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LED lights powered by a small Solar Cell???



Jan 1, 1970
I am an art student with little to no knowledge of electronics, although I
can figure just about anything out as long as i have someone
to tell me where to start.

I am looking to create an array of LEDs in any sort of pattern (creating an
image), and have it powered by a small solar cell... preferably this solar
panel would charge a small battery, and a small light sensor would tell the
lights to become active (ie: the solar cell would charge the battery during
the day, and at night the lights would come on, running off of the battery).
simple enough maybe?

here is the catch..... I cant have it be more than 1/3 of an inch thick,
preferably 1/4 of an inch.... It can be as wide and as long as it needs to
be, but it cant be any thicker than 1/3 of an inch. Any ideas???

Thanks so much!


Jan 1, 1970
well... ok. The apparatus would be placed outside in a sunny location. The
number of LED lights could range anywhere from 50-150. I am also not opposed
to using a battery that would just last a really long time, rather than
using a solar cell to charge it back up, but still using a light sensor to
only activate it at night.


Jan 1, 1970
Typical power consumption.

Red LED 40mW
Yellow LED 42mW
Green LED 44mW
Blue LED 80mW
White LED 80mW

Typical cell energy storage capacity.

AAA alkaline 1650mW/Hr
AA alkaline 3900mW/Hr
C alkaline 11500mW/Hr
D alkaline 27000mWHr

AAA NiMH (750mAh) 900mW/Hr
AA NIMH (1800mAh) 2100mW/Hr

All of the above cells are too large for your application.

Some cells with the required 1/3" thickness requirements:

Varta VH600F6M (600mAh) 720mW/Hr
Varta V600HR (600mAh) 720mW/Hr

To calculate how long each cell type will last, divide the mW/Hr
figure by the LED power consumption, for example red LED and a
alkaline AAA, 1650/40 = 41.25 hours. If you used 50 LED's, the life
would be 1650/(40*50) = 0.825Hr (49 minutes).
If we take the number of LED's at 50 (Red) and use a light sensing
circuit to limit operation to darkness only, say 9 hours, this is 50 *
40mW = 2000mW * 9Hr = 18000mW/Hr. This is the required battery
capacity to light 50 red LED's continuously for 9 hours. If we use AAA
alkaline's as an example, you would need 12 of them. If we use the
Varta rechargeable types, you would need 25 to give the same energy
storage capacity.

Now we need to charge the cells using a solar cell, which needs to put
back during the day at least equal to that which was used during the
night. As the sun does not shine every day, it should ideally have the
capacity to generate several nights worth of energy during each sunny
day to compensate for days when the sun does not shine.
I will need some more time to calculate this, but a gut feeling
suggests that it would need to be several Sq. feet in area. It will
depend on location on the earth's surface on which the unit will
operate. Where is this?


Jan 1, 1970
We have a energy demand of 18000mW/hr (18W/hr) each night.
Let efficiency of solar cells be 10%.
We thus need 0.18W/hr/day worth of solar cell area
Assume an insolation value of 2.5kWhr/m^2/day.
We thus need 0.18/2.5 = 0.072m^2 of solar cell area (approx. 10.6
inches square). This is approx. equivalent to a '9W' solar panel.
But we need some reserve capacity for cloudy day, say 3 days. So the
cell needs to generate 3 days worth of operating power for each sunny
day, so we need around 0.22m^2 of solar cell area (a '20W' solar
And of course, we need to be able to store three days worth of power
as well, so we need to increase the cell capacity by a factor of
three, around 54000mW/Hr. This is the equivalent energy storage
capacity of a 12V, 4.5Ahr gel-cell battery, weight around 4 pounds and
the size of a motorcycle battery.