Smart charging and EV tariffs: how to charge cheaply at home

An electric car usually spends far longer plugged in at home than it needs to charge. Smart charging uses that slack: the charger picks the cheapest hours, follows your solar output, or backs off when the grid is busy. In Great Britain this is not just a feature – it is written into law for new home chargers.

What the law requires

The Electric Vehicles (Smart Charge Points) Regulations 2021 apply to home and workplace charge points sold in Great Britain ¹. The main requirements came into force on 30 June 2022, and the security requirements on 30 December 2022 ².

You can always change the default schedule or override it for a single session. The defaults exist so that millions of cars do not all start charging at 17:30 when people get home.

What the regulations do not do

They do not require a particular app, cloud or protocol. OCPP is one way to meet them, not a legal requirement ². So two compliant chargers can differ greatly in how well they work with your energy supplier.

Time-of-use and EV tariffs

With a smart meter, suppliers can charge different prices for different half hours. EV tariffs typically offer a cheap overnight window; some go further and control the car or charger directly to charge when the supplier’s prices are lowest.

Three ways a tariff can work with your charger:

1. Fixed cheap window – you (or the default schedule) set the charger to run during the tariff’s off-peak hours.
2. Supplier-controlled – the supplier’s system starts and stops the charger or the car, often via an integration with the charger manufacturer.
3. Price-following – the charger or a home energy manager reads half-hourly prices and plans charging to be ready by your departure time.

Before you buy a charger, check which chargers your preferred tariff supports. Before you switch tariff, check that your charger is on the supplier’s list and that the integration does not require a separate subscription.

Charging from solar

Every kWh from your roof that goes into the car is a kWh you do not buy at the import price. To do this, the charger needs to know your export – from a current clamp on the meter tails or a link to your inverter – and to adjust its current continuously.

The charging standard does not allow less than 6 A per phase, which sets the floor:

For the typical single-phase UK home this works in your favour: the charger can start from about 1.4 kW of surplus. On a three-phase supply, a charger with automatic 1↔3 phase switching avoids waiting for 4 kW of spare solar. In our database, 30 of 67 chargers list solar surplus charging and 10 list phase switching; 9 do both. See EV chargers that charge on solar surplus and EV chargers with 1↔3 phase switching.

Smart charging and your supply

Smart charging also protects your own supply. A 7 kW charger draws 32 A for hours; with an electric shower and oven running, that can approach the limit of the main fuse. Load management reduces the charging current automatically, and it is also what your installer considers when notifying the network operator ³. Our load balancing guide explains the options.

Choosing a strategy

Practical tips

• Check whether smart features are built in or need a paid subscription or a particular app.
• A charger with an open protocol (OCPP) can be moved to another app or service later.
• Weak Wi-Fi on the drive? 40 models in our data have a 4G modem: EV chargers with 4G.

Compare all models and their smart features on the EV charger overview.