(1) There is hereby levied and there shall be collected from every district a tax for the act or privilege of engaging within this state in the business of operating works, plants or facilities for the generation, distribution and sale of electric energy. With respect to each such district, except with respect to thermal electric generating facilities taxed under RCW
54.28.025, such tax shall be the sum of the following amounts: (a) Two percent of the gross revenues derived by the district from the sale of all electric energy which it distributes to consumers who are served by a distribution system owned by the district; (b) five percent of the first four mills per kilowatt-hour of wholesale value of self-generated energy distributed to consumers by a district; (c) five percent of the first four mills per kilowatt-hour of revenue obtained by the district from the sale of self-generated energy for resale.