I never knew it could be this good! Charging EVs with solar is ridiculously cheap

Charging your EV with your solar is ridiculously, and almost shamefully, cheap!  

Each week I drive our Kia EV9 Earth from Melbourne to Apollo Bay (return 400 kms).  With a 100 kWh battery and a 10kW solar system, it takes about 2-3 days to put in 80 kWh of charge necessary for next return trip and that costs $2.40 (80 kWh by 3 cents feed in tariff forgone), or the price of one and a half litres of petrol.  

The key is to have a home charger, with a ‘solar’ setting – set and forget.  You also need a job like mine (I take the train to work) that allows you to leave your car at home on 2 to 3 sunny days a week. The figure below shows the Enphase graph of generation in blue and consumption in orange.  

You can’t just use the standard power plug because it has a maximum is 10Amps (2.4 kilowatts). You need to make use of up to 7 kW of solar in the middle of the day, so you need a 7 kW home AC charger. Our solar charger (Wallbox) cost $3,000 installed and saves about $700 a year compared to a 10amp trickle charger that cannot take advantage of all the solar.  

The annual savings from not using our diesel Toyota Prado will be about $4,000 a year.  The table below compares the cost from electricity different sources.  

Now take a few minutes to feel good.

• You’re reducing air pollution in the city that kills 3,200 Australians every year.
• You’re doing your bit for the climate.
• You’re using some of the excess solar during the day when it is often curtailed and wasted.
• You can always It is so quiet that you can hear your passengers speak. 

Every day I say- how lucky am I!

Other tips.  

Make sure your tyres are blown up to the vehicle manufacturers recommended levels.  I run mine at 44psi to maximise efficiency.  Fuel efficiency is 15% lower at 25psi than 35psi.  

Make sure there is not too much mud on the car because this reduces fuel efficiency by creating unnecessary drag.  

Comparison of 80 kWh electricity and 40 litres of diesel 

Notes:

Kia EV9 (20kw per 100 km) vs Toyota Prado (10 litres per 100KM). 

Diesel price 191 cents per litre (7 March 2025).  EV energy plan from OVO energy; 8 cents/kWh (midnight to 6AM and free 11AM to 2PM) (accessed 13 April 2025). 

Fast DC charging varies by speed (40-60 cents).  Electricity prices vary by state.   OVO energy flat rate of 20 cents/kWh. 

References

https://flipthefleet.org/2018/optimum-tyre-pressures-and-tyre-types-for-electric-vehicles-one-click-survey-21/