Take one barrel of oil…

Electrification is the future if the world’s energy use is to be radically ‘decarbonised’ as the IPCC says is necessary. The somewhat contentious Paris accord is the latest stab at a concerted approach to this, albeit without the involvement of the USA and with a number of other countries – notably Turkey – apparently wavering in their support.

Debating the extent of human influence on climate is, unfortunately futile at present; this is one issue where there is precious little common ground, despite the best efforts of some people. But what we do still need to think long and hard about is how this dramatic change might take place and what its implications are for our future energy security and prosperity.

Oil is convenient shorthand for the fossil fuels on which modern societies still depend. Together, oil, coal and gas provide 85% of global energy needs, with oil contributing about a third of the total and projected to remain top of the list even as the domination by fossil fuels declines gradually in coming years.

In 2016, the world consumed a little over 13 billion tonnes of oil equivalent of energy (the standard comparative metric; figures from the BP Statistical Review of World Energy). Of this, over 11 btoe was fossil fuels. This is a staggering amount, over one and a half tonnes for every person on Earth.

For historical reasons, oil production and prices are quoted in barrels, equivalent to 42 US gallons or about 159 litres. A tonne of oil is 7.33 barrels. This brings total consumption of oil, coal and gas to 82 billion barrels annually. Currently, a large amount of the oil itself is used for motorised transport of various forms, while the gas and coal go largely to provide heat and electricity.

The most versatile fuel, and the simplest to consider, is gas. It can be used with minimal post-treatment after extraction and can drive turbines to generate electricity, be burnt in boilers to warm homes and offices or on hobs to cook food and can also be used directly in conventional petrol engines. For the sake of argument, let’s think what the implications are for using gas in various ways, but for easy comparison I’ll use the unit of a barrel of oil equivalent.

In energy terms, a boe is 1.7MWh. Using that directly to fuel a car engine, about 30% of the total energy goes to move the vehicle, with most of the rest being lost as heat (efficiency is very difficult to put a single figure on because it depends on driving conditions, length of journey, speed etc, but this is a good rule of thumb). This sounds incredibly inefficient, but is actually a big improvement even on engines of a decade or two ago.

A better assessment would be to put this in the context of how far a unit of energy would take us. Again, this is a very difficult comparison to make with any accuracy, but figures from the USA (Alternative Fuels Data Center) are for a unit of fuel (the ‘gasoline gallon equivalent’) a car delivers nearly 40 passenger miles, surprisingly close to the 50+ achievable by planes or the 55 by intercity rail, particularly considering that load factors on planes and trains are much higher than for the average car journey. Although they may use road space quite poorly, it turns out that cars are quite an efficient means of transport.

But the really interesting comparison is how that same amount of gas could be used to power an electric car. Burning the fuel in a modern Combined Cycle Gas Turbine, efficiencies of around 55% can be reached. So, in round terms, 55% of the gas will generate useful energy in the form of electricity. Getting that to the consumer will incur transmission losses, which will vary with distance, but a 10% loss is towards the lower end of the range. The result so far is to deliver 50% of the energy from a boe of gas to the consumer as electricity.

To drive an electric car, that electricity must be used to charge a battery. Charging and discharging are not 100% efficient processes, as we can tell when batteries warm up. Let’s conservatively assume a further 10% loss. We are now down to 45%. Electric motors run at up to 75% efficiency. Let’s assume that, even though in practice it is likely to be lower than that for normal driving. The energy extracted from the gas now falls to about 33%, pretty much the same as an internal combustion engine.

So, in round terms, for an all-electric fleet, we would need to use all the oil used to power cars at present and burn it (or its equivalent) in power stations to provide electricity. Total energy demand would be very similar or, in practice, somewhat higher as I’ve assumed quite generous efficiency factors.  However, the situation is a bit different for home heating.

Most homes that are connected to a mains gas supply have gas central heating. Modern condenser gas boilers are about 90% efficient, so nearly all of the energy in the gas is available for useful heating. What happens beyond that, of course, depends on how well a house is insulated and the temperature at which the thermostat is set. Given this very high efficiency, converting to centrally-generated electricity will inevitably mean an increase in overall energy demand.

As we saw above, burning gas to generate electricity is about 50% efficient at delivering energy to consumers. If houses are converted to electric heating, there would be very little further drop in efficiency. Heat is what all other forms of energy ultimately degrade to, so it’s just a case of making sure that heat is generated in the right place. Converting from gas to electric heating would roughly double energy use in this sector.

This back-of-an-envelope estimate shows that energy demand would increase if there is a wholesale move to electrification. But, although that isn’t an inconsiderable challenge, it’s not as simple as that. To have any impact on the decarbonisation agenda, this electricity itself has to be low-carbon. The renewables lobby would point to the falling generation costs of wind and solar, without addressing the continuity of supply issue, but storage technology is simply inadequate to cope with this.

Burning more gas or coal would need carbon capture and storage, which never seems likely to be deployable on a useful scale. Which brings us back to the currently unfashionable topic of nuclear energy. In the UK, the Hinkley Point C fiasco rumbles on but, if it is successfully commissioned, it will be a much more valuable national asset than the hundreds of acres of wind farms that would be its nominal equivalent.

The big problem is how to facilitate a global revival in nuclear construction, as well as pursuing promising options such as Small Modular Reactors and thorium reactors. Until we can do that, fossil fuels will continue to dominate. Electrification coupled with low emissions inevitably means nuclear.

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This entry was posted in Climate change, Energy, Newsletter, Nuclear energy, Transport. Bookmark the permalink.

One Response to Take one barrel of oil…

  1. Derek says:

    The facts above need to be given to the government quickly. Those responsible for implementing the Climate Change Act seem to be under the delusion that all this decarbonisation is simple and that it will make us all better off too. Of course they are only talking about doing it. By the time it actually has to be done they will have retired.

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