Now, I'm no Chris Hoy, but .....
Posted by Stephen Millward, 03 December 2009 10:12:25
It’s my job to find ways to save energy in the home and as my colleagues know I’m a keen cyclist, they often joke; “Why don’t you connect your bike up to a generator? You could power your whole house”.
Or could I? In a good year I cycle around 5000 miles at an average of 15mph, which takes around 333 hours. At 15mph a cyclist on a flat road should develop around 150 watts of energy. So 150 watts over 333 hours would produce roughly 50 kWh per year, which at today’s electricity prices would be around £160. But if I’d sat on a turbo trainer connected to a generator for the same length of time, I would have produced only £5 worth of electricity. Which just goes to show how fantastically efficient the bicycle is in converting human power into forward motion.
This got me thinking; how much food do I consume to produce this energy? A common rule of thumb is 400 Calories for 10 miles of riding, or 200,000 Calories for a 5000 mile year. So a year’s riding needs around 1500 cereal bars at 50p each, costing a whopping £750. So it would be a very expensive means of generating electricity. This just shows how terrible the human body is at converting food energy into power at the pedals. This is actually just as well, for if we were 100% efficient at converting food we’d need to eat 80% less, which would make the café stop far less interesting. We also wouldn’t generate heat when cycling and we’d need to wear masses of clothing to counteract wind chill.
We’re told cycling is great because it doesn’t harm the environment, but how true is this? If we’re riding our bikes instead of driving the car to work each day the reduction in CO2 emissions are significant and there’s no contest. But most of my cycling is purely for the pleasure of riding my bike in the country and I sometimes even drive to different parts of the country in order to do it or even fly to other countries.
So how does cycling for cycling’s sake alone compare with other pastimes such as watching TV? The production and transport of food and drink result in significant CO2 emissions. Those extra 200,000 Calories of food are a 20% increase on what I would otherwise have needed. In the UK the average CO2 footprint of a person is around 10 tonnes per year, of which 500kg is for food and drink. So my 20% increase in food consumption results in an increase of 100kg to my carbon footprint. If I’d spent the year watching TV instead the electricity used would only have increased my carbon footprint by 50kg! This is not the result I expected.
So how many miles do I need to use my bike instead of my car to neutralise this 100kg? For a medium size car the distance is about 420 miles, or just 8% of my annual cycling mileage. If you think this is taking green issues and CO2 emissions a little too far, then I’d agree. However, I predict in 20 years time we’ll be assessing everything we do in terms of C02 emissions as easily as we do so with monetary values today. In the meantime insulate your home, use low energy lamps and enjoy cycling and eating.
Watch out for an interesting programme tonight "Bang goes another theory" 8pm BBC1, explores household energy consumption and explains how many cyclists it would take to power a typical home.