Solar power in Illinois has been increasing, as the cost of photovoltaics has decreased. Illinois adopted a net metering rule which allows customers generating up to 40 kW to use net metering, with the kilowatt hour surplus rolled over each month, and lost at the end of either April or October, as selected by the customer. In 2011, the limit was raised to 2 MW, but is not net metering, as the term is commonly known, as it uses two meters for systems larger than 40 kW.
Illinois ranks 26th nationally in cumulative installed solar capacity. There is enough solar energy installed in the state to power 9,500 homes.
A 2012 estimate suggests that a typical 5 kW system will pay for itself in about nine years. Additionally, a 5 kW system could end up adding around $10,000 to the value of your home. Reports have also shown that a home with a solar panel system will end up selling approximately 15% faster than a home without. Illinois also offers up to a $10,000 tax credit for a solar installation.
In 2002, Illinois' largest solar array was the 99.4 kW array on the roof of the Field Museum of Natural History, in Chicago.
In 2010 the country's largest urban solar array, 10 MW, was installed in West Pullman, on Chicago's south side. In 2012, IKEA installed solar PV on its two stores in Bolingbrook and Schaumburg totaling almost 2 MW. Also in 2012, the 20 MW Grand Ridge Solar Plant in LaSalle County was completed. The University of Illinois built a 5.87 MW solar farm in 2015 which will provide 2% of the university's electricity.
The first experimental solar power plant was in 1902, in Olney, Illinois, by H.E. Willsie and John Boyle, and was based on a design by Charles Tellier. In 1904 they set up the Willsie Sun company in St. Louis, and built a 6-horsepower motor.