(a) Rate of tax. — Upon every person engaging or continuing within this state in the business of generating or producing electricity for sale, profit or commercial use, either directly or indirectly through the activity of others, in whole or in part, or in the business of selling electricity to consumers, or in both businesses, the tax imposed by section two of this article shall be equal to:
(1) Twenty-six hundredths of one cent times the kilowatt hours of net generation available for sale that was generated or produced in this state by the taxpayer during the taxable year, except that this rate shall be five hundredths of one cent times the kilowatt hours of net generation available for sale that was generated or produced in this state by the taxpayer and sold to a plant location of a customer engaged in manufacturing activity if the contract demand at such plant location exceeds two hundred thousand kilowatts per hour per year or if the usage at such plant location exceeds two hundred thousand kilowatts per hour in a year: Provided, That in order to encourage the development of industry to improve the environment of this state, the tax imposed by this section on any person generating or producing electric power and an alternative form of energy at a facility located within this state substantially from gob or other mine refuse shall be equal to five hundredths of one cent times the kilowatt hours of net generation or production available for sale. The measure of tax under this paragraph shall be equal to the total kilowatt hours of net generation available for sale that was generated or produced in this state by the taxpayer during the taxable year, regardless of the place of sale or use, or the fact that transmission may be made to points outside this state.