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Old 05-21-10, 12:02 AM   #1
foodcoloring
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Question Help! Generating and Storing Electricty During Commute

Next year my boyfriend and I will be living in an apartment in Oslo. I'm going to garden indoors, since we won't have a yard and it's usually pretty cold and dark outside, anyway. We were thinking about partially powering all the necessary lighting (for my plants) with electricity generated during our daily bike commute.

He knows someone we can probably get a few old bottle dynamos from for free, and we were thinking that we could hook some of those up to a battery. I like to tinker, but I actually know very little about electricity or this kind of thing. However, I'm not looking for a kit to buy so that I can charge my mp3 player, or AA batteries. I'm looking for something a bit larger than that, and more DIY. The only information I can find on the net is about stationary bike generators. : (

To recap I want to use bottle dynamos to generate electricity during my daily commute, store this electricity, and use it to power a bunch of lights.

I'd like to know if anyone else has documented a project similar to this that I could use as a reference, what kind of battery would be best, the pros and cons of bottle dynamos(I've read the wiki but I'd like a personal opinion,) and most importantly how practical an idea this is. If it's more than a bit unpractical I can handle it, things are more fun that way. But I want to know the facts so that I don't get my hopes up.

Thank you for taking the time to read this post, and thanks in advance for any help. : )
- Diane
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Old 05-21-10, 02:39 AM   #2
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Originally Posted by foodcoloring View Post
To recap I want to use bottle dynamos to generate electricity during my daily commute, store this electricity, and use it to power a bunch of lights.
So the first thing to look at is how much power (Wattage) is used by that "bunch of lights" and for how long per day.

A typical commuting cyclist might be producing a total power output of around 100 Watts, so adding dynamos that consume more than about 50 W of his/her power is likely to add an unreasonable burden and turn the previously pleasant commute into drudgery. And the dynamos won't be 100% efficient at converting that 50W of mechanical energy into electricity, so 40W might be about all you could get (and most bottle dynamos will be much worse than that). So if your commute time is one hour/day then you'd have up to 40 W-hr to work with. But you'll use that to charge a battery which would then run the light(s) and there's a loss of efficiency in the charging/discharging cycle as well, so you might be down to 30 W-hr (i.e. 0.03 KW-hr) of available electrical energy from each day's one hour commute. Enough to run a single 30W bulb for one hour or a 100W bulb for 18 minutes.

Alternatively, you could pay the local utility company for that amount of power. Electricity is considered pretty expensive here in California, but the amount generated by a daily pedaling session of an hour under the above assumptions would only save about 15 cents each month.
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Old 05-21-10, 11:20 AM   #3
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Yeah, it's pretty sobering to realize how inadequate the power output of our bodies is even for little everyday things like making coffee or checking e-mail, never mind the big stuff like heating, lighting, and AC. Good thing the biosphere spent millions of years converting solar energy into stuff we could burn up in a few hundred!
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Old 05-21-10, 12:08 PM   #4
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You also have to consider the extra weight of the batteries you would be bringing along, which would eat up more of your power. The more you crunch your numbers, the easier it is to figure out why nobody else has done it. It is possible, but you would never get your money back out of it and you would need to be putting many extra hours on the stationary bike anyway. The extra food you would need to consume would also be a consideration. If you want to do this for enviro reasons, I would look into getting more efficient grow lights, like LEDs and not worrying about generating the power.
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Old 05-21-10, 03:42 PM   #5
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Physics is a beeoytch.
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Old 05-21-10, 04:51 PM   #6
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Check out the BBC show Bang Goes the Theory. They did a special a few months ago called the Human Power Station, where they hooked up a room full of stationary bikes to generators and used it to power a model house and had a family that didn't know what was going on live in it for a day. It took like 50 cyclists sweating like mad to power the peak load, and 4 or 5 even just to power the clocks and such when the family went out for a walk. And that was fairly fit cyclists with ALL of their power going into high efficiency generators.

At a wild guess, with bottle generators, I'd say that the BEST you could probably do after all the inefficiencies would be to light a high efficiency light source (LED or maybe fluorescent) for about 3 to 5 minutes per hour of cycling, unless you really put enough generator onto it to cause your effort to go up a lot.

In the end, I'd guess that over the course of a year's commuting, you might be able to harvest 50 to 80 cents worth of electricity, MAYBE. It might be a fun project, but honestly, if you're going to put ANY money into this at all, spend $30 on a solar panel and use that instead. A cheap solar panel will put out 5 or 10 watts, but it'll do it continuously all day.
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Old 05-21-10, 08:46 PM   #7
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Super lame! That's such a bummer, but still very interesting to learn about. Thanks for everyone's input. : ) We might be able to use a solar panel during the summer, but it wouldn't work too well in the dark of winter. It's still something to think about, anyways. I'm going to shop around for my lights, and continue to look into alternative power sources. Thanks again!

p.s. ItsJustMe, I think I'll watch that show. : )
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Old 11-03-10, 11:52 AM   #8
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Originally Posted by twinquad View Post
Yeah, it's pretty sobering to realize how inadequate the power output of our bodies is even for little everyday things like making coffee or checking e-mail, never mind the big stuff like heating, lighting, and AC. Good thing the biosphere spent millions of years converting solar energy into stuff we could burn up in a few hundred!
Perfectly said and quite funny if it wasn't also so tragic. This could also be applied to the Oglala acquifer in the midwest of North America (about 1/5 the size of the United States and currently being used for groundwater irrigation to grow grain crops). It is already down by 50% after being used for maybe 60+ years but would take 50,000 years to recharge from empty...25,000 at its present state.

The world is a very big place but it is still finite in size. Many people just don't seem to get that.
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