• Solar cells are used as a power source to charge rechargeable batteries.
For lead rechargeable batteries (Pb), reckon with 6 solar cells per rechargeable battery cell (2V).
For round cell rechargeable batteries (1.2V), such as NiMH, 4-5 solar cells are used.
If a return protective diode is used, the voltage drop at the diode has to be balanced by a further 1-2
solar cells.
• The following number of solar cells are required, roughly, for a charging connection with rechargeable
batteries:
1 NiMH rechargeable batteries
5 solar cells
6 NiMH rechargeable batteries
24 solar cells
2 NiMH rechargeable batteries
8 solar cells
10 NiMH rechargeable batteries
32 solar cells
3 NiMH rechargeable batteries
12 solar cells 1 lead rechargeable battery
6 V 18 solar cells
4 NiMH rechargeable batteries
16 solar cells 1 lead rechargeable battery
12 V 36 solar cells
5 NiMH rechargeable batteries
20 solar cells
If it is necessary to bridge periods of bad lighting, further solar cells will need to be included.
However, a charging controller is always recommended.
d) Size and Power
The power of solar cells depends on their size. Fractions of solar cells are not defective, they only have a
lower power. The following table presents the size and the potential average current for silicon solar cells:
Rectangular
50 x 50 mm
440 mA
70 x 70 mm
1.2 A
100 x 100 mm
1.4 A
Round (diameter)
50 mm
400 mA
76 mm
2 A
100 mm
2.1 A
Installation and Connection
•
The individual solar cells are connected to each other by soldered fittings. Flexible copper conductors
are perfectly suitable for this.
Silicon, however, is very heat sensitive and will be destroyed by excessive heating. Soldering, therefore,
should only be done fast and quickly with a high-performance soldering tip (>50 W).
The maximum soldering temperature is 250°C!
If the joint does not work the first time, let the solar cell cool down before making an another attempt
to solder.
The edge of solar cells must not be soldered, since the two P-N layers are very close to each
other here and a short circuit can arise easily. Always use the prepared soldering spots on the
cells.
• Scratches on the light-reactive layer must be completely avoided.
• First of all, tin the soldering spots on the solar cell and the connecting wire. Carefully hold the connecting
wire with the copper-bit on the soldering area on the solar cell until the solder has liquefied. The solder
-
ing process has to be done quickly, since the metal contacts on the solar cell can dissolve in the solder
within short time.
•
Try not apply pressure on the solar cell when soldering, since it can break easily. Inflexible connection
lines or external assembly parts, such as return protective diodes, should not be soldered directly on to
the solar cell. There is the danger of it breaking, even at a very low mechanical stress.
Examples of Use
The following connection examples show you the most popular uses for small solar cells.
a) Light dependent operation without rechargeable battery
Many applications do not need energy storage. These are mostly used for decoration or only when the sun
shines. These are, for example, mini solar revolving stages or small fans with special solar motors. The
motors will only be supplied with voltage if there is sufficient light reaching the solar panel. The solar panel,
however, has to be constructed according to the power requirements of the device. The device is directly
connected with the solar panel.
The connection principle is as follows:
b) Light dependent operation with rechargeable battery
• The most applications utilise the solar energy in order to charge and to buffer self-contained devices and
installations with built-in rechargeable batteries. The advantage of these installations is their operational
reliability even in the dark. However, in order to be able to charge in the built-in rechargeable batteries
via the solar panels, reliably and safely, further assembly parts are necessary to protect the recharge-
able battery.
• There are differences concerning use with conventional NiMH round cells, as they are built into smaller
devices, such as solar garden lights etc, and the more powerful lead rechargeable batteries for solar
lanterns or construction site illumination.
When using lead rechargeable batteries the maintenance-free lead-gel version is to be pre-
ferred, because it easier and less hazardous to handle. Furthermore, the use of a solar charging
controller is recommended.
c) Charging connection for NiMH round cells
• To limit the voltage and the current, a diode (e.g. 1N4148 max.
100 mA) and an appropriate multiplier are required. NiMH re-
chargeable batteries are sensitive to too high a charging current
and thus, it has to be limited.
• The rechargeable battery buffers the power supply to the device
in bad light and stores the excess solar energy on good lighting
conditions (charging).
d) Charging connection for lead rechargeable batteries (Pb)
• As return protection, a diode (e.g. 1N4001 up to max. 1 A or
1N5400 up to 3 A) is required.
• Lead rechargeable batteries are sensitive to too high a charging
current. These, however, are determined by the number of cells
in the solar panel.
• The rechargeable battery buffers the power supply to the device
in bad light and stores the excess solar energy on good lighting
conditions (charging).
Installation Notes
• For mounting individual solar cells double-sided adhesive soft-tape is best. The solar cells are to be
arranged so they do not touch each other.
• In outdoor areas, a protective cover is necessary, since the solar cells can be soiled by dirty rain, causing
a loss of performance.
• The solar panel should be aligned at 90 degrees to the sun for the best performance. A suntracking al-
lows for longer use of the solar energy.
Care and Cleaning
• Regularly clean the surface, and the protective cover of the solar cell, respectively, in order to ensure
the best performance.
• Do not use scouring, chemical or aggressive cleaning agents such as benzene, alcohol or such like.
These might damage the surface. Furthermore, the fumes are hazardous to your health and are ex-
plosive. Moreover, you should not use sharp-edged tools, screwdrivers or metal brushes or suchlike
for cleaning.
• Use a soft, anti-static dry brush to clean the surface.
Disposal
Electronic devices are recyclable waste and must not be disposed of in the household waste.
At the end of its service life, dispose of the product in accordance with applicable regulatory
guidelines.
You thus fulfill your statutory obligations and contribute to the protection of the environment.
Technical data
Solar panel ....................................................max. 400 mA / 0.45 V/DC
Solar panel size (W x H) ................................95 x 65 mm
Weight ...........................................................36 g
This is a publication by Conrad Electronic SE, Klaus-Conrad-Str. 1, D-92240 Hirschau (www.conrad.com). All rights in-
cluding translation reserved. Reproduction by any method, e.g. photocopy, microfilming, or the capture in electronic data
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represent the technical status at the time of printing.
Copyright 2021 by Conrad Electronic SE.
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