Note 9 - Income Taxes - Reconciliation of Income Tax Expense (Details) - USD ($)	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Income before income taxes	$ 15,457,507	$ 14,791,193
Corporate federal income tax rate	21.00%	21.00%
Income tax expense computed at the federal statutory rate	$ 3,246,076	$ 3,106,151
State income taxes, net of federal income tax expense	763,518	720,749
Net amortization of excess deferred taxes on regulated operations	(315,708)	(162,228)
Amortization of R&D tax credits	0	(131,620)
Net amortization of RNG tax credits	(100,649)	(58,669)
Reserve for unrecognized tax benefits	82,000	0
Other, net	21,374	17,528
Total income tax expense	$ 3,696,611	$ 3,491,911