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

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

• Solar divert — the function of automatically using excess solar generation to charge an EV rather than exporting to the grid
• CT clamp position — for solar divert, the CT must be on the grid connection (import/export meter tails) to measure net flow to/from the grid; some setups use a CT on the solar inverter output instead
• Import/export direction — the CT must be sensitive to direction of current flow: import (grid to house) vs export (house to grid); most solar-divert chargepoints require bi-directional CT clamps
• Minimum current threshold — IEC 62196 minimum charge current is 6A (~1.38kW); solar divert cannot begin until excess solar generation reaches 6A; below this the chargepoint pauses
• Zappi eco mode — Myenergi Zappi's "eco" mode: charges from solar excess only; pauses when solar drops below 6A
• Zappi eco+ mode — "eco+" tops up from grid to maintain minimum 6A (or user-set minimum) even when solar is insufficient; avoids charging pause but uses some grid electricity
• Zappi fast mode — ignores solar; charges at full 32A from grid regardless
• Ohme smart scheduling — the Ohme Home Pro uses a scheduler rather than live CT divert; it can schedule charging to coincide with off-peak tariffs but does not do real-time solar divert
• Inverter communication — some chargepoints communicate directly with the solar inverter via API (Fronius Solar.web, SolarEdge monitoring) rather than using a CT clamp; more accurate but manufacturer-specific
• myenergi Hub — links Zappi, Eddi (solar divert immersion controller), and Libbi (battery) on a local network; allows coordinated solar self-consumption across multiple devices
• Battery storage interaction — where a solar battery is present, the hierarchy matters: battery charges first, excess to EV; or EV charges first, remainder to battery — configurable in the hub
• Yield expectations — in the UK, a 4kWp solar array generates approximately 3,400–4,000kWh/year; in summer months, midday excess may be 2–4kW; in winter, solar-only EV charging is minimal

Quick Reference Table: UK Solar-Divert Capable Chargepoints

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:

• Charges only from solar excess
• Adjusts charge current in real time (6A–32A) to match available export
• If export drops below 6A, charging pauses
• Best for: customers who want maximum solar self-consumption and are happy for slow/intermittent charging
• Summer performance: excellent — typically adds 3–8kWh per sunny day
• Winter performance: minimal — UK winter solar is often insufficient to reach the 6A threshold

Eco+ mode:

• Charges from solar excess first; tops up from grid to reach a user-configured minimum current (e.g., 6A, 10A, 16A)
• Prevents the chargepoint from pausing when clouds pass
• Grid top-up rate is configurable; some customers set minimum to 6A (just enough to keep charging); others set 16A for a predictable minimum rate
• More grid electricity consumed than eco mode, but more reliable daily charge addition

Fast mode:

• Full 32A from grid; ignores solar
• Used when the customer needs a quick top-up regardless of solar
• Smart scheduling still applies (SI 2021/1467 compliance)

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)

• Solar charges the battery to 100% during the day
• Excess beyond battery capacity diverts to EV
• In the evening, battery discharges to cover household load
• EV charges overnight on off-peak tariff (or from battery if V2G-capable)

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

• Solar goes directly to EV during the day (vehicle present and charging)
• Remaining excess charges battery
• Good for drivers who plug in and leave during the day but need the car charged by a set time

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):

• A 4kWp south-facing array may generate 15–25kWh on a clear day
• Household consumption of 8–12kWh/day leaves 5–15kWh potential excess
• At 6kWh/100km, this could add 80–250km of range per day
• Eco mode can easily provide overnight or next-day range for typical urban drivers

Winter (November–February):

• A 4kWp array may generate only 2–5kWh on a short winter day
• Household heating and lighting consumes most of this
• Available excess rarely reaches the 6A minimum threshold
• EV charging in winter requires grid electricity; solar contribution is minimal

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:

• Octopus Go: fixed cheap rate 00:30–04:30; Ohme Home Pro and Zappi can schedule to this window automatically
• Octopus Agile: half-hourly variable pricing; advanced chargepoints (Ohme, Wallbox) can buy the cheapest half-hours; Zappi via myenergi Hub
• Intelligent Octopus Go: Octopus manages charge scheduling automatically via the vehicle API (Tesla, Volkswagen, Hyundai, Kia, BMW); chargepoint interaction may not be needed

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

• Electric Vehicles (Smart Charge Points) Regulations 2021 (SI 2021/1467) — applies to solar-integrated chargepoints equally

• BS 7671:2018+A2:2022 — Chapter 722: wiring of the EV chargepoint and any CT circuits

• MCS 001 / MCS 012 — MCS standards for solar PV; relevant to the solar installation part of the system (not the chargepoint)

• Smart Export Guarantee — BEIS/Ofgem framework for solar export payments; relevant to the economics of solar-EV integration

• Myenergi Zappi installation manual — eco/eco+ mode CT configuration

• IET Guidance Note 7 — EV Charging — chargepoint CT clamp guidance

• Ofgem Smart Export Guarantee guidance — SEG rates and eligibility

• ct clamp load management — CT clamp installation and load management

• ev charger installation types — chargepoint hardware types

• bs 7671 ev wiring requirements — Chapter 722 wiring compliance

• dno g98 g99 applications — DNO notifications for solar PV

• solar battery storage installation — battery storage and EV charging coordination