I am exploring the use of human-powered electrical generation for off-grid third world locations. I have been reviewing sites and solutions such as this one. Most sources site 100W per person/hour as the maximum generated.

However, somehow I need to power 32x that to get a cool new ambient humidity to potable water setup working. To top it off, I have been told that there is a 20% loss from the conversions if the power is stored in batteries (eg car batteries) and then used to power things.

Some say a flywheel adds something (especially those selling plans for that design), others say it does not. I also wonder if cycling is the best harness of human energy and not, say, a step machine or some other approach.

My question is, do you have an idea or know of one for generating more than 100W/person/hour? Any nice tweak ideas for the bicycle concept?

I know most of the readers are physicists and not engineers, but you are still smarter than I am.

[Solar panels are heavily subject to theft, and wind power restricts the concept to areas having enough wind. Human power also has the advantage of creating a source of ongoing jobs for the young and thus an anti-theft motive as well.]

I think cycling is one of the most efficient ways to do it and least tiring.

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I underwent a cardio assessment on a special bike at a gym two days ago and was able to maintain 185W with a steady heart rate of 137 for about 10 minutes. After that my heart rate started to increase and I began to feel tired.

The human-powered flight people probably have good ideas. They went with pedals. I don't think anything else accomplishes the needed thrust to weight.

Wikipedia: Human-powered transport:

You're going to be limited by how fast a body can burn calories (and eliminate the waste products).

Humans might be natural marathoners, bred by nature to have the capacity to trot long distances. Cycling probably uses our most productive muscles most efficiently.

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2000 kilocalories = 2,324 watt hours.
It's also about what a normal sized human needs to consume in food each day to maintain body weight.
If you spread that 2,324 watt hours over the course of a day, you'll be able to get a continuous output of 97 watts.

To exceed that output, you're going to need to feed your workers significantly more calories, and there's no such thing as a free lunch.

Thanks everyone.

It seems the sweet spot is going to have to be a smaller version of the air to water machine. There is a much smaller version that produces up to 14 gallons/day and could easily be powered by a bicycle, but there is little surplus water to go around, and it is too expensive for single-dwelling use. The large version produces 300 gallons a day (enough for ~250 people for drinking and cooking), but requires too many cyclers (32). The inventors are considering something in-between that may strike a better balance.

These are early days and perhaps cycling with a small wind generator will be the best combo. This is going to take some prototype iterations to get right.

Again, thanks all.

I was going to suggest a cycle/wind power combining. Also what about modifying the bike set-up in one like a recumbent style? Less upper body (neck, arms, back) strain on the cyclist and can probably peddle longer.

Also you mentioned issue with the batteries. Is there other possibilities there for improvement with negating the theft factor? I know lithium battery might be an option, but with the price they are bound to be stolen.

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I suspect that if your target market is so poor they can't afford potable water they probably can't afford the energy expenditure to distill water by a mechanism powered by human power pedaling. They'd be better advised to just get a bike and haul water from a well. There are no human populations that live so far from water that they can't haul it. Poor people just can't afford a bike to do so.

This isn't an investment opportunity from a Libirian prince is it?

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ToSeek
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The Bad Astronomer
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No, no Liberian princes nor Nigerian scam artists. But the problem is clean and safe drinking and cooking water, not water access itself. Project is shepherded by a Ghanian-American investor, water machine distributor and friendly philanthropists. We are in early days deciding which prototype to build first. I have local access to a water machine in Barcelona.

@All,
Power solution is shaping up on solar plus stirling engine. There is a great solution (high solar to grid conversion) from people like Tessera, which I believe can be half constructed locally using a simpler design from some MIT students for the dish (uses cheap and flat mirrors in a tinker-toy-like frame). The frame can easily be made from locally available bamboo in Ghana. Granted, it is much less efficient than the "pro" version, but even then can generate enough for our purposes. It is also less theft-prone in that there are no panels nor expensive mirrors; other machines will be locked to the ground.

The Tessera design only generates during daylight, but some added storage for heated water might allow some nighttime stirling + generator operation.

This is fun!

Hmm. . .could some variant on this watercone desalination device be used to distil the bacteria and other unwanted components from river water so it's safe to drink?

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What about just storing the treated water in bottles for nighttime use?

Stainless steel containers would be cheap, durable, easy to sterilize with boiling water, and probably a whole lot more convenient than having to run the machine at night as well. It would neatly avoid both the engineering challenges and the need to haul yourself over to the water machine at midnight just to get a drink of water. And it seems a bit excessive to be heating and storing clean water so you can use it to power a Stirling generator that powers a machine that makes. . . clean water.

Thank you for that. The issue is that we need to produce water 24/7 to get up to the 300 gallons per day, and using the machine as designed now for less time than that makes the cost per gallon shoot up too high.

The water for the Stirling engines can be from any source, and is largely recycled. We certainly would not use the clean, distilled water for that function! (BTW, I am also looking at plastic Fresnel lenses focusing directly on the Stirlings, which seems to be an even cheaper build. We may still wish to heat a reservoir of water to run the Stirlings at night, however.)

Water is periodically drained from the tanks and put in containers so people can cart it home; no one drinks directly from the machine.

Thanks for the link. Will take a close look.

WHat about the hand pumped devices used for camping or in Liferafts?

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The OP is about condensing water from "ambient humidity" not purifying dirty water.

Dirty water is usualy consumed by children because they often are used as water haulers for greedy adults. Deprived of food, water and worked to exhaustion beyond their capacity to haul water for themselves they drink from the most convienient source.

Most reputable world health organizations agree that the best solution is to provide more sources, ie, drilling wells or preventing the supply from getting dirty in the first place.

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ToSeek
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The Bad Astronomer
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I remember seeing a hydraulic powered system working with rope and pulley systems between tree trunks, their movement in the wind operated hydraulics that provided power.
Can't rememebr where it was now though

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