Hello sunshine

The world needs about 13 terawatts of power every year, a figure that will rise to about 20 terawatts by 2020. The amount of sunlight falling on the planet at any one time is around 120,000 terawatts—more than 9,000 times what we need. The case for solar power is simple: capture only a tiny fraction of 1 per cent of the sun’s energy and we could provide much more power than the world needs. Add a little energy efficiency and some renewable energy, and we can do it with ease.

Where to start? The obvious places are the parts of the planet that get the most sun already: deserts. With the right technology electricity could be transported from hot countries on gigantic international energy grids for use in cloudy countries. Most of us associate solar energy with solar panels, otherwise known as solar photovoltaics (PV). But another widely applied technology uses the sun to heat up fluids—in power stations, for example, to heat water to drive turbines—an approach known as concentrating solar power technology (CSP).

To supply all the electricity Europe needs would, in principle, mean capturing just 0.3 per cent of the light falling on the Saharan and middle eastern deserts, in an area smaller than Wales. Knowing this, a group of German industrial giants in July launched what may be the world’s largest solar project: a long-planned partnership of 20 finance and energy companies to build new African CSP plants, led by Munich Re, and including E.ON, Siemens and Deutsche Bank. Picture row upon row of curved mirrors with semicircular profiles, in glittering fields, scattered across the countries of northern Africa. The plan—dubbed Desertec—hopes ultimately to provide 15 per cent of Europe’s electricity needs, and aims to figure out how this can be done within the next two to three years.

Such a giant project will not be easy. The estimated cost, somewhere near a cool €555bn ($788bn), might seem a lot. But given that the International Energy Agency calculates that we need to spend $45 trillion on new energy systems over the next 40 years, it could represent good value. The real problem is getting the power back to Europe. The plan has backing from the European commission, whose Institute for Energy envisages a network of African CSP plants linked to Europe by a new high-voltage transmission grid, which could also capture energy from wind power from across Europe and western North Africa. Building such a grid, using overland lines and submarine cables, is technically challenging, but far from impossible.

With the grid in place, Desertec-type schemes could in the future even run entire nations on solar energy alone. One 2006 study calculated that all US electricity could be provided by covering 200 sq km with new solar plants. The plants would have to be in America’s sunny southwest, and power transmitted to the cooler north. This isn’t as inefficient as it sounds: electricity use is high in summer in the northeast, when air conditioning is needed, and this is just the time when solar generation is at its maximum in the US southwest.

All this would cost the US between $4.5-6 trillion in capital investment, at today’s prices. But at an oil price of $100 a barrel—to take a conservative estimate for the coming decades—the 13m barrels a day that the US imported in 2006 would cost almost half a trillion dollars a year. The “payback” on avoided oil imports would therefore come in just nine to 12 years, with coal and gas savings factored in.

In December 2007 three respected researchers published a plan in the magazine Scientific American that, by 2050, would see solar photovoltaic farms produce 3,000 gigawatts in the American southwest, plus some large Desertec-type solar thermal plants. Excess energy produced during the daytime would be stored as compressed air in underground caverns, which could then be used at night to drive turbines. With a new grid, such a plan could see solar electricity provide 69 per cent of the US’s electricity by 2050. And plans for just such a grid, known as the $10bn “green power express” (built to carry wind power in the first instance) were given funding during President Obama’s stimulus package in February.

When one understands the enormous scope that smart grids and energy storage have, it becomes easier to believe that a fundamental switch to solar and other renewables is possible. Yet challenges still remain. US domestic solar plans, in particular, have an advantage over rival European ventures like Desertec: political stability. A world that relied on foreign solar grids would need to be much less volatile than today, and multilateral institutions more robust. That could happen, of course, especially if the US and China synchronise their interests. But history suggests caution: rich nations will surely balk at replacing dependency on oil in sunny lands with solar from those same sunny lands.

Thankfully, photovoltaics works in cloudy countries too, generating energy right where it is needed, as any survey of rooftops in Germany now shows. We would be unwise to put all our eggs in one giant solar basket, as some of the more enthusiastic engineers appear prepared to. The good news is that we don’t have to.