Crude oil is a fantastically useful energy source, and has become enmeshed in our daily lives. It’s used to make petrol, plastics, and asphalt. Oil products are used in almost all motor vehicles today, but that wasn’t always the case:
The electric motor predates the internal combustion engine, and many early motor vehicles ran on electricity rather than gasoline. However, oil-based fuels had a number of advantages over electricity. The International Energy Agency points out that these fuels gave much more energy per unit of volume or mass than batteries, and were easy to handle, transport and store. These advantages, combined with the fragmented nature of electricity networks at the time, led to oil-based fuels becoming the dominant source of transport energy.
So, crude oil has several advantages over electricity, and many other fuels besides:
- High energy per unit of volume/ weight (see below)
- Easy to handle, transport and store (storing electricity is tough)
- Low infrastructure requirements
That first bullet point is still a major advantage for oil-based fuels, as per the table below which shows energy content (megajoules, MJ) per kilogram or per litre:
Sources: MBIE, Wikipedia
As you can imagine, when talking about transport, it’s important that the fuel isn’t too heavy and doesn’t take up too much space. Petrol and other oil-based fuels are very well suited to this. Gas, coal and wood don’t make the grade – you’d need to hunt further to find some MJ/litre figures for them (and they’ll vary depending on a number of factors), but they certainly don’t compare to petrol. Ethanol, which is the main biofuel being produced today, has much lower energy content on both measures.
The values for batteries, at the bottom of that table, show that we’ve still got a way to go before electric vehicles can measure up to conventional ones. For the time being, their batteries can weigh hundreds of kilograms and take up plenty of precious interior space.
The comparison with batteries brings me to another advantage of oil: it’s relatively cheap, given all the things it can do. It’s pricier than wood and coal, of course, which are abundant worldwide and have less inherent value. But as a means of energy storage, it’s much cheaper than the current generation of batteries in electric cars.
I’ve looked at oil prices over time here. The rosy picture of low prices through most of the 20th century came to an abrupt end in the 1970s, when OPEC formed and the oil shocks began. Which brings me to the first major disadvantage of oil, summarised nicely in the following quote:
“Oil prices have been highly volatile [since 1970], and seem likely to stay that way… the oil market as it is structured today seems inherently prone to further disruption”
So, oil prices can swing wildly, as they did in the 70s and again since 2000. We’re seeing this again now, with oil prices falling dramatically in the last few months, along with many other commodities.
The second big disadvantage started to become clear by the 1990s, as scientists grew increasingly confident that man-made emissions of CO2 – mainly from burning fossil fuels such as oil – were contributing to global warming.
Overall, oil has played a massive role in the last 100 years of human history. Today, oil production has essentially plateaued (or begun to decline if “non-conventional” sources are excluded), with demand also on the wane in developed countries like New Zealand, versus rising demand in the developing world.
Oil is still a critical part of our economy, though, and likely to remain so for the foreseeable future. Its many advantages and uses mean that we’ll still need it for many years to come, although there are plenty of things we could do to try and reduce our dependence on it – indeed, things we should do given its disadvantages. But those can wait for other posts.
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I’ve been quite amused as we try to name the “age” we live in – the jet age, the space age, the information age – when it quite clearly has been the oil age (or fossil fuel age if we count Victorian coal/steam tech) the whole time.
To put the energy in perspective petrol is around 44MJ/kg, mince and cheese pies are around 11MJ/kg (based on a 170g Big Ben pie having 1837kj)
We even have an engine that can run on pies, too. Unfortunately it tends to require other sources of energy in order to maintain optimum output.
I particularly like emphasis that coal, gas, wood, oil, hydrogen fuel cells, lithium batteries are all forms of energy storage, with oil being very dense energy storage that is very easily accessible. Unlike nuclear which has some problems with accessing the energy easily. If you go back to the roots, most are just storing solar energy in different ways. Even wind and hydro power are at least derived from solar energy.
Oil, NG and coal have all been in the ground a very long time and take little effort from us to create it, because they are already there. We are only now seeing the consequences of using up those non-renewable resources.
Then compare with hydrogen and electric batteries where lots of effort is required to create, transfer, store the energy in a useful form. Moving to renewable electricity and bio fuels are probably the main long term options for NZ.
The figure for natural gas in your table is for gas at 1 atmosphere pressure, which isn’t really relevant to vehicles (unless the fuel tank is a balloon). A real CNG tank might compress the gas to 200-250 atmospheres, giving it a proportionately higher volumetric energy density. Energy per unit mass is comparable to oil, somewhere around 49 MJ/kg, depending a bit on which gas field it came from. (Source: Wikipedia “natural gas” & “compressed natural gas”).
Good spotting, thanks Geoff; I hadn’t really spent too long on that table. It should really have had compressed natural gas in there instead. CNG is still well below oil in the energy per litre stakes, though, as your figures suggest.
But internal combustion engines are at best around 30% efficient so the difference is not quite as great as shown here
Oil is too valuable a resource to be burning it indiscriminately as a transport fuel.
One other factor to consider is that oil (especially for transportation) has already consumed a lot of energy before it gets to the petrol tank. There is the power used to extract the raw product, then to refine it and then to transport it to the petrol station. Although electricity doesn’t get magically created from nothing in many instances the energy used/lost with its creation and transport to user is considerably less.
Remember also that when the energy in batteries is used the battery is not consumed and can be re-charged and at end-of-life recycled, while oil is consumed and generally its byproducts of consumption are no longer useful.