Evolution of LED
Lighting in Luxtreks installations
1.
For this installation each house was equipped with a
single 9 diode LED light (using Nichia 0.1 watt diodes) and a 7.2 amp hour,
sealed, lead-acid battery. The charging installation consisted of 5 48 watt
solar panels mounted on the roof of the village school connected to three 75
amp-hour “car” lead-acid batteries which were vented.
There were five regulators, one per panel, and 30
connections which could be used for charging the small individual batteries.
Initially 47 houses were equipped with lights, and
subsequently a further 20 units were provided for houses outlying the main
village.
The lights were initially provided without any protection
for the diodes from smoke and dirt but at the installation time some protection
was provided using plastic bags over the lights and afterwards glass discs were
provided which could be glued onto the front of the light housings.
The system has been operating for 3 years with few
problems reported.
2.
Two villages were equipped with a total of 220 lights,
two per house. Each light consisted of a single 1 watt Luxeon diode, and a
separate power converter produced a 3.5 volt 300 milliampere constant current
supply from a 12 volt input.
The power converter had a switch which allowed only one
of the lights to be used if required. Again each house had its own 7.2 amp hour
battery and took it to a central charging location, one in each village. These
charging locations consisted of 2 or 3 respectively 56 watt solar panels, with
regulators and “car” batteries to act as back up.
To avoid reverse power connections coaxial connectors
were used on the power converters and these were permanently wired to the
individual batteries. The charging stations included equivalent connectors to
ensure polarity was maintained in all cases.
Some problems were experienced with these installations:
the problems included:-
1.
wire
being removed for other purposes
2.
lights
being moved and being wrongly connected so that they did not work
3.
wires
on the power converter being shorted out at the connection point
4.
burn
out of the coaxial connectors due to build up of corrosion arising from
sparking during disconnection and connection
5.
battery
failure due to the connection of other devices
6.
power
converter failures due to transients on the components during switch off ad
switch on
On a subsequent visit these problems were addressed by
replacing the 1 watt lights by 12 0.1 watt diodes lights, and hence removing
the need for the power converters, and using a more robust polarized two prong
connector in place of the coaxial connectors.
A switching unit was also provided to allow for either
light to operated independently.
3.
A system of wiring houses together was tried since the
houses were in a regular array and relatively close together. Two 20 watt solar
panels were installed on each cluster of up to 10 houses and a single 75
amp-hour “car” battery was used to provide all charge storage for the cluster.
No individual batteries were supplied.
Each house was equipped with two lights each consisting
of 6 0.1 watt LEDs and a switch made by using a “bullet” disconnect.
The experience with this was that far more wire, which
was relatively expensive, was used than anticipated. The regulators which were
designed to manage the charging rate of the batteries to be optimized proved
unsuitable for the job since they allowed voltage of more than 15 volts onto
the lights during daytime and this caused a shortening of the lifetimes.
4.
For this installation three charging locations equipped
with 75 watt solar panels ( 2 installations had 2 panels and one had 3 panels)
were established and each house was equipped with two 9 0.1 watt LED lights, a
7.5 amp hour battery which could be taken to the central charging locations and
switches using bullet disconnects.
One of the problems experienced with this location was
that in winter some of the village had no direct sunlight for several months
and so the charging locations had to be as far away from the shielding mountain
as possible.
The wire used was extremely light weight and connections
proved difficult to
maintain particularly where the disconnects created strain on the connections.
The communities have some hydro power for a few months in
the summer and there is some concern that lights could be connected directly to
this rather than having to charge up the batteries.
5.
Three installations were undertaken using small
individual 2 watt solar panels with two 12 0.1 watt LEDs, a 7.5 amp hour battery
and a switching unit for each house. This makes each house fully independent
and completely responsible for their own lighting. The
solar panels have a built in diode but other protection to avoid over-charging
the battery. Prolonged periods of non-use could present a problem.
We had some installation problems in installing panels on
some roofs with the optimum directionality. Again shadowing in the steep
valleys was a problem for some houses. The fragile nature of the roofs also
caused some problems.
These installations are only 6 months old and appear to
be working satisfactorily.
6.
This installation will take place in October 2004.
Experience has shown that wiring is a continuing problem and communal
facilities also raise some difficulties. Accordingly a lantern has been
designed which can be hung outside during the day and brought indoors at night
and switched on. The specifications are below. The advantages of this are:-
1.
there
is no wiring installation with its attendant problems and risk of misuse
2.
the
battery is fully enclosed and cannot be accessed to use for other inappropriate
purposes
3.
the
light is portable which is important both within the house and also to be able
to use it in community activities
4.
there
are no problems arising from non-use if the light is kept in the house
5.
the
light is clearly the responsibility of the owner
6.
in cases of shadowing the light can be taken to appoint where there is
direct sunlight.
7.
repairs can be effected if required by bringing the entire light
to a technician.
Specifications
Each lantern has two groups of 12 0.1 watt diodes, a 2
watt solar panel and a 2.8 amp hour battery. This should provide 5 hours of
light each night for each lantern. The lantern consists of a
housing, a diode board, a switch, a battery and a solar panel. All items
are fully connectorized for ease of assembly. The switch is a standard North
American light switch which is well over specified for its job and should prove
robust in use.
The lantern is 21 cm x 13 cm x 18 cm and weighs
approximately 5 lbs.
7. Future installations
A new lantern using a 1 watt solar panel is being
designed: this will also use a smaller battery and hence the whole system will
be lighter and smaller. The number of lights for a single household will depend
on what they need or on what they can afford if the lights are for sale.
During the period of these installations the brightness
and efficiency of the 0.1 watt diodes has increased considerably. The newest
devices provide about 3.6 lumens per diode and about 55 lumens per watt. They
are considered to have lifetimes of about 100,000 hours (at which point the
light output will have dropped to about 50% of the starting value).
Solar panel performance in the same period has not
changed significantly and the lead-acid batteries also represent a stationary
technology, but are unsurpassed for cost and reliability.