Future of transport: Why EV battery mass-compounding matters
Image: Viritech Jovian™ HGV
What is EV Battery Mass-Compounding?
For heavy vehicles, the biggest problem with battery power is so-called “mass compounding”. This refers to the fact that, as batteries get bigger and heavier, more of the battery’s energy is used simply to move the vehicle’s additional weight due to the battery.
While any source of energy has a degree of mass compounding, it is too small to matter for most liquid or gaseous fuels. For example, 50 litres of petrol gives a typical range of over 350 miles and weighs 37kg, while the amount of petrol used to move that extra 37kg is negligible.
However, a 50 KWH battery pack gives a typical range of 200 miles and weighs around 350kg, which results in a significant amount of energy being used just to move that additional 350kg. As the vehicle gets bigger, the problem gets steadily worse: for an articulated truck, the additional weight of the batteries would be 4500kg – heavier than an adult male hippo.
Battery-only solutions become too heavy to be practical
Lithium batteries are ideal for powering a mobile phone, your garden hedge trimmer and cars of limited size used for short duty cycles. But when the power requirement rises, a longer duty cycle is required, refuelling time is important, or the weight of the thing that is being powered is critical, battery-only solutions quickly become too heavy to be practical.
Let’s take the extreme example of an A320 Airbus. At a recent conference sponsored by AVL List, the issue of mass-compounding was highlighted by demonstrating that,
An A320 powered with lithium batteries would only have the range to fly between the German cities of Stuttgart and Frankfurt
If powered with kerosene, it could fly from Stuttgart to Nairobi in Kenya
If powered with just 18-tonnes of liquid hydrogen, it could fly from Stuttgart to Melbourne in Australia
“As power requirements rise, the weight of the battery becomes part of the problem, and it is an issue that stems from the substantially different energy density (ratio of energy to eight) of lithium batteries, diesel/petrol and hydrogen.”
Why is the range of hydrogen so much better?
Going back to our earlier example of 50 litres of petrol weighing 37kg, the equivalent weight of hydrogen to give the same range would be just 10kg.
This example dramatically illustrates the superior energy density of hydrogen (the lightest, most prolific element in the Universe) over batteries and fossil fuels. And if you then add in the superiority of hydrogen in terms of sustainability and pollution, it quickly becomes obvious why a rapidly growing number of key stakeholders (including many Governments around the world) see the necessity to embrace the emerging hydrogen economy.
Yet there are concerns from some quarters about the efficiency of hydrogen fuel cells (famously described by Elon Musk as “fool cells”) and, for now, it is true that the round-trip efficiency (the percentage of energy available as electricity after deducting the cost of making and storing energy) of fuel cells falls well below lithium batteries, but hydrogen technologies have not yet benefitted from the investment that has taken wind, solar and lithium batteries from commercially unviable technologies to mainstream components of our energy infrastructure within 15-years.
The cost, efficiency, and deliverability of all aspects of hydrogen technologies, including making green hydrogen (made from water with an electrolyser powered by renewable energy) and critical components such as fuel cells (for making electricity) and electrolysers (for making hydrogen) are progressing rapidly, and we can expect to see the round-trip efficiency of hydrogen largely bridge the gap to lithium batteries in the next decade.
Of course, battery technology will not stand still, and its proponents point to expected developments in terms of weight and recharging times, with high expectations in the longer term for solid state batteries. But currently, even the most ardent proponents of solid-state batteries are only predicting a weight reduction of 66%, meaning a similarly powered A320 would then be able to fly from Stuttgart to Lyon in France, still leaving it massively short of the capability of kerosene (Nairobi), let alone liquid hydrogen (Melbourne).
There’s a reason NASA chose liquid hydrogen to go to the Moon in the 60’s
As a final thought, imagine the long-term benefits of hydrogen (which when used to make electricity in a fuel cell simply bonds with oxygen to make water, ready to be used again), which long after humanity has drilled and mined for every useful material beneath the earth’s crust, will still make up 75% of all matter in the Universe. Hydrogen is nature’s natural battery, available to be used over and over again. There’s a reason NASA chose liquid hydrogen to go to the Moon in the 60’s and heavy vehicles, equipment, aircraft and marine vessels will choose hydrogen powertrains in the years to come.
We’d love to hear what you think, get in touch info@viritech.co.uk
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