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(More customer reviews)Don't expect 20 Watts from this product. This is the second purchase of the Extreme Power Corp's 20W Solar Panel. The first unit did not meet the specifications defined on the label attached to the rear of the panel so I purchased this second unit to determine if the first unit was faulty. The second unit performed the same way. Here are the details:
I tested the two units at 1000W/Sq. Meter in the sun (Calibration by Davis Weather station solar sensor) at 25 degC and 55 degC into a resistive 16 ohm load (VPmax/IPmax). Here are the results, spec. values in parenthesis:
Open Circuit Voltage 19.4 volts (21.18V)
P Max at 25deg C - 16.5 Watts (20 Watts)
P Max at 55deg C - 12.8 Watts (Not specified but usual operating temp)
Voltage at Pmax - 14.45 at 55 deg C (17.5 at 25 deg C)
Short Circuit Current at 55 deg C 1.0 Amps (1.33 Amps at 25 deg C)
I reported these resulte to Extreme Power Corp but there has been no comment. Two points to bear in mind. 1. - There is a tendancy to overspecify solar panel performance and 2. - Specifications are for performance at 25 deg C and no solar panel operates at this temperature.
The maximum power output under any load conditions that I can get from these panels when cool (immediately after exposing to the sun) and at 1000 W/Sq. is 16.6 Watts.
In operation do not expect more than about 14 Watts from these panels - if that is ok then the product, although misprepresented gets a pass.
John Beukers
2009.05.19
Click Here to see more reviews about: 20 Watt Black Frame Mono-crystalline Solar Panel and Battery Charger
This is a 20 Watt version of the Mono-crystalline Portable Waterproof Solar Panel in black color (very rare) aluminum frame to charge your 12V battery or to run your science projects. The rare black color frame looks very nice. It is in a factory new package and is 100% brand new. The solar panel is assembled by Suntech, one of the highest quality solar cell makers. It is also waterproof. The working voltage for charging is 18V. If you need to use it to charge a car battery, you may need a charge controller to prevent the battery from overcharging. Connections included: alligator battery clamps. There are three types of Solar Cells on the market. All our Solar chargers use the best - Mono-Crystalline Solar Cells. Amorphous or Dual Junction Solar Glass are the cheapest but are only 7% energy efficient and have 5 years service life. They are big and heavy. Poly-Crystalline have 25 plus years of service life under direct sunlight and are 13% efficient. Mono-Crystalline have 25 plus years service life and are up to 20% efficient. This is the same type used in solar car racing. This type of solar cell is now in a worldwide shortage because only a few companies can manufacture this solar cell.
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