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Good news if you are a fan of Tesla, their Q2 2019 sales numbers absolutely crushed sales forecasts by the many Wall St 'gurus' with an irrational dislike of Tesla (perhaps it is because they have lost so much money shorting Tesla stock) with a record 95,200 cars sold (the Wall St 'gurus' predicted around 86,000 sales). 

This is great news for Tesla as it looks like they will live to fight another quarter and move the world yet closer to sustainable electric transport.   But for a Tesla to be really sustainable it needs to be paired with renewable energy and what better source of renewable energy is there than home grown roof-top solar renewable energy. 

But of course that raises the question just how much roof top solar would I need to power a Tesla (or any other electric car for that matter)?

Of course it does depend on your situation (and how you drive) but let us take the average case.  The average Australian car drives 15,000 km per year or 41 km per day.  A Tesla model 3 (using data from a driver who 'drives like a maniac') uses about 148 Wh/km, so on an average day a Tesla model 3 uses about 6.1 kWh. 

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Let's assume you want to be able to supply 6.1 kWh from a solar system in the middle of winter well, assuming it is not completely overcast or an eclipse, you might get 2 hrs of full production from your solar system meaning you will need a 3 kW array or 3 kW of your larger array reserved for your Tesla model 3 to provide the 6.1 kWh for an average day's driving (of course you will might want to reserve more than this to give you the option of more solar powered driving range).  

This is why it makes sense to 'go big' when installing a solar system; you get economies of scale in terms of the money you pay per watt installed but perhaps more importantly a large solar system (10 kW +) gives you the capacity to power an all electric future (including electric driving), a future that not only saves you money but is better for you and the planet.