Energy by the numbers
University of Cambridge physicist David MacKay puts power use into perspective.
A lot of our discussions about energy policy involve adjectives. Solar power has big potential. Biofuels don't prevent that much carbon from entering the atmosphere. China and India are consuming huge amounts of oil.Skip to next paragraph
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To University of Cambridge physicist David MacKay, this is just fact-free blathering. After all, how much is "big"? How big is "huge"? Unless we can express these concepts in numbers, we have no basis for comparison.
Mr. MacKay wants to cut through what he describes – in a way that only an eminent British physicist could – as "crazy innumerate codswallop." In his forthcoming book, "Sustainable Energy – Without the Hot Air" – a draft of which can be downloaded here – MacKay shows how to estimate those numbers and convert them into a human-scale unit of measurment: the kilowatt-hour.
One kWh, says MacKay, is roughly the energy consumed by burning a 40-watt lightbulb for an entire day. Burning a gallon of gasoline produces about 40 kWh. Flying 8,800 miles on a fully-loaded 747 uses 12,000 kWh. Taking a bath uses 5 kWh. And so on.
The "typical affluent" Briton, MacKay says, consumes 200 kWh per day. The average American consumes 300 kWh per day.
So now we can start evaluating our plans for alternative energies. For instance, installing about 30 square feet of high-quality photovoltaic panels will get you 4 kWh per day. Drawing your home's power from a deep offshore wind farm could deliver 32 kWh per day. Adding tide farms to the mix would get you another 14 kWh. These are numbers for Great Britain; your mileage will vary depending on where you live.
Adding up all the production and consumption figures, says MacKay, paints a bleak picture. Even if we tolerate wind farms in our back yards and solar facilities bigger than Delaware, there's not quite enough sustainable power within the UK to support a typical British lifestyle, much less a typical American one. Getting there will require some sort of major technological innovation, or the willingness to import sustainable energy from abroad.
McKay singles out those who advocate little changes. "If everyone does a little," he writes, "we'll achieve a little." He sets aside some special vitriol for journalists who harp on "vampire" cell phone chargers that draw power even though there's no phone connected. Unplugging your phone charger for 30 days, says McKay, saves an amount of energy equivalent to not driving your car for 30 seconds. All things being equal, he says, you should unplug your charger, but doing so won't singlehandedly save the climate.