Three times this past week I was asked about why don't we make a bike powered generator to watch TV or power our computers. The main reason is that we don't have the umpf to do it! It seems crazy, but we (humans) don't put out anywhere as much energy as we use.
The current record holder for the energy output over an hour for a human is Ondrej Sosenka and the website BikeCult.com has an estimate of his average wattage during his Hour Record at 430 Watts! (just over 1/2 horsepower) If Ondrej’s bike were attached to a bicycle generator and it was super efficient, Ondrej would have been generating enough power to light up 7 60-Watt light bulbs!
Your average desktop computer (Modern LCD, Not old tube style) uses about 60-250 watts. General efficiency ratings for an electric generator is 60% (80% for really high tech good ones). So figure 60% of 430 watts is 250 watts - BY THE RECORD HOLDER!! (and only for an hour!) I think a fairly fit person would be hard pressed to generate a full 100 watts for even a few minutes. High Tide Labs, in Palo Alto, California, recently launched a bike-mounted generator called the RollerGen, which puts out just over 30 watts—as long as you're ride faster than 8 mph for 10 minutes.
Then, if you want to use it to charge a battery - say pedal for three hours and then run some high power demand for 30 minutes or so - you have to figure out the efficiency of the batteries. Typical efficiency in a lead-acid battery is 85-95%, in alkaline and NiCad battery it is about 65%.
So while it seems tempting, the reality is, we just don't put out much energy by ourselves. That's why we (humans) used to use horses and other big animals for hard work, and that's why our world has changed so much in the last century - since we started really using fossil fuels as energy sources.
On a side note, many of the pedal powered solutions being developed for developing countries don't go through the step of generating electricity - they use mechanical energy. Things such as washing machines, etc. I've even seen pedal powered merry-go-rounds. It's crazy, but we waste almost half of the energy in our fuel when we use it via electricity. We waste some energy as heat in the conversion to electricity. We waste a LOT in transmission. We waste a lot storing it in batteries. And, we generally waste a lot in heat when we run the final product (good 'ol incandescent lamps, for example.)
P.S. Some of my favorite diagrams are the "Energy Flow Diagrams" from the Lawrence Livermore National Labs. They show where our energy comes from and how it's used in the US. Note that most - 57% in 2008 - is "rejected" (or wasted) in transmission, etc.
Subscribe to:
Post Comments (Atom)
1 comment:
Then there is the lost efficiency that another IslandWood staffer wrote about in her blog:So, kids are in car, happily munching on their english muffins. Success! And we're right on schedule - amazing.
But wait.... I was going to bike to work today after dropping off Piper at preschool. Where are my bike shoes?? They were at the top of the stairs for a week, but someone actually cleaned the house and put them somewhere. What were they thinking??? Craden!! (Text) "Where arey my bike shoes" (typo included for accuracy.) Run around the house three times. No shoes. All other gear is in the car. Bike is on the rack. I am wearing my whole biker chick outfit and have not showered. I pledged to ride to work four times this month... (ok - LAST MONTH... I'm a little late.) So I MUST bike to work today! Check the Roastery (the storage shed that used to be a coffee roasting building). No sign of shoes. Check the shoe closet for a third time. No shoes. Peek in car to check on children. Sky has finished two of her four english muffins, Piper one. Sky has given Tallis a part of her nutella muffin and he has brown sticky goo ALL OVER his face and hands and shirt. I am BUSTED! I feed my children chocolate for breakfast!!! Check the roastery again, but this time look INSIDE the bike gear bin. THE SHOES ARE THERE! When is anything where it is actually supposed to be? Today.
Stop one: Daycare. Sky and Tallis are deposited. Stop two: Montessori preschool. Piper is deposited (15 minutes late.)
I sprint to the car and jump on my bike, racing across the island to get to work by 9:45 when the monthly all-staff meeting is set to begin. I roll in at 9:46 (an 18-minute ride, about 4 miles), drop my helmet and bike, pull some loose yoga pants over the spandex and dash into the meeting, hoping I can sit my sweaty lycra-clad body in the back of the room. Dang! I forgot this meeting was going to be held in a circle - no hiding this time. Well at least everyone can see I'm fulfilling my pledge (LATE!)
I decided not to shower and dress normal because I figured everyone had already smelled me in the staff meeting and seen my flashy bike jersey - plus I was just going to be getting back on the bike to ride back into town in a matter of a few short hours.
Post a Comment