By Gabriela Baczynska BRUSSELS (Reuters) -The European Union will struggle to fill its gas storage tanks next summer, the head of its executive warned on Wednesday as she announced measures to boost renewable energy supply but stopped short of backing a price cap that has split opinion across the region. Adressing the European Parliament, European Commission President Ursula von der Leyen announced plans to accelerate the granting of permits for renewable power projects. She said that the EU will have added 50 gigawatts of renewable power this year and could do more in 2023. She said the bloc …