Alliant Energy: Files 2010 fuel rate case and 2011 electric rate case

Media Contact: Scott Reigstad (608) 458-3145

Investor Relations Contact: Susan Gille (608) 458-3956

Wisconsin Power and Light experiencing higher fuel costs; investing in additional renewable energy

MADISON, WI – April 30, 2010 – Wisconsin Power and Light Company (WPL), a subsidiary of Alliant Energy Corporation (NYSE: LNT), filed requests today with the Public Service Commission of Wisconsin (PSCW) to implement an electric rate adjustment based on year-to-date actual as well as projected fuel costs for the remainder of 2010 and to adjust its retail electric rates, effective January 1, 2011.

In its first request, WPL is asking to recover $8.8 million or 0.9% from electric retail customers due to increased fuel costs. This fuel-only rate case was filed because actual fuel and purchased power costs through March of this year, combined with projections for the remainder of 2010, exceed the amounts currently recovered in base rates. For residential customers using 600 kilowatt-hours of electricity per month, the requested increase would add approximately 53 cents per month on their remaining 2010 electric bills.

“During the past few years we saw a steep drop in our fuel costs, which allowed WPL to make significant refunds to our customers. Unfortunately, similar refunds are not expected for 2010,” said Barbara J. Swan, President-WPL. “Instead, our fuel and purchased power costs are rising above the levels anticipated when the PSCW approved new rates for 2010. WPL’s ability to recover these prudent costs of providing reliable electric service ensures fairness to customers and shareowners alike.”

The PSCW is expected to issue an interim order on the 2010 fuel-only increase request next month and will hold hearings prior to issuing its interim and final order in the fuel-only rate case. The interim rate increase would remain in effect until a final order is issued. If the amount collected in interim rates is greater than the final rates, customers will receive a refund with interest.

In its second request, WPL is asking that the PSCW reopen its 2010 rate case to increase retail electric rates by $35.4 million or 3.6%, when compared to current rates that went into effect on January 1, 2010. The requested retail electric rate increase is limited to recovering costs associated with the construction and operation of WPL’s Bent Tree Wind Farm, which is expected to be completed in early 2011, as well as net revenue credits that expire on January 1, 2011.

The amount of the requested electric rate increase is partially offset by forecasted declines in electric fuel and purchase power energy costs for 2011. For residential customers using 600 kilowatt-hours of electricity per month, the requested increase would add approximately $3.11 per month on their bills starting in 2011.

“We plan to invest over $450 million in our Bent Tree Wind Farm to help create a cleaner energy future for our customers and communities,” added Swan. “Bent Tree Wind Farm will be capable of powering the equivalent of 50,000 homes with renewable energy when completed and it will also help our company meet required Wisconsin renewable energy portfolio standards.”

The 200 megawatt Bent Tree Wind Farm will be WPL’s second owned and operated wind farm and will include 122 turbines located in Freeborn County, Minnesota. WPL’s first owned and operated wind farm – the 68 megawatt Cedar Ridge Wind Farm near Fond du Lac – began commercial operation in December 2008.

All rate changes must be approved by the PSCW after a thorough review of the data and after obtaining input from the public. The approval process for the retail electric base rate increase is expected to take several months, with new rates becoming effective on or about January 1, 2011.

Additional information for customers on the electric and fuel rate increase requests is available at http://www.alliantenergy.com/wisconsinrates. Documents relating to this filing can be found on the PSCW web site at http://www.psc.wi.gov.

Alliant Energy is an energy-services provider with subsidiaries serving approximately 1 million electric and over 412,000 natural gas customers. Providing its customers in the Midwest with regulated electric and natural gas service is the company’s primary focus. Wisconsin Power and Light, the company’s Wisconsin utility subsidiary, serves approximately 460,000 electric and 180,000 natural gas customers. Alliant Energy, headquartered in Madison, Wis., is a Fortune 1000 company traded on the New York Stock Exchange under the symbol LNT. For more information, visit the company’s Web site at http://www.alliantenergy.com.