amounting to 1 kWh per day, then the power required to make his food is
about 9 kWh per day.
Shadowfax the horse weighs about 400 kg and consumes 17 kWh per
Whether this is true depends on your diet. It’s certainly possible to find
food whose fossil-fuel energy footprint is bigger than the energy delivered
to the human. A bag of crisps, for example, has an embodied energy of
1.4 kWh of fossil fuel per kWh of chemical energy eaten. The embodied
energy of meat is higher. According to a study from the University of
Exeter, the typical diet has an embodied energy of roughly 6 kWh per kWh
eaten. To figure out whether driving a car or walking uses less energy, we
need to know the transport efficiency of each mode. For the typical car
of Chapter 3, the energy cost was 80 kWh per 100 km. Walking uses a net
energy of 3.6 kWh per 100 km – 22 times less. So if you live entirely on
food whose footprint is greater than 22 kWh per kWh then, yes, the energy
cost of getting you from A to B in a fossil-fuel-powered vehicle is less than
if you go under your own steam. But if you have a typical diet (6 kWh per
kWh) then “it’s better to drive than to walk” is a myth. Walking uses one
quarter as much energy.
76A typical dairy cow produces 16 litres of milk per day. There are 2.3 million
dairy cows in the UK, each producing around 5900 litres per year. Half of
all milk produced by cows is sold as liquid milk. www.ukagriculture.com,
77It takes about 1000 days of cow-time to create a steak. 33 months from
conception to slaughterhouse: 9 months’ gestation and 24 months’ rearing.
–Chicken. A full-grown (20-week old) layer weighs 1.5 or 1.6 kg. Its feed has
an energy content of 2850 kcal per kg, which is 3.3 kWh per kg, and its feed
consumption rises to 340 g per week when 6 weeks old, and to 500 g per
week when aged 20 weeks. Once laying, the typical feed required is 110 g
Meat chickens’ feed has an energy content of 3.7 kWh per kg. Energy con-
sumption is 400–450 kcal per day per hen (0.5 kWh/d per hen), with 2 kg
being a typical body weight. A meat chicken weighing 2.95 kg consumes
a total of 5.32 kg of feed [ ]. So the embodied energy of a meat
chicken is about 6.7 kWh per kg of animal, or 10 kWh per kg of eaten meat.