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White LEDs for rural solar lighting

A story in the _Christian Science Monitor_ titled "Low-cost lamps
brighten the future of rural India" (
http://www.csmonitor.com/2006/0103/p01s02-wosc.html ) describes a
solar-powered white LED lamp used to light homes in rural areas
without electricity. The only components it mentions are a solar
panel and the lamp itself, and says the entire assembly costs US $55.

It would be interesting to know what's in these assemblies. I'd think
it could be as simple as a solar panel, a diode, a gel-cell battery, a
switch, a resistor, and (presumably more than one) LED. A supercapacitor
might not have the wear-out problems of the battery, but it probably
costs more. It would also probably require a DC-DC converter to give
a relatively constant voltage output, which happens "for free" with a
battery.

I wonder why these assemblies are not using CF. I suspect it may be the
cost of getting "custom" CF lamps that work from low-voltage DC, or of
including an inverter to turn low-voltage DC into higher-voltage AC for
the lamps. http://www.lutw.org/Technicalinfo.html suggests that it
might be a lamp-life and durability issue.

Also, I was under the impression that presently available solar cells
cannot return as much electrical energy over their lifetime as it takes
to manufacture them. This may not matter compared to the cost of
bringing the electrical grid to remote locations, but it should factor
into the effciency calculations that are being made.

Matt Roberds
 
V

Victor Roberts

Jan 1, 1970
0
A story in the _Christian Science Monitor_ titled "Low-cost lamps
brighten the future of rural India" (
http://www.csmonitor.com/2006/0103/p01s02-wosc.html ) describes a
solar-powered white LED lamp used to light homes in rural areas
without electricity.

Without electricity? That would be a nice trick for LEDs :)
The only components it mentions are a solar
panel and the lamp itself, and says the entire assembly costs US $55.

It would be interesting to know what's in these assemblies. I'd think
it could be as simple as a solar panel, a diode, a gel-cell battery, a
switch, a resistor, and (presumably more than one) LED. A supercapacitor
might not have the wear-out problems of the battery, but it probably
costs more. It would also probably require a DC-DC converter to give
a relatively constant voltage output, which happens "for free" with a
battery.

I wonder why these assemblies are not using CF. I suspect it may be the
cost of getting "custom" CF lamps that work from low-voltage DC, or of
including an inverter to turn low-voltage DC into higher-voltage AC for
the lamps. http://www.lutw.org/Technicalinfo.html suggests that it
might be a lamp-life and durability issue.

12-volt CFLs are quite common for marine and RV
applications, so there must be other reasons.

I agree with the durability issue and believe there are a
number of other reasons why LEDs are used in these projects.
First, the solar panels do not produce very much energy and
this application can survive with rather low light levels.
Very low power CFLs (< 5 watts, for example) are not as
efficient as more typical 15 to 20 watt sizes, so low
power, low light output LEDs may be preferable in some
applications. Then you also have to consider the Hg disposal
issue since there are no recycling facilities available in
these areas. The organizations placing these lamps in
energy poor areas of the world probably do not want to be
accused of promoting Hg contamination. Finally, and perhaps
most importantly, with all the hype about LEDs it seems to
be far easier to get funding for an LED-based project than a
CFL-based project. I have read the web site of at least one
of the organizations involved in this effort and they make
rather amazing claims of LED vs. CFL efficacy and life which
I believe are totally incorrect.

--
Vic Roberts
http://www.RobertsResearchInc.com
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B

Bill Kaszeta / Photovoltaic Resources

Jan 1, 1970
0
While this application seems simple and obvious, there are
challenges in the details.

For this price, the light source can not consume more than half
a watt, far below any normal CF lamp. For this power level
only LEDs are practical. Even a half-watt light can make
a big difference in an otherwise pitch black village. A 35-watt
LPS street light leads to major social changes in a village.

The problem is obtaining decent battery life and low cost of
control electronics. Hard to train the users to NOT over-use
the battery, draining it every night. Deep discharges (small
battery for the load) and/or cycling the battery such that it
does not reach a full charge often is a recipe for short battery
life. A system with a simple low voltage disconnect still
cycles the battery on the partial charge range. Without extra
circuitry to indicate status (for trained users) or to enforce a
use pattern, it is almost impossible to assure long battery life.
There is no available recycling for worn out batteries in most
developing countries.
Bill Kaszeta
Photovoltaic Resources Int'l
Tempe Arizona USA
[email protected]
 
C

Clive Mitchell

Jan 1, 1970
0
Bill Kaszeta / said:
The problem is obtaining decent battery life and low cost of control
electronics. Hard to train the users to NOT over-use the battery,
draining it every night. Deep discharges (small battery for the load)
and/or cycling the battery such that it does not reach a full charge
often is a recipe for short battery life. A system with a simple low
voltage disconnect still cycles the battery on the partial charge
range. Without extra circuitry to indicate status (for trained users)
or to enforce a use pattern, it is almost impossible to assure long
battery life.

Perhaps they should consider NiHm cells as opposed to the old lead acid
technology. SLA batteries are OK for a few applications, but not this
one.
 
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