El Hierro is the smallest of the main Canary islands, with only 278 Km2 and 10000 inhabitants maybe for this reason it was the perfect place to accomplish an ambitious project: Get its electricity only from renewable sources. 5 wind mills will be enough for that but supported by an energy storage system, when the mills are not producing electricity for the grid they will feed pumps to raise sea water to a natural deposit. In case electricity is needed and there is no wind a hydropower station will work with this water coming from the deposit. A more detailed explanation is here.
Although small (10000 people) this project is ambitious and promising at the same time. Why? Because it works in a scale between the big country and the familiar house but at the same time it is a complete electrical system as Canary islands are not connected to other grids and for this reasons they have been reluctant to introduce too many renewable sources that would challenge the stability of their small grids fueled with diesel power plants. So it has been easier to try a total replacement (although fuel power plants will continue to be operative for backup) that a mixed system.
At the same time this is an opportunity, because Canarian electricity is expensive, more expensive than standard renewable technology and I haven’t found the cost of this project but it would not surprise me to find it is cheaper in the long-term that standard power production in El Hierro. This data would be great to make a more precise assessment.
Anyway, the most important achievement of this project in my opinion is that renewables have been able to become the main power generation source in a whole electrical system that clearly is in another scale compared to a household. It is a 10000 people scale distributed in a 278 Km2 location. By itself it will not change the general emission trend of the world because even if there are 700 million people living in islands, most of those inhabitants live in much greater islands. But it is a step to change scale and every difficult achievement has been done step by step.