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How to Understand and Compare Solar Panel Specifications

Feb. 04, 2024

The specifications outlined in a solar panel's datasheet provide insights into its expected performance under specific conditions. When shopping for solar panels, it can be hard to identify the most crucial metrics to pick the best solar panel.

We recommend focusing on key specifications such as power output, efficiency, and the temperature coefficient of the panel. Depending on your location, other ratings may also prove valuable. Considering these factors, you can make a more informed decision when selecting a solar panel and comparing solar quotes.

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    Power output

    Listed as: Pmax, PMPP

    The power output of solar panels is a fundamental rating measured under Standard Test Conditions (STC), a standardized set of laboratory conditions for testing all solar panels. Sometimes referred to as the panel’s wattage or size, the power output describes the amount of power a solar panel can produce. 

    Most home solar panels today typically boast power ratings of around 400 watts. However, panels with at least 370 watts can effectively meet the needs of most homeowners.

    Understanding a panel's power output is crucial as it directly influences the number of panels required to cover your electricity bill. Higher power output means fewer panels are needed.

     It’s important to note that although panels are tested under STC for comparison purposes, how they operate in real-world conditions will differ. To better understand performance in practical scenarios, some panels undergo additional testing under PVUSA test conditions or PTC (PVUSA Test Conditions). Some manufacturers, like Silfab, provide PTC ratings, which can also be labeled NOTC (Nominal Operating Cell Temperature).

    Module efficiency

    The efficiency of a solar panel represents the percentage of sunlight that the panel can convert into usable electricity. The average solar panel has efficiency ratings ranging from 19% to 21%, while the highest efficiency home solar panels currently available boast maximum efficiency ratings of up to 22.8%.

    Some brands prominently feature the efficiency rating in their marketing to attract customers. However, it's crucial to note that the power output is a more reliable indicator of a solar panel's energy production. The panel's efficiency is already factored in when its output is rated.

    Efficiency becomes particularly significant for homeowners with limited roof space. High-efficiency panels can generate more power in less space, making them an excellent choice for smaller roofs. However, for those with ample space, panels within the average efficiency range are more than capable of meeting energy needs.

    Temperature coefficient

    Listed as: Temperature coefficient (PMPP), Temperature coefficient (Pmax)

    Solar cells, constructed from semiconductor materials, see a decrease in voltage as their temperature rises. Simply put, as solar panels get hotter, their power output decreases slightly. 

    The effect temperature has on solar performance is represented by the temperature coefficient, which measures how much power output drops for every degree above 25°C the surface of a solar panel reaches. 

    Most solar panels today have a temperature coefficient between -0.3% and -0.5% per degree Celcius. The closer the temperature coefficient is to zero, the better. For example, Panasonic’s EverVolt panels stand out with some of the market’s best temperature coefficients at -0.26%. 

    Keep in mind that the performance decreases due to temperature are generally minimal. Nevertheless, the temperature coefficient shows how the panel can handle real-world conditions. 

    Cell type

    Each solar panel is made up of a number of individual solar cells that have been wired together. The type and construction of the solar cells will impact how the panel performs. 

    Monocrystalline solar cells are widely preferred for home installations as they are the most efficient and look great! Some websites may mention polycrystalline and thin-film solar panels, but these aren’t typically used in home installations. 

    Monocrystalline solar cells can be manufactured in several ways to enhance performance. Modern solar panels use PERC (passivated emitted rear contact) or TOPCon cells, which feature additional layers to boost efficiency and output ratings. 

    Many manufacturers use half-cut solar cells, where the traditional cell is cut in half to decrease resistive losses, and the entire panel is wired to minimize shade's impact.

    Dimensions

    The physical size and weight of a solar panel are crucial factors, particularly for homes with complex or older roofs.

    Typically, solar panels weigh around 40 pounds, with dimensions exceeding five feet in length and 3.25 feet in width. Specific dimensions can vary among different solar panel models.

    In most cases, residential roofs can easily bear the additional weight of solar panels and accommodate an average-sized solar system. However, for older homes, you should seek a professional inspection to ensure the roof can safely support solar panels. Additionally, if your roof features a complex shape, the dimensions of the panels become more important.

    Generally, your solar installer can find the right-sized panels for your home based on your roof’s characteristics. 

    Maximum surface loads

    Listed as: Maximum static load, snow load, wind load

    Solar panels are installed on your roof, exposing them to all the elements! Manufacturers design panels with this in mind, so they’re built to weather high winds and snow. 

    Most solar panels are rated to hold 5,000 or more pascals (Pa) of pressure, which equates to two to four feet of snow, depending on the snow’s density. Some homeowners don’t have to worry about this - but those who live in snowy regions may want to know how much snow their solar panels can handle! 

    Additionally, panels are built to endure wind speeds of about 141 miles per hour, typically only experienced in hurricane-like conditions. If you experience these winds, you’ll have more than damaged solar panels to worry about!

    Finding the right solar installer can help you get the best solar panels

    We believe it’s important for consumers to understand some of the technical aspects of solar panels, like their power output and efficiency, so that they are better prepared to compare solar quotes and not get tricked by unsavory solar salespeople. 

    But, when you find a reliable solar company, you can trust that they will use good quality solar panels. Finding a trustworthy solar company is the key to getting the best solar installation possible. Check consumer reviews, see how long the company has been in business, and shop around to better understand what is offered in your area. 

    Find trustworthy solar companies near you
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    Solar Panel Comparison

    How do you compare solar panels? I’m glad you asked! A couple of very useful comparison tools available here on SolarQuotes are:

    • NEW! Compare solar panels side-by-side – pricing, technical specifications and more of products currently available in Australia (updated regularly)
    • Solar panel comparison chart (performance information on older models)

    If you want a higher level view on the differences between brands, then in the video below  I go through 3 simple things you can look out for when comparing products.

    If you’re in a hurry, just watch this and you’ll massively reduce your risk of buying a crappy product that won’t last. After the video I go into even more detail if you are feeling like getting knee deep in solar panel comparisons!

    There is a bewildering array of solar panels on the Australian market. At the last count, there were over 4,600 models approved for use in Australia!

    If you look at a solar panel specification sheet (aka datasheet), it can often look like a physics textbook, full of numbers and strange symbols. For those of us without a degree in rocket-science, how do we make an informed solar panel comparison?

    Well, I reckon there are 5 things you need to look at when choosing solar panels for your home to maximise the chances you are getting good quality products.

    But first, let’s get one thing out of the way that doesn’t matter: whether the module is monocrystalline or polycrystalline. Despite what a lot of salespeople will tell you, these days there is very little difference between mono and poly panels.

    Right! Onto the things that actually matter when comparing:

    1) ‘Tier 1’ solar panels – does it matter?

    ‘Tier 1’ refers to a ranking given to solar panel manufacturers by ‘Bloomberg New Energy Finance’. They publish a quarterly list and charge thousands of dollars to access it.  Tier 1 is not a direct measure of quality or performance. It measures how ‘bankable’ the solar panel manufacturer is.  In other words – how likely are they to stay in business. Solar farm builders use it to reduce the risk of panel manufacturers going bust. If you are building a large-scale solar power station, your investors won’t go near you unless you use solar panels from a Tier 1 company. Getting a panel from a Tier 1 manufacturer is pretty low risk because the big manufacturers used in solar farms are almost all on top of quality control.

    Just be aware of less-than-honest salespeople who will insist their panels from WaWaSuperHappySolar are Tier 1!

    Tier 1 manufacturers include: Trina, Canadian Solar, SunPower, JA Solar, Hanwha QCells and REC to name a few.

    Non-Tier-1 manufacturers are the smaller players that produce panels. You can get some good panels from the these players, but unless you know the solar manufacturing landscape, it is a lot riskier – because 80% of the lower tier panels are junk. Also, the smaller companies are less likely to be around in the future. For those reasons, I always recommend the non-solar expert to stick to Tier 1 panels. You can read more about the tier ranking system for solar panels here.

    2) Comparing Warranty

    Be aware that all solar panels come with two warranties – a performance warranty and the manufacturer’s warranty (also known as the product warranty). 

    Generally, the performance warranty is 25 years – I’ve never seen a solar panel without a 25 year performance warranty!

    Ignore this warranty. It is so easy for the manufacturer to get out of that it is worthless; although Australian Consumer Law may come into play.

    The warranty that matters is the manufacturer’s warranty – so this is what you should compare on. Don’t buy a panel with a manufacturer’s warranty of less than 10 years. Some solar panel manufacturers are now offering up to 30 years of product warranty.

    3) Power Tolerance

    Power tolerance refers to how close to the specified wattage the module will be in real-world conditions. For example, if it is a 300-watt panel and the power tolerance is +/-5%, your actual wattage could be from 285W up to 315W.

    These days quality panels have a “positive only” power tolerance. That means a 300W module will never be less than 300W. That’s a good thing.

    4) Efficiency Comparison

    When comparing panels, efficiency is not as important as most people think. As long as the module efficiency is over 20%, it should be fine. More efficient panels don’t produce more electricity, they are just a little smaller on your roof. Unless roof space is critical, don’t stress about efficiency.

    5) Compare Temperature Coefficient

    Solar panels love sunlight, but they hate heat. Their power drops as they get hotter. The temperature coefficient measures how much the power reduces for every degree rise in temperature above 25°C – and that’s panel temperature, not ambient temperature. The temperature coefficient generally ranges from -0.3% per °C (good) to -0.5% per °C (not as good). In the latter case, if the panel temperature goes up 20°C, the power will drop 0.5 x 20 = 10%.

    By keeping the above 5 points in mind, you can compare solar panels with a good degree of confidence and sift out the spin.

    >> Next: Is Your Roof Angle Suitable For Solar Panels? >>

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