Charging An EV With Solar - Everything You Need To Know

Every sci-fi or time-travel story in the previous century has imagined transport in the 21st century to be flying cars (any Back to The Future fans?). Instead, the future now seems to be silent, emission-free cars with a possibility of free-of-charge usage.

We might be a bit sad about not having flying cars, but electric vehicles are a wonderful invention. They simplify the definition of a vehicle, while also promising a relatively milder impact on the climate.

However, EVs still need electricity as fuel and that costs money. Coupled with the cost difference between EVs and traditional vehicles, this means it is not a strikingly attractive deal for many people. Of course, it has environmental benefits. But EVs use conventional grid power, which has around 20% fossil fuel energy generation in the mix.

Enter solar panels! Both the above mentioned arguments can be addressed by using solar panels for charging your EV. By using solar, you make your EV truly emission-free, while also being able to charge it for free (once you’ve paid off your system). Let’s discuss some important aspects of charging your EV with solar.

Can You Charge an EV Using Only Solar Power?

One thing that separates solar power from not just fossil power but also other renewables, is its astonishing flexibility. It can power everything from a wristwatch to entire cities. As such, the question of whether it can charge your EV doesn’t remain much relevant.

However, nobody can guarantee the availability of sunlight on a certain day (apparently not even weather forecasters). And that means it is a good idea to have another power source ready to use whenever you need it. In most cases, this source is your grid power, which is readily available for use in most places.

The conventional way to do this is to have a grid-tied solar power system that powers your appliances as long as it can, after which the grid power takes over if more electricity is needed. This method does not always guarantee that your solar panels prioritize your EV charger over other appliances in your house.

Another, smarter option is to use a smart EV charger that automatically uses available solar power, while switching to grid power as and when needed. Since such a circuit doesn’t always include your other appliances, your EV gets to be your solar power’s exclusive recipient, making the arrangement more reliable.

Let’s go over the types of EV chargers, from the perspective of charging with solar.

Types of EV Chargers

1. Traditional EV Chargers

Traditional EV chargers haven’t been designed with solar power in mind. They come in level-1, level-2 and DC fast models, with slow, moderate and fast charging respectively.

Traditional chargers can also be supplied with solar power like other appliances, but they do not have the necessary software, aka “smartness” to prioritize solar power while also drawing power from the grid when needed.

2. Smart EV Chargers

No offence to traditional chargers, but as we said, they aren’t really that smart - especially when you compare them with modern, “smart” EV chargers which have some neat tricks up their sleeve.

To begin with, these chargers allow you to optimise charging in multiple ways. Firstly, they can charge your EV using only solar power, thanks to the ‘solar-only charging’ feature. 

Secondly, they can also be made to optimise charging based on the times of the day, in order to charge when the electricity rates are low, such as off-peak times. On that note, this feature can also be implemented on a regular charger by using a timer for charging.

Another novel feature is Load Balancing, where the charge rate is dynamically adjusted to avoid overload when other heavy appliances are also drawing power.

If you are using solar panels solely for your EV’s charging, you can also opt for an all-in-one solar EV charger that not only has all the smart features mentioned above, but also integrates some other necessary hardware, eliminating the need for an inverter.

If you are wondering which charger you should buy, the cost might be one thing you might want to consider. Smart/all-in-one EV chargers are slightly more expensive. If you do not use your EV every day, or if it is not your primary vehicle, then you could opt for a regular charger.

How Many Solar Panels Do You Need to Charge an EV?

We have covered this in one of our previous articles, but this question is so frequent that we decided to discuss it briefly once again.

Asking how many panels you need to charge your EV is like asking how many litres of petrol your car needs. The immediate response, of course, is that it depends. It depends on the fuel/energy consumed per day (based on the travelling distance) as well as the vehicle’s efficiency.

The same thing applies when talking about solar panel requirement for EVs. In addition to the above-mentioned factors, another decisive one is the availability of sunshine.

Let’s begin with energy consumed per day. Below is a table that shows battery capacity in kWh for some of the popular EVs available in NZ. We have also included the numbers for the driving range and efficiency in terms of km/kWh.

Now, the average kiwi drives about 28 km per day. Based on the above table, let us consider that the average EV covers about 7.5 km for every kWh of its battery. This means the average EV user in NZ needs 28 ÷ 7.5 = 3.73 kWh of charging per day. This makes it a total of 3.73 x 365 = 1361.45 kWh per year.

And now we come to the last factor that decides how many solar panels an EV owner will need to charge it fully off solar power - the sunlight potential in their location. Here’s our super-useful table of approximate yearly generation from different solar systems located in some of the main cities in NZ.

Based on our previous figure of 1361.45 kWh per year, it is clear that you will need anywhere between a 1 kW and a 2 kW system to charge an EV completely with solar. It might also make sense to oversize the system a bit, since the above numbers are yearly, while sunny hours change throughout the year. This means you may run out of solar power in the winter months of May-July if you haven’t oversized the system a little.

Of course, all of the above is based on the average use, and you might need to recalculate based on your travelling distance per day and your model of EV. But the calculations, as we’ve seen above, are a piece of cake, so you can easily figure out the exact size of system needed within a minute or two.

Should You Use Solar Panels to Charge Your EV?
Ultimately, everything comes down to the question of whether it is worth the expense. And again, we have numbers coming to our rescue. Remember the number of kWh we calculated per year that your EV will need on average? Yes - 1361.45 kWh.

On average, a power consumer in NZ pays about 31.5 cents per kWh of electricity used. This means your EV will cost 1361.45 x 31.5 = 42,885 cents, or $429 per year. Over 25 years (lifespan of a solar system), this turns out to be $10,725. Add in the increase in grid power prices and you have an even higher number.

On the other hand, if you look at the costs of solar systems, it is clear that you can charge your EV for a whopping three decades for less than $5000. Compare that with the ever-increasing fossil fuel prices and EV+solar looks like an even more lucrative deal.

In conclusion, both the questions of whether you should get an EV and whether you should charge it with solar have a big yes as their answer!