Alliant Energy Unveils 2006 - 2013 Generation Plan

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MADISON, Wis., Aug. 8, 2005 - Alliant Energy Corp. (NYSE:LNT) announced today its domestic utility supply plan for the 2006-2013 time period. The supply plan updates Alliant Energy's 2003 generation plan that addressed the 2004-2010 time period, and reflects increased growth in demand and the need to increase base load generation in both Iowa and Wisconsin.

"Over the past 6 years, electricity demand in our service territories has grown on average about 3 percent per year, and we expect this growth rate to continue," said Vice President of New Energy Resources, Kim Zuhlke. "The plan we've developed to meet this growing demand is balanced and will keep our rates competitive."

2003 Domestic Utility Generation Summary

The company outlined a plan in December, 2003 proposing to add a diversified portfolio of approximately 1,600 megawatts (MW) of generation between 2004 and 2010 to serve its 1.4 million domestic electric customers.

Since the plan was announced, Alliant Energy has added the 565 MW natural gas-fired combined-cycle Emery Generating Station near Mason City, Iowa and the 300 MW simple-cycle natural gas-fired peaking plant in Sheboygan Falls, Wis. In addition, Alliant Energy has contracted to purchase 481 MW from the natural gas-fired combined-cycle Riverside Energy Center near Beloit, Wis. and recently contracted to purchase 150 MW of wind generation from the Endeavor Wind Farm in Iowa. When the Endeavor Wind Farm is completed, Alliant Energy's wind portfolio will total more than 500 MW.

After a thorough review of future demand through 2013, Alliant Energy will look to add new base load generation and wind farm ownership as a means to meet increasing customer demand. Alliant Energy will continue to research and nurture less developed renewable sources of energy such as the switchgrass burn in Ottumwa, Iowa, and on-farm anaerobic digesters throughout our service territory. Additionally, Alliant Energy has a well documented commitment to energy conservation through aggressive demand side management programs. Alliant Energy's energy efficiency portfolio includes a mix of products and programs targeted at reducing peak demands and saving customers' energy.

2006-2013 Domestic Utility Generation Summary

The updated plan calls for the addition of 600 MW of owned-generation for the period 2006-2013 and includes:

-- 100 MW of wind generation in Iowa in 2008

-- 500 MW of clean-coal technology generation

- 250 MW-Wisconsin in 2012

- 250 MW-Iowa in 2012 or 2013

The 250 MW of clean-coal technology to meet increased demand in Wisconsin was previously announced as a 200 MW plant slated to begin operation in 2011. Based upon new demand information, Alliant Energy has increased the size of the plant and determined the plant should be operational by 2012. Studies of the potential sites' impacts on the transmission system are under way. The 500 MW of clean-coal technology and 100 MW of wind generation will require approximately $1.1 to $1.2 billion in capital expenditures.

In addition to adding base load and wind generation, the company anticipates saving 250 MW through energy efficiency programs to construct a "Virtual Power Plant;" adding approximately 20 additional on-farm anaerobic digesters in both Iowa and Wisconsin; and may purchase an additional 200 MW of wind generation. Alliant Energy continually works to ensure the development of the transmission infrastructure to allow energy transfers into and out of its service territories to complement the planned growth in generation assets. Alliant Energy also has the option to purchase the 466 MW RockGen Energy Center in Christiana, Wis. and the 603 MW Riverside Energy Center in Beloit, Wis. from Calpine Corporation in 2009 and 2013, respectively.

"We have planned carefully on behalf of our customers' energy future," Zuhlke said. "We are fortunate to operate in legislative and regulatory climates that understand the need to invest in our infrastructure, demonstrate commitment to energy conservation, and allow us to keep our rates competitive."

Greater Regulatory Certainty

Alliant Energy's Chief Financial Officer Eliot Protsch noted that progressive legislation passed in both Iowa and Wisconsin relating to the ratemaking principles of rate-based utility plants has increased regulatory certainty creating opportunities to invest in generation that did not exist a few years ago. For example, the 565 MW Emery plant in Iowa had advanced approvals for a 12.23 percent return on common equity and a 28-year depreciation schedule.

"The potential for reasonable and known returns based on generation built to service customers of our domestic regulated utilities has been enhanced in both Iowa and Wisconsin," said Protsch. "We intend to capitalize on these opportunities to the benefit of our customers, our investors and our employees."

Alliant Energy Corporation is an energy-services provider with subsidiaries serving more than three million customers. Providing its customers in the Midwest with regulated electricity and natural gas service remains the company's primary focus. Alliant Energy's domestic utility subsidiaries, Interstate Power and Light and Wisconsin Power and Light, serve 982,000 electric and 416,000 natural gas customers. Other business platforms include the international energy market and non-regulated domestic 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 .