As with hydro storage, efforts are under way to adapt the basic concept of CAES to make it more efficient and easier to install.

ECONOMIST: Energy storage

One critically important element used today is hydro storage capacity in neighboring Norway (which is supplied by 99% hydro) and Sweden (over 50% hydro), supported by robust interconnection transmission lines.

FORBES: Denmark: 1,000 Megawatts Of Offshore Wind, And No Signs of Slowing Down

The Danes have been blessed with an enormous wind resource, and with a geographic location that places them between much larger markets (that they can sell to and buy from), as well as huge hydro storage potential to the north.

FORBES: Denmark: 1,000 Megawatts Of Offshore Wind, And No Signs of Slowing Down

The pump storage hydro scheme is designed to "soak up" excess power generated by wind and wave farms, using it to pump water up to a reservoir.

BBC: Highland councillors support Lochaber hydro plan

"Hydro electric schemes, which use impounded water to generate electricity, are an excellent means of energy storage, " said SSE Renewables managing director Jim Smith.

BBC: The Great Glen, picture taken by Fiona Carr

Only after the cost of generation and storage of renewable energy matches the cost of on-demand generation from fossil, nuclear and hydro we will we see a transformation of the energy industry.

FORBES: Storage, Not Generation, is the Challenge to Renewable Energy