35 ILCS 200/10-600
For the purposes of this Division 18:
"Wind energy device" means any device, with a nameplate capacity of at least 0.5 megawatts, that is used in the process of converting kinetic energy from the wind to generate electric power for commercial sale.
"2007 real property cost basis" excludes personal property but represents both the land and real property improvements of a wind energy device and means $360,000 per megawatt of nameplate capacity.
"Trending factor" means a number equal to the consumer price index (U.S. city average all items) published by the Bureau of Labor Statistics for the December immediately preceding the assessment date, divided by the consumer price index (U.S. city average all items) published by the Bureau of Labor Statistics for December 2006.
"Trended real property cost basis" means the 2007 real property cost basis multiplied by the trending factor.
"Allowance for physical depreciation" means (i) the actual age in years of the wind energy device on the assessment date divided by 25 years multiplied by (ii) the trended real property cost basis. The physical depreciation, however, may not reduce the value of the wind energy device to less than 30% of the trended real property cost basis.
35 ILCS 200/10-600