Hydro dams best for massive power storage - Iberdrola's Galan

* Pumped storage accounts for 98 pct of power storage

* Utility-scale storage in batteries still rare

* IHA sees fast growth of global pumped storage capacity

* Seaside cliffs hold potential for pumped storage

By Geert De Clercq

PARIS, Dec 16 (Reuters) - Pumping water to higher levels when power is cheap and releasing it at times of peak demand is still the best option for massive energy storage and seaside cliffs have potential for that, Spanish utility Iberdrola’s chief executive Ignacio Galan said.

Despite attempts to use more batteries, traditional pumped storage systems still account for more than 98 percent of storage worldwide, although that has slipped from 99 percent due to the developments of other technologies, according to the International Hydropower Association (IHA).

“Batteries are a good solution for certain areas, but for massive power storage, you need pumped storage,” said Galan, adding that he has been a battery engineer for 16 years.

He said rapid growth of intermittent power from solar and wind will force utilities to build ever more storage systems.

Iberdrola, Europe’s biggest utility by market value, operates 5.5 gigawatts of pumped storage - 4.4 GW in Spain and 1.1 in Scotland - and has 1.1 GW under construction in Portugal.

The world has 145 GW pumped storage capacity, including 50 GW in Europe, with new stations planned mainly in Austria, Portugal and Switzerland, according to the IHA. It estimates 40 GW of pumped storage is being built or planned worldwide.

Most pumped storage systems are in mountainous areas and consist of two lakes, one high, one low, with turbines that pump water up at night and release it by day to produce electricity when demand is high.

Galan said utilities could consider building pumped storage stations on high seaside cliffs, such as on the British south coast. “Nobody has done it yet, but it is feasible,” he said.

Companies such as U.S. Tesla, France’s Saft and Germany’s SMA Solar are developing batteries for power storage at homes and businesses. Some scale up to a few megawatt, but gigawatt-size batteries for utilities do not exist.

Pumped storage technology is reliable and mature, but the dams and installations take years to build and cost billions.

And while intermittent renewables boost the need for pumped storage, the flood of cheap solar energy at midday has also reduced the traditional price gap between daytime and nighttime power prices that makes pumped storage dams profitable. (Reporting by Geert De Clercq, editing by David Evans)