar generation.

For electricians installing or commissioning solar-integrated EV chargepoints, understanding the CT clamp positions, operating modes, and limitations is essential. This article covers the common UK chargepoints that support solar integration, how to configure them, and what to tell customers about realistic expectations.

Key Facts

Quick Reference Table: UK Solar-Divert Capable Chargepoints

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Chargepoint Solar Divert Method Min CT Input App Required Notes
Myenergi Zappi Real-time CT clamp divert CT on grid tails myenergi app Most widely used; eco/eco+/fast modes
Indra Smart PRO Real-time CT clamp CT on grid Indra app Similar eco modes to Zappi
Ohme Home Pro Scheduled + solar tariff CT (optional) Ohme app Better for Agile Octopus; less true live divert
Wallbox Pulsar Plus Via CT + Wallbox API CT on grid Wallbox app Eco-smart mode; less granular than Zappi
Hypervolt Home 3 Via CT + API CT on grid Hypervolt app ECO mode; API for Octopus Agile

Detailed Guidance

CT Clamp Position for Solar Divert

The CT clamp position determines what the chargepoint measures and how it responds.

Grid tails (import/export measurement): The CT is clamped on the main incomer tails — the cables between the electricity meter and the consumer unit. This measures the net flow of electricity: positive = importing from grid; negative = exporting to grid.

When the property is exporting (solar generation exceeds demand), the chargepoint detects the export current and matches its charge current to absorb the export. If the property is importing (demand exceeds solar), the chargepoint reduces its current to zero (eco mode) or maintains a grid-top-up rate (eco+ mode).

This is the standard configuration for Zappi and similar chargepoints. It requires a bi-directional CT clamp (one that can detect current flow in either direction).

Solar generation output: Alternatively, the CT is placed on the solar inverter AC output cable. This measures total solar generation, not net export. The chargepoint must subtract household demand (estimated or separately measured) to calculate available excess.

This method is less accurate but useful where the grid tails are inaccessible (e.g., in a sealed head-end housing).

Inverter API integration: Some chargepoints (and the myenergi hub) can query the solar inverter directly via API or MODBUS to get real-time generation and household consumption data, providing more accurate excess calculation without a CT clamp on the tails. This requires the inverter to support remote monitoring APIs.

Zappi Modes and Configuration

The Myenergi Zappi has three charging modes, selectable from the device touchscreen or the myenergi app:

Eco mode:

Eco+ mode:

Fast mode:

Configuring Zappi with the myenergi app:

  1. Install the Zappi and connect to the local Wi-Fi network during commissioning
  2. Install the CT clamp on the grid tails; connect to Zappi's CT input
  3. In the myenergi app, confirm CT orientation (arrow direction): if import/export readings are reversed, flip the CT or invert the polarity setting in the app
  4. Select default mode (eco recommended for solar customers)
  5. In eco+ mode, set minimum charge rate
  6. Set the minimum guaranteed charge time (e.g., always charge at 6A from 11pm to 6am on off-peak tariff)

Coordinating EV Charging and Battery Storage

Where a property has both solar battery storage and an EV chargepoint, the charge priority hierarchy must be set:

Scenario 1: Battery first, EV second (most common)

Scenario 2: EV priority (for time-sensitive charging)

The myenergi Hub coordinates Libbi (battery) and Zappi (EV) to implement these priorities automatically. Other battery/chargepoint combinations may require manual scheduling or API integration.

Customer Expectations: Realistic Yields

Customers often overestimate solar-EV integration performance. Set realistic expectations:

Summer (May–September):

Winter (November–February):

Practical advice: Install a combined eco+ scheduler: solar divert when available; scheduled overnight off-peak top-up (e.g., Octopus Go, Economy 7) for reliable overnight charging. This maximises solar use without leaving the vehicle under-charged in winter.

Tariff Integration

Smart chargepoints increasingly integrate with time-of-use electricity tariffs:

For customers on variable tariffs, the combination of solar self-consumption during the day and cheap overnight grid charging can reduce EV running costs to <2p/km.

Frequently Asked Questions

The Zappi eco mode charges very slowly. Is it working?

Yes — if solar excess is low (e.g., 8A), the Zappi will charge at 8A (~1.84kW). This adds approximately 5–6 miles of range per hour. On a cloudy day with modest solar, this is expected. The customer should also use eco+ or fast mode when they need faster charging. The eco mode performance in summer will be significantly better.

Does the CT clamp need to be on the consumer unit or can it be anywhere on the tails?

It must be on the cables between the electricity meter and the consumer unit — the main incomer tails. It should not be on the solar inverter output or on a sub-circuit. The CT measures the net flow of electricity to/from the property; placing it anywhere else gives inaccurate readings. Some chargepoints accept a second CT for the solar output — check the specific product manual.

Can I use a Zappi with an AC-coupled battery (e.g., Tesla Powerwall)?

Yes, but the configuration requires care. An AC-coupled battery shows up as a generation or load on the grid tails CT, depending on whether it's charging or discharging. The Zappi will interpret battery discharge as solar generation and attempt to divert it to the EV. In some setups this is desirable; in others it is not. Check the myenergi documentation for battery integration settings — the Hub can differentiate between solar and battery in some configurations.

Is solar-divert EV charging compliant with the Smart Charge Points Regulations 2021?

Yes. The regulations require chargepoints to respond to a demand flexibility signal and to have scheduled charging capability — they do not prohibit solar-divert operation. Eco mode is a form of demand flexibility. Smart scheduling compliance still applies; eco mode chargepoints must still be capable of grid operator override if required.

Regulations & Standards