What Makes A Quality Panel
This applies to mono or polycrystalline panels.
The solar cells are laid between a superstrate layer on the top and a backing sheet on the bottom. The superstrate is usually glass, and the backing plate is plastic laminate. This is then placed inside an anodised aluminium frame to create a finished solar panel. The junction box is glued to the backing sheet. Electrical cabling joins the junction box and the inverter.
Remember the panel should last 25 to 40 years so all parts of the panel should be top quality to achieve a long life and protect against fire risk.
Silicon
Not all silicon is of the same grade. Cheaper panels are more likely to be constructed from a lower grade of silicon. Unfortunately the customer has no way of knowing the grade of silicon used. Low grade silicon can lead to early cell failure and loss of output in your system. Generally solar modules that are in the higher price are made using A-grade silicon. Cheaper modules are made using B-grade or lower quality silicon.
Frame
- Anodised aluminium (aluminium oxide) is extremely tough and is the second hardest substance known to man.
- The thicker the frame the better as it can cope with more load and thus more storm stresses. At least 45mm is considered good.
- The frame should be well made and have a twin-wall design.
- The section of the frame overlapping the glass should be as wide as possible. This ensures that the bond between the frame and the glass is strong.
- A self locking frame construction will be more durable than one which requires the frame to be screwed together.
Backing Sheet
- In inferior panels the backing plate, laminate, can lift. If this happens the panels can become dangerous as the electrical current is not insulated.
- Making a quality laminate is the most important process to guaranteeing at least 25 years performance.
Understanding Panel Brochures
- Panel rating - if a panel is rated 170 watts but tolerance is stated as + /-5% then the panel has been manufactured to produce between 161.5 watts and 178.5 watts. Some panel manufactures state the minimum wattage and tolerance is then a positive figure - so you are potentially getting more watts for your dollar.
- Solar cell efficiency % -this is how efficient each solar cell in a panel is. The bigger the percentage the better, however module efficiency is more important.
- A solar module (panel) is made up of lots of solar cells. The module efficiency % tells you how efficient the panel is (including the frame and areas not covered by a solar cell). The bigger the percentage is the better. This measure is better than solar cell efficiency % because you can compare the efficiency of different panels as all panels are measured in watts per square meter.
- Temperature co-efficient (V/o C)- this measures how much the performance of the solar cell reduces as the temperature changes from standard testing conditions, usually 25oC. This is a negative figure. The smaller the percentage is the better it is.
- Panel certification - you can only receive solar credits if your panels are accredited under IEC61730 and one of IEC61215 or IEC61646. Unfortunately there may be unaccredited panels for sale in Australia. Some companies talk of their panels being accredited under other standards but beware as the manufacture may be self certifying i.e. reporting on their own tests rather than independent tests to internationally agreed standards. Only panels which have these IEC certifications can be listed on the Clean Energy approved panel list and the certificates must be produced in order to be listed.
- Each panel has bypass diodes in the junction box. These dictate the flow of electricity to minimise the effect of shading. The bypass diodes allow current to pass around shaded cells and thereby reduce the voltage losses.
- A lot of information makes monocrystalline panels look better than polycrystalline panels but the top quality systems on the market tend to be polycrystalline even though it is older technology. Read more about the mono vs poly debate.
Panel warranty
Most panel manufacturers offer an 80% 25 year power output warranty and a 90% 10 year power output warranty. This warranty is only of use if the manufacturer is still around in 25 years time to honour it.
