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Note 9 - Income Taxes (Details Textual) - USD ($) | 12 Months Ended
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Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2021
Deferred Tax Assets, Tax Credit Carryforwards | $ 1,437,670 | $ 1,662,400 |  |
Deferred Income Tax Liabilities, Net | 1,890,562 | 2,008,458 |  |
Deferred Income Tax Assets, Net | 771,746 | 1,163,594 |  |
Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions | $ 273,936 |  |  |
Income Tax Examination, Year under Examination | 2018 2019 |  |  |
Domestic Tax Jurisdiction [Member] | Internal Revenue Service (IRS) [Member] |  |  |  |
Actual Tax Credit Recognized in Income Tax Returns |  |  | $ 659,920 |
Effective Income Tax Rate Reconciliation, Tax Credit, Amortization, Period (Year) |  |  | 20 years |
Tax Credit Carryforward, Annual Amortization Amount | $ 0 | 129,600 |  |
Deferred Tax Assets, Tax Credit Carryforwards, Research | $ 0 | $ 990,219 |  |
Open Tax Year | 2018 2019 |  |  |
Domestic Tax Jurisdiction [Member] | Internal Revenue Service (IRS) [Member] | Federal Energy Investment Tax Credit [Member] |  |  |  |
Effective Income Tax Rate Reconciliation, Tax Credit, Amortization, Period (Year) |  | 20 years |  |
Tax Credit Carryforward, Annual Amortization Amount | $ 127,404 | $ 74,265 |  |
Tax Credit Carryforward, Amount |  | 1,892,164 |  |
Deferred Tax Assets, Tax Credit Carryforwards |  | 655,862 |  |
State and Local Jurisdiction [Member] | Virginia, Jurisdiction [Member] |  |  |  |
Actual Tax Credit Recognized in Income Tax Returns |  |  | $ 58,065 |
Effective Income Tax Rate Reconciliation, Tax Credit, Amortization, Period (Year) |  |  | 20 years |
Tax Credit Carryforward, Annual Amortization Amount | $ 0 | $ 2,020 |  | $ 0
Open Tax Year | 2019 |  |  |

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