Intermittency is a well-known weakness of solar and wind power—they're good when the sun shines and the wind blows, say critics, but what about when it doesn't? (Though there are some questions about all that.) The response of alternative energy enthusiasts tends to come in two flavors: better grid balancing—where reliable power sources, such as nuclear, take up the slack when needed—or improved energy storage. The trouble with many of today’s storage methods, though, is that they are either not very good or too expensive. There are several new ones, including salt, but none are yet ready at scale.
If you wanted to be hopeful about renewables, you might look at a project 900 miles off the coast of Spain, on the smallest of the Canary Islands. El Hierro measures only 104 square miles, but it is being viewed as a model for projects combining renewable power with pumped hydropower storage—perhaps the most viable currently available storage method.
El Hierro’s $87 million scheme consists of an 11.5 megawatt wind farm (five turbines) that will provide the island's 11,000 inhabitants with the majority of their power. When the system produces excess energy, it pumps water 2,300 feet up to an extinct volcano. When there is insufficient renewable power, the water gushes through a hydroelectric plant. The closed-loop is topped out with series of solar thermal units that provide about a fifth of the overall needs.
El Hierro currently generates electricity using diesel oil imported by tanker from the mainland, and the costs and environmental impact are big. Officials estimate the island emits 18,200 tons of CO2 a year, just from power generation alone.
"We now rely on the outside, the fuel that comes on the boats, which is expensive and polluting. But with the launch of the new power station, we have our own power and profits will go to the island," says Cristina Morales Clavijo, a spokesperson for the company managing the project.
Officials are confident the new system, which is due for completion this year, will allow the island to do away entirely with fossil fuels, and allow it to invest additional revenues in further infrastructure projects. Just in case, the island will keep its diesel generators as backup. There may still be occasions when there is not enough wind or enough stored water to meet demand, and the reservoir only has enough capacity for seven days' worth of electricity. But El Hierro might just get the chance to prove that true energy self-sufficiency is possible, even on a semi-large scale.
"It is very important for the development of El Hierro, but also for other Canary Islands who are already working on similar systems. Internationally, there are other territories that want to know about the project because they think we are an example. The pumping system is the only solution at the moment to store wind energy, and it could be used on other islands and mainland territories," says Clavijo.