Alliant Energy filed a request with the state Public Service Commission to raise electric and natural gas rates effective Jan. 1.

The request, which would be effective through the end of 2018, includes a 1.1 percent increase in electric revenues and a 12.9 percent increase in natural gas revenues. An Alliant news release said the rate hikes would translate into a 4.7 percent increase on average residential electric bills and a 6 percent increase on average residential natural gas bills.

The news release said the increases are to pay for environmental improvements in two power plants, safety and reliability investments, and expansion in Alliant’s natural gas pipeline infrastructure.

The rate increase request includes increases in the fixed residentail electric charge, now $7.67 per month, to $12 in 2017 and $18 in 2018.

New pricing plan options are also being proposed to offer more customer choice: Nights and Weekends, for those who can limit daytime weekday use; and Fixed Bill, which gives residential customers a set bill amount for 12 months. The green energy option, Second Nature, would also be offered at a lower cost, dropping from 2 cents per kilowatt–hour to 1.4 cents per kilowatt–hour.

The PSC must approve any rate increase. A PSC decision is expected in the fourth quarter.