Rural lighting
Practical Action
using renewable energy such as photovoltaic or wind charging systems
using a hybrid system
Using a generating set imposes considerable problems as, unless power is being generated for
other purposes too, the charging current, which is acceptable for small battery storage for just one
or two lights is rather low for even the smallest generating sets; hence the engine needs to be run
at part load which results in inefficient fuel use and is bad for the engine.
A photovoltaic system is often the most applicable stand alone option, as adequate sun for
charging can be found in most parts of the world, and such a system, apart from occasional
cleaning of the array, requires little attention.
The main drawback is that solar photovoltaic arrays are still expensive. Current cost (delivered and
installed) are in the region of £3-5/Wp (peak watt); the supplier should be able to advise on the
size needed (and can generally supply a battery and lighting system too).
To run a 30W light for six hours would typically require, in a sunny tropical location, two nominal
40W solar modules, and would therefore cost in the region of £400. Areas with extended cloudy
periods may need up to twice this capacity.
Another option is to use a small wind generator; this can be cheaper than solar power in locations
with mean wind speeds above 4.0m/s in the least windy months. Some of the WLED lamps used
in Practical Action’s Nepal project were charged by small wind turbines rated at 200 watts also
supplied by Krishna Grill & Engg. (P) Ltd. A separate technical brief gives further information on
wind turbines and gives a rule of thumb that the required rotor area of the wind generator for
small-scale applications like lighting will be:
Rotor area (m²) = Energy demand (kWh/day)
0.0048 V³
Where V is the mean windspeed in the least windy month of the year. For the 30W lamp for six
hours example, it follows that a 0.5m² rotor wind generator will suffice at 5m/s, a 1m² rotor is
needed at 4m/s and a 2.3m³ rotor at 3m/s. The typical cost of wind generators is around £400-
600/m² for small machines (installed).
In our example of a 30W fluorescent light, which is comparable in illuminating power to a 100W
tungsten filament lamp and brighter than a pressure kerosene lantern with a mantle, in a rural
'off-grid' location using wind or solar power, the following items would be needed:
Item
Approximate cost
12V 30W fluorescent light with built-in inverter unit
£ 10
10m cable, connectors, etc
£ 10
1200Wh battery (rated) giving 6000Wh usable capacity
£ 80
plus either:
60-90W (rated) solar array with battery charge regulator
(depending on solar irradiation)
or
0.5 to 2m² rotor area wind generator with battery
charge regulator
£200-500
£200-900
This may sound a lot to pay for 2 to 5 lights, but the running costs will be negligible and good
quality light will be reliably available. A pressure lantern, which is much less satisfactory, would
cost only about £15-30, but it would consume in the region of 5 litres of kerosene per week on
6