Talk of 'kinetic energy plates' is a total waste of energy

The emissions saved by driving over plates in a car park amount to just one four-thousandth of the energy used by the trip to the supermarket, writes David MacKay

David MacKay
guardian.co.uk, Wednesday 17 June 2009 11.59 BST

I'd like to suggest a 1% rule for news articles about energy-saving gadgets or renewable energy systems. The rule says: "A gizmo may be discussed only if it could lead to energy savings of at least 1%." I suggest this rule not because minnow-sized savings are worthless, but because the public conversation about energy surely deserves to be focussed on bigger fish.
The latest piece of green twaddle that's wasting people's attention is the story about a supermarket car park that has "kinetic road plates" creating "green energy" from the motion of customers' cars.
I'm not saying that these systems don't actually work; perhaps they do save a little bit of energy that would otherwise be wasted in the brakes of the cars arriving in the car park. But my suggestion is that these systems save so little energy, we shouldn't waste newspaper space on such stories. There must be more important things to discuss (assuming we are serious about getting off fossil fuels).
To prove my point, let's compare the energy that might be saved by the "kinetic road plates" with the total energy used by a typical trip to the supermarket. Let's guess that the kinetic road plates extract one fifth of the kinetic energy of the arriving car. For a car weighing one tonne travelling at 20mph when it hits the road plates, the extracted energy comes to 0.002 kilowatt-hours (kWh). Now, the energy used by the car, assuming it is driven three miles to and three miles from the supermarket with a fuel efficiency of 33 miles per gallon, is about 8 kWh. The savings from parking at the green car park thus amount to one four-thousandth of the energy used by the trip to the supermarket.
That's much less than 1%. So this "green energy system" is just eco-bling, creating a delusion of happy progress while distracting people from serious change.
What are some ideas that satisfy the 1% rule? Well, there's lots of examples: a domestic solar hot-water panel will generate roughly 4 kWh a day of hot water, which is roughly 50% of a typical family's hot water consumption, and a bit more than 1% of their total energy footprint. Example two: wind power – a ten-fold increase in Britain's wind turbines would produce on average 4 kWh a day for each person, which is about 4% of our total energy footprint.
So solar panels and wind turbines deserve to be on the public's radar. Of course, solar panels and wind turbines are old news. So let me suggest a new topic of conversation that also satisfies the 1% rule.
When we are planning wind farms, it makes sense to put them up first in the windiest spots, where the hardware will give the biggest return. So let's talk about wind farms in the Falklands.
Mean wind speeds in the British overseas territory of the Falkland Islands are 9-11 metres per second, compared with 6-9 metres per second around the British Isles. 1,250 3MW turbines in the Falklands would probably produce an average power of 2.5GW (or 1kWh a day for every one of the Queen's 60 million subjects). That's roughly 1% of the total energy footprint of the UK.
Are there any problems with this idea? Well, first, as usual, the wind farms "would spoil the view". There's no free lunch. Serious renewable power requires industrial facilities in the countryside; the point of proposing wind farms in the Falklands is to reduce the area of countryside "spoiled". The total area of the Falklands is 4,700 square miles; the area occupied by 1,250 windmills would be about one-twelfth of the Falklands. Sheep could, of course, still safely graze among the turbines.
Second, the average power produced by these windmills would probably exceed the electricity demand of the 3,000 inhabitants of the Falklands, so we'd need to find other ways of using the power. A traditional way of handling the problem of excess electricity is to produce aluminium. Iceland and Norway, for example, produce 1% and 4% of the world's aluminium respectively. The Falklands wind farm sketched above could produce 1.5m tonnes of aluminium a year – 5% of the world's aluminium production. Aluminium is just one example of a storable product; the electricity could be used to make other energy-intensive materials such as magnesium and cement.
A crazy idea? Perhaps. But we do need a plan that adds up.
• David MacKay FRS is a professor in the department of physics at the University of Cambridge. His book, Sustainable Energy - Without the Hot Air, was published in December 2009, and is available free online from withouthotair.com.