If you decide to install a solar PV system in your house, there are some important things you should look at before buying.
1. System Size
The size of a solar PV system is measured in Kilowatts (KW). The most common size being installed in Australia nowadays is 4KW – this would typically produce around 75-80% of the average Australian household’s annual electricity needs. A large 5KW system would cover almost all of an average household’s electricity needs. The system size you end up choosing depends largely on how far your budget stretches.
2. Warranty Period
Most of the leading brands have a 10 year workmanship warranty on the rooftop solar panels. They also typically come with a 25 year warranty to produce at least 80% of their rated output under normal test conditions – so for a 1.5KW system, they warrant to produce 1.2 KW under test conditions for the first 25 years. Most inverters come with a 5 year warranty. You should be careful about considering systems with shorter warranties than these – after all, you don’t want to be paying for replacement parts before you’ve recouped your installation costs.
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Having 10 year and 25 year warranties on your solar panels is useless if the manufacturer is out of business before then. While no one can guarantee that a particular manufacturer will be around in 25 years time, you can minimise your risk by going with a well-known brand. Popular household electronics brands such as LG, Sharp and Panasonic produce solar panels. There are also a number of big solar specialist manufacturers with a reputation for high quality – these include Jinko, Canadian Solar, Sunpower and Trina Solar. The solar manufacturing market is highly competitive, with manufacturers coming and going, so before you install it might be worth checking that the company you go with is financially stable.
SMA, ABB (formerly Power One), Sharp and Fronius are among the higher quality inverters in the market. You should look for a minimum of 5 years’ warranty on an inverter.
4. Inverter Size
The size of your inverter is also measured in KW. You should ideally aim to match the inverter size to your current panel size. Undersizing your inverter could cause it to overheat, and reduce its life. Oversizing your inverter gives you the option to add more panels at a later date. However oversizing can cause your inverter to operate less efficiently in the meantime. Plus, when you decide to expand, the solar panel types available in the future may not be compatible with your inverter.
5. Panel Efficiency
In the specifications for your solar panels, you’ll see a figure called “Module Efficiency”. This figure measures the amount of electricity produced from the total sunlight that hits the panel’s surface area. The less efficient the panel, the more roof space you’ll need to use to generate a particular amount of power. Panel efficiency is particularly important if your roof space is limited. Panel efficiencies have been slowly rising, with top brands now able to achieve up to 18-20% efficiency compared to 15-17% a few years ago.
6. Temperature Coefficient
The expected power output of all panels is calculated when the panel temperature (not air temperature) is 25 degrees. In most parts of Australia, the panel temperature will normally be above this.
For every degree that the panel exceeds 25 degrees Celsius, the power output of the panel drops. The Temperature Coefficient of the panel (referred to as Temperature Coefficient – PMax” in the panel specifications) measures the percentage by which power output drops for every degree by which the panel temperature rises above 25 degrees. The higher the Temperature Coefficient, the greater the drop off in output.
For example, a panel with a 0.5 Temperature Coefficient, operating at 45 degrees Celsius, would produce 10% less power: (45-25) x 0.5%.
As you can see, too much sun and heat is actually a problem for solar panels. If you live in a very hot area, then choose a panel with a lower Temperature Coefficient. Thin-Film panels are great for hot inland and tropical areas of Australia, as they have low Temperature Coefficients of around 0.2, compared to 0.3 to 0.5 for standard Mono-crystalline and Poly-crystalline panels.
7. Module Power Tolerance
This measure is listed in the specifications for a solar panel, and is expressed in the form of 0% +/- x%. The Module Power Tolerance tells you how much the power output is expected to vary (positively or negatively) from the output amount specified by the manufacturer – that is, it’s a margin of error. Most manufacturers have started quoting a “positive” Power Tolerance of 3-5% (eg 0 + 5%) – that is, they guarantee that the output will be equal to, or greater than, what they’ve specified (eg 0 + 5%). Therefore, be wary of any models that list a negative Power Tolerance.