Integrating solar panels with EV charging

How do EV charging and solar panels work together?

Solar panels generate electricity through photovoltaic (PV) systems, which convert sunlight into electricity. This energy can then charge your EV directly, or you can store it in batteries to use later.

An inverter is essential for this process, acting as a transformer that converts the solar power from DC - generated by the panels - into AC, which most home appliances including EVs use. 

You can take it a step further and consider smart charging. This helps you to manage energy flow and balances the needs of your home and EV to ensure efficient use of the solar power you generate.

How many solar panels do I need to charge my EV?

The number of solar panels required to charge your EV depends on several factors:

• Battery size - larger batteries need more energy
• Daily mileage - more driving increases energy needs
• Solar panel wattage - higher wattage panels generate more electricity
• Sunlight availability - more sunlight hours boost energy production.

A typical 4kW solar panel system, made up of 8 to 12 panels, can generate approximately 3,400 kWh annually under UK conditions. 

A 40kWh EV battery can fully charge in about 10 hours of good sunlight with a 4kW system, so this output is usually sufficient to cover the daily charging needs of most EVs. But that ultimately depends on your driving habits and, of course, enough sunlight. During winter months or overcast days, you might need to top-up with grid electricity.

To determine the exact number of panels you need, consider your EV's battery capacity, your daily driving distance and the average sunlight hours in your location. Chatting with a certified solar installer can help you find a tailored solution to meet your specific requirements.

What are the benefits of combining solar with a TOU tariff?

TOU tariffs charge different rates depending on the time of day. These tariffs align well with solar energy, as you can charge your EV during cheaper off-peak hours when solar output is low - such as in the evening - and rely on TOU rates to import the extra energy you need at a cheaper cost. 

You can also combine TOU import tariffs with export plans like Outgoing Octopus, where you can receive a fixed rate of 15p per kWh for any excess solar energy you export back to the grid. This helps you earn money from any extra solar energy you generate during the day. 

Cost breakdown: solar vs off-peak charging

Charging your EV from solar during the day is free once the system is installed, but you need to factor in the initial cost of the solar panels and inverter. In contrast, off-peak charging at night uses grid electricity, which might come at a lower rate but still costs money all the same.

Unsurprisingly, seasonal cost comparisons show that solar charging tends to be more cost-effective in summer when solar output is high. In winter, when solar generation drops, you may need to rely more on off-peak rates. The cost savings from solar during peak sunlight hours may still outweigh the additional cost of grid energy, though.

Adding battery storage can improve your return on investment by allowing you to store excess solar energy for later use, especially during periods of low sunlight. If your home uses a lot of energy, or you’re located in a region with limited sunlight, battery storage can make solar charging more practical year-round.

Tariffs for homes with solar and EVs

Several TOU tariffs work well for homes with solar panels and EVs, such as Octopus Go, Agile and Intelligent. These tariffs offer lower rates during off-peak hours, aligning well with solar generation patterns and the need for regular EV charging. If you can shift energy use to off-peak times, a TOU tariff can offer significant savings. 

However, if off-peak times don’t fit your schedule, a fixed-rate tariff might be a better option. Fixed-rate provides consistency and stability, making it ideal if you prefer predictability over flexibility.

When choosing an EV tariff, you should also consider their compatibility with solar export plans. TOU tariffs like Octopus Outgoing let you earn from exporting excess solar energy back to the grid, increasing savings when solar output is high.

Are there UK grants for solar and EV chargers?

Yes. UK residents may access two main grants:

1. Smart Export Guarantee (SEG): This scheme pays out for electricity exported from solar panels or other renewable sources back to the National Grid. You can apply directly to an SEG licensee, such as Octopus Energy, to receive payments for exported electricity.
2. EV chargepoint grants: These grants assist with the cost of installing an EV chargepoint. The grant covers up to 75% of the installation cost, capped at £350.  

To determine your eligibility and to apply, visit the specific grant pages. 

How to choose the right solar EV charger

Smart EV chargers that integrate with solar panel systems allow for efficient energy use by directing any excess solar power to charge your vehicle. Look for features such as:

• Solar diversion - this allows the charger to prioritise solar power for EV charging, minimising your reliance on the grid
• App control - manage your charging schedules, monitor usage and adjust settings remotely for convenience and efficiency
• Dynamic scheduling – set charging times to align with peak solar output or off-peak rates to save money.

What about portable solar chargers?

Portable solar chargers may seem appealing, but they’re generally not so good for UK drivers. Dealing with both limited solar generation in winter months and the high energy demand of EVs, these portable units struggle to provide enough power. They may be useful for short trips though, or as an emergency backup, but they won't yet fully replace a home charging setup.

How to optimise solar and EV charging

To optimise solar and EV charging, charge your EV during solar generation hours when energy is free. If that’s not enough, use TOU tariffs to top up during off-peak low-cost periods, typically at night.

Load balancing tools - such as the SolarEdge Energy Hub - and smart home energy apps help manage the flow of energy between your solar panel system, home and EV. These tools use solar power efficiently, prioritising EV charging when solar output is high and reducing grid reliance during peak prices. 

By tracking your solar generation and EV charging patterns with real-time dashboards, you can make adjustments to boost any savings and ensure effective energy use.

Home battery storage: game changer or nice-to-have?

A home battery adds value by storing excess solar energy for later use. It allows you to charge the home battery during off-peak hours when electricity rates are lower and discharge it back to your vehicle during peak demand, avoiding those higher grid prices.

By integrating solar, EV charging and battery storage, you can enhance your overall energy use. The battery stores surplus solar power for use when the sun isn’t shining, reducing future reliance on the grid and increasing your overall savings.

Real-world setups and savings

Here's how different setups perform in real-world scenarios:

Solar and EV without battery

Uses solar power for daytime charging, with any shortfall covered by grid electricity, ideally at off-peak rates with a TOU tariff.

Full solar, EV and battery setup

Stores excess solar energy in a battery for use at night or during cloudy periods, reducing grid reliance and boosting savings.

Flat vs. dynamic tariffs

Flat tariffs offer predictable costs, while dynamic tariffs, such as TOU, offer savings by charging during off-peak hours. The dynamic setup often results in higher savings.

Payback periods and energy independence

Payback periods for full solar, EV and battery setup can range from seven to 12 years depending on your initial investment and energy savings. The higher your energy independence, the greater your savings.

What to consider before installing solar panels and an EV charger

Before installing solar panels and chargers, consider the following:

• Costs and grants - installation costs for solar panels and chargers vary. Grants like the EV chargepoint grant can help with installation expenses
• DNO permissions - you may need approval from your Distribution Network Operator (DNO) if you’re installing a large solar panel system, EV charger or exporting excess energy to the grid
• Smart meter requirements - a smart meter is essential for tracking energy use with TOU tariffs and monitoring any exported energy.