When every sales person tells you that they have the best solar panels, who do you believe? With the vast range of solar panels on the market, how can you be sure that you are not forking out a significant amount of your hard earnt cash on a lemon?
As with most products these days there is a vast range to choose from, some products are quality that will perform admirably, others are nothing short of cheap and nasty. Here are a number of things to keep in mind when choosing a solar panel and listening to a sales person and their sales pitch.
Panel Data
All solar panels have different characteristics. Are these available? If not it is probably due to the fact that this information is not good. Be very wary if this is the case, this is like buying a car with no engine specifications at all. The following is a list of specifications that all solar panels will have, but the values can differ greatly.
Test Conditions (STC) All solar panels are tested in a laboratory under what is called STC (Standard Test Conditions). STC conditions are taken at an Irradiance (light) level of 1000W/m2 with a cell temperature of 25ºC. Now the main thing to consider here is this is how the solar panel performs in laboratory conditions. In the real world up on your roof these conditions are constantly changing, which is where the following information is very helpful.
Nominal Operating Cell Temperature (NOCT) The NOCT is given because of the fact that in the real world solar panels are usually operating in hotter conditions and at lower irradiance levels than what the STC of the panel is. NOCT is defined as the temperature reached by open circuited cells in a solar module under the following conditions:
- Irradiance (light) falling on the solar panel at 800W/m2
- Air temperature of 20ºC
- Wind speed at 1m/s
- The panel is mounted with an open back (air can circulate behind panel)
For a quality solar panel you can expect the NOCT to be 47ºC or lower. This means that the panel will be running cooler in real world conditions than a panel with a higher NOCT, and a cooler panel means a more efficient panel.
Temperature Coefficient (Pmax) The temperature coefficient is very important, please click here to read a seperate article all about it.
Tolerance or Performance Deviation When you purchase a solar panel which is rated at say 175W, do you expect it to produce 175W? If you do expect 175W, check the solar panels tolerance. Quite often it will be ±5%. This means that your 175W solar panel could be producing 5% less than 175W, or only 166W straight from the factory, something to keep in mind.
Warranty Solar panels are designed to operate in a very harsh environment dealing with ultra-violet radiation, heat, cold, wind and hail for 25 years plus and they are usually warranted for that whole time. This is a very long time. Is the manufacturer of your solar panels going to be around to honour the warranty they offer? If they start having warranty issues will they change names and totally void your warranty? This is not really an option for reputable companies such as Sharp or Sanyo. If you sell your property, will the solar panel warranty pass to the next owner? With Sanyo, Sharp, Solarfun & Suntech panels it will.
Keep this information in mind and you should see right through the lemons and you hopefully won’t make a purchase that you will later regret!
