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How much solar power do I need to charge my electric car at home?

How much solar power do I need to charge my electric car at home?

Petrol prices are skyrocketing and, as a result, interest in electric cars is going through the roof.  Driving around, it’s amazing to see the number of new electric vehicles on the roads.

Whilst powering your EV with grid electricity is cheaper than fueling at the pump, using your home-produced solar power is best because it’s completely free!  But how much solar do you need to charge your EV?  And what size battery is required for overnight charging?

On this blog:

  • Fully charge your EV with your solar. Is it possible?
  • How much solar do I need to charge my EV?
  • What about a battery for charging my EV?
  • How much can I save?

 

Fully charge your EV with your solar.  Is it possible?

Pure electric vehicles – like the Nissan Leaf, Tesla Model 3 and Tesla Model X – have batteries ranging in size from 40 kilowatt hours to 100+ kilowatt hours.

Kilowatt hours, or kWh, are a measure of electricity. You can think of kilowatt hours of electricity for an EV as the equivalent of litres of petrol for conventional petrol-based cars.

 

Pure electric EVsPetrol cars
Unit of measure for energy inputKilowatt hours of electricityLitres of petrol

 

Before getting started it’s important to know that on average in Australia, each kilowatt of solar panels installed generates 4 kilowatt hours of electricity every day.  (This varies depending on where you live – with Melbourne at around 3.7 kWh and Queensland around 5kWh).

This means that a 5kW solar panel system will produce around 20 kilowatt hours of electricity a day.  The table below provides more examples of the power output and number of panels for different size solar systems.

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Solar system sizes and electricity production (average)
Size of solar panels system in kilowattsKilowatt hours of electricity produced per dayNumber of solar panels (approx.)
6.6kW26.4kWh17
10kW40kWh26
15kW60kWh38
25kW100kWh64

To fully charge a Nissan Leaf with a 40kWh battery using power from your solar panels, you’d need a dedicated 10kW solar system and around 26 panels (however this wouldn’t need any solar power for your home).

Fully charging the 100kWh battery of a Tesla Model X using solar power would require a 25kW solar panels system.  That’s a whole lot of panels so you’d need a massive roof, not to mention deep pockets!

The take-away message is: Don’t expect to fully charge your electric vehicle with your solar power system every day.  You don’t fill up your car with petrol every day, so why do that with your EV?

Realistic goal

The more realistic goal for most homeowners is to produce enough solar power to charge your electric vehicle(s) so the daily commute is covered.

Given that most car owners travel between 10km and 60km every day, it is entirely feasible to charge your EV for free with your solar to cover this commute.

Think: partial charging of your electric vehicle every day with your solar – rather than full charging – and you’re on the way to mega savings!

Plus: consider going bigger with your solar panels.  10kW or more is a sensible choice if you are planning on purchasing an EV now, or down the track.

How much solar do I need to charge my EV?

To work this out, you first need to know:

  • Range of EV
  • Battery capacity of EV
  • Daily commute distance
  • Hours of ideal sunlight

Here are some examples which we’ll use in the calculations that follow:

 Nissan LeafTesla Model 3 Tesla Model X
Range of EV (est.)270km547km536km
Battery capacity of EV40kWh73.5kWh (long range battery)100kWh
Daily commute distance100km100km100km
Hours of ideal sunlight444

 

Now, we’ll do some simple maths to calculate the amount of solar power you’d need to cover the daily commute in your EV.

There are three steps:

  • Step 1: Work out the number of kWh of electricity to travel one kilometer
  • Step 2: Work out total kWh per day to cover your daily commute
  • Step 3: Work out solar system size to cover your daily commute
  • Step 4: Size up to compensate for conversion losses

 

Step 1: Number of kWh of electricity to travel one kilometer

Calculation: Battery capacity ÷ range

Battery capacity, kWhRange, kmkWh/km
Nissan Leaf402700.148
Tesla Model 373.55470.134
Tesla Model X1005360.187

 

This shows it takes 0.187 kilowatt hours of electricity to travel one kilometre in a Tesla Model X.

 

Step 2: Total kWh per day to cover your daily commute

Calculation: Kilometres/day x kWh/km

Km / daykWh/kmTotal kWh per day

 

Nissan Leaf400.1485.9
Tesla Model 373.50.1349.9
Tesla Model X1000.18718.7

 

This shows it takes approximately 18.7 kilowatt hours of electricity to travel 100 kilometres in a Tesla Model X.

 

Step 3: Solar system size to cover your daily commute

Calculation: kWh/day ÷ sunlight hours/day

  Total kWh per day

 

Sunlight hours/daySolar system size, kW
Nissan Leaf5.941.5
Tesla Model 39.942.5
Tesla Model X18.744.7

 

This shows you’d need an extra 4.7kW of solar panels installed to cover a daily commute of 100km in a Tesla Model X.

 

Step 4: Size up to compensate for conversion losses

The above numbers assume a 100% efficient system, but there are always losses in power conversion process (from DC to AC and vice-versa) and also the tilt/orientation of your roof may not be 100% ideal.

That’s why we recommend increasing your solar system size by 20% to allow for these typical conversion losses.

 Solar system size increased by 20% for conversion losses, kW
Nissan Leaf1.8
Tesla Model 33.0
Tesla Model X5.6

 

This shows you’d need an extra 5.6kW of solar panels installed to cover a daily commute of 100km in a Tesla Model X.   If you have two Tesla EVs, you’d need to double this.

 

What about a battery for charging my EV?

A battery is a great way to charge your EV overnight using your stored solar energy.  However, most batteries are around 10kWh or 13kWh in storage capacity.  So, if you have an EV with a 100kWh battery and you’re travelling around 100km a day, even a 13kWh battery won’t be big enough to cover you.  However, if you have a Nissan Leaf, this is entirely do-able.

Battery storage is a great way of charging your EV overnight.  But you may need to supplement it with grid power depending on the size of your EV’s battery and how much charge you need.

How much can I save with solar charging my EV?

With pump prices at a record $2.00/litre in Melbourne in early March 2022, the economic rationale for switching to an EV is stronger than ever.

The average petrol car uses 10.6 litres of fuel per 100km. If fuel is $2.00 per litre (current price in Melbourne March 2022), it costs $21.20 to travel 100km. This is more than 4x the cost of the Tesla Model X and more than 13x the cost of the Nissan Leaf.

Costs of powering an EV versus petrol car for a daily commute of 100km

  Total kWh per day

 

Daily cost with grid electricity at 27c/kWhCost with petrol at $2.00 for average petrol carDaily savings using grid electricity to power EV
Nissan Leaf5.9$1.60$21.20$19.60
Tesla Model 39.9$2.70$21.20$18.50
Tesla Model X18.7$5.00$21.20$16.20

 

With the average kilometres travelled in Australia for private vehicles at around 13,250/yr, car owners switching from petrol to electric could save up to $7,154 (with the Nissan Leaf).  This is based on using grid electricity 100% to charge the car.

However, if the EV owner charges their car 100% for their daily commute using their own solar power, they’ll save an additional $580 to $1,800 a year depending on the model EV they own.  (The higher savings figure of $1,800 is for EVs with 100kWh batteries such as the Tesla Model X).

Whichever way you look at it, the financial benefits of upgrading an EV and using your solar to charge it are excellent.

It’s also startlingly clear that the value of your solar electricity is so much greater if you use it to reduce your motoring costs rather than exporting it to the grid which pays peanuts (around 6-7 cents per kilowatt hour).

One thing for sure, we’re all going to get a lot more savvy calculating the value we can get from every precious kilowatt hour of electricity produced by our solar panels systems!

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Getting the right solar to power your EV

Get in touch if you’d like the best solar power system to charge your EV.  We have a range of solar panels systems and batteries that can meet the needs of all homeowners, no matter whether you want to:

 

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