* EDF says storage key to balance intermittent renewables
* Investment to focus on grids, retail solar, Africa off grid
* UK battery project for National Grid to launch by summer (Adds CEO comments, detail)
PARIS, March 27 (Reuters) - French state-owned utility EDF plans to invest eight billion euros ($9.94 billion) between 2018 and 2035 to become a European market leader in electricity storage.
EDF, which already operates pumped storage hydropower plants and some utility-scale power storage batteries, said on Tuesday it aimed to become a French and European market leader, offering storage batteries for customers in the retail power sector.
"With storage we can smooth out the intermittence of renewable energy and guarantee the balancing of power grids," EDF chief executive Jean-Bernard Levy told reporters.
Power storage usage by European utilities is growing as the intermittent supply from renewable energies like solar and wind forces them to have more power reserves on standby.
EDF's investment in power storage will focus on boosting the resilience of power grids, on individual storage for retail customers with solar panels, and on off-grid solar plus storage systems in Africa, notably in Ghana and Ivory Coast.
The company will finance the plan with a mix of equity and debt but Levy did not give a breakdown.
EDF plans to develop 10 gigawatts of additional storage capacity worldwide by 2035 - in addition to the 5 GW of pumped storage hydropower it already operates.
The company will develop some 6 GW in industrial-scale storage systems, notably in pumped storage and batteries, and 4 GW of individual batteries for retail customers, companies and municipal customers.
Pumped storage stations pump up water while power prices are low and release it when power prices are high, but their profitability is currently low because of the relatively small difference between peak and trough prices.
Levy said that EDF Energy's 49 megawatt West Burton, Nottinghamshire, battery storage project for Britain's National Grid - which will be one of Europe's largest battery storage projects - is set to launch before the summer.
In the next 12 months, EDF plans to launch two more battery projects aimed at stabilizing grids.
Working with local partners, EDF also aims to develop a portfolio of 1.2 million off-grid customers in Africa by 2035, equipping them with solar panels and individual battery systems.
Asked for a detailed breakdown on how and when EDF will spread the planned eight billion euro investment over the next 17 years, Levy said there was not yet a detailed plan.
He said EDF would double its research and development into power storage to 70 million euros for the 2018-2020 period.
In the coming two years, EDF's New Business division also plans to invest some 15 million euros - about a third of its investments - in projects and startups linked to power storage and flexibility.
EDF's storage plan is the second major investment project in its energy transition towards renewables.
In December, EDF said it would invest about 25 billion euros to build 30 gigawatt (GW) of solar capacity from 2020 to 2035, mainly funded by equity partners, project financing and loans. ($1 = 0.8046 euros) (Reporting by Geert De Clercq; Editing by Sudip Kar-Gupta and Jane Merriman)