Spain's Endesa this week launched the country's first grid-connected energy storage plants, aiming to demonstrate the viability of a key renewable technology.

The electric utility said Monday the storage units, located on the Canary Islands of Gran Canaria, La Palma and La Gomera, are meant to test the technical and economic viability of large-scale energy storage systems, which are needed to fully integrate intermittent wind and solar power sources into grids.

Storage systems are also key to help make isolated electricity generation systems, such as those on islands, more reliable by offering backup generation.

"This project paves the way to finding new solutions to help isolated systems become self-sufficient, bringing environmental and cost-efficiency benefits," the company said.

Called Project Store, the $15 million effort was backed by Spain's Ministry of the Economy and Competitiveness and the European Union through its European Regional Development Fund and was carried out by a consortium including Endesa, Schneider Electric, Isotrol and Ingeteam.

Electricity storage, which has been called the "holy grail" of renewable energy by its backers, is seen as an essential "enabling" technology to capture and redeploy generation capacity from intermittent renewable energy sources such as wind and solar and to make localized community electricity generation feasible.

It's a problem for the 10 million people who live on the 286 islands in the EU, who often suffer from energy shortages due to isolated networks that can't adjust to changes in demand. Storage technologies are also regarded as essential to the full energy integration of the bloc and necessary to removing obstacles hindering local economies.?

So far, storage technologies have only been achieved in self-sufficient systems not connected to grids due to problems with costs and durability, but Endesa says its Canary Islands effort will show they can be "efficiently integrated in a real-world environment" and perform well when hooked up to a functioning grid.

The Gran Canaria facility at La Aldea de San Nicolas will use electro chemical storage in the form of lithium-ion batteries. The unit at Alajero on La Gomera will employ a flywheel system, while at Brena Alta on La Palma, Endesa says it is deploying an ultracondenser system.

The La Gomera and La Palma facilities will boast "very fast response times, which means they are perfect for avoiding unexpected events that can lead to partial power failures in small electricity systems or even widespread outages."

The facility on Gran Canaria, meanwhile, has greater storage capacity and can operate as a "manageable generation group," with loading and unloading programmed daily.

Italian utility Enel is also experimenting with large-scale electricity storage systems.

The company says it has launched the installation of the first Italian smart grid -- which will also include a large electricity storage system using lithium batteries -- in the southern province of Isernia.

In Livorno, Enel is testing three types of storage technologies -- lithium ion batteries, oxydoreduction vanadium batteries and "zebra technology" (zero-emission battery research activity) for high-temperature electrochemical storage.

?Other energy storage tests performed by Enel include with flywheels, ultracondensers and compressed air, as well as special projects such as electrochemical storage at geothermal plants and storage system management for industrial energy districts.