One of the ways I try to reduce my carbon footprint is to keep my office and classroom lights off as much as possible. As I have a window in my office, I hardly ever need a light on in my office. And, increasingly, I try to keep lights off in my classrooms in Alter Hall. Opening the curtains provides enough light for my daytime classes. When I need to show PowerPoint slides or a DVD, I close the curtains and turn on one bank of lights, if necessary. I reverse the process when I no longer need the equipment. Mark Hanlon, associate director for operations in Physical Plant, gave such actions his stamp of approval, noting that energy reduction is one of their top priorities and that each of us using less electricity for lighting on a regular basis would not only be good for the environment but also for Xavier's budget.

According to my resident energy guru (a.k.a. my husband) in the coal-fired Midwest, electricity emissions are about two pounds of CO2 emissions per kilowatt-hour of energy produced. There are six 32-watt fluorescent tube lights in my office in Hinkle Hall, each fluorescent tube light requires the local coal plant to emit about 1 ounce of CO2 for every hour of use. Therefore, if I had them on for about 20 hours each week, I would produce about 7.7 pounds of CO2 per workweek, or one-and?a-half pounds per day.

There are 64 fluorescent tube lights in each Alter Hall classroom. All those bulbs turned on for an hour require about 4 pounds of CO2 emissions. If I teach nine hours a week, that is a bit less than 37 pounds of CO2 per week if I keep all the lights on for the entire class. Of course, to get "my share" of that, I would technically have to divide that by the 30 people occupying the classroom, so it turns out to be nearly 1.2 pounds per person per week.

To help put all this in perspective, the average American generates about 41 pounds of CO2 a day. Sustainability estimates put the world's ability to continuously absorb carbon emissions at about 9 pounds/person/day. By keeping lights off in my office and classroom (most of the time), I can reduce that "average" number by about 1.8 pounds a day, a 4.3-percent decrease from the average of 41 pounds/day.

Unfortunately, this is a simplified version of reality. For me to really achieve these numbers?and the University and planet to significantly benefit?we all need to act together. For those of you who really want to know how turning off your lights reduces our university's carbon footprint read on.

Again, this is courtesy of my energy guru. As stated above, Duke Energy plants in Ohio emit on average 2 pounds of CO2 per kilowatt-hour (kWh) of energy generated. However, that does not directly mean that turning off appliances and reducing energy power demand by 1kW for an hour (using 1kWh less energy at the customer point) necessarily results in a savings of 2 pounds of CO2 emissions.

The emissions reduction depends on the total amount of the power reduction and the time of day that the reduction occurs. The utility company has one overriding requirement: ensure that enough power is available in the lines to meet whatever customer demand occurs immediately anywhere in their territory. Considering that they provide power to several million people and even more appliances, and they have no idea when most of them will flip their power switches, this is no small feat.

To do this the utility estimates based on past history what its demand will be at any hour of the day every day of the year. They are required by law to have enough extra power in reserve to meet that varying demand plus expected increases and to maintain enough reserve to handle any unexpected increases in demand.

The highest power demand occurs in the afternoon on a hot summer day. The utility must have access to enough power to meet that demand plus a certain percentage reserve. To do this they use baseload generators which run nearly constantly, peaking plants that can turn on and off relatively quickly, and spinning reserves which are plants left running but not outputting power just in case an immediate increase is needed. They can also buy power from neighboring utilities if need be. The baseload capacity is sized to meet the bulk of the power demand as it also provides the cheapest power for the utility. Peaking plants, spinning reserves, and buying power on the spot market are much more expensive ways to meet the demand.

Coal and nuclear plants are used as baseload generators as they take days to weeks to turn on or off and run most efficiently at full throttle. In fact EPA emissions laws require coal plants to run at nearly full throttle to maximize efficiency. These baseload plants do not respond significantly to fluctuations in demand. In essence once they shovel the coal into the burner, it will be burned, whether or not anyone needs the electricity it creates.

Peaking plants are those that can be throttled on and off rapidly to meet changing demand. Most of these use natural gas, which produces lower emissions per kilowatt-hour than coal.

So when you switch off a single light bulb and use 1kWh less energy, the actual amount of emissions reduction depends on whether or not a power plant reduced its power output as a result and by how much. A very slight and short-term reduction would likely be lost in the noise of a spinning reserve station and result in no reduction in emissions. However, the actions of many, many people turning off switches does have a noticeable impact as it allows a peaking plant to turn off or a spinning reserve to slow down. More importantly, over the long term, continual reductions in power use day after day affect the utility's long term planning and result in the lower expected future demands. This results in the utility turning on fewer or smaller power plants in the first place. That is where the real emissions savings occur. When this happens then we truly get the 2 lbs/kWh advertised.

Kathleen Smythe 
Department of History