Developing World Electricity Concepts

 

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 of around $1. Simplicity, reliability and
minimal-cost are the key drivers as I'm sure you can guess. I've posted
this on another forum and spent a week feilding speculative alternative
distribution designs - I'm sorry to sound bossy but ideas for expanding
'grid' capacity are not the focus here. There is 100-400W coming
through the wall and that's it.

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.
I've been looking at timer relays and the like. This timer unit in
conjunction with a double throw switch or contactor 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 timer unit and circuit breakers will be
simply secured, though can be re-set - I believe most cannot be
manually over-ridden.

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 ? The electisave retails for
around $35-40. I'd need to get a trade price of at least $10.

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 timing, metering and
cut-off ? Labour is not an issue but reliability of the result would
be.


3. Some villages have alot of unused, 'off-peak' electricity during the
day. Many villagers also have 12V 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. It also acts as a platform for richer
families to add solar, pico-hydro etc. to satisfy their wants without
waiting for the community grid capacity to increase.

I've seen the issue of synchronous inverters argued many times on these
forums often without conclusion. I'm trawling Alibaba and the like for
a roughly 1000W (or less) unit but the synchronous feature clearly only
makes market sense as a Western household backup or UPS which is
overpec'd and too costly for my application. People have brought up the
subject of flashing light bulbs, gemini inverters and home made systems
... can anyone apply a low-cost principle to this problem bearing in
mind that the 'grid' supply here is only 100-400W ?

Huge thanks in advance for any help you can provide,

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

Cheers,

Morgan.

 



If peak power is the problem, then the cheap simple solution is a
non-tamperable fuse that blows out at 400 watts and has to be replaced
(for a large fee) by the person maintaining the grid.  The fuse could
be as simple and cheap as a bit of small guage wire or solder between
two pegs in a locked box on the distribution pole.  The boxes would
have to be randomly inspected, to stop scofflaws.

A second thought is to have a tiered system of costs based on fuse
size.  People with a 200 watt fuse pay $1, those with a 400 watt fuse
pay $4, and those with an 1200 watt fuse pay $20.  The money then goes
into increasing the size of the power system.

Using electricity for heating is a very poor use of power in such a
situation and alternatives should be considered.  However, boiling a
kettle of water and heating an old style iron could fit into the
scheme fairly simply.  A 100 or 200 watt resistance heater placed in a
heavily insulated ceramic jar containing a thermal mass, like bricks,
sand, oil, or water, could supply a household with a small source of
available high temperature energy storage.  

Heating a pot of water could be as simple as removing the top
insulation and placing the kettle on the exposed heated bricks.
Similarly, a pair of irons could be heated by placing them in the
container, re-covering it, then removing and using one until it
cooled, swapping it with the other, etc.

The keys are to have the correct amount of thermal mass, and good
thermal insulation.  While somewhat dangerous, a pot of hot oil allows
for rapid heat transfer to irons, and by partly immersing a metal
coffepot in it, a small amount of water can be brought to a boil as
quickly as with a much higher wattage electric element.  Oil and sand
might be safer, and in using anything with oil, there would have to be
a thermal cutout that tripped below the oil's flash point.

Charging batteries and using inverters could allow the short use of
high power appliances, but the cost of the setup for a household to do
this is high, and battery life is an issue.

Without metering, you'll find a natural flow of one neighbor getting a
high powered connection, and then other neighbors coming over to use
that connection to do laundry, watch videos, etc.  The neighbor then
has the option of charging a small amount to offset his costs, and
monitoring the system so it isn't overloaded.  The effect is a self
regulating load on the electric "grid" and a micro-economy.

 

Great response, thanks. Am I right in thinking you've worked in
developing countries yourself ? I think I saw you posting on a Nigerian
synchronous generator issue a couple of years back ?

I think the fuse idea is a goer ... circuit breakers may be a
friendlier solution, but I'm doing a workshop next week and will leave
the final choice to them. I'm not sure about the discipline value of
fines in this location ... they own the turbine after all and the
amount of income they have available to save for grid expansion is
pretty minimal. I'd rather leave this issue for now.

The peak/off peak switch is critical to the concept however. Eric Sears
idea is interesting - using a 'ripple' to trigger the switch, or mine
of having a timer relay installed. They less components we have to
install (and thus, pay for) in the home, the better. A remote trigger
also gets round the issue of timer error, batteries going flat in
power-cuts etc. A radio signal would be good if it is reliable
(interference etc.) and there is a 'radio activated relay' component
commercially available at low-cost.

Any ideas ?

I'm glad you brought up the issue of thermal storage. It does seem like
the perfect solution for this power application. There is a semantic
'challenge' here though - many villagers can afford cheap Western
appliances and their aspirations are towards this 'lifestyle'
regardless of the reality. You can't blame them for falling for it as
we have. Unless I can 'package' a thermal concept into a device that
doesn't look too backward to them, I think they'll view it as an
inconvenience rather than an enabler. Do you know of anything
commercially available that exploits this principle ? Or even elements
of it, such as the thermal bricks etc. ? I have experience of product
development and while I know we don't have the sales volume or resource
to produce a 'consumer product', a village-manufacture solution using
mass-market components could be a viable project.

Thanks again for the interest.

 



This is an interesting question - and the other poster has suggested
some possible solutions. The idea of storing heat is not silly. My
wife grew up on a farm which had its own low-power hydro, and they
used thermal storage stoves (low power elements with fire-bricks and
insulated covers - commercially made) for many years.

So here's my twopence worth:

In NZ (and I guess many other developed countries), one way of coping
with "peak loads" (your main problem), is by tone (or ripple) control
of loads such as water heating.
If some simple way could be found to switch in the lower-power circuit
breaker (by means of an external tone for example - or even a radio
signal if power usage is very localised) - that might do the trick.
But I suspect that this would be too technical for a small system.

However, as you point out - there are times when the power is
underutilised (presumably there is some control mechansism to prevent
the alternator from "running away").

Having some sort of "grid synchonised" inverter is probably not an
option.
But modified square wave inverters are very cheap now - and most that
I have used have proved quite reliable.
If ALL houses were limited to 200 watts, those who want to invest in
an inverter (maybe about 2kw at 12v), and a battery (deep cycle),
would have an independent source of power for such things as the
electric kettle or iron mentioned. This would be charged during the
normal "off peak times" - and over a period of time, as more people
did this, the load would become more "even".
As you say - solar or other microhydro could be added to this quite
independently - with the 200 w "mains"acting as very good "backup".
Note that an "inverter/charger" would probably have to be sinewave -
which is fine if it can be afforded. A cheaper solution might be the
mod-sq inverter and a 100 watt charger - though you "gets what you
pays for!"

I run a holiday home on a similar system - I have only about 150 watts
most of the time - but with a battery and mod sq inverter I run a
small fridge, lights, and most other small appliances that are needed.

The beauty of micro-hydro is that in most 24 hour periods you know
what you will get, so the battery can be sized smaller (you don't need
three days standby).

By the way - 200 watts is 12kwh a day - which a slightly more than I
use on grid here in the city! - and we don't have gas.

Personally - I think these people are on the pigs back!
360 kwh for a $1 !!!! (it doesn't matter WHICH dollar it is at that
rate).

If it were me I would put it all into a battery bank - run a
reasonable sinewave inverter (say 3kw), and forget about running
anything directly. Those who can't afford to do so can still run the
200 watts they have now, or maybe go with a smaller mod-sq inverter, a
4amp car charger and (horrors!) a large car battery.

The advantage of sticking with 200 watts max for everyone (or whatever
the system will supply), is that is won't get overloaded and "go
down"! Its also fairer for everyone.

Best wishes from New Zealand.

Eric Sears.

 

On Sat, 23 Dec 2006 10:56:00 GMT, phoneme@025379386.for.email.address
(Eric Sears) wrote:



DUH!!  NOT 12kwh  -  4.8 kwh. That's what comes of doing sums in your
head at midnight!
I realised my mistake after going to bed, but it was too late to get
up and correct it.

Even so, I still think its a bargain.
140 kwh a month, with line charges (that's the "low use" tariff),
would cost about $NZ40.

Mind you, I don't know what $1 represents elsewhere - it could be a
substantial part of a month's income.

But 4.8 kwh a day is not too difficult to deal with. If half were used
directly, the other 2.4 kwh a day might only need about a 5kwh-size
battery (400 amp-hr at 12v for instance).

Eric Sears