05-11-2012, 05:44 PM
More Efficient Use of Solar Panels
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INTRODUCTION
EXTRACTING useable electricity from the sun was made
possible by the discovery of the photoelectric mechanism
and subsequent development of the solar cell – a semiconductive
material that converts visible light into a direct
current. By using solar arrays, a series of solar cells
electrically connected, a DC voltage is generated which can be
physically used on a load. Solar arrays or panels are being
used increasingly as efficiencies reach higher levels, and are
especially popular in remote areas where placement of
electricity lines is not economically viable.
This alternative power source is continuously achieving
greater popularity especially since the realisation of fossil
fuel’s shortcomings. Renewable energy in the form of
electricity has been in use to some degree as long as 75 or 100
years ago. Sources such as Solar, Wind, Hydro and Geothermal
have all been utilised with varying levels of success.
The most widely used are hydro and wind power, with solar
power being moderately used worldwide. This can be
attributed to the relatively high cost of solar cells and their
low conversion efficiency. Solar power is being heavily
researched, and solar energy costs have now reached within a
few cents per kW/h of other forms of electricity generation,
and will drop further with new technologies such as titaniumoxide
cells. With a peak laboratory efficiency of 32% and
average efficiency of 15-20%[1-4], it is necessary to recover as
much energy as possible from a solar power system.
A PROTOTYPE SOLAR TRACKER
The final stage involved coupling the circuitry to the motor
and mounting it onto the bracket. The final product is seen
complete in Fig. 5. It has a Solarex 9W solar array made of
polycrystalline silicon mounted on the flanges, which was
borrowed from the tech officers.
Quite simply having two test subjects carried out testing.
The first scenario involved removing the panel from the
tracker and laying it in a flat orientation. The output was
connected to a load that would dissipate 9W that would match
the panel’s rating. 9W at 12V corresponds to a current of
0.75A, so by Ohm’s law; a load resistance was calculated as
being 16Ω. A 15Ω 50W resistor was the closest value found
and was connected to the panel. The tracking device still
requires power, but a 12V battery that is connected in a
charging arrangement with the solar panel supplies it. The
voltage across and current through the load was monitored
using two separate multimeters, and was recorded every halfhour
on a clear day into an Excel spreadsheet.
CONCLUSION
A solar tracker is designed employing the new principle of
using small solar cells to function as self-adjusting light
sensors, providing a variable indication of their relative angle
to the sun by detecting their voltage output. By using this
method, the solar tracker was successful in maintaining a solar
array at a sufficiently perpendicular angle to the sun. The
power increase gained over a fixed horizontal array was in
excess of 30%.