July 30, 2019
Sizing Solar For Your Electric Ute

Having grown up in a car loving household, before falling out of love with cars when I learned about climate change, I am letting myself fall in love again, with the idea of an electric ute. Why? They say a picture tells a thousand words.

Rivian Electric ute

Zero emission driving. Built in electric cooktop and work bench. I’ll bet you when these things hit the market, it will include a bar fridge too. Hmmm, cold carbon neutral beer.

Ok, enough of that. Why are we here again? Oh yeah, solar powered electric Utes.

The Rivian is a beast of a thing. They are saying it will come with a 135kWh or 180kWh battery back inside. See rivian specifications here - https://products.rivian.com

To put things in perspective, a typical Australian house might use about 15-20kWh per day. A frugal, efficient new home could use about 5-7.5kWh a day. So you are looking at a car that can run your home not just for a day or two, but potentially a week or longer!

How do you size solar for a beast like that? Here are some hints:

  • A solar system produces three times more energy in summer than winter
  • For each kW of solar you have installed, you might generate:
  • 6kWh in a summers day
  • 4kWh on a spring or autumn day
  • 2kWh on a winters day.
On average, you might produce about 4kWh a day from 1kW solar - you can see how it varies across Australia using our simple solar calculator.

Most of that solar production is going to occur between about 9am-3pm in summer, or a more narrow band of time in winter, say 10am - 2pm. This variation occurs because of where the sun rises and sets season to season, and how quickly it rises and falls.

PV yield

So, here is the crazy thing. If you wanted to charge your Rivian Ute with rooftop solar in summer, and you had the full 180kWh battery back, you are going to need something like 30kW of solar on your roof! That would need more than 240sqm of roofspace to install ?!?

Luckily for you, the trend is towards EV charging stations in commercial zones, like shopping centre’s, or on the side of the freeway. So you probably won’t be charging at home much. It’s also unlikely you would need, or want to do a full charge at home so quickly.

Another way to think about your electric ute being solar powered, might be to generate as much solar energy at home, as your car uses each year - carbon neutral over the course of the year so to speak.

In that case, you would need to look at how many kilometres you would travel in a year, and convert that back to a solar system size. Here is the maths.

  • Km travelled per year - let’s call it 15,000km
  • Average kWh used by the electric ute, per 100km. Likely to be around 20kWh, or put another way, you travel 5km for every kWh of electricity in your electric ute
  • Divide 15,000km by 5km, to get total kWh used… 3,000kWh!
  • Now, an average solar system might produce 4kWh, per kW, per day, or 1460kWh per annum. Let’s call it an even 1500kWh, per kW.
  • So, how much solar do you need, to make 3000kWh per annum? A grand total of 2kW, or 2.5kW to be sure - much more doable than 30kW :)
Thinking about buying an electric Ute? So are we. Unfortunately we will be waiting a little while longer, but in the mean time we can sort out the solar bit, right? Just contact us if you get stuck, or need help thinking through your electric ute hopes and dreams.