The initial step in tackling the formidable challenge of moving away from fossil fuels is to calculate precisely the sheer scale of the problem: determining the total energy we consume. The current sustainable energy discourse is often mired in emotion and “twaddle,” obscuring the fundamental numerical challenge ahead. To create viable strategies rather than “pipedreams,” we must quantify our energy use—the “red stack”—and compare it directly against potential sustainable production—the “green stack.”
For clarity, these calculations are expressed using a precise, standardized unit: kilowatt-hours per day per person (kWh/d/p). This personal unit scales directly to national power figures (1 kWh/d per person nationally equals 2.5 GW) and allows for transportable comparisons worldwide.
Total Energy Consumption: 125 kWh/d per person in affluent societies like Britain
The goal of this analysis is to quantify where these 125 units of energy are being consumed, starting with the most significant categories: transport, heating, and electricity.
The Core Drivers of Consumption: Transport
Transportation, encompassing cars, planes, and freight, constitutes a massive portion of affluent society’s energy demand.
The Typical Car Driver: 40 kWh per Day
For an accurate assessment, consumption figures are estimated based on the lifestyle of a “typical moderately-affluent person” who drives, rather than depersonalizing the answer by using a national average that mixes drivers and non-drivers.
The calculation for a typical car driver uses simple arithmetic:
$$\text{Energy per day} = \frac{\text{Distance travelled per day}}{\text{Distance per unit of fuel}} \times \text{Energy per unit of fuel}$$
- Distance: A typical daily distance of 50 km (about 30 miles) is assumed.
- Fuel economy: A consumption rate of 33 miles per UK gallon is used, approximately 12 km per litre.
- Energy density: Automobile fuels, being hydrocarbons, have an energy content estimated at 10 kWh per litre.
This calculation yields a consumption estimate of 40 kWh/d per person for a typical car driver. This estimate focuses on the energy burned by the engine itself and initially excludes the significant additional energy required to manufacture the car or produce the fuel.
The Physics of Car Movement
To effectively reduce this 40 kWh/d consumption, it’s essential to understand where this energy goes. In a standard fossil-fuel car, 75% of fuel energy is wasted as heat, meaning only about 25% goes toward useful motion.
The remaining energy is consumed primarily in two ways, depending on the driving scenario:
1. Short-distance/city driving (braking-dominated): In short-distance travel with frequent stops, most energy goes into accelerating the vehicle (kinetic energy), which is then wasted as heat when braking.
- This braking dominance occurs if the distance between stops is less than about 750 meters.
- Key strategies: reduce the mass of the car, drive more slowly, and utilize regenerative braking (which can salvage roughly 50% of energy during braking).
2. Long-distance/motorway driving (drag-dominated): When traveling long distances at a steady, high speed, most energy is spent overcoming air resistance (drag).
- The total power dissipated scales roughly as the cube of the speed ($P \propto v^3$). Driving half as fast uses four times less total energy to cover the same distance.
- Key strategies: reduce cross-sectional area and drag coefficient, and crucially, drive slower. In drag-dominated scenarios, the weight of the car matters much less.
The Cost of Flying: 30 kWh per Day
A single intercontinental round trip per year (such as London to Cape Town, roughly 10,000 km) has an average energy cost of 30 kWh/d per person. This immense figure equals leaving a 1 kW electric fire running non-stop, 24 hours a day, all year.
For a silver frequent flyer status, the energy cost rises to 60 kWh/d per person.
The Energy of Shelter: Heating and Cooling
Heating buildings is the second major pillar of consumption, often supplied by natural gas in the UK.
Quantifying Heating Demand: Approximately 40 kWh per Day
The total energy spent on space heating, water heating, and workplace heating is estimated at approximately 45 kWh/d per person, placing it comparable to car driving in consumption. Cooling, in contrast, is small in the UK, estimated at just 1 kWh/d per person.
The power required to heat a building is constantly lost through two main routes:
- Conduction: Heat passing through walls, windows, roof, and floor
- Ventilation: Warm air escaping and being replaced by cold outside air
The Impact of Lifestyle on Heat Demand
The amount of heat required depends heavily on the internal temperature set by the thermostat. This demand can be visualized using degree-days (the total area between the external temperature and the desired internal temperature over time).
- Turning the winter thermostat down from 20°C to 17°C reduces heating demand by 30%.
- Turning it down further to 15°C results in a 45% reduction in demand.
This highlights that changes in comfort levels—such as wearing a woolly jumper—can result in major energy savings (estimated at 20 kWh/d per person).
The Ubiquitous Red Stack: Electrical and Embodied Energy
While transport and heating dominate, the remainder of consumption includes direct electricity use, food, and the massive hidden cost of manufacturing and imports.
Direct Electricity Use
The delivered electricity consumed for lighting, gadgets, and appliances amounts to 18 kWh/d per person.
The myth of the charger: Public concern often focuses emotionally on “vampire power” devices like mobile phone chargers left plugged in. However, an older, power-guzzling charger (3 W) uses only 0.07 kWh per day. The energy saved by switching off this charger for a year equals the energy in a single hot bath. Focusing on this small action should not lead people to believe they have “done their bit.”
The real electrical sinks: In the UK, average consumption for a fridge-freezer is about 18 W (approximately 0.4 kWh/d). Much larger consumers include computer servers and associated infrastructure.
Efficiency gains: Replacing incandescent bulbs with LEDs or fluorescent bulbs is listed as an easy action yielding a worthwhile saving of 4 kWh/d.
The Energy Cost of Food and Farming
The minimum chemical energy content a moderately active person consumes is about 3 kWh per day (2600 calories). However, the total energy footprint of our diet is far larger due to farming, processing, and transportation.
Meat vs. walking: A common myth suggests that driving a fossil-fuel car uses less energy than walking, due to the high energy footprint of food. Walking uses a net energy of 3.6 kWh per 100 km, 22 times less than a typical car (80 kWh per 100 km). Walking is four times more energy-efficient than driving.
The Hidden Cost of Stuff and Imports (Embodied Energy)
“Stuff”—everything manufactured, bought, and ultimately disposed of—is a major energy sink. The energy “embodied” in imported goods can be immense, potentially being the “biggest fish of all.”
Examples of embodied energy:
- Paper has an embodied energy of 10 kWh per kg
- A person’s typical daily consumption of junk mail and newspapers (200 g/day) embodies about 2 kWh per day
- A single drinks can embodies approximately 3 kWh
The Total Red Stack and Global Responsibility
Adding up the major categories—transport, heating, and the delivered electricity for domestic consumption—provides the foundation for the total energy input to Britain of 125 kWh/d per person. This is the massive consumption figure that sustainable production must match.
This high consumption is typical of affluent nations. The UK, being a “fairly typical high-GDP country,” serves as a suitable case study for achieving sustainable energy while maintaining a high quality of life. Historically, however, the UK’s energy debt is enormous: assessing cumulative CO₂ emissions per capita between 1880 and 2004, Britain ranks second only to the USA.
Globally, per-capita greenhouse gas emissions show stark disparity: Europe’s average emissions are twice the world average, and North America’s are four times the world average. To avoid catastrophic climate change, global emissions must fall drastically—perhaps by 70% or 85% by 2050. If the world adopts a system of “contraction and convergence” toward equal per-capita emissions, Britain must aim for cuts greater than 85%.
This monumental reduction necessitates identifying solutions that are demonstrably big. Focusing on peripheral, emotional appeals like changing ship paint or unplugging phone chargers distracts from the numerical truth that replacing fossil fuels requires radical action across transport, heating, and electricity generation. The next posts will quantify the maximum possible output of the “green stack.”