(a) Annual base charges. Owners of conventional run-of-river hydroelectric power plants that benefit from water storage facilities owned or partially owned by the commission shall pay an annual base charge to the commission. The amount of the base annual charge shall be $1 per kilowatt of installed capacity.

(b) Annual variable charges. In addition to the base charge established in subdivision (a) of this section, annual charges based on power generated at each facility will be assessed as follows:

(c) Credits. The owner of any hydroelectric generating facility shall receive a credit against the current year water use fee otherwise payable to the commission for any amount which the commission receives from the U.S. Army Corps of Engineers or from the Federal Energy Regulatory Commission for each calendar year.

(d) Exemptions. No payment will be required when hydroelectric power facility water use charges would amount to less than $25 per year. Retroactive charges will not be assessed for facilities which have already obtained commission approval pursuant to section 3.8 of the Delaware River Basin Compact. All hydroelectric generating projects that do not benefit from storage owned or partially owned by the commission are exempt from these commission water charges.

(e) Payment of bills. The amount due each year shall bear interest at the rate of one percent per month for each day it is unpaid beginning 30 days after the due date. Payments are due within 30 days of the end of each calendar year. Annual base charges will be prorated for periods less than a year.