Could the Sahara’s sun save us?

The Sunday Times
June 7, 2009

David MacKay examines the possibilities of Britain importing the clean energy that it needs

Our present lifestyle cannot be sustained on Britain’s own renewable energy resources unless we are prepared to cover huge areas of land and sea with wind turbines, tidal farms or solar cells.
So what are our options if we wish to wean ourselves off fossil fuels? We can balance the energy budget either by reducing demand or by increasing supply, or both.
And these reductions in demand and increases in supply must be big. Don’t be distracted by the myth that “every little helps”. If everyone does a little, we will achieve only a little. We must do a lot.
“But surely,” people say, “if 60m people all do a little, it will add up to a lot?” No. This “if everyone does it” concept is just a way of making something small sound big.

Take power. We all use it. So to achieve a “big difference” in total power consumption almost everyone has to make a “big” difference to their own power consumption.
Demand for power could be reduced in three ways: by reducing our population, changing our lifestyle, or by keeping our lifestyle but reducing its energy intensity through efficiency and technology. My goal is not to pick winners but to present honest, quantitative facts about the options.
Hydrogen-powered vehicles, for one, are a disaster. Most prototypes use more energy than the fossil-fuel vehicle they are designed to replace. The BMW Hydrogen 7 uses 254kWh per 100km while the average fossil car in Britain uses 80kWh per 100km. In contrast, prototype electric vehicles use 10 times less energy: 20kWh per 100km or even 6kWh per 100km. Electric vehicles are far better than hybrid cars. Today’s hybrid cars, which are typically at best about 30% better than fossil-fuel cars, should be viewed as a brief, helpful stepping stone on the way to electric vehicles.
Decentralised combined heat and power (CHP) is another looming mistake. Yes, combined heat and power (that is, putting individual power stations in each building, generating local electricity and heat to keep the buildings warm) can be a slightly more efficient way of using fossil fuels than the standard way but they are only about 7% more efficient. And they use fossil fuels. Isn’t the goal to get off fossil fuels?
The fact is there is a much better way to generate local heat: heat pumps. These are back-to-front refrigerators. Powered by electricity, they pump heat into the building from the outside – either from the air or from the ground.
The best heat pumps, recently developed in Japan, have a coefficient of performance of 4.9. This means that using 1kWh of electricity, the pump delivers 4.9kWh of heat in the form of hot air or hot water.
This is a far more efficient way to use high-grade energy for heating than simply setting fire to high-grade chemicals, which achieves a coefficient of performance of only 0.9. Recent trials of heat pumps in Germany have confirmed that ground-source and air-source heat pumps can deliver hot air and hot water with an average coefficient of performance above 3.0.
Demand is only one side of the equation. We also need to increase supply, which could be done in three ways.
One would be investing in clean-coal technology. Oops. Coal is a fossil fuel. Well, never mind – let’s take a look at this idea. Britain is estimated to have seven billion tonnes of coal left. If we share this between 60m people, we get just over 100 tonnes a head. If we want a 1,000-year solution, this corresponds to 2.5kWh of energy per day per person.
In a power station performing carbon capture and storage, this sustainable approach to UK coal would yield 0.7kWh per day per person. For comparison, Britain’s total energy consumption today is 125kWh per day per person. Our conclusion is clear: clean coal is only a stop-gap.
We could invest in nuclear fission. The average British person consumes about 16kg of fossil fuels per day – 4kg of coal, 4kg of oil, and 8kg of gas.
That means that every single day an amount of fossil fuels with the same weight as 28 pints of milk is extracted from a hole in the ground, transported, processed and burned somewhere on your behalf.
In contrast the amount of natural uranium required to provide the same amount of energy as 16kg of fossil fuels in a standard fission reactor is two grams; and the resulting waste weighs one quarter of a gram. But the fact that the nuclear waste stream is small doesn’t mean that it’s not a problem.
The third option would be to buy, beg or steal renewable energy from other countries – bearing in mind that most will be in the same boat as Britain and will have no renewable energy to spare. If we import renewable energy from other countries to avoid building plants the size of Wales in the UK, someone will have to construct those facilities on their own land.
One idea is that “all the world’s power could be provided by a square 100km by 100km in the Sahara”. Is this true?
Concentrating solar power in deserts delivers an average power per unit land area of roughly 15 watts per square metre. So the power delivered in such a square would be 150GW. This is not even near current world electricity consumption, which is 2,000GW. Total world power consumption today is 15,000GW.
So the correct statement about power from the Sahara is that today’s consumption could be provided by a 1,000km by 1,000km square in the desert, completely filled with equipment designed to concentrate solar power. And that is four times the area of the UK.
And what area would be needed in the north Sahara to supply everyone in Europe and North Africa with an average European’s power consumption? Taking the population of Europe and North Africa to be a billion, the area required drops to 340,000 sq km, which corresponds to a square of almost 600km by 600km. This area is equal to one Germany or 1.4 UKs.
Whatever mix of technologies we choose, decarbonising Britain’s energy system requires a lot of building.
If we find dependence on Saharan sunshine unpalatable, or if we don’t like the idea of building 60 new nuclear power stations, we can revisit our attitude to big renewable facilities in Britain. For every nuclear power station we remove, we must find somewhere to put 2,000 wind turbines. We needa plan that adds up.
Sustainable Energy – Without the Hot Air, by David MacKay, is published by UIT Cambridge, priced £19.99. Copies can be ordered for £17.99 with free postage and packing from The Sunday Times Books First on 0845 271 2135