I seem to be missing something about this project. I was under the impression that it was pumping sea water into the storage facility, then releasing it later to generate electricity.

If so, then the energy used to pump it up will be slightly greater than the energy produced when it is let go. If it takes 1 unit of energy to pump it up, and we get 0.85 units back, we are not creating new energy.

I have encountered several projects that pump up during the night when electricity rates are low, and selling that electricity back when rates are higher during the day. There is enough differential in the prices to justify losing 15% of the energy.

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A long time ago, I thought of using hydrogen as our storage for the electrical grid.

http://www.tiereddemocraticgovernance.org/blog_details.php?blog_cat_id=27&id=38

There would still be losses as we convert electricity to hydrogen and back to electricity. But because the original source was the wind, the electrical losses were essentially "free."

The electrical grid did not go in this direction. There are probably some good reasons.