The U.S. Energy Information Administration reports that residential energy consumption per household has decreased over the last 30 years. Improvements in building insulation plus more efficient windows, heating and cooling equipment, and major appliances have more than offset the increase in the average size of homes and the dramatic rise in the use of consumer electronics.
The EIA's most recent (2009) Residential Energy Consumption Survey details this shift in how energy is consumed in homes. It found that heating and cooling no longer account for the majority of home energy use, down from 58 percent of home energy consumption in 1993 to 48 percent in 2009. Making up the difference is the growth in energy consumption for consumer electronics and appliances (including refrigerators), up from 24 percent in 1993 to 35 percent in 2009.
More specifically, the survey found that space heating accounted for the largest share (42 percent) of energy usage in homes, followed by electronics, lighting, and appliances (30 percent), water heating (18 percent), air conditioning (6 percent), and refrigeration (5 percent).
Home energy consumption is responsible for a major fraction of the average American's carbon emissions -- roughly 32 percent, according to the Union of Concerned Scientists -- and offers significant opportunities for greater efficiencies. The first step in making our homes more efficienct is to get some answers to basic questions about our energy consumption. How much energy do I use right now. How is that energy produced? What is the environmental impact of the energy I use? What can I do to make a difference?
HOW MUCH ENERGY DO I USE RIGHT NOW?
Start by becoming familiar with the information contained in your natural gas and electric bills and then track your energy usage from month to month. This will make you more aware of just how much energy your home is consuming and more conscious of energy issues generally. It can also provide a big incentive to test various strategies to improve your home's energy efficiency and will help you monitor the impact of those changes.
Understanding Your Gas Bill
(A detailed discussion of the components of a Nicor Gas bill is available here.)
How do you know whether the number of therms you used is "reasonable"? The answer to this is . . . it depends. It depends on how cold it was outside.Your gas bill may give you this information if it reports the total number of degree days in that billing period. Or you can find degree day records for your area on Weather Underground. (To get started, go to the History Data section and enter your location and a date for which you want weather data.)
Degree days are used to calculate the effect of outside air temperature on building energy consumption. Heating degree days (HDDs) are a measure that indicates how much colder the outside average temperature was compared to a baseline temperature of 65°F. (This baseline reflects the observation that houses generally require heating if the outside temperature is lower than 65°.) If the average of the high and low temperatures for a particular day was 35°, that would add 30 HDDs to the total for the billing period.
Similarly, cooling degree days (CDDs) are a measure of how much warmer the outside average temperature was than 65°F.
Dividing the number of therms used by the total number of degree days for that period provides useful information about the energy performance of your house. It reflects the temperature setting of your thermostat, the tightness of your house, and the efficiency of your home's heating system.
With this calculation, you can compare your energy consumption from month to month, and year to year, despite variations in the weather and the fluctuating cost of energy.
(The number of therms used also reflects the energy consumed in heating water and any cooking done with gas. Your summer gas bill will give you a rough idea of how much these uses contribute to your energy consumption year-round.)
Understanding Your Electric Bill
Most consumers pay a fixed per-kWh rate for their electricity no matter what time of day or which day they use it. In some areas, however, consumers may choose an alternative system called Real Time Pricing (RTP) and pay a rate based on the wholesale market price of power, which varies from hour to hour and day to day.
For much of the day, the "real time" price is lower than the standard fixed price, but at times of peak demand--on steamy afternoons in summer, for example--the price of electricity can soar. RTP customers can save money by reducing their electrical usage during these high-demand hours. (Participants in ComEd's RTP program, for example, have saved on average more than 15 percent on the electricity supply portion of their bills since the program began in 2007.) For the utility, lower peak demand decreases the need to operate more expensive "peaker" plants (to supplement the power from less expensive base load plants), reduces the risk of blackouts, and delays the need to build new power plants.
Another rate structure that rewards customers who cut usage during peak periods is Time of Use (TOU) pricing. With this system, the utility company establishes two or more tiers of prices, setting peak and off-peak rates for different times of the day, days of the week, and seasons of the year. During winter months, for example, the peak period may be early morning and early evening whereas in summer months, it may be midday through early evening, reflecting air conditioning usage. The higher rate charged during peak periods encourages customers to shift usage to off-peak hours.
(A discussion of the components of a ComEd bill and the utility company's various energy-saving programs is available here.)
WHAT ARE THE SOURCES OF THE ENERGY I USE IN MY HOME?
Most of the energy consumed in homes is produced by burning fossil fuels like coal, oil, and natural gas. When burned, each of these fossil fuels emits various greenhouse gases, principally carbon dioxide (CO2). But they differ significantly in the level of emissions that each gives off.
Close to three-fourths (72 percent) of the carbon emissions related to operating a home is attributable to the electricity used in the home. This is due in part to the relative inefficiency of most power plants in converting the energy in the fuel they burn into electricity. It typically takes three or four units of fuel to produce and deliver one unit of electricity.
The other factor is the electric power industry's heavy reliance on fossil fuels--carbon-intensive coal in particular. Two-thirds of the electricity generated in the U.S. in 2011 was produced by burning fossil fuels, with 42 percent coming from coal, 25 percent from natural gas, and a small percentage from oil. Non-fossil fuel sources accounted for the rest: 19 percent from nuclear power, 8 percent from hydropower, 3 percent from wind power, and the remainder from other renewable sources.
WHAT IS THE ENVIRONMENTAL IMPACT OF THE ENERGY I USE?
To answer that question, you will need 12 months of data about the energy used in your home. If you do not have a year's worth of utility bills at hand, you should be able to obtain your account history from your local utility companies.
For most Americans, driving ranks along with electrical usage at the top of the list of daily pollution-causing activities. (For others, air travel can be the biggest contributor to their greenhouse gas emissions.) The DOE/EPA Fuel Economy website offers tips for getting the best gas mileage from your car, can help you find and compare cars, and explains the information provided on the new fuel economy label. The EPA's Green Vehicle Guide is another helpful resource.
WHAT CAN I DO TO MAKE A DIFFERENCE?
There are lots of things you can do--many of them no-cost or low-cost steps--to cut your energy consumption and reduce your greenhouse gas emissions. Frequently mentioned action steps include the following:
More detailed lists of energy-saving measures can be found at these websites:
LINKS AND RESOURCES