Case C-100/20: Judgment of the Court (Fifth Chamber) of 9 September 2021 (request for a preliminary ruling from the Bundesfinanzhof — Germany) — XY v Hauptzollamt B (Reference for a preliminary ruling — Taxation — Taxation of energy products and electricity — Directive 2003/96/EC — Article 17(1)(a) — Tax reductions on the consumption of energy products and electricity in favour of energy-intensive businesses — Optional reduction — Arrangements governing the repayment of tax levied in breach of provisions of national law adopted on the basis of a power granted to the Member States in that directive — Payment of interest — Principle of equal treatment)