Introduction
I was curious about Solar panel. I knew solar panel technology advances tremendously in last 10 years. Top solar cell converts more than 20% solar energy to electrical power. However, I have not tested one yet. I got my hand on a Harbor Freight Model ES884 solar changer recently. Here are the test results.
Description of solar panel
The solar cell is 3.5” x 4.5” (roughly 89mm x 115 mm) with total area of 15.75 square inch (10235 mm^2). The solar charger has 4 settings, 3V (200 mA), 6V (100 mA), 9V (50mA) and 12V (50 mA). The charger can charge 2 AA rechargeable batteries in its built in battery charger or output power through its included adapter.
Testing Data
Test 1, under 27 W compact fluorescent light with 2170 omega resistor as load.
| Settings | Setting | Actual Voltage | Current | Power |
| (V) | (mA) | (V) | (mA) | (mWATT) |
| 3 | 200 | 1.60 | 0.60 | 0.96 |
| 6 | 100 | 3.73 | 0.48 | 1.79 |
| 9 | 50 | 5.68 | 0.24 | 1.36 |
| 12 | 50 | 7.43 | 0.24 | 1.78 |
Basically, it does not work under room light.
Test 2, under direct sun light with 2170 omega resistor as load.
| Settings | Setting | Actual Voltage | Current | Power |
| (V) | (mA) | (V) | (mA) | (mWATT) |
| 3 | 200 | 3.00 | 1.31 | 3.93 |
| 6 | 100 | 6.09 | 2.71 | 16.50 |
| 9 | 50 | 9.14 | 4.05 | 37.02 |
| 12 | 50 | 12.20 | 3.50 | 42.70 |
Second test confirmed that the solar charge worked as it was designed.
Test 3, under direct sun light to charge 2 NiMH 2500 mAH rechargeable batteries
| Settings | Setting | Actual Voltage | Current | Power |
| (V) | (mA) | (V) | (mA) | (mWATT) |
| 6 | 100 | 6.32 | 85.00 | 537.20 |
The actual current is 85% of design current of 100 mA. That could due to not enough sun light. However, I would consider the charger reached design requirement.
Overall Efficiency
Industry standard is 1000 W per 1 square meter of solar energy. That is 1,000,000 square millimeters. The test solar panel was 0.0102 square meter. Maximum solar energy for that surface is 10.24 Watt. Yet the panel only generates 0.54 Watt. Actual efficiency is 5.2%. It would take 29 hours to charge up these two 2,500 mAH batteries. This indicated that solar panel is usable for small appliances with direct sunlight exposure. For $10.00, this is an OK purchase for any environment conscious consumer. If the overall efficiency increases to 15% and charges the batteries in 10 hours (in one sunny day) , it will be a great buy.