35 ILCS 200/10-725

Improvement valuation of commercial solar energy systems in counties with fewer than 3,000,000 inhabitants. Beginning in assessment year 2018, the fair cash value of commercial solar energy system improvements in counties with fewer than 3,000,000 inhabitants shall be determined by subtracting the allowance for physical depreciation from the trended real property cost basis. Functional obsolescence and external obsolescence of the solar energy device may further reduce the fair cash value of the commercial solar energy system improvements, to the extent they are proved by the taxpayer by clear and convincing evidence.