2 Key characteristics of the firefly system previous

2.1 Micro Hydro systems in general index page

Micro Hydro systems are always `run-of-the-river' systems, meaning that there is no large dam to create a reservoir (see box 2.1). Having just a weir instead of a huge dam means that it makes no sense to install a turbine there since there is too little head (= water pressure) available there. So the turbine itself is placed a distance downstream at the river bank. Then the height difference between the water level at the weir and the place where the turbine is located, minus friction losses, creates the net head the turbine needs.

In principle the water could be transported from the weir to the turbine by a long penstock pipe. But this is done only in some rare cases, where a waterfall or a very steep section in the river makes it possible to achieve the necessary head without needing too long a pipe. Usually, the water is first transported through a power canal that follows the valley side downstream. The slope of the canal is minimal, just enough to let the water in it flow fast enough, while the weir is located somewhere before a steep section of the river itself. So going downstream from the weir, the height difference between the water level in the power canal and the river bank, increases. Then at a place where this height difference is large enough to create the head the turbine needs, the water is fed into a penstock pipe that connects to the turbine down at the river bank.

The charger of the firefly system is a very small M.H plant and usually its layout in the field hardly differs from this basic layout, see fig. 2.1. Larger M.H. systems often have some more components and these could be relevant to the firefly in special cases.

Fig. 2.1: Typical layout of an installed firefly charger, schematic drawing.

Instead of just a weir, there might be a more complicated intake structure. It might have a trashrack to keep out floating debris. Often there is a silt basin to allow silt to settle so that the power canal itself won't get silted (the silt basin itself is made in such a way that it can be emptied easily). And there will be a spillway where excess water will flow back to the river itself so that only the designed amount of water will enter the canal. This is to prevent that the canal wall will overflow somewhere else, causing erosion. Along a long canal there might be more spillways, to dispose of excess rain water that came down the valley side and was collected in the canal.

At places where the canal has to cross a difficult stretch, sometimes special measures are needed. An aqueduct could bridge a small side valley. A length of pipe could be used to get past a steep piece of hard rock. If the soil is very sandy, seepage losses could become excessively high and erosion forms a big risk. So there the canal might need a lining from clay, masonry or concrete. At places where the canal crosses a gulley, a canal crossing might be needed.

Where the canal ends, usually there is a forebay tank before the water enters the penstock pipe. It could function as another silt basin, to prevent that silt will pass through the turbine and cause excessive wear. There must be a rack or screen that keeps out objects that could block or damage the turbine. And there will be another spillway to safely dispose of excess water.

At different points at the intake, the forebay tank and at the beginning and the end of the penstock pipe there could be sluice gates, stop logs, pipe plugs, valves etc. to regulate, divert or cut off the water flow.

Box 2.1: Hydro power at different scales

Hydropower can be used at different scales. HARVEY, 1993 distinguishes between full scale hydropower schemes (more than 10 MW), Mini Hydro schemes (300 kW - 10 MW) and Micro Hydro schemes (200 W - 300 kW). Most people will have an idea of what full scale hydropower schemes are about and for good reasons, these ideas are not always positive. Mini Hydropower systems and Micro Hydropower systems are not just scaled-down versions of those large hydropower schemes and therefor some of the negative points of those large scale hydropower schemes do not apply to Mini- and Micro Hydropower.

Who invests in it and who will get the profits: Almost by definition, large hydropower schemes produce electricity for large cities or energy-intensive industries. People living in the area where the scheme is implemented, will hardly profit from it. Maybe plant management will not even bother to install transformers in the area and all electricity will leave the area as high-voltage electricity. Large hydropower schemes need tremendous investments and often foreign money is involved. It is only logic that they are designed to supply economic centers and that profits flow back to these investors.

In this respect, mini hydropower schemes are comparable to full scale hydropower: They will be financed by investors outside of the area (although they could be from the same country) and profits will flow back to these. They must be connected to the national grid in order to be used economically and local people might remain in the dark.

Micro Hydropower schemes are different: Normally, they run independent of the national grid so they are meant to supply a local demand. Money for these might come from the users themselves or it might be supported by a development project that expects no profits in return.

Reservoir schemes and run-of-river schemes: As a general rule, full scale hydropower schemes have reservoirs to store water so that electricity (or irrigation water) can be produced `on demand'. These reservoirs are designed for storage over periods of months so that the plant can still produce electricity when river flows are minimal towards the end of dry season. This means that the capacity of these reservoirs must be made extremely large and they often submerge whole valleys where many people used to live and work. Hence the awkward issue of local people being dislocated by force and not properly compensated for the loss of their land, homes and whatever more.

Apart from their tremendous costs, these big reservoirs also cause adverse environmental effects:

  • Downstream of the plant, the river flow pattern has changed: It now follows the pattern of electricity demand rather than its own natural pattern. Areas that used to be flooded for part of the year, remain dry exept for the unpredictable times the sluices are opened because otherwise the reservoir might overflow.
  • The biological system of the river itself is cut in two. When trying to swim upstream, no fishes can pass the dam unless special measures are taken.

In principle, hydro power is a renewable form of energy and a positive environmental effect would be that it replaces the use of fossil fuels or nuclear power. But the reservoir could make that it is not so renewable: Due to erosion upstream, the reservoir could become silted in just a few decades and then dredging it out again probably is too expensive.

Mini hydro and micro hydro schemes are almost always run-of-river schemes. This means that there is no large dam to create a big reservoir but a weir across the river that diverts as much water into a power canal as the plant needs. Therefor no valley will become submerged and also the river is not cut off biologically since part of the river flow will continue along its usual bed.

Sometimes Mini or Micro hydro schemes do have a reservoir, but then it is designed for storage over a period of a day or less. This makes it possible to follow the pattern of electricity demand over the day or to use a plant that can only run at full power. Then if the flow is less than this plant needs, it can still be used intermittently: Water is stored until the reservoir is full, the plant is turned on until it is empty etc.


2.2 The firefly system itself

The firefly system is a battery charging system. There is the firefly charger, a car alternator driven by hydro power, that is used to charge batteries for users. Because the ultimate objective is to produce light (with some side uses) and not just electricity, the home system described in chapter 5 forms an integral part of the system. The batteries are 12 V so 12 V lamps and other appliances should be used.

The firefly was designed as a lighting system for poor people living scattered in a remote area with hydropower possibilities. Therefor it was important that it would be cheap, simple, easy to use, easy to introduce and fit for local production. If one would look only at costs per kWh of electricity produced, the firefly system is not optimal because it doesn't use the `economies of scale'. The charger could be made much more powerful at little extra costs (see annex B). However, it is not all about producing kWh's of electricity but to produce light, as much as users need, at times the users need it and at affordable costs. Designing a bigger charger would go against the other design objectives: Simplicity, easy to use and to introduce.

Those other design objectives more or less meant that the firefly should be small: As small as possible without arriving at too high costs per user or too high costs per amount of light produced. And it is: The standard firefly charger even produces just a bit less than the 200 W that HARVEY, 1993 mentiones as the lower limit for a Micro Hydro system. Sometimes such low capacity schemes are referred to as `pico Hydro' (`pico' means `times 10 to the power of -12'). But for simplicity, it is treated as a Micro Hydro scheme in this book.

The civil works part of a firefly system is basically the same as described for larger M.H. systems (see par. 2.1 and fig. 2.1). But because it is that small, also the weir, canal, forebay tank and penstock pipe can be more simple.

Fig. 2.2: The first prototype in the workshop where it was built. There was no drill, holes in the frame had to be cut using an electric arc welding set at full blast. Covers are not fitted yet.

Some technical characteristics of the firefly system:

Some points in the firefly system deserve special attention as they are critical for overall performance:

Reliability of the water source. This is a major issue, as a firefly charger running dry (or rather: Not running at all) could cause series of other problems, see par. 3.1.

Organisational problems. These are discussed in the next paragraph.

Then there are some issues related to the technical design:

It is only wise to keep these possible problems in mind. But let's not forget about the advantages:

The advantages mentioned above all contribute to what could be seen as the major advantage of the firefly over alternative M.H. systems:

Please note that the standard firefly design described in this manual is not necessarily the best option. In annex B and K, some adaptations are discussed that could lead to lower costs or other advantages under specific circumstances, but often at the expense of some of the advantages mentioned above.


2.3 The user group

The firefly system can be used most effectively if one charger serves a user group of ca. 10 families. Whether such a user group functions well, is very important for the success of the technology.

Size of the user group: Of course the charger that is owned and managed by a user group, should have such a capacity that it can charge all batteries. Calculations on this are difficult because it is hard to estimate how much electricity a family will consume, so how many times per month each battery needs to be recharged. Still, with only 10 users per charger, most likely the charger itself will be under-used. When running 24 hours per day, it could easily charge 3 heavy batteries per day while on average, it might have to charge only 1 per day. So most of the time, it will be standing idle, a waste of the energy supplied by the creek. At little extra costs, the capacity of the charger could be doubled or tripled (see annex B.3) and that would make that electricity could be generated at an even lower price per kWh.

However, it is not about generating kWh's of electricity, but about providing electric light reliably and at affordable costs. Reasons for keeping user groups small are:

To conclude, having a dense grid of chargers running in a certain area is preferable over having only a few, large capacity ones.

Of course the number of chargers that could function in a certain area, also depends on the number of useable sites. If the number of sites is limited, it makes no sense to install two or 3 chargers at the same site, each with its own operator, and having them compete for water. In that case it makes more sense to install one large capacity charger, maybe keep a smaller one as a spare and have one large user group.

The user group plays a key role in dealing with the organisational problems that are associated with installing a charger. And if it is the first user group to pilot this new technology, it will also play a very important role in introducing this new technology. Organisational problems are:

Most likely, outsiders (e.g. people from a development project trying to introduce the technology) can not deal with those issues as effectively as a well-functioning user group could do. If such outsiders are present at meetings where such issues are discussed, it could work out counter-productive. Then quite likely people will expect a solution to come from them: Money, to compensate for every thinkable and unthinkable damage anyone might suffer because of a charger being installed and used (at least that is what happened in Cambulo when discussing the use of an existing irrigation canal as a source).

Fig. 2.3: The Cambulo coop store.

There are no general rules on how such a group could be set up, as things depend strongly on local culture and local circumstances. The only sensible advice I can give is to keep an open eye and and deal with such issues carefully. One interesting option is to approach existing groups that could serve as a start for a user group, although many things could go wrong with this as well, see par. 3.4. This is what happened in Cambulo: A succesful coop store initiated by an employee of PRRM who came from that village, became interested in PRRM's Micro Hydro plans. The members and management of this coop store served as a partner to PRRM's people working on developing this new technology. Within 10 months, the firefly was developed, build, tested, demonstrated and introduced with users paying realistic costs (see par. 1.1). Things would never have gone so fast if this coop store would not have become involved.

If an approach based on user groups seems not feasible because people are unwilling or unable to cooperate, the firefly could still be introduced in a more commercial way, see box. 2.2.

Box 2.2: Privately owned chargers.

Instead of chargers owned and managed by user groups, private people might obtain a charger and charge batteries for other people for a fee. This might seem an attractive option. It means that many of the organisational problems mentioned above, could be dealt with in a liberal, market-oriented approach by people who see it as a business opportunity to get a charger, install it and earn from the charging fee. However, it also brings in additional problems:

  • There is a conflict of interest between users and the owner of the charger. Key points are the charging fee and the quality of the service rendered: Are batteries charged properly, is charging always possible on the same day etc.
  • There are increased risks for both parties: Users will have no benefit from their expensive battery if they can't have it recharged whenever necessary. Also the owner of the charger will gain little from his/her investment if there are no users who want to have their battery charged. For both parties there are risks associated with the charging fee becoming too high (the users) or too low (the owner of the charger).

Probably in some situations, this will be the best option. I don't know of this approach being tried out somewhere. If one family could afford to buy a charger mainly for their own use, such a situation could grow gradually, with battery charging for frends and neighbours starting as a side use and becoming more and more important as more people get batteries and want to have them recharged. At least it would be a perfect way to demonstrate the technology.


2.4 Battery is the most important component

Intuitively, people will see the firefly charger as the heart of the system. This is the part that produces the electricity and it does so in a very imaginable way: It has distinctive components performing different functions, runs at an impressive speed, produces noise, splashes around water and all these things reacts to the setting of the controls on the switchboard. Compared to this, the battery is just a container with some invisible chemical processes going on inside. If this would lead to people neglecting the batteries, performance of the system as a whole is at risk.

Costs of batteries roughly make up half of the investment costs so from that point of view, they deserve attention. Even more important is the effect of battery life span on running costs. With good care, car batteries should last about 1.5 years and the more expensive solar batteries about 3 years. But if, due to poor care, batteries would last only half a year, replacement costs for batteries alone end up about as high as total investment costs! In such a case it is likely that users will be dissatisfied and the firefly project will fail.

To compare: Suppose that the firefly charger would last only half a year and a completely new charger would be needed, including a new penstock pipe. In this case, users end up paying only 1/3 of investment costs per year for buying new chargers (assuming 10 users per charger). Losing 2 complete chargers per year due to excessive wear, bad use or bad maintenance is difficult to imagine because destroyed parts could be replaced and damages repaired. Only if it is because of theft, deliberate destruction, flash floods or landslides, so many replacement chargers could be needed. To conclude: Battery life span is critical for succes of the firefly. And life span of the charger is not critical, as long as a malfunctioning charger does not cause batteries to wear out fast because they can not be recharged.

See par. 5.1 for a discussion on the different types and sizes of batteries that could be used in the firefly system. Below, there is a brief discussion on what measures could be taken to reduce the risk of batteries wearing out prematurely.

There are several mechanisms that could lead to premature battery failure (see annex C.3), but the most important ones for the firefly are:

The danger is especially in this invisible, creeping process of sulphatizing. Things are made even worse because:

Fig. 2.4: Ben Nanglihan is preparing a battery for use. Connections are made and it must be filled with acid: A tricky job. He'd better wear safety glasses and have his son playing somewhere else.

In the firefly system, the following measures could be taken to reduce the risk of batteries becoming sulphatized as much as possible:

In a demo project, it will be difficult to reach all these conditions and therefor risks of batteries becoming sulphatized will be higher. This means that in the demo phase, technical assistance and maybe financial assistance in case of unexpected costs, makes sense. This could be seen as helping to overcome initial problems and not as subsidizing the real costs.

The above conditions have consequences for the way the firefly system was designed. These were behind the choice of having a low number of users (typically 10) per charger. This has the following advantages:

Finally, batteries deserve attention for two other reasons:


2.5 The firefly compared to other lighting systems

Relevant alternative lighting systems are (see LOUINEAU et al, 1994 for a more thorough discussion on different lighting systems):

  1. Connection to the national grid.
  2. Solar energy.
  3. More sophisticated M.H. systems producing 220 V.
  4. Generators driven by combustion engines.
  5. Pressure lamps.
  6. Candles.
  7. Hurricane lamps, or simply bottles filled with kerosene with a wick.

To draw sensible conclusions, criteria are needed:

  1. The amount of light produced. Some of these systems are so powerful that apart from lighting, other uses become possible. Then especially `productive end-uses' are interesting as these could make that relatively costly systems become affordable to poor users.
  2. Costs. Apart from monetary costs, one should also look at the labour users themselves should put in to get a system installed and keep it working.
  3. For what kind of users they is most suitable. Clearly one could rate users according to their wealth (or rather: their poverty), as this will determine the amount of light they would like and the costs they can bear. A less obvious effect is that poor users will mainly want light while richer users might be interested in other uses as well. Light is needed only a few hours every evening while those other uses might mean an energy use that is more evenly spread over the day. This spread of energy use has a large influence on the costs of some of those systems.
  4. The kind of area these systems are most suitable for, see also chapter 3.

Below, the different lighting systems will be discussed briefly, with special attention to their advantages and disadvantages compared to the firefly:

National grid: From the point of users, connection to the national grid is almost always preferable over any other solution in the long run, at least when the electricity system is working fairly well and the high costs of connecting remote areas are divided over all electricity users or paid for by the government. From the point of the government or an electricity board, the situation looks different: Connecting up remote areas where only few voters live and hardly plays any role in the national economy is not a profitable investment. Connecting an area to the national grid becomes excessively expensive if:

Electricity from the grid is easy to use, as there is light when one switches it on. It is powerful enough to connect also other electrical appliances, some of which are `productive end-uses'. And in the long run, costs are relatively low. This all makes that there is no sense in trying to introduce the firefly in an area where the grid is already present or where it might come in the foreseeable future. But connection costs to the grid could be too high for poor people who might therefor stick to hurricane lamps or kerosene bottles.

Solar energy: It is easier to use than the firefly, as there is light when you turn the switch and no carrying with batteries is needed. The investment costs of solar energy however are about 10 times as high as the firefly. So when there is year round water and potential users are rather poor, those solar energy guys could pack their bags.

The solar panel is the most expensive part of a solar energy system. It is produced only in hi-tech factories in a few countries so almost always this part will have to be imported. This means that before it reaches the end user, there will be a number of intermediaries who will all want some profit. This makes solar energy even more expensive if components are bought in small series only.

Monthly costs of solar energy depend heavily on interest rates since investment costs are so high. Credit from banks is often not available to poor people and moneylenders usually charge very high interest rates. In such a situation, solar energy is only affordable to people who can pay back the loan in a short period or who can pay cash. At such high interest rates, the long life span of a solar energy system becomes less of an advantage since writing off a loan in 2 years gives hardly higher monthly costs than writing it off over 10 years.

For the above reasons, solar energy will only be affordable to poor users if it is introduced by a solar energy project that buys components in bulk and provides credit at an acceptable interest rate and pay-back period.

220 V M.H. systems also are easier to use than the firefly and they could provide more power so that e.g. a refrigerator could be connected and productive end-uses become possible. Monthly costs of locally produced 220 V M.H. systems probably could end up as low as the firefly as there are no replacement costs for batteries. If there are good sites for the firefly in an area, most likely there are also sites that provide enough power for a 220 V M.H. plant. This could mean that in the long run a 220 V system might be more advantageous and then it would seem more logic to go for 220 V right from the start.

The firefly however has some major advantages over 220 V M.H. systems:

Generators driven by combustion motors are not too expensive in investment costs. But running costs are too high to allow daily use: They consume a lot of petrol or diesel and repairs could become costly. In remote areas or areas where roads are inaccessible during part of the year, also transport costs for fuel could become excessively high. But above all, one can not expect the motor to last much longer than 5000 operating hours (just half a year of continuous use) and with poor mainenance, it might stop at only 1000 hours. So generators are only an option for richer people and/or use at special occasions. Like with the national grid and 220 V M.H. systems, other electrical appliances could be connected and productive end uses become possible. However, it is not so suitable for powering a refrigerator since this would mean that the generator has to run nearly 24 hours per day and running costs would become excessively high.

Pressure lamps provide a lot of light and investment costs are low. But like generators, operating costs are too high to allow daily use because of high fuel consumption.

Hurricane lamps and kerosene bottles are a lot cheaper than any other option at the present, low fuel rates so these can usually be found with the poorest people. But they produce only a minimal amount of light, sometimes produce soot, are smelly and there is a fire risc. Only when more light is needed than these can provide, the firefly becomes attractive. When bringing in fuel would be very costly or when fuel rates would increase, the firefly could become competitive also on the point of costs, especially if people use a lot of dry cell batteries for radio's, cassette players etc. which could then be connected to the firefly battery as well.

Candles provide about as much light as a hurricane lamp while they are more expensive, so they aren't used that often.

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