Geekspeak: Why Life + Mathematics = Happiness. Graham Tattersall
A few more examples are in the table, starting with the least powerful and working upwards. The cost of the energy delivered by any of these machines is phenomenally low. Imagine that someone offered to pay you to climb onto a treadmill to generate power to boil a kettle for a pot of tea. How much money would you expect to receive?
Most kettles are 3 kW, which is equivalent to 40 slaves. It will take about one and a half minutes to boil with that power input. With only you on the treadmill it’s going to take 40 times as long. You will have to tread the mill for 1 hour to boil the water to make the tea.
If you get paid the current minimum legal wage, you’ll get £5.35 when the kettle boils. Compare that with what you’d pay for electricity generated by fossil fuel or nuclear power – about 10 pence for each thousand watts for each hour. The kettle will use 3 × 1.5/60 = 0.075 kilowatt-hours, costing you about 0.75 pence. So human power, even at its cheapest, is about 700 times as expensive as using fossil fuel.
Even worse, after an hour on the treadmill you will need a change of clothes: you’re going to need the washing machine. That means more work on the wheel. There is no escape.
Domestic washing machines have a motor with a power of up to 250 W, about one-third of a horsepower, which is more than twice the power that you could generate, even if you rigged the washing machine to some form of treadmill or pedalling system.
A typical wash cycle can take over an hour, and the motor’s energy consumption will be about 0.3 kilowatt-hours, costing you just 3 pence. More significant is the electricity used to heat the water in the machine. Getting the water temperature up to 50 or 60 degrees Celsius will use over 1 kWh of electricity – three times the amount used for turning the drum.
Climb back on your treadmill again: you’ll be there for twelve hours to heat the water to wash your clothes. And then you’re going to need another change of clothes…
SPEAK GEEK
MORE THAN 60% OF THE ENERGY FROM BURNING PETROL IN YOUR CAR IS WASTED.
There is an unassailable limit to the proportion of the heat energy that can be converted into mechanical power by any kind of engine. The unconverted energy is then dissipated: in the case of a car, out through the radiator and in the hot gases from the exhaust pipe.
To figure out that wasted energy, you take the temperature, T1, of the hot gases made by burning the fuel and subtract the temperature, T2, of the exhaust gases leaving the machine. Then divide this difference by 273+T1 (don’t ask – too geeky). Multiply that by 100 to get the percentage of the energy that could be converted to mechanical power. The wasted energy is the difference between 100% and the number you just calculated. As a formula, it looks like this:
For a car engine, T1 is the temperature of gases in the cylinder just after it has fired, and T2 is the temperature of the same gases after they have forced the piston down and are pushed into the exhaust pipe. The formula will give you a wastage figure of 60–70%; the same limit applies to the turbines in coal, gas and nuclear power stations. The clouds you see billowing out of the big towers at power stations are not smoke: they are formed from hot water vapour carrying away the percentage of the fuel’s energy that is wasted as heat.
SAFE AS HOUSES
How heavy is your house?
Nowadays we all want to live in our own space. Children leave home in their late teens and want a place to live; newly-weds don’t expect to camp with their in-laws; successful people want houses with offices, double garages and kitchens the size of a canteen.
Dealing with these changing demands requires new houses, and making the materials for building them takes a lot of energy. Oft-cited examples of energy profligacy –flying from London to Birmingham, leaving your TV on standby – pale by comparison.
There is a simple reason for this: building materials such as metal and bricks and concrete that are preformed into a useful shape are normally processed using heat. Heat means energy, energy usually means burning something which is often carbon based, and that means CO2 emission.
Take concrete. There’s probably tonnes of it under you as you read this book. The key ingredient of modern concrete is cement, a processed form of limestone and ash. Mix it up with some water, sand and stones, pour into a hole in the ground, and wait a few days. The slurry changes into a solid of enormous compressive strength that will support a tower block or a motorway bridge.
It sounds benign. But note that word ‘processed’ preceding ‘limestone’. The limestone has to be heated in a furnace at the cement factory to change it into a substance that will combine with water to form solid concrete. The furnace is fired by a fossil fuel, usually gas or coke, and releases CO2. Worse still, heating causes a chemical change in the limestone which releases even more CO2 from the stone itself.
Manufacturing a tonne of cement pumps about three-quarters of a tonne of CO2 into the atmosphere. That’s the
amount of CO2 produced by burning 204 kg of carbon. If you had to go and buy the carbon as sacks of coal from your local shop, they would fill all the seats in your car, leaving only room for you to sit in the driver’s seat.
The story is similar for bricks. Brick is made from clay which is fired in a furnace to make it strong and hard. Lots of energy goes into the furnace to get a usable building material, although with bricks there is fortunately no release of CO2 from the clay itself.
Lightweight blocks are better. They’re often made by taking the ash left over from burning coal at power stations and mixing