(a) The electric cooperative tax shall be computed as follows:

1. (1) one-fourth mill per kilowatt hour for cooperatives that have furnished electric energy and power to consumers for less than five years as of December 31 of the preceding calendar year;
2. (2) one-half mill per kilowatt hour for cooperatives that have furnished electric energy and power to consumers for five years or longer as of December 31 of the preceding calendar year.