Pursuant to and for the purposes of the third paragraph of Article 21(5) of Directive 2003/96/EC, must entities which produce electricity for their own use be small producers in order for them to be … regarded as distributors, and [thus] subject to tax in accordance with the first paragraph of Article 21(5) of that directive, so that other entities (those which are not small producers) which produce electricity for their own use are excluded from that classification as distributors, or must all entities which produce electricity for their own use (regardless of their respective size and of whether they do so as their main or secondary economic activity), and are not exempt as small producers under the second sentence of the third paragraph of Article 21(5) of that directive, be regarded as distributors, and [thus] subject to tax in accordance with the first paragraph of Article 21(5) of that directive?