Very Small Scale Power Generation in Rural Asia

[RaGun]

Hi,
I volunteer for a small group who try and help the families who live in the rural parts of Sri-Lanka
We have built and donated a large number of solar powered lanterns but during the rainy season (or even on cloudy days) we don't get enough sunshine for the lights to work for their intended duration.

Temporarily we are solving the problem by having local entrepreneurs charge batteries for the families for a small fee but we feel that this should not be a permanent solution. It's not the price that's the issue it's that sometimes the people have to walk for a number of kilometers to get to the nearest charging station.

Over the last 3 years we have helped over 5000 families by giving them solar lights so we would like to modify all those units to have more stable energy generation. Our current version has an output of 5 watts. We are looking to buy or build a unit which produces a maximum 8wh an hour until the fuel source runs out or something that can generate in a more slower rate such as 40wh in 16 hours so we can let it run overnight and have the power stored in a battery.

We are primarily a donation driven group so something with low cost and maintenance would be ideal.

I personally think that something which can generate electricity from hydrocarbons due to their high energy density would be ideal but I'm not an engineer so what do I know.

I'm not sure if this helps in any way but a number of years ago we transitioned a large number of houses from wood fired stoves to gas and as all the families that we help actually have access to gas I was wondering if any good technology exists where electricity can be generated by gas that can meet the low cost and maintenance criteria.

I've searched on the internet but honestly I don't even know what exactly to look for which is the reason that I registered here and am posting this thread so that people much more knowledgeable than me can possibly think outside the box and help us.

Thank you and Regards
Raj

 

[etudiant]

There are a variety of direct heat to electric power modules available, such as:
http://www.termo-gen.com/pages/generators.html

Do note that these are not easy to make and they need reasonable care to function reliably, as abuse will damage them. Plus the fuel need is not immaterial.
I wonder whether a bicycle driven generator with a battery might not be a more effectively sustainable alternative. The efficiency of LED lights is such that a 10 watt bulb is very ample and that level of power is achievable by anyone.

 

[johnbbahm]

A quick look at the weather looks like Sri-Lanka gets good winds.
A very simple wind generator.
http://paginas.fe.up.pt/~feliz/e_paper15_BicycleWindTurbine.pdf
another option would be the Biolite stove.
http://www.biolitestove.com/homestove/overview/

 

[Borek]

Spring, crank and winding? Or - if not a spring - perhaps just a weight that can be raised and runs generator through some simple gear made of bicycle parts?

 

[Danger]

Why restrict it to one technology? A combination of bikes, wind, etc. can cover most circumstances.

 

[RaGun]

Thank you for the replies, I actually wasn't expecting this many especially so soon.

At first thermoelectrics seemed ideal but after doing more research it's seem like 95% of the energy would be wasted as heat because they only operate at around a 5% efficiency. Our country is hot enough as it is and I don't want to make it any hotter or waste valuable fuel.

I don't think that the Biolite stove is for us because we've already moved everyone we help from biomass to gas. I did think of combining our stoves with a teg like they do to produce electricity but our families usually use the cooker for less than 3 hours a day which means that you would need a module that produces at least 13 watts to meet our daily electricity requirements.

It's funny that you send a link to the bicycle wheel wind turbine and mention about combining technology because when we were starting off a wind and solar system was one of the combinations that was suggested but was ruled out because the people didn't like the appearance (the height) and they were also a little afraid of lightning.

Borek, I don't understand what you mean by 'Spring, crank and winding' could you explain it a bit more please?

For generating electricity by using a weight don't you work out power by mass x height x gravity? So if you have a mass of 50kg a height of 2 meters and 9.8 for gravity then after converting from joules to watts you get 0.272wh and much less after you've lost a part of it through the generator.

A bicycle / hand powered generator sounds very interesting how can I work out about how much you would need to peddle to generate 40wh.
To me if an average strength man or woman can generate 8wh by using their feet or hands in one to two minutes then I think that this would have to be looked into much further.

I was also thinking about batteries.
Batteries start to degrade after constant charging and discharging so are there any other energy storage methods that we could use? I was looking at supercapacitors but I'm having a hard time finding out how to convert their numbers into watts.

 

[Borek]

Borek, I don't understand what you mean by 'Spring, crank and winding' could you explain it a bit more please?

http://en.wikipedia.org/wiki/Human_power#Windup_radio

For generating electricity by using a weight don't you work out power by mass x height x gravity? So if you have a mass of 50kg a height of 2 meters and 9.8 for gravity then after converting from joules to watts you get 0.272wh and much less after you've lost a part of it through the generator.

Your calculation is right, but I wonder how it compares to the size of the batteries used in the solar lamps you mentioned in your first post?

I believe alkaline AAA battery has around 1.5Wh, three such batteries run my headlight lamp for 20 hours or even longer. 0.27 Wh is what my lamp requires for about an hour, make it 30 minutes after taking losses into account. But "recharging" is pretty easy and fast. And you don't need weight to be part of the design - more like a hook for a sandbag.

Yes, there is plenty of handwaving in this line of thinking, and there are some obvious hurdles, but I am not convinced it can't work at all.

 

[syhprum]

I have seen gravity storage systems that were used for electricity generation at the end of the nineteenth centaury but they were large with several hundred Kgs wound up tens of meters.

 

[RaGun]

Our lamps use a lead acid battery with a usable capacity of 40wh, the actual capacity is higher but because it's not deep cycle the system cuts off at a certain % which I can't remember. I think that this number was decided so a family can use 20wh on one day and still have another 20wh left on another day if there was barely any usable light but the weather doesn't like to follow a set order.

The current system uses a number of lights a small fan as well as the ability to charge a phone from dead to full charge. The fan and lights together use 5 watts so to charge a phone we recommend only running two lights which is the reason that I'm looking to up the power output to 8 watts though if there is a good solution we can keep the output at 5 watts because nobody has ever complained about having to switch things off to charge a phone.

Even if we remove one of the lights in the system we will need a bare minimum of 4 watts so if you apply the m x h x g equation for 4wh with a height of 3 meters you need a mass of 490kg. I really don't think a gravity based solution is possible.

 

[anorlunda]

A small lead acid battery typically might have a capacity of 40 amp-hours, not 40 watt-hours. Are you sure? The difference is roughly a factor of 12.

 

[RaGun]

I'm pretty sure that that is correct.
The battery is pretty small, it says 12V 6Ah which is 72Wh but like I said you can't use all the capacity so I think the manufacturer recommended the 40Wh figure for long term use.

 

[Borek]

OK, with these numbers it looks different. At least the situation is clear.

Wikipedia (human power) claims you can get at least 50 W of continuous power from a healthy individual. That means around 24 minutes for 40 Wh (less from someone better fit, more after taking loses into account).

 

[RaGun]

I'm not understanding the maths.
If you pedal continuously at a rate of 50 watts wouldn't it take nearly 50 minutes to generate the 40Wh (50/60=0.833W/minute then 40/0.833=48 minutes).

The really important question is, will people actually do it?
Even if you split it up so you do it 10 times for 5 minutes each that's quite a bit.


I need to ask what the others think as well as speak to some of the families to ask for their opinion. This will probably take a couple of days.

 

[Borek]

Let's see, perhaps I did some error. 40 Wh = 40*3600 J, at 50 W you need 40*3600/50 = 48 minutes. Yes, you are right, and I was wrong by a factor of two.

Most likely I used 100 W initially for calculations, then edited the post but only partially. Sorry about that.

 

[DrZoidberg]

A combination of wind and solar sounds like a good solution. If the people don't like to have wind turbines in front of their homes you can just put the turbines outside the village. They don't have to be close to any buildings.
Also with bicyle generators a single person can create more than 200W. That would mean 12 minutes for 40Wh. And you can build one yourself relatively cheaply. There are a few videos on youtube on that topic.

 

[Borek]

Also with bicyle generators a single person can create more than 200W.

Some googling shows power output of a highly trained pro biker (think doped Armstrong) to be somewhere between 6-7W per kilo body weight, and they can keep it for up to an hour (close to 6W for whole hour, more on shorter distances; and we don't talk about sprinters on the last straight, as they hit four digits numbers, but for less than half a minute). I doubt existence of massive, highly trained bikers in the rural Asia, so more than 200W doesn't look realistic. 100W does.