Alliant Energy: Interstate Power and Light Announces Decision Regarding Future Ownership of Duane Arnold Energy Center

Media Contact: Ryan Stensland (319) 786-4171

Investor Contact: Becky Johnson (608) 458-3267

Company intends to sell its 70 percent ownership share of nuclear generation facility and will seek contract for plant’s energy output

CEDAR RAPIDS, Iowa – December 22, 2004 – Interstate Power and Light Co. (IP&L), a utility subsidiary of Alliant Energy Corp. (NYSE: LNT), announced today its intent to sell the company’s 70 percent ownership interest in the 583-megawatt Duane Arnold Energy Center (DAEC), a nuclear generating facility located near Palo, Iowa. IP&L plans to enter into a definitive agreement with a prospective owner within six months and will then seek to obtain all appropriate state and federal regulatory approvals.

IP&L’s pursuit of a sale at this time provides the best opportunity for a prospective owner to seek renewal of DAEC’s operating license and continue the long-term operation of the generating facility. In pursuing the sale of DAEC, IP&L expects to reduce customer and shareowner financial and operational uncertainty associated with nuclear generating facility ownership and operations. The evolving nationwide trend to consolidate ownership and operations within the nuclear energy industry is also a factor in the company’s decision.

DAEC was commissioned in 1974 and has an operating license that expires in 2014. IP&L anticipates that a new owner will pursue the opportunity to secure regulatory approvals for DAEC’s re-licensing. IP&L expects to enter into a Purchase Power Agreement (PPA) with the prospective owner through 2014.

The trend toward consolidation of United States nuclear generating facility ownership and operations provides for centralized resources and management expertise, which further reduces operational and financial uncertainty associated with nuclear generating facilities. In a similar operational effort in 1999, IP&L co-founded the Nuclear Management Company (NMC) to specialize in the operation of multiple nuclear generation facilities throughout the country, including DAEC. NMC has had great success in managing DAEC’s operations in an efficient and cost-effective manner. NMC will continue to manage DAEC’s operations throughout the sale process.

Two partner companies own the remaining 30 percent interest in DAEC. IP&L’s decision is independent of any future actions by other DAEC partners.

“IP&L’s decision is based upon sound business fundamentals and will minimize the financial and operational uncertainty confronting our customers and shareowners as DAEC’s license to operate expires within the next ten years,” said Tom Aller, President IP&L. “Our company is committed to providing safe, reliable and environmentally sound electric service at a reasonable cost. Nuclear energy will remain a part of our diverse energy portfolio through an agreement to purchase the electricity generated by the DAEC. It is our intent to find a buyer committed to re-licensing DAEC, ensuring that nuclear energy will remain central to fueling Iowa’s energy future and economic growth.”

Alliant Energy is an energy holding company that serves more than three million customers worldwide. Providing domestic utility customers in the Midwest with regulated electric and natural gas services remains the company’s top priority. Other key business platforms include targeted international energy markets and non-regulated generation. 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

This press release includes forward-looking statements. These forward- looking statements can be identified as such because the statements include words such as “expects” or “anticipates” or other words of similar import. Similarly, statements that describe future financial performance or plans or strategies are also forward-looking statements. Such statements are subject to certain risks and uncertainties that could cause actual results to differ materially from those currently anticipated. These risks include those related to this announcement with regard to IP&L’s proposed sale of its interest in the Duane Arnold nuclear facility, including IP&L’s ability to enter into a definitive agreement to sell its interest in the Duane Arnold nuclear facility on IP&L’s expected timetable and for anticipated proceeds, IP&L’s ability to obtain required regulatory approvals for such a sale; the operations of the Duane Arnold nuclear facility pending sale; and developments that adversely impact Alliant Energy’s ability to implement its strategic plan. These factors should be considered when evaluating the forward-looking statements and undue reliance should not be placed on such statements. The forward- looking statements included herein are made as of the date hereof and Alliant Energy undertakes no obligation to update publicly such statements to reflect subsequent events or circumstances.