Answer: about 40 years in the case of Desertec, the world's most ambitious solar power initiative. Announced last July by 10 German companies, one Spanish and one Swiss, the Desertec Industrial Initiative aims to provide 15 per cent of Europe's electricity from solar and other renewable plants located in North Africa and the Middle East, by 2050.
Solar technology could be a perfect match for the desert, where "the same technology will generate three or four times the energy as it does in northern Europe", notes Thomas RÃ¼schen, the global head of asset finance and leasing for Deutsche Bank, one of Desertec's backers.
Just a few small details remain, not the least of which is the $400 billion (US) that Desertec will have to raise before all is finished. No one has figured out exactly what technologies they'll use. Nor do Siemens, ABB, Eon, RWE, Deutsche Bank, Munich Re and the seven other Desertec companies know where they'll locate the plants.
Options include Morocco, Algeria, Tunisia and Egypt.
Although the 12 companies themselves are in a honeymoon period, a consortium like Desertec often hits internal strife. No great signs of strain have yet surfaced. But Desertec consists of companies that compete head to head so it's easy to imagine tensions as utilities E.ON and RWE try to work together. Then again, Desertec members say that if all goes as planned, there will be plenty of work for all, as Desertec could eventually include about 200 plants. Solar Millennium's Gladen says another 200 companies could come on board.
In a strange way, Desertec's members might welcome the luxury of fighting with each other, because that might mean they will have together leapt over their biggest common hurdle: establishing a political and regulatory framework that supports their initiative. North African and Middle Eastern governments will have to facilitate planning permission for plants, and will want to know what's in it for them. Desertec members say that host countries would be able to use power themselves, would be able to sell power to Europe, and would gain technological knowledge.
They also face an equally daunting political fight closer to home. The EU, according to several Desertec members, has no clear policy in place permitting or prohibiting importing electricity from Africa and the Middle East. "We need a regulatory framework that allows the import of electricity," says Ernst Rauch, the head of the corporate climate centre at Munich Re.
Assuming the EU enacts a favourable policy, the technology challenges will ensue full force. No one expects Desertec's first plant to come on line soon. It might take three years to simply figure out where to put it. But in the context of a 40-year project, that would be a sunny start.