How we generate energy is the question that seems to underlie all others when discussing environmental issues, so this article will focus on just discussing some “facts” about energy usage, as best we know them.
In 2017, total U.S. primary energy consumption was equal to about 97.7 quadrillion (97,728,000,000,000,000) Btu. But what does this mean in practice? Well (and apologies for any people still using “Imperial” units, but this article will be in metric) one Joule is enough energy to apply a force of one Newton for a distance of 1m in 1 second. Or it is very roughly the energy released by a small apple falling one meter down from its tree. If the World used 500EJ per year, then it uses 16 * 1012 Joules every second. Since one joule per second is a Watt we can say that the World needs 16 * 1012 Watts of power to operate.
According to an IEA estimate, we humans produced and used 5.67 × 1020 joules of energy in 2013, equivalent to about 18.0 terawatt-hour (TWh)Source – https://www.zmescience.com/ecology/climate/how-much-renewable-energy/
However, what does it mean to “consume” energy? After all the physical law of the conservation of energy states that in an isolated system the total amount of energy remains constant. Well by “consume” we actually mean “convert”: for example we convert the chemical potential energy of fossil fuels into electrical energy (and a lot of waste heat) in a power station. We then distribute that electricity around the country (converting some more of it into heat in the process) and eventually convert that electricity into, for example, the light, sound and heat generated by a TV. (Quite quickly even the light and sound will also become heat as their energy dissipates.)
In each isolated system (say the power station) if we add up all the energy outputs (heat, sound, light and electricity) they will equal the energy inputs (in a power station, fuel oil). However that isn’t to say that all the energy output is particularly useful and much of the energy (such as the heat disappearing out of the chimney) is wasted.
Looking at another system, if you stick one liter of petrol in your car, you will have access to around 35,000 Joules of energy (stored as chemical potential energy of the chemical bonds that make up the petrol) of which only about a fifth (20%) will be converted into the kinetic energy (ie the “movement energy”) of your car, while the rest will be converted into heat (of the engine block, tires and break blocks etc), light (of the break blocks, or of the explosion of combustion), and sound.
Your car may also have converted some of the energy of the drive shaft into electricity and then stored it as chemical potential energy in a battery, and if you were driving up a hill you may have also converted the energy in the petrol to gravitational potential energy. However, in both these circumstances the “cost” of the stored energy is that less of the chemical energy of the fuel will have been converted into kinetic energy.
So if the World needs 5 * 1020 J per year, where does it come from? The following table shows the contributions different energy sources make to overall usage:
Resource – Percentage usage – Energy/year in EJ (10^18 Joules)
- Oil – 37% – 185
- Coal – 25% – 125
- Nuclear – 6% – 30
- Biomass – 4% – 20
- Hydro – 3% – 15
- Solar Heat – 0.5% – 2.5
- Wind – 0.3% – 1.5
- Geothermal – 0.2% – 1
- Biofuels – 0.2% – 1
- Solar Photovoltaic – 0.04% – 0.2
The first three items on the list are fossil fuels, and together with nuclear energy are classified as being “non-renewable” since there is a limited supply of oil, coal, gas and uranium in the Earth’s crust. Estimates of precisely how much energy is stored as these non-renewable sources is speculatively given as something between 300 * 1024 and 400 * 1024 joules of energy. Although this high figure might indicate otherwise, many commentators suggest that oil and gas might only last another 50 years, while we only have 150 years supply of coal and 250 years supply of uranium remaining.
However major caveats should perhaps be added to these figures of fossil fuel and uranium reserves. Oil was stunningly cheap throughout the 1990s despite the fact that even then China’s economy was growing rapidly. Cheap oil means not only that we have more than we need, but also that there is little spare cash to invest in finding new oil fields and bringing them online (hence the World’s reserves may appear lower than they actually are because we don’t have the financial incentive to look for them).
Recent political instability and ongoing global economic growth have done much to limit the availability of oil, driving the price up. But the price signal of increased prices has stimulated new investment in the search for and development of new oil fields and also has made the World’s vast reserves of oil sands (which exceed the World’s reserves of conventional crude oil, but which aren’t traditionally included in estimates of global oil reserves) cost effective to develop driving down the price of energy as supply improves. Furthermore, since fast breeder nuclear reactors generate more nuclear fuel as part of their waste, to a degree nuclear power might even be renewable.
The remaining items on the list are renewable fuels most of which gain their energy more or less directly from the Sun (which provides the earth with 4.57 * 1024 Joules of energy per year, of which 2.34 * 1024 actually makes it to the planet surface). This is a phenomenal amount of energy, and redirecting just 0.02% would be enough to meet all our present energy requirements, while having the added benefit of emitting no carbon dioxide. However all the renewables bring their own particular problems including the fact that they are generally accessible for only a limited amount of time: solar power isn’t available at night (also the technology to convert sunlight into electricity in the day is expensive), while wind power is less available at night and during summer, tidal power relies on the twice daily tides, and wave power is also limited during the summer months.
Although it isn’t a point that is often dwelled upon in great detail, electrical energy is also very difficult to store on a large scale (which is another factor in favor of fossil fuels, which are natural stores of energy). National grids tend to store energy by pumping water to high dams and then releasing it when they need the energy, but other than that they are limited to turning power stations on and off. The large scale use of batteries to store megawatts of electricity is not particularly practical. Much has been said of the use of hydrogen as an energy source, however since the hydrogen would probably be extracted from water, using electricity, it would be fairer to say that hydrogen is primarily a mechanism for storing electricity. Having isolated the hydrogen using electricity, the stored hydrogen is then used in a fuel cell to generate a smaller amount of electrical energy.
As outlined at the beginning, this article is only designed to be an accelerated and sweeping overview of the manner and extent of the World’s energy consumption, which I hope remained reasonably realistic about the merits of the different technologies. The key point to take away is that the World requires truly massive amounts of energy, and that fossil fuels, for all their faults, are used because they are effective. Most people would agree that CO2 emissions make the long-term use of fossil fuels undesirable, however when promoting alternative and renewable energy sources we shouldn’t be unrealistic about the size of the problem of making these viable at an industrial level.