How To Read a Solar Panel Datasheet
After we’ve surveyed your home or business for solar, you’ll receive a detailed proposal outlining the size, type and cost of the solar system best suited to your priorities and needs.
The proposal includes a breakdown of the make and model we suggest for the different components – solar panels, inverter and battery – with links to the datasheets for each.
This guide is designed to help you navigate the technical specifications of a solar panel datasheet. We’ll highlight the specifications that are useful to understand, explain how they contribute to the performance of a solar system and give you some benchmarks to look out for when comparing different panels.
If you don’t already have one, you can follow along by opening these datasheets for solar panel products we use and trust:
Understanding a Solar Panel Datasheet
Brand
Choosing a reputable manufacturer that aligns with your values is a great first step. But unlike shoes or cars, it’s likely you’ve never heard of even the biggest solar panel manufacturers! Look for signs like whether the company specialises in producing solar panels, what warranties they offer (more on this later), how long they have been around and what your installer has to say about them. Some companies might align better with your values too, like using sustainable manufacturing practices or a commitment to worker’s rights.
Some trusted solar panel brands include Hyundai, Sunpower, REC, Jinko, Canadian Solar, and Winaico.
Warranty
Next up is an important one, your warranty. Solar panel warranties are usually broken down into three categories:
Product Warranty
This covers any defects or failures in the product after installation. So if a panel stops working, or there is a physical defect such as water ingress, you’re protected.
Performance or Power Warranty
Like any product, some degradation in the performance of a solar panel is expected over time. However, it’s remarkably less than your phone or computer. You’ll see this expressed as Annual Degradation. The REC datasheet tells us that they expect around 0.25% Annual Degradation. This means that after 25 years, your panels will still be producing at least 92% of the 430W of power they were producing in year one. If they drop below this, the Performance warranty has you covered.
Service or Labour Warranty
This covers the wider costs of a warranty claim, such as removal, shipping and installation. It makes the warranty claim process super simple and means there shouldn’t be any issues getting an installer back to replace a solar panel under warranty. Not all solar panels come with a service or labour warranty. If this is offered, it’s usually attached to a ‘Certified Installer’ status, so your installer needs to be certified with the manufacturer for this warranty to apply.
Performance and Output of a Solar Panel
Wattage / Watts / Power Output
The main way solar panels are described is in terms of their Wattage or Power Output. Solar panel power output is measured in Watts, commonly abbreviated on specification sheets to W for Watts or WP for Watts Peak.
This is the peak amount of power – or Watts – the solar panel can produce under Standard Test Conditions. So for a 430W panel, the absolute peak amount of power it can produce under Standard Test Conditions is 430W.
As the name suggests, Standard Test Conditions are environmental conditions produced and controlled in a lab, used across the industry to test the performance of solar panels in a standardised way. These conditions are an irradiance of 1,000 W/m^2, an air mass of 1.5, and a cell temperature of 25°C.
Interestingly, these test conditions are remarkably similar to what we experience in NZ with our clear skies, position on the globe and temperate climate. That means, in the hours around midday, a solar system installed in NZ will produce a peak output that is pretty close to what’s listed on the specification sheet.
There’s one thing to watch out for here. The eagle-eyed among you will have noticed that most datasheets state a Wattage range. For Example 400–430W.
That’s because the testing process usually finds some variation in the Wattage of individual panels, even when they are the same brand and model and are manufactured in the same way. So you might have two identical solar panels, but one produces a peak of 410W under Standard Test Conditions and one 430W.
Of course, both wattages are good, and it doesn’t really matter so long as you’re given the one you’ve been sold. We have seen instances where customers were promised and quoted on a 455W panel and only received the 440W version. Because they’re on the same datasheet, technically they could argue you were told. But we think that’s misleading. So it’s checking the Peak Wattage of the exact panels you’re getting, with your installer.
Watt Class Sorting or Power Tolerance
Now you know the expected peak power output of your solar panel, you’ll also want to check how much you can expect performance to vary outside of this. This will be described on your solar panel datasheet as Power Tolerance or Watt Class Sorting. In the Sunpower example, it’s called Power Tolerance and expressed as a percentage. Sunpower panels have a power tolerance range of +3/0%. This means that the module might produce 3% more peak power than the stated 455W, but never less. In the REC example, it’s called Watt Class Sorting and expressed in Watts. These panels can produce 3 Watts more than the 455W stated, but never less than that. As you might expect, cheaper panels often have a lower range of tolerance.
Panel Efficiency
Panel efficiency is one that’s easy to understand, but matters less than most people think. It is simply how much power is produced per square metre of panel, expressed as a percentage. The higher the percentage, the more efficient the panel. A very efficient panel is useful if you’re limited on roof space, but as they usually come with a higher price tag, it can be more economical to simply add another panel to achieve the same output.
As a general guide, any panel with an efficiency above 20% is considered good.
Power Density is really the same as panel efficiency, just expressed as Watts per square metre. This figure can be used to quickly calculate how many panels you could roughly fit on a roof. For example, if you have a 50 square metre roof, you can take REC’s 430W panel power density of 223W/m2 and multiply it by 50 to know you could roughly fit a 11,150W or 11.15kW system. This is helpful when estimating the possible size of your system.
Dimensions
In reality, your roof isn’t straight square metres. It has different angles and proportions, as well as things like chimneys or skylights to avoid. The size and shape of solar panels will ultimately determine the number and configuration that can fit on your roof. Finding the right configuration can be a bit of an art, which is where an experienced solar designer is worth their weight in gold.
Environmental Conditions
Solar panel specification sheets also give you useful information about their ability to operate in different environmental conditions.
Temperature
Maximum ratings for operational temperature are exactly that, the absolute extremes of temperature your panel will operate in before it is no longer covered by the warranty. Hopefully something you’ll never need to worry about!
Temperature coefficient of Pmax
The temperature coefficient of Pmax tells you how well you can expect a solar panel to perform on a very hot day. It is the percentage decrease in efficiency expected for every degree over 25 degrees. Here you’re looking for as low a figure as possible, to give you a benchmark, the 0.24% listed on REC’s datasheet is very good.
Materials
As with any product, higher quality materials make for a longer lasting product. The longer the life of your solar system, the more years of free power you’ll enjoy.
Test loads tell you about the solar panel’s ability to withstand damage from things like earthquakes, hailstorms or falling debris. The higher the rating here, the stronger the panels and the more likely they are to last a long time.
The datasheet will also state any specific certifications or ratings the solar panels have been tested to, such as Hail, Fire Class and Salt Mist Ratings. If you live near the ocean, you’ll want to take note of what the panel is made from too. The general data section will give you information about the makeup of your panel. An anodized frame and highly resistant polymer will ensure longevity in corrosive, sea air. In some cases, you can get a Framed Glass-Glass panel, which means the solar panel has glass on the underside, rather than polymer. Which offers even more strength and longevity.
Summary
These are the most important things to look out for on your solar panel datasheet. The rest of the information is mostly used by your installer to design and commission your system safely. If you’re unsure of anything, ask your installer. Our team has a wealth of knowledge and are always happy to delve into the details with you, to ensure you have everything you need to make the right choice for you.