6 Sep 2010 19:42
Google Maps Street View has a nice shot of the house across the street from where I grew up. The current owners moved in almost four years ago, and the outdoor wall lamps (installed by the owners previous to them, who flipped the house never having lived in it) have been lit day and night since.
How much have the current owners paid to brighten their Mulberry Drive neighborhood?
[Note: There should be a Google Maps Street View image here, but unfortunately Google Maps Street View can’t correctly produce embedding code. Pretend there’s an image of a house with some lights on the front or click the link below.]
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The pinpoint light sources shine brightly through the Phoenix sun, suggesting that each fixture houses a 60-watt (or brighter) incandescent lamp. Three 60-watt bulbs running continuously consume a kilowatt-hour of electricity every 5½ hours. That’s 4.32 kWh per day or just over 130 kWh a month. The electric utility for the area, Salt River Project, offers several rate plans, so it’s impossible to say exactly how much the lamps cost to run. Because the lights run day and night, SRP’s Basic Plan, which has no peak/off-peak pricing, would be the best value. During the seven summer months (May–October), SRP charges about 11¢/kWh. In “winter” the cost drops to about 8¢. Under any plan, the annualized cost will exceed 10¢/kWh, or $13/month. The cost of electricity hasn’t changed much over the past several years, so come December, when the owners celebrate four years in their house, they’ll have spent over $600.00 for the outdoor lighting.
On the brighter side, hydroelectric and nuclear power produce much of Arizona’s electricity, so the carbon footprint from running these lights isn’t as big as it might be. The big truck, on the other hand…
Another interesting question to answer is this: How much ice could these lights have melted? One kilowatt-hour equals about 860,000 calories (that’s 860 food “Calories”), or enough to melt a little more than 22 pounds of ice. The energy that runs these lights is all converted to heat, and if that 180 kW heat were used to melt ice instead of heat the Phoenix air, it would melt a lot of ice over four years — 68 or 69 tons, in fact, which would produce enough water to fill a good-sized in-ground swimming pool.