Last week in “The Manufacturing and Science behind Solar Energy Panels” we talked about the different types of solar panels you could purchase and what all those complicated names meant. This week we shall focus on all the reasons why your cells might not be performing up to specification and whether its a temporary problem or it’s something you need to contact your installer about.
Before we begin to focus on the area’s where a loss in efficiency can take place it is important to get the basic assumptions of how a solar cell works out of the way. In short in the diagram above a “Cross-Section-of-a-Solar-Cell” light will enter from the top and after passing the anti-reflection coating enter the emitter layer and depending on the wavelength of light that enters the cell, this wave of light will excite the electrons in the emitter and/or base after which they get collected by the busbars and transmitted to load.
There are several areas where a loss in efficiency can occur however the biggest area or cause is always optical, and that makes sense because a cell can only generate energy from the light it is able to absorb.
1) Front surface soiling – this is when the surface has been covered with dirt or pigeon droppings and doesn’t get washed by the rain. This causes areas of the cell to not be able to absorb light as effectively.
Making physical inspections and spraying water on your modules can help reduce the problem.
2) Finger design – this is the concept of balancing the pros and cons of big vs busbars so there is a greater ability to collect the electrons that get excited by the light that enters the cell and lower area that directly blocks light from entering the cell.
This dilemma is optimized through rear-surface-contact cells and buried contact cells.
3) Partial shading – this is when part of your solar energy panels are being shaded by a cloud or another object and this causes a larger problem which is called mismatch across the several cells that are joined together in series. What this means is that when 3 out of your 36 cells in your panel are shaded the drop in performance is limited by the 3 cells. Thankfully there is a solution to this and they are called bi-pass diodes, this allows the performance to not be limited by the 3 cells by cutting them out of the system when their performance drops.
This is something you can ask about when you purchase you panels as this helps reduce the drop in performance during the uncontrollable weather issues.
There are several other areas of loss but thankfully the panels you purchase and the warranty that you get from the respective company takes this into account before they rate a panel at a certain power output.
If you would like to know more about these losses let us know.
Written by Prateek Chourdia
MEngSc – Photovoltaics and Solar Energy, UNSW
Solar Energy Analyst
© 2010 Solar Choice Pty Ltd
“Applied Photovoltaics” by Stuart R. Wenham et. al.
“Solar Cells” by Martin A. Green