Types of solar panels
There are three common types of solar cell:
- polycrystalline; and
- thin film.
They are made in different ways and have different performance qualities. If you’re interested in the detail of their different manufacture techniques, performance characteristics, and the pros and cons of each, find out more in Renew magazine’s Solar System Buyers Guide.
Otherwise, the important thing to know is that regardless of the panel type, the specifications of solar panels show their capacity, price, expected lifespan and other performance characteristics that determine what their energy output will be. These specifications are discussed here.
Why is panel wattage and size important?
When buying a solar panel system the main specification to be familiar with is the system size in watts. For example, a 3kW system may be made up of twelve 250 watt panels. This watt specification is known as the rated peak power, which is the maximum power generated by the panel under the manufacturer’s test conditions. But what does panel wattage mean for energy generation?
A larger wattage system will generate more energy in the same installation, but actual energy generation will depend on many factors, such as sunlight hours, clouds, temperature, shading and panel orientation. As a rough rule of thumb, find out the average peak sun hours per day in a particular location to get the average energy generation over a year. For example, a 4kW system in Melbourne with average peak sun hours of around 4.6 should theoretically generate around 14.5 kWh of electricity per day, on average, over a year—more on sunny days and less on cloudy days; more in summer and less in winter.
For example, it’s common for solar systems in Victoria to generate more than twice as much in December as July.
Some solar panel manufacturers and retailers have solar output calculators on their websites to help you work out how much energy a proposed system might generate.
When to use larger wattage panels and smaller wattage panels
Using panels with a larger wattage means that fewer panels need to be installed. This simplifies installation, making it faster and cheaper. However, panels of any size can be used for any type of system. For odd-shaped roofs a larger number of smaller panels may enable more generating capacity than fewer larger panels, but the final.
Advice on panel quality and selection
Quality counts at the cell level but the overall manufacturing of panels is also crucial. If assembly systems are substandard, some issues can arise that may shorten the life of solar panels or cause increased degradation over time.
One such issue with crystalline cells is that of microcracks—tiny cracks in the cells that can enlarge over time with thermal cycling (as the panels heat up and cool down each day) or with poor handling practices.
Microcracks have the potential to reduce the current generating capacity of any cells affected, and hence the overall output capacity of the panel.
How can you really tell which panels have been manufactured to the highest standards?
Some solar businesses may refer the ‘tier system’. For example, they may say that their panels are Tier 1, 2 or 3. The tier system relates to the reputation of the manufacturer and solar industry analysts assign panel manufacturers into one of three groups, with the big long-standing manufacturers with a good reputation for quality and performance in Tier 1, and smaller, newer manufacturers in Tiers 2 and 3.
The Clean Energy Council maintains a list of all solar modules (panels) and inverters that meet Australian Standards for use in the design and installation of solar PV systems. This is a more reliable indicator of good quality panels.
To be eligible for rebates, including the Solar for Business rebate, panels sold in Australia must have Clean Energy Council approval, demonstrating that they have been tested and meet Australian and international standards.
Panel efficiency is a measure of the output of the panel in relation to its collection area. Currently, panel efficiencies are in the range of around 4% to 22%, with most being in the 14% to 18% range. If you have limited roof space, panels with higher efficiency will mean you can fit more generation capacity than you could with lower efficiency panels. Of course, higher efficiency panels will generally cost more, too.
Panel efficiency is largely dependent on the technology used, though, and isn’t necessarily an indicator of quality.
If a panel has a power rating of 250 watts with a tolerance rating of + or - 5% then this means that the actual panel wattage could be 5% more or 5% less than 250 watts. Higher quality panels tend to be underrated and so have a positive power tolerance rating, for example ‘+5%’.
Testing and consumer feedback
There are a number of other testing and certification systems that can help identify higher quality panels. The Clean Energy Council’s Approved Solar Modules list indicates which panels also meet these higher standards:
- VDE Quality Testing and IEC 62941 Certification are two quality standards for solar PV module durability that meet a higher level than the International Standard
- IEC 62804 Certification is an international standard for crystalline solar PV modules’ durability against degradation caused by high voltages
- IEC 61701 Certification is an international standard for resistance against salt mist corrosion for solar modules installed in coastal areas.
The Clean Energy Regulator also has a solar module validation scheme for solar installers to check that the panels they are installing are genuine, and on the approved solar modules list. Ask your installer whether they are participating in the Solar Panel Validation (SPV) Initiative.
The Desert Knowledge Solar Centre has tested numerous solar panels and the results are published on their website. Based in Alice Springs, the DK Solar Centre has around 37 individual solar arrays of various brands and models being continuously tested. Read the data at the Desert Knowledge Solar Centre website.
Another source of information on panel quality is from those who own them. Solar system owners like to write reviews on their systems, both good and bad, so look around in the popular forums for owner experiences. One of the most popular Australian forums is Whirlpool Green Tech.
If I’m planning to get batteries down the track, which panels should I get?
The solar panels used in systems with batteries are no different to those used in systems without batteries. Systems with batteries usually have a different inverter and when adding a battery to an existing system it’s not uncommon to replace the inverter, however it’s not always necessary. Alternatively, you can add a second inverter, and some battery systems come with them included.
For more information, see Finding the right inverter for your system.
Recent developments in panel design
A variant on crystalline cells are PERCs (passivated emitter and rear cell). Already in use in some modules, these are designed for higher efficiency by reducing recombination in the cell (where electrical charges recombine before they have a chance to be used); however, this currently comes at a price premium.
Another recent development is the ‘half-cell’ or ‘half-cut cell’ panel. Instead of 60 large cells for example, the panel may have those 60 cells cut in half to form 120 cells half the size. This means that the connections between the cells are carrying half the current, reducing resistive losses by a factor of four. Not only do half-cut cell panels produce greater output than full cell panels, they also have better shade tolerance as they have twice the number of cell strings, so a smaller area is affected if just one cell is shaded. Click here(opens in a new window) to find out more.