Date: October 19, 2012
There are 2 main types of solar panels on the market, namely mono crystalline and polycrystalline panels – this article does not discuss amorphous solar panels. Basically, main the difference between these types of solar panels is the manufacturing of solar cells used in solar panels and their relative efficiency.
Although quality technology is important in selection of solar panels, it is also critical to keep in mind that both monocrystalline and polycrystalline silicon solar cells are proven technologies, and one should not automatically be considered better than the other.
Monocrystalline solar panels have been widely used for over 30 years and have a slightly smaller area for the same output than polycrystalline solar panels – this may only be applicable where limited roof space is available.
The actual panel temperature under normal operating circumstances is considerably higher than the ambient temperature – the higher the panel temperature (anything above 20 degrees) will cause a loss of voltage, known as temperature co-efficient. Typically solar panels can reach 75+ degrees.
Monocrystalline solar panels have a slightly higher efficiency than polycrystalline solar panels, that is they perform slightly better than their counterparts. Similarly, when temperatures rise, monocrystalline solar panels perform more efficiently then polycrystalline.
As temperatures rise, the performance of solar panels decrease – as they rely on UV light. The temperature co-efficient of any panel gives an indication of their performance at varying temperatures, measured as a percentage (%). The lower the percentage, the better the performance of the solar panel. That is, the percentage is a negative value and typically measured at a percentage loss per degrees rise in temperature.
For instance, a monocrystalline solar panel manufacturer states that their panel has a temperature co-efficient of -0.45%/´C, that is the temperature above 20´C. To take the example of 75´C then for the additional 55´C there is a loss of -0.45% per ´C – a loss of 24.75% of the stated power of the panel. E.g a 200 Watt panel would produce 150.5 Watts – this is at 1000Watts of UV light/M², although the actual Watts will differ if the UV light is more or less.
Similarly, a polycrystalline solar manufacturer states that their panel has a temperature co-efficient of 0.50%/´C, again at a temperature of 20´C. To use the above example of a panel temperature at 75´C for for the additional 55´C there is a loss of 55 Watts, or in other words, the panel under these conditions will produce 145 Watts at 1000Watts of UV light/M².
To apply this to real world scenarios, although the actual difference between both these types of panels is not all that significant, over the period of a day and considering that solar power systems are comprised of several solar panels it becomes increasing apparent that there is a significant loss of the polycrystalline type.
To take the example of a 10 kW Off Grid solar system comprising of 50 x 200 Watt monocrystalline panels located in South East Queensland where the typical amount of Peak Sunshine Hours for September is 6.42 hours. Typically, under real life conditions a 10 kW system would be producing 7.525 kW continuously (50 x 155.5 W) for 6.42 hrs – therefore an average production of 48.3 kW/hrs per day.
For a system of polycrystalline solar panels of the same capacity i.e. 10 kW located at the same location at the same time of year, where the typical amount of Peak Sunshine Hours is 6.42 hours the system would be producing 7.25 kW continuously (50 x 145 W) for 6.42 hours – therefore an average production of 46.5 kW/hrs per day.
As the above example shows, monocrystalline panels can over perform polycrystalline yet as mentioned previously this is a general rule of thumb and depends on the quality of the panel. It is therefore necessary to know what the temperature co-efficient is (the lower the percentage the better) and to make an informed decision from then. As a general rule of thumb, mono crystalline panels do have slightly higher efficiencies than polycrystalline and an increased production of 2 kW/hrs per day can be the difference between a system which is reliable and can offer more convenience than a system which is compromised.