On this post, we show you how to work out the size solar panel system you’ll need to charge your electric vehicle, or EV, from home.
The good news is that working this out is simple. Once you’ve got a handle on how the method works, you’ll find it a quick and useful way to check you’re getting the right size solar power system to charge your EV from home.
Essentially, what we’ll be showing you is the number of extra kilowatt hours of solar panels you’ll need to charge your EV, which will be in addition to the size of solar panel system you’ll require to power the rest of your home.
On this blog:
- Information you need to get started
- Example: Nissan Leaf and Tesla Model X
- Four steps to calculating the solar panel system size you’ll need
- Conclusion
Information you need to get started
To get started, you need to first gather four key pieces of information:
- Range of the EV (i.e., how far the electric car can go on a single charge)
- Battery capacity of the EV (in kilowatt hours)
- Your daily commute (averaged across a year, in km)
- Hours of ideal sunlight (peak sun producing hours for solar)
These are all self-explanatory apart from the hours of ideal sunlight or peak sun producing hours. What this refers to is the number of sunshine hours that are optimal for solar power generation.
So, whilst you may get 7 or 8 hours of sunshine on your roof on average throughout the year, the average peak sun hours will always be less than total sunshine hours.
Depending on what part of Australia you live in, the average peak hours could be as low as 3.7 in Hobart and as high as 6.1 in Alice Springs. In Melbourne, it’s around 4 hours.
Contact us if you want to know the peak sun producing hours for your property.
Example: Nissan Leaf and Tesla Model X
Here is the data for two popular EV brands – the Nissan Leaf and Tesla Model X. We’ve also assumed a daily commute of 100km and 4 hours of ideal sunlight (which is about right for Melbourne).
| Nissan Leaf | Tesla Model X | |
|---|---|---|
| Range of EV (est.) | 270km | 536km |
| Battery capacity of EV | 40kWh | 100kWh |
| Daily commute distance | 100km | 100km |
| Hours of ideal sunlight | 4 | 4 |
We’ll use the data from this table to demonstrate in the next section how to work out the size solar panel system you’ll need to cover a 100km daily commute for both the Nissan Leaf and the Tesla Model X, assuming you live in Melbourne and get 4 hours of peak sunlight on your roof on average throughout the year.
Four steps to calculating the size solar panel system you’ll need
Step 1: Number of kWh of electricity to travel one kilometre
First, we’ll work out the number of kilowatt hours of electricity (kWh) it takes to travel one kilometre for both the Nissan Leaf and the Tesla Model X.
The calculation to use is this: battery capacity (in kWh) ÷ range (in km) = kWh/km
| Battery capacity, kWh | Range, km | kWh/km | |
|---|---|---|---|
| Nissan Leaf | 40 | 270 | 0.148 |
| Tesla Model X | 100 | 536 | 0.187 |
This shows that a Nissan Leaf requires 0.148 kilowatt hours of electricity to travel one kilometre; and the Tesla Model X needs 0.187 kilowatt hours to drive the same distance.
Step 2: Total kWh per day to cover your daily commute
Next, we work out the total number of kilowatt hours of electricity you need to cover a daily commute of 100km.
The calculation is: (kilometres travelled per day) x (kWh/km) = total kWh to cover the daily commute
| Km / day | kWh/km | Total kWh per day | |
|---|---|---|---|
| Nissan Leaf | 100 | 0.148 | 14.8 |
| Tesla Model X | 100 | 0.187 | 18.7 |
This shows that the Tesla Model X needs an extra 3.9 more kilowatt hours of electricity to travel 100km than a Nissan Leaf.
Step 3: Size solar panel system (kW) to cover your daily commute
The calculation for this step is: kWh/day (i.e., the total kWh of electricity to cover your daily commute) ÷ number of peak sunlight hours/day = size solar panel system (kW)
| Total kWh per day | Peak sunlight hours/day | Solar system size, kW | |
|---|---|---|---|
| Nissan Leaf | 14.8 | 4 | 3.7 |
| Tesla Model X | 18.7 | 4 | 4.7 |
This shows that you’d need about 4.7kW of solar panels on your roof to cover your average daily commute of 100km in a Tesla Model X, and 3.7kWh of solar panels for the same commute in a Nissan Leaf.
Step 4: Size up for conversion losses
The above numbers assume a 100% efficient system. However, that’s in a perfect world.
In the real world there will always be power losses when charging your car battery, and because of the solar power conversion process (due to shading, panel orientation and tilt, dirt, panel deterioration, etc.).
To compensate for these losses, we generally advise increasing the size of your solar panel system by around 20 per cent.
| Solar system size increased by 20% for conversion losses, kW | |
|---|---|
| Nissan Leaf | 4.4 |
| Tesla Model X | 5.6 |
For a Nissan Leaf, this means you’d need an additional 4.4kW of solar panels on your roof to charge your car for the daily commute. And for a Tesla Model X, you’d need an additional 5.6kW of solar panels.
Conclusion
What this method shows, is that adding more solar panels to cover your EV charging requirements to cover a typical daily commute is realistic.
It does however mean ensuring you get a large enough solar panel system to cover both your EV charging requirements and your household electricity needs.
Given that you’d need around 4-5kW of solar panels just for the EV charging, it’s easy to see why bigger solar panel systems of 10kW plus are becoming so popular.
Get in touch
If you’re interested in getting a solar panel system that’s all set-up ready for EV charging, get in touch.
There’s exciting new technology from leading solar manufacturers that allow you to get solar panels installed and progressively add more functionality to your solar system as your needs evolve.
Whether that’s adding more panels to charge your EV, adding battery storage, or running your smart appliances from just one app – the technology is here today to make this possible!
Even if you’re just at the start of considering how EV charging and solar may work together in your home, feel free to contact us for advice.
