ComEd's emissions and nuclear waste in 2009 was significantly higher than five years ago, and it's not completely clear why.

Each year, electric companies like ComEd are required by the Illinois Commerce Commission to release data, called an "environmental disclosure," indicating where their electricity comes from and the emissions and nuclear waste generated by the sources.  

ComEd, a subsidiary of Exelon, distributes electricity to homes and businesses, but does not produce any. It can only buy 35 percent of its power from other Exelon companies; regulators require that it buy the remainder from others.

Since 2007, the Illinois Power Agency has procured power for all Illinois utilities through a bidding process, and ComEd began using this process in 2009.

Sources of electricity can vary for a number of reasons, said Mark Pruitt, director of the IPA.  

"We have a procurement cycle every year, which is very competitive," Pruitt said. "We put blocks of electricity up for bid and people respond, and we take the best price."

Taking the best price means that the sources will change from year to year depending on market price, which could be one reason carbon dioxide and other emissions have increased significantly over the last five years. Bidders don't have to disclose the source of the power, Pruitt said.

Neither Pruitt nor Jeff Burdick, of ComEd's media relations staff, could provide a definitive reason for the increase in emissions. Neither could Paula DuPont-Kidd, of PJM Interconnection, which administers the wholesale market through which ComEd acquires and sells power.  

All said that the power sources change based on market price and availability, which could vary the environmental effects, depending on the power source. For instance, using more coal to power electricity will increase air emissions, while more nuclear energy will increase radioactive waste.

While ComEd can't control the pollution from the sources of its electricity, it is taking action to reduce its environmental impact, Burdick said. For example, the company uses alternative fuels in its fleet of vehicles. It also is applying to participate in a federal program to place solar generators on customers' roofs. After the customer's electric needs are filled by the generators, the additional energy goes back into the power grid.

"We'd be looking at both the environmental gains as well as how these technologies would affect the power grid," Burdick said.

Illinois EPA's tips for reducing energy usage and costs Body:

-Compact fluorescent light bulbs (or "CFLs") use 75 percent less energy than incandescent bulbs and last as much as 10 times longer. They provide the greatest savings in fixtures that are used at least 15 minutes at a time or several hours per day. Go to the energystar.gov site to match the right CFL to the right kind of fixture. And look for opportunities to recycle spent CFLs because they contain a small amount of mercury.

-Use your programmable thermostat. It saves more energy to let the house cool down when you're not home during the day and while you sleep than to keep it at the comfort zone continuously. You can save around 10 percent a year on your heating and cooling bills by simply turning your thermostat back 10 to 15 degrees for eight hours. Programmable thermostats are not generally recommended for heat pumps.

- Many electronics (TVs, DVD players, etc) draw electricity ("standby power") 24/7 even when switched off. Identify which appliances in your home are using standby power and unplug them or plug them into a surge protector power strip that can be turned off when not in use. If you have a high-speed cable connection to the Internet, plug that modem into a separate outlet and keep that "on" all the time to allow for overnight updates to your system.

- Unplug battery chargers for cell phones and other equipment until needed.

- Screen-savers are not energy savers. Be sure to enable your power-down or sleep mode feature for your monitor if it comes with your PC. As a general rule, consider turning off your monitor if you aren't going to be using your PC for more than 20 minutes, and both the PC and monitor if you're not going to be using your PC for more than two hours.