Up to a point, higher energy consumption brings higher quality of life: lower infant mortality, longer life expectancy, higher literacy, etc. In communities where the main sources of energy for work are people and livestock, there isn’t much energy available, and what there is must be used in survival activities that produce a bit more energy than they consume, like subsistence farming. Quality of life in these communities is correspondingly low.
In the UK, energy is cheap and readily available, particularly in the forms of mains natural gas and grid electricity, and quality of life is generally high. We spend so little on the large amounts of energy we consume that we take cheap plentiful energy for granted. In fact, the electrical energy equivalent to a person working all day can be bought for less than 10 pence. Here’s how:
A man doing hard physical work will burn about 3800 calories a day. Human muscles are at most 27% efficient, so only about a quarter of the energy used gets transferred to useful work and the rest is lost as heat. That’s just over 1000 calories (or 1.2 kWh) of useful work from a man working all day.
If you consider per capita UK energy consumption in terms of its equivalent in human labour, the average UK resident has 87 people working for them. That’s the equivalent of 87 men working 7 days a week 365 days a year on each person’s behalf. And although the concept is a bit abstract, the implication is not: energy is worth much more than we pay for it. And deprived of my energy slaves, my quality of life would revert to that of a peasant. Here’s what our energy slaves are doing for us in the UK:
Recreation:
16 men. Includes energy for leisure activities plus production of goods and services.
Heating: 
12.2 men. Self explanatory
Food: 
11.4 men. Energy for cooking, eating and drinking, including food miles and production of raw materials
Household:
11.2 men. This includes non-heating energy consumed in the home by appliances, furnishings and from the construction of the building itself
Hygiene:
11 men. Includes energy for the NHS and from individuals bathing and washing
Clothing:
8.2 men. Energy for producing, transporting and cleaning clothes and shoes.
Commuting: 
6.6 men. Travelling to and from the workplace on both public and private transport including flights for work
Aviation:
5.6 men. Flights other than for work
Education:
4 men. This is energy relating to schools, educational travel, books and newspapers
Telecommunications:
0.8 men. All sources of energy for communications including computing
When you’ve got a team of 87 people working for you around the clock, 16 of them who only want you to enjoy yourself, is it any wonder your life is so easy? But others have it even easier. In the US, for example, each person has nearly 200 energy slaves working for them. Yep, nearly 200.
Given that energy cannot be created or destroyed, where do these energy slaves come from? Almost all are fossil fuels: solar energy stored in hydrocarbons underground. But my generation will see the end of cheap and plentiful fossil fuels and, because the transition to other energy sources is unlikely to be a smooth one, a sharp drop in the number of energy slaves. The extent of the drop will determine just how big the impact is on our quality of life.
In the interests of thoroughness, here’s how I arrived at the numbers:
The Carbon Trust came up with a new carbon footprint report in December last year which breaks down the average UK resident’s emissions by end use. In the report, they say each UK resident is responsible for just over 11 tonnes of CO2 per year.
To estimate the equivalent in human labour we need kWh, not kgCO2 and we can’t go directly from CO2 to kWh because of the varying carbon intensities of fuels. But we can work out an average carbon intensity weighted by fuel for all energy consumed in the UK using information published by the DTI . You could just use the DTI information directly but it doesn’t break down by end use in the same way as the Carbon Trust information.
With this average carbon intensity figure, which came out at 0.28 kgCO2/kWh, we can work backwards from the Carbon Trust figures for emissions by end use. This ignores the fact that particular uses might use more of one type of fuel; for example heating relies mostly on gas with a carbon intensity of 0.19 kgCO2/kWh.
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