November 2, 2021

How to charge your EV with 100% Solar energy

How to charge your EV with 100% Solar energy
Updated Jan 2024:

Investing in an electric vehicle can help lower your use of fossil fuels. However, you’re still not driving an emission-free EV if it’s being charged with electricity generated from your local grid.

New Zealand’s grid energy mix may be high in renewable energy sources compared with other countries. But around 20% is still generated by non-renewables like coal and gas that produce emissions to generate the electricity needed to charge your car.

So how can you charge from 100% clean energy, run your electric car without generating emissions, and even reduce your charging costs?  

Today we’re covering solar EV charging and answering these FAQs about charging your EV with solar power at home.

Is solar EV charging right for you?

If you don’t already have a solar system installed and your EV is parked at home for a couple of hours or more during the day, you could be recovering a significant amount of your daily commute in a cost-effective, low-impact way.

The benefits of solar EV charging

  • Save on EV charging costs (charge your EV from free electricity).  

  • Reduce your carbon impact (harness up to 100% clean energy to charge your EV).

  • Optimise your unused solar energy export  

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

To achieve meaningful charging speeds, we recommend at lease a 3-5kW rooftop solar installation for your home. How many solar panels you need for your situation will depend on location, weather conditions, and how fast you want to charge your EV.  

For reference, charging at a constant 3.6kW will recover a range equivalent of around 20km in one hour. If you are driving a standard NZ commute it will take two hours of solar EV charging at this speed to recover your range with 100% renewable and free electricity.

Keep in mind though, that’s not considering any changes in output from your solar inverter due to shifting weather conditions, or other energy demands from your household. The higher your solar output, the faster the EV charging speeds are possible.

You can use our EV charging costs calculator or EV charging speeds guide to help create accurate estimates for your situation.

Do I need a special EV charger to harness my solar power?

Evnex E2 smart EV charger with app showing solar export diversion to charge an EV

There are many home EV charger solutions out there, and you can use just about any of them to charge your EV from solar. However, how fast you can charge, your visibility of solar use, and control over your solar charging session are all affected by the type of EV charger you use.

For instance, you could plug your EV into a standard 3-pin household outlet using a portable EV charging cable. While this would technically charge from solar power if available, you won’t know when or how much is going to your car.

Your 100% free solar charge could become 100% paid for grid power if a cloud moves overhead, and you can’t easily monitor or control this short of stopping and starting your charging session manually. Much of your solar energy will also go unused at high-generation times due to slow charging speeds* and exported to the grid at a potentially lower value than ‘self-consuming’ it to charge your EV.

*1.8kW portable EV charger = roughly 10km of range / hour of charging.

These downsides can greatly waste the potential benefits of optimised solar EV charging and why EV owners consider upgrading to a faster (Wi-Fi connected) smart EV charger with dedicated solar monitoring and control features.  

How can a smart EV charger optimise my solar?  

Evnex smart charging app showing solar export diversion features

Some EV chargers, like Evnex’s E2, utilise a smart feature called solar export diversion to maximise the benefits of your solar generation for charging. In a nutshell, it helps automate your EV charging speed to match your fluctuating solar generation and avoid unwanted grid power from charging your vehicle.  

Evnex chargers are cloud-connected, allowing you to control and view solar charging history on your mobile device. You can also control when your EV starts charging from solar, when it stops, and ultimately set preferences for 100% solar charging.  

There’s clear visibility of both your current and historical solar charging sessions to you know how much solar has gone into your EV each session or throughout the entire year.  

With a power rating of 7.4kW, there’s also potential to charge up to 4x faster than the previously mentioned portable EV charging method.  

Walk through setting up solar export diversion with your smart phone

Solar EV charging in action

For solar export diversion to work, a power sensor is attached to your home’s main switchboard and connected to a smart EV charger that constantly measures the electricity your home is importing or exporting to the grid.  

Sometimes your home solar system will generate little-to-no power and require additional energy from the grid to meet your household demands. In this case, your solar charger will detect that you’re importing grid power and won’t start an EV charging session unless you override it.

Solar energy and grid energy being used by a home

If your solar starts producing more power than what your home is using, you’ll start exporting that electricity to the grid. When your solar export reaches a specific threshold (set by you), the smart charger will automatically start a charging session and divert that excess power to charge your EV. It then dynamically varies the charging speed to match your available solar energy as it fluctuates.‍

Solar energy being exported to the grid

If available solar power drops below your set threshold, the charging session will be paused until it increases again. As you can adjust these preferences for starting and stopping a solar charging session, you have the power to choose how much grid energy vs solar is utilised to charge your car, including only charging your EV only from 100% renewable energy during the day. ‍

Solar energy being diverted to charge an EV instead of being exported to the grid

Maximising your renewable energy after dark

Unfortunately, the most convenient time to plug in your EV won’t always alight with your solar energy availability.

You might consider storing your excess solar energy in battery systems to be used overnight or during poor weather conditions. A high-capacity battery storage systems like a Tesla Powerwall is currently around $12,000 (NZD) before installation. Understandably, these systems may be too expensive for homeowners to justify when considering installing a solar panels.

An intelligent solar EV charger is one solution to this puzzle. Although not a perfect home battery alternative, it does allow for free energy to be diverted to your electric car’s battery at potentially greater value than being exported to the grid.  

*It's important to note here that solar export diversion is a one-way energy flow and not the same as V2H (Vehicle to Home) bi-directional charging technology.

Are these EV chargers compatible with my home solar system?

EV chargers like the E2 include smart charging capabilities like solar export diversion as standard with every home installation. Our system relies on a power sensor placed at a building’s main switchboard board and is not integrated with the solar inverter itself. So regardless of what home solar system you have or plan to install in future, our EV chargers are ready to use this feature.

Here you can see a relationship between a home solar system, battery storage, and Evnex’s smart EV charger. The charger acts independently of the other two systems and is the last link in the chain allowing you to prioritise your household consumption first, with excess going to your battery storage system second, and finally filtering to charge your car last.  

Thanks for reading and helping support EV charging for a low-carbon future in New Zealand.

Did you find this article helpful? Or have topic ideas you’d like us to cover? Send us a message below. Learn more or buy an Evnex E2 for your home charging setup.

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November 2, 2021