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Developing World Electricity Concepts

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morg

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Hi there,

I don't have an electrical background (mechanical engineer) though currently find myself in Sri Lanka, working for a local NGO on off-grid electricity projects for the rural poor, and could really use your help.

Small, village-run micro-hyro plants of around 10-20kW are a mature solution here for getting power to isollated mountain communities. They provide between 100-400W peak power, per household, via a simple mini-grid. While 10 years ago when these projects began, villagers were happy to recieve this humble amount of power, their aspirations have grown. Now, the use of power-hungry western appliances is causing friction due to the lack of available capacity for all.

My main focus is to look technically and socially at the best ways to distribute what power there is fairly. At present there are no meters and a flat monthly tariff. Simplicity, reliability and minimal-cost are the key drivers as I'm sure you can guess.

If I get any response on this I should maybe split my ideas into different posts but for now I'll just go through them:


1. Working with the exisiting (very simple) household fuse-box, I'd like to wire in a 24 hr timer that runs on scavenged power (very low consumption) and that has battery backup, as power cuts are common. This clock (manual or digital whatever is cheapest) will be programmed to switch a relay or contactor that will re-route mains power from a 200W circuit breaker through a 700W circuit to correspond with peak (evening) and off peak (daytime) power capacity. The idea is to bar overuse of the agreed household power allocation.

Honesty is an issue, so the clock will be simply secured, though I'd like the family to be able to reset the circuit breakers if overuse is accidental. The village prefer fuses ... Does anyone know whether circuit breakers can be manually overridden or not ? (provided they cannot be removed).

Can anyone advise me on the technical feasibility of this idea and if keen, perhaps suggest good sources for components ?


2. Per-unit meter systems aren't practical here as peak demand is the real problem. Demand meters seem to be more expensive than normal meters, and being designed for the first world, most actually use quite alot of power or are not very good in low-power scenarios.

I'm attracted to the simplicity of clip-on household power meters like -http://www.electrisave.co.uk/ - that have clearly borrowed components from conventional probes and 'consumerised' them. In parallel with the system above these could be really useful. Does anyone know of an absolute bargain basement Chinese copy ?

Looking at a longer term product development route, or even combining existing bits ad-hoc, could the timing function on the PCB be hacked to control the relay mentioned above thus integrating the system.


3. Some villages have alot of unused, 'off-peak' electricity during the day. Many villagers also have 12V car batteries at home. I'd like to wire-in a charger/inverter unit to charge and regulate the battery and then, if possible, could the user draw power from the inverter and the grid simultaneously to double capacity for a limited period ? This would allow them to use a 1000W iron or boil a kettle without going over their household limit.

If anyone could advise me on a very cheap charger/inverter (roughly 500W) and again advise on the feasibility of this concept. Using back-up and grid power concurrently is a topic I can't find anything on ...


Huge thanks in advance for any help you can provide,

If I'm reinventing the wheel anywhere here, please let me know.

Cheers,

Morgan.
 
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An interesting problem, maybe some of the lazy "I want a project" student oiks that we get on here could apply their minds to this problem.
No, maybe not!

morg said:
their aspirations have grown. Now, the use of power-hungry western appliances is causing friction due to the lack of available capacity for all.
I guess that is progress!

morg said:
Does anyone know whether circuit breakers can be manually overridden or not ? (provided they cannot be removed).

Can anyone advise me on the technical feasibility of this idea and if keen, perhaps suggest good sources for components ?

The consumer level circuit breaker that I am familiar with cannot be "jammed closed" to override an over current situation.
However be aware that circuit breakers, do not trip as soon as their rated current is exceeded. There is a time-current graph published by their manifacturers which defines the tripping time at various overloads.

morg said:
I'm attracted to the simplicity of clip-on household power meters like -http://www.electrisave.co.uk/ - that have clearly borrowed components from conventional probes and 'consumerised' them. In parallel with the system above these could be really useful. Does anyone know of an absolute bargain basement Chinese copy ?

If you read the user manual on that website, it does state that the unit is made in China! Like most things these days.

morg said:
3. Some villages have alot of unused, 'off-peak' electricity during the day. Many villagers also have 12V car batteries at home. I'd like to wire-in a charger/inverter unit to charge and regulate the battery and then, if possible, could the user draw power from the inverter and the grid simultaneously to double capacity for a limited period ? This would allow them to use a 1000W iron or boil a kettle without going over their household limit.

A good idea, but the inverter would have to be designed so that the AC output is synchronised to the mains supply, otherwise the thing just goes BANG.

If a significant part of the electrical load is used for heating water, why not heat a well insulated water tank during the off-peak times?

JimB
 
Hi Morgan

Srilanka being an eqatorial region, it shold be easy for you to try Harvest Solar Power to the Max extent. I understand, mountenous locations. wherever possible it can be tried. locally it may be costly- with international funding a project , perhaps it can become feasible.

similarly, we need not look at electrical ways only- eg., 1000w iron or boiling a kettle-- if one could save heated water using a solar water heater- the time taken to boil will come down-reducing the KWH needs. even with 250 watts , one could manage the rest as we are using pre heated items.

as time passes only solar power could be the lone solution for regions of this kind.

anxious to see the developments-
 
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Encourage them to go back to using fire for heating water and irons.

Get them to use compact flurosecent energy saving light bulbs as opposed to incandescents; they last five times linger and use a fith of the power.

What voltage are you using to distribute the power?

Please don't say 110V, that's no where near high enough.

Are you using single or three phase?

What's the maximum distance between the generator and consumer?

Normally a high voltage (in the oder of 10kV) is used to distribute power then it's a transformer is used to step it down to 240V.

Whilst 10kV is very dangerous you could always use 720V for transmission on some longer routes, but you really need an electrical engineer on this project to do this sort of thing.

Are you sure that no one's stealing electricity from you?

Batteryies and inverters are good ideas but a car battery aren't really suited to this and for any reasonable power level you need more than 12V, I'd go for 48V, amd modifierd sinewave inverters are perfect for powering heating appliances but they can't be used for some electronic loads like computers and can't be used to inject power back into the grid.
 
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Hero999 said:
Encourage them to go back to using fire for heating water and irons........................ .

Hi

I fear, what little forestation they might have will diaappear within 2 to 5 years :(

the alternative can perhaps be pro aforestation, whereever possible....
 
The issues you're dealing with are of a managerial aspect, NOT an electronics one, and need to be approached that way. If everyone is using high load devices at the same time then simply forbid it. Confiscate all such devices and come up with a scheme that would allow proper usage.
Example, if everyone wants to iron their clothes at the same time take all the irons away, have them all send their clothes to an ironing 'family' that runs 24 hours a day, schedual the work shift so that ironing is constant but there is only as much ironing going on as is required to get the given work load done. It might take a day to get your laundry back but it completly eliminates the peak power usage problem with that kind of device.
 
Thanks so much everyone for your interest. If you'd really like to help out though can I please steer you back on to the subject at hand before this ends up becoming a hypothetical post. To answer your tangents though:

First, I may have lead you astray on the issue of water heating and ironing ... very few families presently do this. This is not where the missing power is going, it's not there to start with. In the daytime (off-peak) in many villages, it is possible. The point is that they's like to ... and the villagers that flaunt the rules and DO do this, compromise the rest to the village.

MVS Sarma: Solar is popular in Sri Lanka (at a household level) and we have been involved heavily in that for the last 7 years, but unless costs come down drastically it will not compete with micro-hydro in these areas. A 10kW plant with all the necessary converstion and distribution equipment is just not feasible. As I metioned though ... I am working directly WITH specific hydro villages. It's for THEM I seek your help. I'd be more than happy to discuss long-term alternatives elsewhere. Good idea about the water heating, thanks. I'll try and think about 'packaging' that in a way they find convenient and ultimately, use.

Hero999: Again thankyou. The brief here however, is not to re-design the distribution network. I'm in no position to assess it (as I said, I'm looking to you guys for technical input) but national standards have been approved by the government, so I assume they are 'acceptable'. You have to bear in mind the scale of these schemes is very small and in very difficult terrain. 10-30kW for a village. A limit radius of 2km is normal to avoid 'uneconomy' in distribution loss. As they are so close to generation and cost is so critical I don't believe they use transormers.

Car batteries may not be 'appropriate' but I need you to tell me what's POSSIBLE, because as I will keep reminding you all - cost is the big reality here. It's not about what's 'best' from an academic point of view but what is the best use of the resources available.

Sceadwian: You are correct, the issue here is not ENTIRELY technical. It's a fascinating social problem too. These people borrowed money and bulit the power station themselves, in great unity, and now own this power collectively - but there's not enough to go round and inveitably, human nature manifested as neighbourly feuding, greed and dishonesty and will gently thwart any 'system' without strong, democatic leadership. And this, to varying degrees, is in place in all the villages. These villagers are also very energy conscious as you can imagine - they use CFL, wood and solar stoves etc ... what choice do they have ? But if you think long enough, I'm sure you'll agree it is patronising and unworkable to try and deny people's innate desire to use their OWN power in some 'luxury'. Unlike the West these people don't get a kick out of being 'energy efficient' - to them it's like wartime rationing.

When resources are short, the greater the need for accuracy in disseminating those resources. If humans can be avoided, then corruption and conflict can be avoided too. Hence my solutions. If you'd really like to help out, can we please discuss the feasibility of them ?

Jim B: "A good idea, but the inverter would have to be designed so that the AC output is synchronised to the mains supply, otherwise the thing just goes BANG." Where possible, I'm striving to use cheap, off-the shelf bits. I'm encouraged that there could be a solution here though ... can you elaborate on what would have to be done to get this working ? You mean it has to synchronise in order for the user to draw grid and inverter power simultaneously ?

On the circuit breakers: "However be aware that circuit breakers, do not trip as soon as their rated current is exceeded. There is a time-current graph published by their manifacturers which defines the tripping time at various overloads" - as long as it trips within a few minutes that would be fine. Great.

How feasible is my mains switching idea ? (given that it's lower than our mains) Any dangers there ?. Would this cause TV's to standby and lights to flicker ? Maybe not a bad thing (feedback, of a form). How about the clock, is there a component anyone can think of that I can source ?

I hope I haven't dissuaded any of you. I just want to keep things practical rather than hypothetical. Rightly or wrongly this is the set-up as it stands and these are the general solutions I'm feeling out. I'm not afraid of criticism though ... just as long as I can do something with it, practically.

Thanks for your time guys,

Hope to hear more from you,


Morgan.
 
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What you need is a KiloWatt hour meter that only allows a household to draw X number of KWHs for the day and then cuts the power. Once a 24hr period is complete it resets it's "KWH ration counter" for the next 24Hr period. This will be cheaper than any battery backup system of sufficient capacity. If the people can see how much reserve they have they will soon learn how to conserve and will have motivation to do so.
Anyone in the "west" who has rented out a room in their house knows what happens when the utilities are free or flatrate...
 
The problem here is peak capacity - there is no need for a kilowatt hour tarif, just a way of stopping people drawing too high an instantaneous current.

I agree though, knowledge of what's going on helps people make decisions on how to manage their resource. These people are already far more energy aware than we are however and are running at most 5 lights a TV and a couple of occasional appliances. I need a meter that is simple and above all, cheap.
 
Seeing as how you stated one of the main problems was peak demand and you said some villagers were already using lead acid batteries have you given any thought to using a battery bank at the generator itself for hold up power during peak loads? I imagine the hardware for this would be expensive but it would be transparent to the end users.
 
I have thought of that ... I don't think it's a great solution though. Keeping it as an 'in-home' system allows richer families, with the more money and more appliances, to supplement their 'household allowance'. Passing the costs and the losses onto the entire community just wouldn't stack up in terms of cost-benefit.

Do you have any practical experience of how to draw inverter and 'grid' current simultaneously and at the same time 'island' it to avoid feeding the grid ? If I can crack this configuration it will allow users to supplement their supply with solar, pico-hydro, pedal power (joke !) - whatever they want. Expanding the grid capacity is a separate issue that I really don't want to dwell on here.
 
morg said:
Isupply with solar, pico-hydro, pedal power (joke !) - whatever they want. Expanding the grid capacity is a separate issue that I really don't want to dwell on here.
Don't joke about pedal power, I believe that if we powered generators from gym equipment, we should be providing power from it, this way when the lights run out or the TV goes off, it's time to stop being a lard @rse and get back to work on the treadmill!! :)

Think of the improvement in health.

As a much simpler method of dealing with the synchronised inverter, you could go for a very simple two pole switch where the user could choose either power from their mains supply at limited power or alternately switch it to their local battery/inverter source. All you'd need is a switch. Admittedly it wouldn't be transparent but would be simple and as such could meet your requirements.

As you say, daytime usage isn't the problem so this would let them localise their power by charging the batteries during the day.

David.
 
Circuit brakers.

Most MCB's are designed not to be manually overridden when tripping or closed in under a fault condition, the switch will simply not latch.
They also have thermal OL protection by means of a bi metallic strip which needs to cool down after a sustained OL.

MCB's are made in different categories, A,B,C,D.

A is fast tripping under minor OL's
B and C are most common domestic type house conditions with small OL's up to a couple of hours at 125% Inom.
D is motorrated with the D curve which allowes for heavy starting currents and slow tripping.

In your case the A type braker would be the best.

Switching arrangement is best with a single pole change over switch in the phase, from which the common contact goes to the house load.
One way to 200 Watt circuit (0.91 A, say 1A at 220 V)
Two way to 700 Watt circuit (3.18 A, say 3.5A at 220 V)
 
In fact, for a small additonal complexity, it wouldn't be difficult to detect the current in the load and switch over automatically and for a bit more complexity, only if there's sufficient charge in the batteries.
 
There's certainly a lot of info on the web about lead acid batteries. They have plenty of limitations.

A nice big battery might be good for 120 AH at very light loads, but only 80 amp-hrs or even less at higher loads (tens of amps). Discharging and charging at high currents will lower their life span.

Lead acid batteries vary greatly in quality. There are some which can get 10 yrs of life if used very conservatively- no deep or fast discharging and no overcharging, and regular maintenance. In general though, plan on about 2-5 yrs with common cheap ones. Delivering 10 or 1000 100 lb batteries to a remote village and carting away the dead lead every few yrs is problematic and very expensive.

It does make more sense to have one big central battery. It will still have maintenance issues. But then you don't have many batteries out there, some dying quickly from overuse and others being unused and eventually dying from old age. The main problem is you have to make sure people don't turn on a lot of power when the generator is off and that's hard to ask of them.

I saw some sealed lead acid cells on eBay once that were I think 2000 amp-hrs, physically huge and massive cells. He had some sort of solar installation I think. If you made a 120v or 220v string and a fairly simple inverter, that would be able to run your whole house with central air conditioning for days. But keep in mind a genny would have to run full power for days to charge it too, nothing is free. Those batteries require a small building just to house and again last only so many years.

Batteries won't do anything to help your efficiency either. Cycle efficiency is about 80%, could be less depending on how you use it. Inverter losses may be another 10%.

There are some high-tech "miniature" flywheels (maybe couch-sized? but very heavy) with built-in generators that can do a neat job of filling in when the genny's off or filling in for changing loads that the genny can't keep up with. That's more complicated but the important part is the flywheel has a virtually unlimited lifespan.

One thing to look at is biogas. Manure, anything that decays can be used to create methane. There's something called a Capstone Microturbine which is really good at taking any gas that burns and making electricity out of it. Supposed to be quite reliable too.

You are right on a "smart grid" to coordinate the power loads. You might say "this is a plug for little thing like a clock you reallly need, this is the other plug for big things or things you don't need for sure. If the generator is running low it will try to switch off the second plug. If that is not enough because you put it all on the first plug, it will turn them both off and you will have nothing." The devices will need to be capable of two-way communication. Note once you shut off a plug, unless you give them a "Reset" button then the box won't have any way of knowing they may have decided that leaving the TV on the second plug was a bad idea and have made amends by unplugging it but want power again for a light bulb. The box has to power up the line again, for at least several seconds, to know if they've changed the load. That's where a Reset button may help. If they get cut off they can turn things off and try again.

It is somewhat unsafe to cut off their power and automatically turn it back on. For example, say they had a hot plate that was cut off. It's cold, they forget about it and leave clothes on top of it and they go to sleep. The generator turns on and starts a fire and there is no one awake to check on the appliances. If you require them to press a Reset button for that too, maybe they'll think about if they left anything like that on. There would at least be someone awake who should realize if something is burning.

Some things like VCRs may be damaged if unplugged while running.

I agree that billing by power used- and possibly by using too much peak power- is necessary. I suspect otherwise you may have trouble getting people to cooperate with the capabilities of the grid simply by asking them to do so.

Here in Austin the power company has been offering "smart" thermostats. It will coordiante it so some houses will be guaranteed to have their AC cycled off while others are cycled on, instead of living with simple probability that they won't all turn on at once. More important, they will override the thermostat setting completely under emergency scenarios, turning off the AC for awhile to prevent grid blackouts. A few houses may get a couple of degrees warmer for a brief period but the grid is much more secure.
 
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morg said:
....................Do you have any practical experience of how to draw inverter and 'grid' current simultaneously and at the same time 'island' it to avoid feeding the grid ? --------------------.


Hi Morgan,

it is sarma back here. it appears simple for me to have a sync inverter. imagine the power supply taken thro a step down transformer and used to drive a push pull poer drive, ( the o/p trnsformer wold work from 12/24 DC and with a centre tapped primary. the secondary would be 230v +/-15%

Now the power is used only to signal an inverter ( call it amplifier) the output is what you derive from the house owner's battery. Selective part of the load coud be on this arrangement and this could time switched witha change over contactor operating from a clock signal. this can be ON for the peak load period( say 2 to 3 hours- beyond which the battery would drain out.)

Ofcourse efficiency is a n issue here. if so they could dirctly use devices from 12 / 24 DC ( Eg., a TV lighting , electric iron. from DC instead of 230V public mains. this wold make the battery use more efficient. ) every conversion has its own eff factor and nothing is 100%. priliminary thoughts-- we could expand further.

we may have to advertise and change designs to work from mains and 12/ 24 battery also-- like a 14" portable TV for eg.,

all the best -- really an nGO's effort plays a lot.
 
Making some progress, thanks.

I don't want to discourage anyone but I do have to steer the discussion a little to get the most out of it, so a few things to remember:

- please keep the context in mind. By Western standards these people are poor, living in basic housing, in very remote, mountainous jungle, farm or pick tea for a living and only have 100-400W of power. Their monthly electricity tariff is between 50-150p ($1-3) dependent on their loan repayments.

I say this to remind you that issues relating to PC's, air conditioning, cookers etc. are not relevant. Also that the budget for these changes can perhaps come partly from funding, but to be truly replicable elsewhere, it obviously has to be very cheap. Efficiency, is another issue that has to be looked at in context - turbine efficiency is of course, critically important but additional battery charging using otherwise wasted power - cost must take priority.

I'm aware of the limitations of car batteries as opposed to deep cycle and all the other continuously advancing technologies. I plan to use them purely because families have them already and keep them as a back-up (previously their only source of power). Richer families can later purchase more efficient batteries if they choose. Or aid agencies can perhaps donate them.

RODALCO: Excellent. Thanks. In terms of integrating the SPDT switch into the timing function - can you recommend any components ? I've been pricing up timer relays that would then activate the switch - https://daquan.en.alibaba.com/produ..._and_Time_Relay__Time_Switch__Hour_Meter.html - for example, though if there's something a bit cheaper, simpler and more intergrated, I'd love to hear about it. This one costs around $6 US, import price.

mvs sarma: Ah yes ... been looking at synchronous inverters on the net now. For grid-connected Californians it seems to be a popular green/economic solution. They have inverters wired up to automatically supplement grid power, store or sell back the grid. What I need to do is take these principles and scale them down - price again being the driving factor. Synchronising to 'mains power' in the above case is different from the 100-400W I have coming through the wall and hopefully some of the cost can be factored out as a result ... hopefully.

Inverters do seem to drop quite a bit in price around the 800W mark.

I get the feeling this may be too rare an application though - charging and sychronising what is classed by the West as 'in-car' or 'camping' rated power. I may be better off buying a cheap charger, inverter and 'synchroniser' (what would that be ?) separately.

Any thoughts ?
 
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morg said:
I'm aware of the limitations of car batteries as opposed to deep cycle and all the other continuously advancing technologies. I plan to use them purely because families have them already and keep them as a back-up (previously their only source of power). Richer families can later purchase more efficient batteries if they choose. Or aid agencies can perhaps donate them.

It's still a matter of cost. A car battery for example might have 50AH in there. If you used 400W for even 1/2 hr, that's about 15 AH. A car battery really can't sustain this for a great many cycles. Do this daily or go much deeper- pull 30 AH even a few times- and the battery will be worn out in a very short period of time. Realistically, this is expensive as hell, I wouldn't be surprised at all if the battery were useless within a couple of months.

A deep cycle is an expensive addition, I realize this and cannot explain how to afford the cost in your scenario. But the reality of the situation is that using the wrong type of battery for deep cycling will be far more expensive even in even the short run, and the lack of money for another type of battery doesn't change that issue.
 
Thanks. Good point.

I guess all I can do is try to find the cheapest deep cycle option. Perhaps doubling up orders of whatever the solar systems are using.

Any experience you can share on the inverter front ?
 
I think the most cost effective method may be another 2nd micro-hyrdo turbine running off the same dam as the one you have now. It could be left idle until times of peak demand and then brought on-line as needed to save on water behind the dam. I think this will be simpler, cheaper & require less maintenance than an inverter and battery/solarpanel in every house.
 
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