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Perpetually Dreaming?

Ford's E-Transit has a 68 kWh lithium battery for a factory-quoted range of 307 km, or about 240 km in this motorhome conversion application.

The question has been raised about could an e-motorhome be self-sustaining for it’s main power battery. In theory it sounds a little bit like the concept of a perpetual motion machine, but theoretically it is doable. Let's look at the following hypothetical example.

The number of solar panels required to recharge a 68 kWh battery, like the one in Ford's new E-Transit would depend on a few variables, including:

  • Panel Efficiency: This determines how much sunlight is converted into electricity. Most commercial panels currently have an efficiency between 15% to 22%

  • Sunlight Duration: How long the panels receive effective sunlight each day, and varies based on location and time of year

  • Panel Capacity: The power output rating of each panel.

Let's make some assumptions…

  • You're using a 300 W solar panel.

  • You get an average of 5 hours of effective sunlight per day.

  • The efficiency losses (from the inverter, potential shading and other factors) is around 10%, so we'll only get 90% of the theoretical value.

Using the above assumptions:

  • The daily energy production per panel equals 300 W X 5 hours = 1.5 kWh

  • Considering 90% efficiency, that equals 1.5 kWh * 0.9 = 1.35 kWh

  • To charge a 68 kWh battery, the number of panels required = 68 kWh divided by 1.35 kWh per panel = 50.37

So, you'd need about 50 panels, using these assumptions!

In 2017, Dethleffs debuted the e.home, a self-charging motorhome with 31 sqm of ultra-thin solar panels producing 3000 watts to recharge its 228 Ah NiCad battery. Range was claimed at 160 km, with a battery life good for some 250,000 km of charging cycles. It quietly disappeared not too long after release, but shows there is potential when technology improves.

Keep in mind, this is a simplified calculation. In reality, the number of panels you'd need would vary based on many factors, including panel rating and efficiency, local weather conditions, orientation of the panels and any potential shading. Still, it's an interesting thought experiment and no doubt somebody will achieve it some day. Of course, as solar panel and battery technologies continue their rapid advance, the possibility of the elusive “perpetually free travel" moves ever closer and is a tantalising prospect…

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