This article was published in: Energy for Sustainable Development, Volume II No. 2, July 1995
FIREFLY MICRO HYDRO SYSTEM
The firefly system is a very small Micro Hydro system that is primarily intended for lighting purposes in isolated communities without grid connection. For storing electricity, 12 Volt car batteries can be used but `solar' batteries will last longer. Batteries also serve as a means of transporting electricity from the charger site to the houses since cables for 12 V would become too expensive.
Twelve volt lamps and other 12 V appliances can be powered directly from the battery. Other appliances that work at 3, 4.5, 6 or 9 V and are normally powered by dry cell batteries, can also be connected by fitting a simple electronic part in between. With an inverter, ordinary 220 V appliances can be used as long as their power demand is not too high.
|The first prototype firefly system was designed, built, tested and introduced in a pilot community by the author in 1992 while working at the Philippine Rural Reconstruction Movement (an NGO) in Ifugao prov., Philippines. Back in Holland, the design was developed further and documented in a building manual. Meanwhile, the Ifugao pilot project faced serious technical and organisational problems. End of 1993, a successor arrived, things started to roll again and 3 other PRRM branches now have plans for introducing the firefly in their work area. Two `Affiliated Non-conventional Energy Centers' (`ANEC's', projects under the Dept. Of Energy, affiliated to universities) have chosen the firefly design for their Micro Hydro activities. These two ANEC's have given trainings to staff of 17 other ANEC's and through this Philippine-wide network, the firefly could be introduced on a wider scale.||
Fig. 1. The firefly charger seen from below: Not a big thing.
Fig. 2: Cross-section through runner and nozzle. To get a paper copy at the right scale: Print drawing at 150 DPI.
The runner is made of 61 x 19 x 1.25 mm blades soldered with brass into 3 mm thick side disks. To make side disks, use copies of this drawing, glue them on material and mark relevant points with a centre punch. The slots in side disks can be cut using jigsaw sawblades for metal fixed in a makeshift sawframe. To be able to cut slots with such a small radius, the sawblades must be reduced in width by grinded off at the rear end, opposite the teeth, see lower inset. The 20 mm central hole in the free side disk is needed to fit the thick washer (see fig. 4), the alternator side disk has a 6 mm central hole.
The nozzle is made from 2 mm steel, 53 x 83 mm for the runner side and 53 x 138 mm for the bent side. For alternator side and free side, use copies of the drawing. The rounded-off edge of runner side (see top inset) is not essential but without it, flow and electrical output will be ca. 10 % lower than given in fig. 3. Weld nozzle parts together in such a way that inside width (the direction perpendicular to the drawing plane) is 51 mm.
When welding on the frame (see fig. 1 for how this could look like), make sure that welding current will never pass through the alternator bearings.
Fig. 3: The seal and the way the runner is
fixed on the alternator shaft.
For simplicity, not all visible lines are drawn. Parts hatched to the left come with the alternator, parts hatched to the right have to be made, use 1 or 1.25 mm steel, preferably galvanised. The seal has clearances of only some 0.5 mm between moving and stationary parts and this will protect the alternator against water coming from the turbine (covers around the alternator should protect it against rain and tailwater splashing back from rocks etc.). The runner can be fixed by one M6 bolt, but make sure it pulls the runner against the rim of the alternator pulley, not against the end of the shaft itself. Under the bolt head, there should be a 6 mm thick washer (outer diameter: 20 mm, hole: 6 mm) to prevent the alternator side disk from bending too much.
In this drawing, the anti-splashing disk is not included, see with Leakage around seal for pulley in one piece
To get a paper copy at the right scale: Print drawing at 150 DPI.
|The firefly system consists of 2 major
components: The firefly charger and the home systems. The
charger basically is a second hand car alternator with a
`crossflow' runner mounted directly on the shaft, see
figs. 1, 2 and 3 (see HARVEY, 1993 for a description on
crossflow turbines). It might seem this charger is the
major component as it is the part that generates
electricity. However, economically speaking it is not:
batteries and other materials for the 10 home systems
that are typically served by one charger, are about 5
times as expensive as a locally built charger. Also in
running costs, the batteries are the critical element so
proper battery care is vital. This means among others
that batteries should not be discharged too deep and
should never be left in discharged condition for long.
Therefore the charger should always be ready for charging
batteries, which it will when it is built properly, the
operator is around and knows his/her job and there is
water to power it.
The firefly charger is quite flexible with respect to the head (= water pressure in m) it can operate at, see the characteristics in fig. 4. At high head, flow and output power can be reduced by inserting a blocking timber in the nozzle. Over the whole head range, the charger can operate at its optimum speed because field current can be regulated, see fig. 5 for the electrical circuit of both charger and home system.
The home system includes the battery, lamps, switches and the wiring to make these work. It also includes the firefly charge indicator, a small piece of electronics that shows how far a battery has been discharged by means of 10 LED's. It is located near the switch of a lamp that is often used and is activated when this lamp is turned on. The fact that it lights up will draw the attention of users, even more so because before showing its final reading, the LED's indicating a lower voltage light up briefly. For more accurate readings, there is a push-button switch to activate the charge indicator without any lamps being switched on. So prime responsibility for not discharging batteries too deep, lies with the users who own them. As a back-up, the operator of the charger should check whether batteries were discharged too deep before charging them.
Major advantages of the firefly system are:
Fig. 4: Charger characteristics.
Above 7 m head, electrical power would become too high for charging only one battery. Then output power can be limited by inserting a blocking timber in the nozzle that blocks part of nozzle width. Above 15 m head, a blocking timber of at least half nozzle width is needed to keep forces on runner blades within limits.
These characteristics are based on an assumed overall efficiency of 0.30 . For a neatly built charger fitted with a good alternator, overall efficiencies of up to 0.40 are achieveable. If electrical power is disappointingly low, check:
5: Electrical circuit.
Experiences in the Philippines indicate that many technical problems had to do with the electrical system, some comments:
|The firefly system is not the ideal
solution for all situations. Heavy batteries have to be
carried to the charger site and back every 1 - 2 weeks
and running costs (charging fees, replacement costs for
worn-out batteries) are relatively high while power
output is too low to allow fridges, ironers and most
electrical motor-driven appliances. However, it is an
interesting option when the following conditions are met:
A first step towards introduction of the firefly would be to build, install and operate a charger as a demonstration project. The draft building manual (PORTEGIJS, 1995) is meant as a guide for this. It requires no more technical background than physics at high school level.
Lighting usually is not a `productive use': A better quality of light at night does not mean a user will generate extra income with this. Still it has its impact on development issues since proper light could facilitate education, health care, organisation building etc. In the Ifugao pilot community, people did appreciate electrical light, see fig. 6. It adds to the quality of life (see LOUINEAU, 1993). When this could lead to people staying in their community rather than migrating to big cities, it would help alleviating the social and environmental problems there. One could think of many other uses for the firefly that are productive. But generally these will have a limited number of users while a high number of potential users is needed to make local production feasible.
Other organisations active in Micro Hydro (e.g. ITDG, see HARVEY et al, 1993) work mainly on much more powerful systems, either to produce 220/110 V AC electricity or to drive certain machines directly. Probably this is because in their eyes, productive end uses are essential to make an M.H. scheme economically feasible and those end uses need that much power. Such systems are more expensive, require better trained operators, more users to start with, all investments have to be made before a working system can be demonstrated and their feasibility depends heavily on whether those end-uses are economically feasible. Consequently they are much more difficult to introduce, especially in areas where M.H. is still unknown. Apart of being a useful concept in itself, it is hoped that the firefly will serve as a step towards these more sophisticated systems.
Fig. 6: A 20 W car bulb provides enough light for a
native Ifugao house.