How About A Pilot Project To Demonstrate The Feasibility Of Fully Wind/Solar/Battery Electricity Generation?
[Excerpt] A reasonable question is, has anybody thought to construct a small-to-moderate scale pilot project to demonstrate that this is feasible? Before embarking on “net zero” for a billion people, how about trying it out in a place with, say, 10,000, or 50,000, or 100,000 people. See if it can actually work, and how much it will cost. Then, if it works at reasonable cost, start expanding it.
As far as I can determine, that has never been done anywhere. However, there is something somewhat close. An island called El Hierro, which is one of the Canary Islands and is part of Spain, embarked more than a decade ago on constructing an electricity system consisting only of wind turbines and a pumped-storage water reservoir. El Hierro has a population of about 11,000. It is a very mountainous volcanic island, so it provided a fortuitous location for construction of a large pumped-storage hydro project, with an upper reservoir in an old volcanic crater right up a near-cliff from a lower reservoir just above sea level. The difference in elevation of the two reservoirs is about 660 meters, or more than 2000 feet. Here is a picture of the upper reservoir, looking down to the ocean, to give you an idea of just how favorable a location for pumped-storage hydro this is: [Photo at link]
The El Hierro wind/storage system began operations in 2015. How has it done? I would say that it is at best a huge disappointment, really bordering on disaster. It has never come close to realizing the dream of 100% wind/storage electricity for El Hierro, instead averaging 50% or less when averaged over a full year (although it has had some substantial periods over 50%). Moreover, since only about one-quarter of El HIerro’s final energy consumption is electricity, the project has replaced barely 10% of El Hierro’s fossil fuel consumption.
[Much more at link above]

Found additional operation data on the sustainability of the island project. Not efficient. Good report.
http://euanmearns.com/an-independent-evaluation-of-the-el-hierro-wind-pumped-hydro-system/