Solar energy inverter: What is it, how does it work?

In recent years, photovoltaic systems have gained great interest. If you decide to choose a network, you are sure to be interested in the power of the panels or their size. An extremely important element in the entire installation is also the Solar energy inverter. The device is, so to speak, the heart of the entire installation, without which the energy consumed would be useless. What is the investor for and how to choose the best one?

Solar energy inverter

Photovoltaic installation is gaining more and more popularity in residential construction. The prospect of getting free energy from a solar power plant makes more and more investors decide to install solar cells. One of the most important elements of this installation is the inverter. What does this name mean, what are its types? A handful of tips below.

What is a Solar energy inverter?

A   solar inverter (  inverter, frequency converter  )  converts the direct current  produced by the photovoltaic panels  into alternating current  as it is in the plug. In addition, it  monitors the  operation of the installation and has security functions 

A Solar energy inverter is an essential element of any photovoltaic installation, low and high power. Its task is to convert direct current, produced by panels, into alternating current, which flows in household electrical outlets. 

The direct current generated in photovoltaic cells is not suitable for the supply of household appliances, therefore it must be converted to the nominal voltage, that is, 230 V. The inverter market is divided into many categories: transformer and without transformer, single phase and three-phase, string and central inverters. A lot of knowledge is required to adapt the inverter to the installation; if we know the necessary parameters of the inverter, for example, the designer of the installation, we can explore the market offer in search of the suitable device.

How does it look? Oh, a box like that, smaller or bigger. It is usually hung on the wall in a basement or laundry room.

                                                                         The investor in the natural environment.

Grid or island Solar energy inverter?

The most recognizable criteria for selecting solar inverters is the type of photovoltaic installation. For this reason, we distinguish between grid-connected and off-grid inverters.  Off-grid inverters are not synchronized with the electromagnetic grid, so they cannot return power to it; however, they can charge the batteries in case of excess solar energy. Grid inverters are  synchronized with the public grid, so we can sell electricity on preferential terms, for example by  using a bidirectional meter  . 

Hybrid inverters are new to the market that can work both in grid and island mode. This is due to the built-in battery that works as a power buffer. In such a solution, the inverter stores part of the energy in the battery if the current energy demand of the building is less than the energy produced by the photovoltaic system. If it is the other way around, that is, the energy supplied by the photovoltaic modules falls below the energy demand of the building, the inverters take the missing part of the energy from the batteries.

Inverter parameters: what do they matter?

The choice of inverter is determined by the size and configuration of the photovoltaic system. For small installations, we need a low power inverter of 2-5 kW. An important parameter of the inverter is efficiency: the higher it is, the better the cooperation between the inverter and the panels. The best  inverters  achieve an efficiency of 92 percent. – higher power inverters can obtain more than 98 percent  energy transmitted by cells. When comparing the inverters to each other in terms of efficiency, that is, in terms of the weighted average efficiency for different inverter loads, this appears on the catalog card under the name  EURO– It should also be mentioned that the efficiency of the inverter drops dramatically with loads below 20-30 percent. rated power. For this reason, the selection of an inverter is based on the fact that it produces as much electricity as possible throughout its useful life.

To obtain the highest possible efficiency from the partial load inverter (NOCT), devices with a power lower than the peak power of the photovoltaic panels are selected. The  most desirable NOCT value  for an investor is 20 to 25 percent. Each investor must have an electronic device called  MPP Trader  , whose task is to correctly charge the system so that energy production takes place under optimal voltage and current conditions, that is, with maximum power. If there is a risk  that the installation will be heavily shaded For example, through nearby trees: in such field conditions, an inverter with two MPPTs will perform more efficiently than its counterpart with one MPPT. 

It is also worth remembering to locate the inverters as close as possible to the modules, in the attic or on the exterior wall of the building under the roof. Two independent MPPTs also allow us to configure the installation more freely. If possible, before buying an inverter, it is advisable to consult its parameters with the installation designer.

Ok, putting the basics aside, which investors are the  best  ?

Classification

If you want to quickly know the strengths of a certain brand, the following ranking will help you:

Click on a certain brand name to read its detailed review.

In addition to brand selection, you will need to make one more decision regarding the type of installation.

Installation types

Due to the operating principle of the inverter, there are three types of installation:

• with  string inverter  (one inverter per installation, as in the initial image)
• with string inverter and  optimizers  (one inverter per installation, but each panel is optimized)
• with  microinverters  (each panel has its own inverter)

You can read about which solution to choose in a certain situation in  this text  . Instead, let’s focus on the technical details of investors and how to tell the good guys from the bad.

The easiest way is to tell you what we pay attention to when we write reviews.

Reliability

An inverter is a complex system of sensitive electronics that must constantly process large amounts of energy from photovoltaic modules. By its very nature, it has a shorter lifespan than solar panels.

Also, an inverter failure usually means power outages throughout the facility.

In a word, the reliability of the inverter and the ability to quickly carry out any repairs is a very important matter and it is worth paying more for higher quality.

What factors should you consider?

Certificates

Saying that a good investor should have the proper certificates is like saying that stable ground might be needed to build a house. Normally, you don’t have to worry about it:  serious producers always have the required certificates  , so if a brand is in our ranking, everything should be fine.

Either way, it is absolutely necessary for the investor to have

• certified in accordance with PN-EN 61000-3-2 and PN-EN 61000-3-3 (for inverters with current <16A per phase); PN-EN 61000-3-12 and PN-EN 61000-3-11 (for those with a current of 16-75A per phase)
• certified in accordance with the PN-EN 50438 standard
• declaration of conformity with Directive 2014/35 / EU (low voltage)
• declaration of conformity with Directive 2014/30 / EU (electromagnetic compatibility)

Sometimes, however, these certificates can be difficult to find online or are only available to installers. If you are looking for one and can’t find one, ask your installer.

If any inverter does not meet the above conditions, it should not be used. Certificates are not a quality determinant, but a necessary minimum.

Mechanical resistance and IP protection class

The inverters are designed to operate in harsh environments. The mechanical resistance can be evaluated on the basis of the IP protection class and the tests carried out by PVEL.

The IP protection class indicates the extent to which a product is resistant to dust and water. This is especially important in solar parks, where investors are often installed outside, but it also gives prosumers some information on the quality of the home.

The vast majority of inverters are  IP65  , which means that they can operate outdoors without being affected by rain. Some even have  IP66  , which makes them even more waterproof.

The longest lasting inverters

The TOP PERFORMER award in 2019 for the results in mechanical resistance tests was awarded to:

• Delta
• high school
• Fronius

Warranty

The details and duration of the guarantee are one of the best indicators of an investor’s quality. Sometimes it may not be easy to distinguish a good warranty from a bad one, as manufacturers often offer the option of a warranty extension paid for many years and sometimes even the same product has a completely different warranty on different countries.

Warranty details  are important and include issues such as crash reports, guaranteed customer service, covered or non-warranty covered damage, maximum time to report defects, etc.

When writing investor brand reviews, we read their guarantees. If we find anything disturbing, we will definitely let you know.

The duration of the warranty  demonstrates the manufacturer’s confidence in its own products. The standard warranty is 5 years, the really good ones start at 10 years. However, there are additional factors to consider. Let’s compare the example inverters in the table:

Inverter brands with the best guarantee

• SolarEdge  : 12 years for an inverter, 25 years for optimizers
• SMA  : 5 years for the investor, the possibility of a paid extension up to 20; in Australia and the USA, the warranty starts at 10 years
• Delta  : 5 years for the investor, the possibility of a paid extension to 20
• Fronius  : 5 years for an investor, the possibility of a paid extension up to 20; in Australia and the USA, the warranty starts at 10 years
• Enphase  : 25 Years for Microwaves

The longer the warranty, the better, right? Well, following this logic, SolarEdge and Enphase systems are much better than standard inverters. This is not necessarily the case. Keep in mind that they contain many more elements, and the more complex the design, the more things can go wrong.

The issue of warranty is also always strongly related to price, which is painfully evident in all brands that offer a 20-year warranty … as long as you pay almost double the amount you originally paid.

What can we learn from this? What can be the   real  lifespan of investors  ?

It is safe to assume that  good quality inverters will function without repair for 10 to 15 years  . Whats Next?

The most sensitive components will start to break down and you will have to call your installer for help. If you choose a brand that offers good support in Poland, the installer will most likely know which part to replace to keep the inverter running. Repairing them  during this period should still  pay off  .

After 20 years, string inverters, even the best ones, are likely to break down so badly that they are not worth repairing.

Investor efficiency

Photovoltaic cells generate electricity, but they are pretty simple and “dumb” devices, let’s say like muscles. The “brain” of the operation is the investor. Just as an efficient brain makes optimal use of muscle power, an efficient inverter extracts maximum power from the installation.

When determining performance, it is worth paying attention to three factors:

• efficiency  – the larger the inverter, the less electricity it uses for its own operation and produces less heat
• MPPT quantity and quality  – the better, the less individual panels interfere with each other
• without failures  , because each failure and restart of the inverter supposes an interruption in the operation of the installation and does not generate profits

What companies are the best here? There is no single performance test, but an important guideline is the 30-day real-life performance test conducted by the PVEL institute.

The best investors in terms of efficiency

In 2019, PVEL awarded the TOP PERFORMER award for performance in the 30-day trial to the following manufacturers:

• high school
• Huawei

Unfortunately, it is impossible to say how many investors have passed this test. Therefore, receiving this award confirms high performance, but its absence does not necessarily mean its absence.

Let us now analyze the performance components by shift.

Efficiency

How well an Solar energy inverter converts direct current to alternating current describes the  efficiency  . It is variable and varies according to the voltage and the power generated by the installation, the voltage depends mainly on the design and the power depends on the climate. The  maximum legitimacy  is, therefore, a less important parameter because it occurs only in the best. We are more interested in:

A weighted efficiency  that takes into account the performance of the inverter in different conditions (morning, full sun and night). The two most popular weighted efficiency systems are the  European efficiency  and the  CEC  (US) efficiency  , which differ but not much, while the European is, well, more suited to Polish conditions.

Microinverter and inverter brands that achieve a weighted efficiency greater than 97% include:

• Enphase
• high school
• Fronius
• Delta
• TISSUE
• Schneider
• Huawei
• SolaX
• Up to this point
• Praise
• Growatt

97% is a really good result and you can stop there. However, if you want to know which brands are the best among the best in this regard, we recommend that you read the PVEL research results again.

The TOP PERFORMER award in 2019 for the results in the conversion efficiency tests of the PVEL institute was awarded to:

• Schneider
• Huawei

MPPT number and optimization

MPPT is a maximum power tracker. Calculate the ideal load for the installation or its part, thanks to which it can generate the highest possible power. Why is it necessary to make such changes?

Well, it is because photovoltaic cells influence each other. The weakest and least illuminated cells affect the entire panel section and, unless disconnected by bypass diodes,  the weaker  power  panels  reduce the power of the entire installation  , in   well-designed installations by a maximum of 15- twenty%.

A good MPPT system can correctly determine the maximum power point in any situation, and it is not always easy. Let’s see which chain inverter brands do the best.

Solar energy inverter with the best MPPT

The 2019 TOP PERFORMER award for MPPT fitness test results was awarded to:

• Delta
• Schneider
• Huawei

But beware, in addition to the quality of the MPPT, its  quantity  is also important  .

Consider: With an MPPT, the shaded panel will have a negative effect on the entire installation. With two MPPT: half installation. On the other hand, when investing in power optimizers or  microinverters  , the  MPPT will be calculated for each panel separately  .

Even the best MPPT system has its limitations, so if you want to improve your performance by a few or a dozen percent, you should invest in optimization.

Better optimization

If you want the best  possible optimization  , you have the following options:

• Microinverters
  • Enphase
  • ABB  : they also produce ordinary inverters
  • Andalay
    pretty much any brand of mic will give you both MPPT as panels, or 1 MPPT for two panels, which is also good and cheaper.
• Optimizers
  • SolarEdge
  • Huawei  : works with inverters from Huawei and other brands
  • Tigo  : works with inverters from other brands, it is not necessary to optimize the entire installation
  • Maxim  : In theory, the best optimization system in the world, in practice, your product had disadvantages. Perhaps we will hear of them again.

Fail-free photovoltaic inverters

The Solar energy inverter is the bottleneck of the installation. Any malfunction, even a system restart, will  interrupt electricity generation  , sometimes for several minutes. A temporary interruption in operation can be caused by a sudden change in voltage in the installation, a sudden change in temperature and similar events.

Which Solar energy inverter manufacturers are known for the reliability of their products? How do you measure it? PVEL tests that measure resistance to temperature and changing working conditions are a good indicator.

Temperature resistant Solar energy inverter

In 2019, PVEL awarded the TOP PERFORMER award for temperature resistance to the following brands:

• Fronius
• Schneider
• Huawei
• high school
• Delta

In turn, the following brands were distinguished by their resistance to changing conditions:

• Delta
• Fronius
• Huawei

What is more profitable, a single-phase or three-phase inverter?

For small installations: up to 3kW, only single phase is available, so there is nothing to think about. Above 3.68 kW, the OSD requirements require you to buy a 3-phase, so there is nothing to think about. But in the range of 3 to 3.68 kW, which Solar energy inverter to choose?

A three-phase inverter is  10-20% more expensive  , but also  more efficient  . Thanks to the interface balance, it allows to increase the annual effective level of balance from approximately 82% to 84%. Over the course of 15 years, this will bring savings, but significantly lower than the costs initially incurred.
The 3 phases should not be chosen for purely economic reasons.

Facility performance monitoring and hazard detection

The installation of solar panels with all the necessary components and cables is part of the whole process. During use, it is important to  monitor all the parameters  of the photovoltaic systems. Thanks to this, we can be sure that we obtain an optimal energy expenditure, and we can also react to irregularities.

The simplest way is, of course, to read the data from the screen, which is equipped with practically all commercially available inverters. However, these data are not always sufficient and complete. That is why many manufacturers and service providers decided to focus on additional solutions and  special software  . Thanks to them, we can not only analyze, but also record the input and output parameters of the Solar energy inverter, collect and process historical data. All with the help of universal network access. Advanced PV inverters can be  connected to the grid , allowing data to be automatically transferred to the data collection and processing center. The investor owner can view this data through the website or a dedicated app.

But the monitoring of the operation of the system is not only to inform the client about the good decision they made when investing in photovoltaics. The Solar energy inverter are also designed to detect and report serious faults, such as arc flash or grounding problems.

The safest investors in 2021

The TOP PERFORMER award in 2019 for results in the detection of arc flash and grounding problems was awarded to:

• Delta
• Fronius

A summary at the end.

We’ve covered a wealth of parameters, factors, tests, and tips to help you choose the best investor. The reasonable question is which are the most important? What should you pay more attention to?

Somewhat contrary to the previous content of the article, I believe that the most important thing is not efficiency, nor a guarantee nor a low price. If I had to point out two key things to pay attention to, the first would be the brand and the installer. Why?

This is the fastest way to make a safe decision. And in case of any problem, a solid brand with customer support in our country and a trusted installer will work together to solve it as quickly as possible.