A Train of Thought

The future of New Zealand’s domestic transport needs should be trains.

Robert McLachlan and Paul Callister, in a 13 February article in the Conversation, make a good case for restoring long distance passenger rail in New Zealand as a way to decrease the emissions of passenger travel and reduce our energy use. 

Decreasing greenhouse gas emissions is a given; rail yields only a small fraction of the emissions per passenger kilometre compared to personal automobile or air travel.  Electrified, rail would do even better.

The case for decreasing our energy use is just as important. 

One of the cold, hard facts of our times is that humanity is losing the ability to use its most abundant, readily available and convenient form of energy – petroleum.  Losing it, by giving it up to prevent run-away climate disruption, or losing it simply by running out of it.  Either way, finding an energy source that will replace it will be difficult and cost us more - cost us more in terms of the energy investment required to produce it in the first place.

Scientists call this Energy Return on Investment or EROI; the ratio of the energy you get out of a fuel or energy collecting device, divided by the energy it takes to find it or build it.  For modern oil production, this ratio is about 20:1.  In other words, it takes the energy equivalent of one barrel of oil to get another 20 barrels of oil. 

Since it requires much less oil to produce new oil, we have been living in in times of surplus energy.

Think of what it would be like if it took one barrel of oil’s worth of energy to find two barrels of oil, or an EROI of 2:1.  We’d be spending half our energy just getting more energy, and that’s not including the energy needed to transport and refine that oil into fuel, nor the energy needed to build the machinery to use that fuel.  There certainly wouldn’t be much energy left to do other things.  

Since the discovery of oil, we’ve grown used to having a large surplus of energy. And, our modern society has put that surplus energy to good use – producing our food, heating our homes and travelling the world – all the good things about modern life.  It is estimated that today’s society requires an overall EROI of at least 14:1; anything less and we start lose things we’ve come to expect.

This all matters because the EROI of new renewable energy is generally less than what we’ve become accustomed to.  Wind power is the best of the bunch, coming in between 10:1 and 30:1, but it is intermittent and needs backup power or some type of energy storage, such as batteries.  This adds cost and energy, bringing the EROI of wind down. The EROI of solar is less, between 4:1 and 7:1 and again needs backup or storage because the sun doesn’t shine all the time. 

What about renewable fuels?  Bio-methane has an EROI of about 3.5:1 and ethanol from corn is 1.6:1; it takes almost as much energy to make ethanol as you get back.  The EROI of green hydrogen is less than 1:1, which means it takes more energy, in the form of electricity, to make it than you get back when you use it. These low EROIs might be worth it, if the fuel has high energy density and is easily transportable, but they leave very little surplus energy for the rest of society. 

The reality is that we will struggle to replace petroleum with energy that has even half the EROI of oil.

You can see where we’re headed.  As we replace fossil fuels with renewable energy, we’ll need to expend much more of our energy budget just to get that energy.  There will be less energy around for other things.  Barring some miracle technology, such as cheap nuclear fusion power (remember the old saying: just 20 years away and always will be), we are headed for a world where energy availability will be much like it was when our grandparents were children.  We need to start planning for that low energy future now.

This is where electric trains come in.  They are the most energy-efficient, low emissions way to move goods and people over land. 
Steel wheels rolling on steel rails are far more efficient than rubber tyres on asphalt roads.  Trains can be electrified without the need for batteries and charging stations, replacing long distance trucking, which is presently struggling to find a low emissions replacement for petroleum fuel.
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So, thinking long term, our best investment for domestic transport will be in upgrading, expanding and electrifying our existing rail system.