As part of their round-the-world sailing trip in search of sustainable solutions, the Sailors for Sustainability visited the Spanish island of El Hierro. Propelled by the northeast trade winds, the Sailors sail to the smallest of the seven main Canary Islands, which makes good use of the constant wind, too. Wind turbines generate a large part of the island’s electricity needs. Yet the Sailors come to see another element of the island’s energy system: the innovative way energy is stored to match supply and demand. How did the islanders manage to set a world-class example in renewable energy storage and what are the success factors?