Sunday, January 15, 2006
Electric Mower
One of the things that I enjoyed, that may not have a positive benefit for the environment, is my electric mower. The first mower I had was a gas one. Fortunately, I hit a big rock and bent the crank shaft irreparably. About that time our county had a rebate program that gave you credit for an old gas mower to get a non-gas powered one. I got a manual push mower. Aah, silent mowing with just a little “thwip, thwip, thwilp” sound of the reel on the cutter. The best part was being able to mow barefoot on warm summer days. But it was didn’t do well in my lumpy, branch-strewn yard, or if the grass got too tall. I got tired of either raking the yard before each mowing, or getting an unexpected Heimlich maneuver every time the mower got jammed with a branch or Douglas Fir cone. This one was eventually given to an interested carpooler.
So, the next time the county offered a rebate, I got a rechargeable electric mower. While it is a bit heavy, it doesn’t stop dead every time it runs into a pitiful branch. It is quiet, and has no fumes (my son has asthma, so removing every possible irritant is important to me). No direct pollution. There is some pollution involved in generating the electricity, but not near as much as a small, relatively inefficient, gas engine produces.
One just has to remember to recharge it. Lead-acid batteries do not recover well if left for long in a discharged state. This is how the first set of batteries met an early demise. A friend mowed our lawn while we were on vacation, and did not hook it up to the charger. Two weeks later we returned, and I finally plugged it in. It did recharge, but it no longer mowed the entire lawn on one charge. Over the next few months it degraded further, and stopped working at all at about three years age. It was easy to install a replacement, but it made me think about the environmental cost.
The battery shop took the old battery for recycling. The Battery Council International says that “more than 93% of the lead” from a battery is recycled (http://www.batterycouncil.org/news-041902.html). The EPA estimates that "Nearly 90 percent of all lead-acid batteries are recycled" (http://www.epa.gov/epaoswer/non-hw/muncpl/battery.htm). That sounds pretty good. But what happens to the other 7% to 10% of the lead?
Ecological footprint analysis:
(footprint values from “Radical Simplicity” by Jim Merkel)
Push mower: 20 lb (mostly metal), 20 year life
20 lb / 240 month * 397 sq.yd.-month/lb = 33 sq.yd
Gas Mower: 30 lb, 10 year life
30 lb / 120 month * 397 sq.yd.-month/lb = 99 sq.yd
2 pint gasoline/month (average over year) = 0.25 gal/month
0.25 gal/month * 500 sq.yd.-month/gallon = 125 sq.yd.
(I am not sure that this includes all of the pollution effects of a small, inefficient engine)
Total: 224 sq.yd
Electric, rechargeable mower: 30 lb, 10 year life frame
30 lb / 120 month * 397 sq.yd.-month/lb = 99 sq.yd
Battery: 30 lb, 3 year life
30 lb / 36 month * 335 sq.yd.-month/lb (recycle metal) = 279 sq.yd
2 mowings/month * 400 W *0.5 hour/mowing * 1 kw/1000W * 31 sq.yd.-month/kw-hr = 12.4 sq.yd
Trickle charge of battery:
5 W * 24 hour * 31 day/month * 1 kw/1000W * 31 sq.yd.-month/kw-hr = 115 sq.yd
Total: 506 sq.yd
(I am not sure how accurate my estimate of the footprint of the battery is, but by this estimate it is larger than the entire footprint of the gas mower!)
The most environmentally sound solution would probably be to not have grass to mow. We are slowly headed in that direction. Our garden takes up the small, prime sunny spot. The back yard is already partly wild, and laziness and neglect may soon send it the rest of the way.
copyright 2006 by Milliwatt
So, the next time the county offered a rebate, I got a rechargeable electric mower. While it is a bit heavy, it doesn’t stop dead every time it runs into a pitiful branch. It is quiet, and has no fumes (my son has asthma, so removing every possible irritant is important to me). No direct pollution. There is some pollution involved in generating the electricity, but not near as much as a small, relatively inefficient, gas engine produces.
One just has to remember to recharge it. Lead-acid batteries do not recover well if left for long in a discharged state. This is how the first set of batteries met an early demise. A friend mowed our lawn while we were on vacation, and did not hook it up to the charger. Two weeks later we returned, and I finally plugged it in. It did recharge, but it no longer mowed the entire lawn on one charge. Over the next few months it degraded further, and stopped working at all at about three years age. It was easy to install a replacement, but it made me think about the environmental cost.
The battery shop took the old battery for recycling. The Battery Council International says that “more than 93% of the lead” from a battery is recycled (http://www.batterycouncil.org/news-041902.html). The EPA estimates that "Nearly 90 percent of all lead-acid batteries are recycled" (http://www.epa.gov/epaoswer/non-hw/muncpl/battery.htm). That sounds pretty good. But what happens to the other 7% to 10% of the lead?
Ecological footprint analysis:
(footprint values from “Radical Simplicity” by Jim Merkel)
Push mower: 20 lb (mostly metal), 20 year life
20 lb / 240 month * 397 sq.yd.-month/lb = 33 sq.yd
Gas Mower: 30 lb, 10 year life
30 lb / 120 month * 397 sq.yd.-month/lb = 99 sq.yd
2 pint gasoline/month (average over year) = 0.25 gal/month
0.25 gal/month * 500 sq.yd.-month/gallon = 125 sq.yd.
(I am not sure that this includes all of the pollution effects of a small, inefficient engine)
Total: 224 sq.yd
Electric, rechargeable mower: 30 lb, 10 year life frame
30 lb / 120 month * 397 sq.yd.-month/lb = 99 sq.yd
Battery: 30 lb, 3 year life
30 lb / 36 month * 335 sq.yd.-month/lb (recycle metal) = 279 sq.yd
2 mowings/month * 400 W *0.5 hour/mowing * 1 kw/1000W * 31 sq.yd.-month/kw-hr = 12.4 sq.yd
Trickle charge of battery:
5 W * 24 hour * 31 day/month * 1 kw/1000W * 31 sq.yd.-month/kw-hr = 115 sq.yd
Total: 506 sq.yd
(I am not sure how accurate my estimate of the footprint of the battery is, but by this estimate it is larger than the entire footprint of the gas mower!)
The most environmentally sound solution would probably be to not have grass to mow. We are slowly headed in that direction. Our garden takes up the small, prime sunny spot. The back yard is already partly wild, and laziness and neglect may soon send it the rest of the way.
copyright 2006 by Milliwatt
# posted by Theepdinker @ 8:27 PM 
