How do we choose the right solar panels for your house?

Today, with a plethora of technical jargon and marketing speak it can be difficult to identify a great quality solar panel from the bunch of lesser ones. At the same time, the internet is filled with “information” and discussion forums claiming that brand X is better than brand Y, or that this technology outperforms that other one. At Otovo, we know that it can be difficult to know what information to trust, and that figuring out which solar panels to buy can be a challenging task. That's why we have built a rigorous quality assessment and selection process, so that when you purchase your installation at otovo.no you can always trust that you'll get the highest quality available at the right price.

High quality solar panels

Still, many are interested in the technological aspects of what makes for a high quality solar panel. In this blog post we’ll try to isolate the important factors and differentiators between great solar panels and the rest of the bunch, without comparing or pitting different technologies up against each other. Here goes!

Technology

Most solar panels manufactured today are made from silicon. Silicon is the second most abundant element in the earth’s crust (after oxygen), and is used in close to all the electronic devices we use and love everyday. The technology of choice for the vast majority of solar panel manufactures is based on silicon wafers - thin cut slices of silicon processed as stand-alone solar cells which are later interconnected into a solar panel.

While silicon wafer based solar cells is the go-to choice for most manufacturers, there are some alternatives commercially available on the market. In addition, there’s variations in the manufacturing technology within silicon wafer based solar cells and panels - often heard terms comprise PERC, back-contacted, hetero-junction, half-cut, shingle etc etc. Furthermore, there are alternative technologies to silicon wafer based solar cells and panels, most notably thin film panels which are made from deposition of a homogeneous layered structure across the entire solar module - silicon thin film, cadmium telluride (CdTe) and CIGS/CIS being the most common commercially available. And finally, there are and have always been lots of research and emerging technologies, such as cuprites, perovskites, tandem or multi-junction cells, and others.

Which one should you choose?

The simple answer is that you choose the one that meets your expectations with respect to price, performance and appearance. Look at the power output of the panel at conditions relevant to you, evaluate the aesthetics of the panel for your application, and consider how much you’d like to spend. And then observe all the points below in this blog post. If the panel you like fits the bill, the technology inside is less important. New technologies will come and go. Right now though, the obvious choice for most of us is a silicon wafer based solar panel.

Certifications

Once you have decided that you want a silicon wafer based solar panel (good choice!), it’s important to ensure that the product meets the relevant technical standards with respect to electrical characteristics, mechanical strength, durability and safety.

So, which certifications should I look for, and what does it mean? It's very understandable that this is a confusing topic, with lots of technical jargon. We've therefore created a simple overview below. In essence, though, if the panel you're looking at isn't certified according to these standards by a reputable third party accreditor (more on that later), you should be cautious and consider the risk before you buy.

IEC 61215:2016 - This is the "type approval" for solar panels, setting requirements on the properties and characteristics of the panel. It also establishes minimum requirements for how well the performance of the panel is maintained with exposure to the climate and mechanical loads. In short, this certification ensures that the solar panel has the properties that it claims and will last for a long time under normal use.

IEC 61730: 2016 - This standard sets requirements on how the solar panel is designed, constructed, and documented. It also establishes requirements on how well the materials and construction of the panel holds up to tampering, heavy use and even fire. In short, this certification ensure that the solar panel is safe to install and use, and that it's documentation is correct and honest.

IEC 61701: 2017 - This is known as "salt-mist corrosion test", and ensures that the panel is protected against any harmful effects of a salt-rich climate, such as near the sea.

IEC 62716: 2013 - Similar to the previous standard, this certificate relates to protection against ammonium corrosion, which can occur particularly in or near industrial sites or on farms.

IEC 60068-2-68:1994 - Another standard regarding protection from the environment is know as the "dust and sand test". It sets out requirements for how well the solar panel is protected agains dust and sand suspended in the air, which often happens particularly in dry seasons. And even if you don't plan on getting solar panels installed in a coastal area, on a pig farm or near the desert, these last three certificates make sure the manufacturer takes all necessary precautions to minimize any negative impacts from the environment.

So what does all this mean? Well, it means that an accreditor have tested the product according to a set of predetermined set of tests and concluded that the product meets the requirements set forth in the standards that the certificate is issued towards. Most of these accreditors are serious, respected, and independent organizations. TÜV Rheinland, TÜV Nord, TÜV Süd, Kiwa, Dekra, CQC, SGS, CENER, and many others all offer testing and certification services for solar panel manufacturers. and they all do a great and honest job at that. But for most truly serious and dedicated manufacturers and buyers, the one certification bureau to go for is TÜV Rheinland. Think of it as the gold standard in testing. If a module type is tested and certified by TÜV, you can be sure that the tested products are absolutely top notch.

Factory inspections are important

Now, testing and certification is just one part of the story. In reality, just a few out of thousands or millions of solar panels are actually tested by the accreditor. That's why factory inspections are so important. The accreditor should always perform, and the manufacturer should embrace, factory inspections to ensure that the manufacturing of products meet the quality requirements in the standards. Really dedicated and serious manufacturers also commit to yearly reviews and inspections, making sure that quality is maintained at a sufficiently high level over time.

So, in conclusion, make sure that whatever solar panel you are interested in buying that the manufacturer can provide certifications towards the standards mentioned above, that the certificates ideally are issued by TÜV, that the accreditor also has conducted factory inspections, and that the manufacturer ensures yearly reviews and testing of their products towards these standards. At the end of the day, that's your security for getting a safe and long lasting product.

Module power. And sorting tolerances

Many of us choose solar panels based on the power, but not so many know what module power actually means. To understand module power we need to understand the concept of "Watt peak". Watt peak, or Wp for short, is what's known as the nominal power output of the solar panel, meaning the electric power produced at very specific laboratory conditions. A solar panel having for instance a nominal power of 320Wp will exert that amount of electrical power with a certain intensity of sunshine (referred to as 1 sun) and at at controlled temperatures of 25 degrees Celcius. That doesn't mean that the solar panel will actually produce 320 Watt power when installed on the roof. Some times actually power output will be higher, other times less, depending on the actual amount of sunshine hitting the solar panels and the temperature the solar panels have.

Comparing the performance of solar panels

Since we (unfortunately) can't control how much sunshine there is from day to day, nominal power output is the best we have to describe and compare the performance of solar panels. But that's not the whole story of course. In real life conditions some types of panels may perform better or worse than others, even if they have the same nominal power. The reason for this is that certain technologies will benefit or hurt more than others from higher or lower amount of sunshine, higher or lower real-life temperatures, or even direct versus diffuse light hitting the solar panels.

What about sorting tolerances? Word of caution - don't believe the internet forums on this one. If you read discussion forums or follow on-line debates, you're likely to encounter untrue statements with respect power tolerance. Power tolerance is simply stated the uncertainty in measuring exactly how much power a particular solar panel will be able to produce. If the tolerance is +/- 3%, which is quite common, it means that due to known error sources in measurement equipment, it's not possible to be certain that even if you measure for instance 320Wp in the lab, the actual power of the module will be exactly 320Wp. It can be a bit lower or a bit higher, simply because of the measurement accuracy.

Some discussion forums will claim that you have to buy panels that have only a positive power tolerance, or that negative tolerances is not serious or even not allowed. These statements are unfortunately not true. Positive measurement tolerance only simply doesn't exist (unless you measure 0...). Rather, some manufactures will state "positive sorting" or "guaranteed positive" with respect to power tolerance. What this means is that they will label a panel with a nominal power of 320Wp only if they measure 320Wp or higher, typically up to +5Wp. This is in fact industry standard, and most if not all serious manufacturers will do this. This ensures that a solar panel labeled 320Wp is never measured to have a lower power, even if you can never be certain that the accuracy of the measurement technique is absolutely perfect. Actually, the latest 2016 version of the solar panel standards discussed above requires the module manufacturer to state the measurement tolerance for nominal power.

Choose a silicon solar panel

But at the end of the day these are not considerations most of us need to dwell in. For residential and commercial roof-top solar installations, choose a silicon solar panel with the nominal power output that matches your needs. And make sure you base your evaluation on energy production estimates from a reputable source. The amount of sunshine hitting your roof is the same no matter which provider to buy a solar installation from, so use your best judgement, choose the solar panels that meets your requirements and buy from a trusted and serious retailer or installer.

Manufactured in …?

When it comes to volume manufacturing of solar panels there’s really just one country to speak of - China. A vast majority of all solar panels are made in China, and the share of global manufacturing of solar panels from China is increasing. In fact, in 2018 an estimated 70% of all silicon solar panels are manufactured in China.

Other manufacturing countries than China do exist, obviously. South Korea, Taiwan, Vietnam, Singapore, Malaysia, Bangladesh, USA, Lithuania, Spain, France, Germany, and several others. A common initial customer request is for “European panels”, but the fact is that such manufacturing is very limited. While Europe was on top of the solar panel manufacturing throne about 10 - 15 years ago, most if not all of the larger manufacturing sites have since been shut down. In fact, just 3% of global solar module manufacturing in 2018 took place in Europe.

The rapid decline in solar panel manufacturing costs combined with a mature and well-tested technology has eliminated the advantages European manufacturers once had. Fact is that the newest and most modern solar panel factories are found in China - using cutting edge manufacturing and processing technology, with a very high attention to quality and certifications. Still-remaining European manufacturing on the other hand tend to be done in out-dated production lines, using older manufacturing equipment with limited investments in new technology over the past years. While there's certainly exceptions to this, parts of the remaining European solar panel manufacturing tends to be kept alive for political reasons, due to job creation, import restrictions or specific market preferences for European content or speciality tailor-made products.

Manufacturing country is not necessarily that important

Much of the advanced electronic products we use everyday - our cell phones, computers, television sets, or household utilities to name a few - are made in China. And, increasingly, so are solar panels. As long as the solar panel you are considering to buy is from a reputable and solid manufacturer, the product is of good quality and is well documented with certifications, and the manufacturing is done sustainably and with attention to safety, manufacturing country is less important.

Warranties

When it comes to solar panels, there are two different types of warranties - the product warranty and the performance warranty. While both are important for making sure you get a quality product, at the end of the day what really matters is what happens in case the warranty isn't met. But first, let's explore what product warranty and performance warranty actually is.

Product warranty is the guarantee from the manufacturer that the solar panel is manufactured without any defects or faults, and that the product works as intended, both with respect to mechanical integrity and electrical function. In essence, this warranty is similar to product warranties for other products - it simply guarantees that there's no hidden defects in any parts of the solar panel, including frames, glass, cables and other parts that may or may not affect performance, and that it will continue to work as designed. All serious solar panel manufacturers offer at least 10 years product warranty, with some even offering 12 or 15 years. This indicates that the manufacturer is confident that the solar panel is made to last.

Performance warranty

Performance warranty on the other hand is simply related to the electricity production from the panel, and only related to nominal power output. Most solar panel manufacturers today offer what is referred to as linear performance warranty - meaning that they guarantee that the solar panel does not degrade more than a certain percentage, typically maximum 0.5 - 0,7%, per year. And most manufactures offer such warranty for a duration of 25 years, ending typically at a guaranteed minimum nominal power after 25 years of between 80 and 90% compared to what's stated on the label. It is not advised to buy a solar panel that doesn't offer linear performance warranty or guarantees less than 80% after 25 years (or shorter). Simply because these are industry standards, and worse warranties than this would indicate the manufacturer is not confident with the long term performance or would like to reduce its future liability. Neither are particularly trustworthy.

Consider product and performance warranties

Now, it's important to understand that the product warranty and the performance warranty are not exhaustive. A product may fail the product warranty without being in breach of the performance warranty - typically if the frame is broken or some other mechanical property of the panel does not meet requirements. In such cases the panel could continue to produce more than its guaranteed power and one relies on the product warranty to cover any faults. Should such faults occur after the product warranty has ended, the manufacturer has no obligation to fix the problem unless the power output is affected to the extent that the performance warranty is not met. Therefore, it's important to consider both the product and the performance warranties.

Even more important than exact warranty durations is what happens in case the solar panel does not live up to its warranties. In certain cases, quite strict requirements and burden is put on the customer to warrant a claim. And at the end of the day, for the warranty to have value if a solar panel underperforms the manufacturer must still be around to fix the problem. Product warranties and performance warranties offered by a solar panel manufacturer is almost never backed by the retailer, who's rather liable for warranties according to local consumer or commercial sales regulations.

So what does this all mean? Aren't the warranties valuable? Of course they are! They're a sign that the solar panel is made to last, that the manufacturer is confident in the quality of its products and assume liability for future faults. And they're valuable as long as the coverage is acceptable and the manufacturer is financially solid and in it for the long run.

Bankability

Bankability is a funny term. And it's one of the more misused and misunderstood terms in solar. In essence, bankability is the ability to obtain external financing for larger solar installations - think utility scale solar energy farms. A bankable project using bankable solar panels simply means that banks are willing to finance the project using these panels. Which again means that banks consider the risk to be limited, including the risk for the realization of the project not being completed, the prospected energy production not being met, or that the solar panel manufacturer will not be around to fix any warranty claims that may arise. That doesn't necessary mean that the solar panels are of high quality. It simply means that the financial solidity of the manufacturer is considered to be good, and that the have not been and is not likely to be under financial stress or even insolvency.

There are several ratings for bankability of solar panel manufacturers, the most common one being the Bloomberg Tier 1 list. Tier 1 rating by Bloomberg is a coveted label for many solar panel manufacturers, but is in essence a pure metric of banks' willingness to finance projects using solar panels from that manufacturer. Other bankability rating than the Bloomberg Tier 1 list also exists, and lately PV-Tech has developed a transparent bankability rating methodology in order to have a more rigorous evaluation of the future prospects and financial outlook for solar panel manufacturers.

For most of home owners, however, bankability isn't something we typically spend much time thinking about. But choosing a "bankable" solar panel at least means that it's a higher likelihood for the manufacturer to be around to fix things if problems should arise in the future.

Sustainability

When investing in a solar panel installation we're taking a position than not only do we want to save money on our electricity bill, we also contribute to renewable and locally sourced energy production. Therefore, it's only reasonable that we want to know that the solar panels we buy are sustainably manufactured. Unfortunately, there's still some distance to go in order to obtain a full and transparent documentation of the environmental impact of most solar panel manufacturing. Actually, the work to crate environmental product declarations (EPD's) for solar panels has recently been initiated. Otovo is proud to be a part of this effort!

Certifications

In the meantime, the best way of ensuring that the manufacturer of solar panels is dedicated to both quality, sustainability and labor rights is to check their ISO certificates and their dedication to product recycling. So what should you look for? A serious and dedicated manufacturer or solar panels will be able to provide certifications for the following:

ISO 9001:2015 - Quality management system. This is the most common and most coveted quality standard, and ensures that the manufacturer has a systematic approach to quality and improvement work.

ISO 14001:2015 - Environmental management system. This shows that the manufacturer has a systematic and documented approach to environmental consequences of the manufacturing, such as waste treatment, emissions, and handling of toxic substances.

OHSAS 18001:2007 / ISO 45001:2018 - Health, safety and environment management system. This ensures that the manufacturer has a systematic approach to the health, safety and working environment of workers and staff. The OHSAS standard is only valid until 2021, after which the new ISO standard is the norm.

Choosing a solar manufacturer that's certified according to the above standards is at least a security that the manufacturer is dedicated to minimize, document, and learn from any unwanted events, and that they are serious about sustainability and responsibility.

Conclusion

Choosing solar panels for your home can seem daunting. But at the end of the day, once you decide to invest in a solar installation we want to make sure that you will benefit from that investment for a long time, exceeding 25 years! Following the recommendations in this article is the best way to ensure that the solar panels you buy delivers what they claim, are of high quality with good warranties, and are made by a manufacturer who is dedicated to quality and sustainability and is likely to be around for a long long time. Just like your solar panels!

Our solar panels are high quality

And even if it's a daunting task to choose, with Otovo you don't have to. Our rigorous selection process ensures that the solar panels you get are always of the highest quality. Check your roof at otovo.no and see for yourself!