Most of us these days are concerned about how we use energy. We tend to be aware of a light left on or a cell phone charger left plugged in. So we turn the light off or unplug the charger and tell ourselves we have made a difference. If you have been following our columns you may well guess the next question: HOW MUCH DIFFERENCE? Compared to what?

Let’s start with some basics on electricity usage. When you buy electricity, it comes in units of kilowatt-hours (kWh). Your electric appliance or device uses energy at a rate determined by its wattage (e.g. a 100 W light bulb). So, wattage is the RATE at which it uses energy. To get the AMOUNT of energy it uses (kWh), divide the wattage by 1000 and multiply it by the hours it is used.

If a 100-watt incandescent bulb is left on for 5 hours it uses 100W/1000, or 0.100 kW. Multiplied by 5 hours this comes to the amount of 0.5 kWh. It will cost you about 7½ cents (at Maine electricity rates of around 15 cents/kWh).

Appliance ratings vary a lot, of course. A hair dryer uses 1500 W, while a 42-inch LED television uses around 25 W. Does this mean your hair dryer uses more energy than your TV? No, because it is the combination of time and power that matters: you might use the hair dryer for 3 minutes/day, and the TV for 4 hours/day. The hair dryer will use 0.075 kWh per day while the TV will use 0.1 kWh/day. The hair dryer costs you 1.1 cents/day and the TV 1.5 cents/day.

Some devices and appliances are always on (refrigerators, modems), while some spend little time on (hair drier, coffee grinder). Some use power when left plugged in even if you are not using them (chargers, microwaves, printers). All of this makes it tricky to figure out how much and where your energy is actually being used.

So let’s take a few examples. The values are approximate, but they are all typical for up-to-date appliances and electronics. For each we will state the daily average usage and the annual cost or possible savings here in Maine.

Unplug your cell phone charger: 0.01 kWh/day, less than 65 cents/year

Unplug your microwave oven when not in use 0.025 kWh/day $1.60/year

Turn off your computer/printer powerstrip when not in use: 0.1 kWh/day, $6.50/year

Replace 5W night light with auto-shutoff LED night light: 0.1 kWh/day, or $6.50/year

Cut daily shower usage in half (with shorter showers, lowflow showerhads or fewer showers): 0.6 kWh/day, or $33/year

Change your 5 most-used light bulbs from 75W incandescent to equivalent LED (assuming on-time of 2 hours per day): 0.65 kWh/day, $36/year.

Use cold water in clothes washer. (assuming 3-4 loads per week) 1.5 kWh/day, $83/year

Hang clothes instead of using the dryer: (3-4 loads per week) 2 kWh/day, $110/year

This totals $277 per year in savings. There are a few points to make here.

First, it seems sensible to balance convenience with savings. Do you unplug your microwave 700 times a year to save $1.60? On the other hand, might the inconvenience of hanging out your clothes might be worth $110?

Second, sometimes a small financial investment can quickly yield savings, such as spending $10 to replace 5 light bulbs for a $36 savings/year.

Third, note that some of these savings are much, much larger than others – such that a whole bunch of the little ones don’t even add up to one of the larger ones, and are much more time-consuming.

Finally, can we say that all of these little things add up to something big?

Well, let’s add up all the savings, and then double them to account for those we’ve left out. We get a total savings of 10 kWh/day, or 3600kWh/year ($550). The average per capita (not even per-household!) usage of a U.S. citizen is around 250 kWh/day. So if you are average, these savings make a dent of 4% in your energy usage.

Incidentally, the average per capita CO2 output in the U.S. is around 20 tons. Our savings above is about 1.5 tons. It’s not nothing. It’s a little. The little things add up – a little!

As David Mackay says in his excellent book, Sustainable Energy Without the Hot Air, “If everyone does a little bit, a little bit will get done.” Even if everyone does what seems like a lot, there will still be a long way to go to reduce our world’s CO2 emissions to near zero!

So, by all means, do these things if you find them worthwhile, but keep the big picture in mind, and meanwhile perhaps look for something big to do.

Paul Stancioff, PhD., is a professor of Physics at the University of Maine Farmington who studies energy economics on the side. He can be reached at [email protected] Cynthia Stancioff, MA, Public Administration, is an amateur naturalist/wordsmith. Previous columns can be found at https://paulandcynthiaenergymatters.blogspot.com/


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