Opinion of Advocate General Tanchev delivered on 24 October 2019.#Proceedings brought by Energiavirasto.#Request for a preliminary ruling from the Korkein hallinto-oikeus.#Reference for a preliminary ruling — Internal market in electricity — Directive 2009/72/EC — Article 3 — Consumer protection — Article 37 — Tasks and powers of the regulatory authority — Out-of-court dispute settlement — Concept of ‘party’ — Right to appeal against a decision of the regulatory authority — Complaint made by a household customer against an electricity distribution system operator.#Case C-578/18.