Solar Panels and Electric Cars: Charging Your EV with Solar in NI

Solar and EVs: A Natural Pairing

If you drive an electric car, or you are thinking about getting one, adding solar panels to your Northern Ireland home is one of the smartest financial moves you can make. The logic is simple: instead of paying 24 to 28p per kWh to charge your car from the grid, you can charge it for free using electricity your panels generate.

The combination of solar panels and an electric vehicle is becoming increasingly popular across NI. As electricity prices remain high and more affordable EVs come to market, the savings from solar charging are substantial. This guide explains how it works, how to size your system, what equipment you need, and how much you can realistically save.

How Solar EV Charging Works

At its simplest, solar EV charging means plugging your car in during the day when your panels are generating electricity. Instead of exporting that surplus solar power to the grid (where you receive around 4 to 6p per kWh under the Smart Export Guarantee), you divert it to your car’s battery, effectively “storing” it as miles driven.

There are three ways this can work in practice:

1. Manual Charging During Solar Hours

The simplest approach. You plug your car in when you get home and set a timer (on the car or the charger) to charge during peak solar hours, typically 10am to 3pm. This works well if your car is parked at home during the day, for example if you work from home or have a second car.

2. Smart Solar Diversion

A smart EV charger can automatically adjust its charging rate based on how much surplus solar electricity is available. When the sun is shining and your panels are producing more than your home is using, the charger ramps up. When a cloud passes over or you turn on the kettle, it ramps down or pauses. This maximises the amount of free solar charging without you needing to think about it.

3. Battery Storage and Overnight Charging

If you have a home battery as well as solar panels, you can store surplus daytime solar generation and use it to charge your car overnight. This is the most flexible option, as it means your car does not need to be at home during the day. It is also the most expensive to set up, as it requires both a battery and a solar system.

Sizing Your Solar System for an EV

How Much Electricity Does an EV Use?

The average electric car in the UK uses around 3 to 4 miles per kWh (depending on the model, driving style, and weather). For a typical NI driver covering 8,000 to 10,000 miles per year, that translates to roughly 2,500 to 3,500 kWh of electricity annually.

To put that in context, the average NI household uses around 3,500 to 4,000 kWh per year for everything else (heating excluded, if you are on gas or oil). Adding an EV effectively doubles your electricity consumption.

How Many Extra Panels Do You Need?

In Northern Ireland, a 1kW solar panel system generates approximately 850 to 950 kWh per year. So to cover 3,000 kWh of EV charging, you would need roughly 3 to 4kW of solar capacity, which translates to 7 to 10 additional panels (depending on panel wattage).

If you are installing a new system from scratch and want it to cover both your household electricity and your EV, you should be looking at a 6 to 8kW system. That is 15 to 20 panels, which requires a south-facing roof of approximately 25 to 35 square metres.

If you already have a 4kW system and want to add capacity for EV charging, speak to your installer about adding extra panels. You may also need an inverter upgrade to handle the increased capacity.

Smart EV Chargers: Your Key to Free Fuel

While any home EV charger will work with solar panels, a smart charger designed for solar diversion makes a significant difference to how much free charging you actually achieve.

Zappi

The Zappi (made by Myenergi) is the most popular solar-compatible EV charger in the UK and Ireland. It has three charging modes:

• Eco mode: Charges using surplus solar only. If there is not enough solar, it does not charge. This maximises free charging but means slower fill-ups.
• Eco+ mode: Uses surplus solar plus a small top-up from the grid to maintain a minimum charging rate. A good balance between free charging and convenience.
• Fast mode: Charges at full speed from the grid, ignoring solar. Useful when you need a quick charge and do not care about the source.

The Zappi communicates with a CT clamp on your electricity meter to monitor real-time import and export. It adjusts its charging rate every few seconds, ensuring your car absorbs as much surplus solar as possible.

Ohme

The Ohme charger takes a different approach. It connects to your energy tariff data and can schedule charging during the cheapest periods. While it does not have the same real-time solar diversion as the Zappi, it works well with time-of-use tariffs and can be set to prioritise daytime charging when solar output is highest.

Other Options

Most modern smart chargers (Andersen, Wallbox, Tesla Wall Connector) can be scheduled to charge during specific hours, which allows you to target peak solar generation periods. They lack the automatic surplus-matching of the Zappi, but with some manual scheduling, they still enable significant solar charging.

Cost Savings: The Numbers

Let us work through a realistic example for a Northern Ireland household.

Assumptions:

• Annual EV mileage: 9,000 miles
• EV efficiency: 3.5 miles per kWh
• Annual EV electricity consumption: approximately 2,570 kWh
• Grid electricity cost: 26p per kWh
• Smart Export Guarantee rate: 5p per kWh

Charging entirely from the grid: 2,570 kWh x 26p = £668 per year

Charging 60% from solar, 40% from grid (realistic with a smart charger and daytime availability):

• Solar charging: 1,542 kWh x 0p = £0
• Grid charging: 1,028 kWh x 26p = £267
• Lost export income: 1,542 kWh x 5p = £77
• Net cost: £267 + £77 = £344

Annual saving: approximately £324

Over five years, that is over £1,600 in savings on top of any savings your solar panels are already delivering for your household electricity. If electricity prices rise further (as many analysts expect), the savings grow accordingly.

For comparison, the petrol cost for 9,000 miles in a typical combustion car at 40 mpg and £1.40 per litre would be roughly £1,440 per year. Charging your EV with solar costs £344, a saving of nearly £1,100 per year compared to petrol.

Typical Daily Driving in Northern Ireland

Northern Ireland’s compact geography works in favour of EV and solar owners. The average daily commute in NI is around 20 to 30 miles, which requires roughly 7 to 9 kWh of electricity. On a decent spring or summer day, a 4kW solar system in NI can generate 15 to 20 kWh, meaning there is plenty of surplus to charge your car even after powering your home.

In winter, solar generation drops significantly (3 to 6 kWh per day from a 4kW system), so you will rely more on grid charging during the darker months. This is where a time-of-use tariff can help, allowing you to charge cheaply overnight even when solar is not available.

Adding Battery Storage to the Mix

A home battery (such as a GivEnergy, Tesla Powerwall, or Fox ESS unit) adds another dimension. During summer, your panels may generate far more electricity than your home and car can use during daylight hours. A battery stores that surplus for use in the evening or overnight.

For EV charging specifically, a battery means:

• You can charge your car overnight using stored solar electricity, so the car does not need to be home during the day.
• You capture more of your solar generation instead of exporting it at the low SEG rate.
• You have backup power during grid outages (with compatible systems).

The trade-off is cost. A 5 to 10 kWh home battery typically costs £3,000 to £6,000 installed. Whether the extra cost makes financial sense depends on your specific usage patterns and how much surplus solar you are currently exporting.

Vehicle-to-Grid: The Future

Vehicle-to-grid (V2G) technology allows your EV to feed electricity back into your home or the grid, effectively turning your car’s battery into a giant home storage unit. A typical EV battery holds 40 to 70 kWh, far more than any domestic home battery.

V2G is still in its early stages in Northern Ireland. The technology exists (the Nissan Leaf and some other models support it), but V2G-compatible chargers are expensive and the tariff structures to make it worthwhile are not yet widely available.

However, it is worth keeping V2G in mind when choosing your next EV and charger. As the technology matures and energy markets evolve, the ability to use your car as a home battery could become a significant financial benefit.

Getting Started

If you are considering solar panels and an EV (or you already have one and want the other), here is a practical starting point:

1. Assess your driving needs. Work out your annual mileage and daily patterns. If your car is parked at home during the day, solar charging is straightforward.
2. Size your solar system accordingly. If you already have panels, check whether your roof can accommodate additional capacity. If you are starting fresh, aim for at least 5 to 6kW to cover both home and car.
3. Choose the right charger. If maximising solar charging is a priority, a Zappi or similar solar-diverting charger is worth the investment.
4. Consider a battery. If your car is not home during the day, a home battery bridges the gap between solar generation and overnight charging.
5. Get multiple quotes. Compare prices from MCS-certified NI installers who have experience with combined solar and EV charging setups.

The combination of solar panels and an electric vehicle is one of the most effective ways to reduce both your energy bills and your carbon footprint. In Northern Ireland, where electricity prices remain among the highest in the UK, the financial case is particularly strong.