Panel Selection
SunPower E18 Panel
HIT Sanyo 195W Panels were first looked at for their additional performance in hot climates. They are designed to utilize both sides of the panel by exposing the back face to reflected sunlight. These panels achieved gains of five to thirty percent more power production per square foot above the stated power rating. However they were ultimately not chosen because the additional performance rating is dependent on sunlight reflecting off a high albedo surface, which does not include our parking lot's paving surface.
The SunPower E18/225W Panels were analyzed for their increased efficiency and power production. The design of these panels increases power production by placing the electrical contact gridlines on the backside of the monocrystalline silicon solar cells. This configuration completely exposes the cells to sunlight and eliminates losses attributed to shading from the gridlines. It also permits enlarging the contact gridlines. This minimizes the resistivity losses found within the thinned gridlines of other panels that are compensating for shade loss. Finally the backside placement of the electrical contacts means the panels are all black. This added some aesthetic appeal to the technical attraction, as the panels act as black ˝mirrors,˝ softly rendering the images of clouds floating by. Yet this model was also abandoned once the following were discovered.
The SunPower E18/225W Panels were analyzed for their increased efficiency and power production. The design of these panels increases power production by placing the electrical contact gridlines on the backside of the monocrystalline silicon solar cells. This configuration completely exposes the cells to sunlight and eliminates losses attributed to shading from the gridlines. It also permits enlarging the contact gridlines. This minimizes the resistivity losses found within the thinned gridlines of other panels that are compensating for shade loss. Finally the backside placement of the electrical contacts means the panels are all black. This added some aesthetic appeal to the technical attraction, as the panels act as black ˝mirrors,˝ softly rendering the images of clouds floating by. Yet this model was also abandoned once the following were discovered.
SunPower E20/327W Panels were selected for their superb efficiency and power production capabilities. The anti reflective coating provides for more capture of sunlight and minimizes the directional dependence for maximum absorption. This means rotating the panels would provide an insignificant increase in electrical production. As the picture above shows, the panels are designed with a back layer of silicon dioxide and metal on oxide layer that reflects unabsorbed light back to the solar cells. Finally, the low voltage temperature coefficient gives these panels greater power output in high temperature conditions. All this increased efficiency allows for maximum energy production per square foot, which means fewer panels are needed for the same output. This will reduce cost initially on installation and ultimately on maintenance over the life of the panels. The total daily output for a 640 panel array will be approximately 1,082 kWh with average insolation and accounting for an efficiency variance of about thirty percent. |