Solar panels + inverter = inseparable duo

The inverter is the head of the entire system. This machine draws all the power from photovoltaic solar panels. If not selected properly, it can significantly reduce the performance of solar panels.

Solar panels + inverter = inseparable duo

Therefore, if you decide to install solar panels, it is worth checking what to pay attention to when selecting an inverter.

Photovoltaic solar panels produce energy and the inverter converts it into the current that we have in our plugs. These two elements must be well combined.

The second most important element of a photovoltaic installation is the photovoltaic inverter. Other names are frequency converter or solar inverter. Regardless of its name, it has one main task: to convert direct current (DC), which solar panels capture, into alternating current (AC), which is what we can use in our home (AC).

What is an investor?

As we have written before, a solar inverter is responsible for converting the energy of the photovoltaic modules into alternating current with parameters identical to those of the low voltage electrical network, that is, 230 / 400V 50 Hz. But that is not all. An additional task of this device is to control the processes and collect energy production statistics.

One of the elements of this device is a system for monitoring the maximum operating point of the modules – MPPT. The lifespan of a solar inverter is shorter than that of solar panels, which can operate for up to 25 years. It is assumed that, depending on the model and brand, its useful life is 8 to 12 years. There are also micro-inverters on the market, which can operate for up to 25 years.

The grid inverter is installed during the installation of the solar panels. It is usually located near the panels or near the main supply, it is mounted vertically and its connections are located at the bottom of the device.

Depending on how far it is placed, it can have up to a 5% loss of performance. This can be slightly offset by the quality of the cables, which can ensure less power loss.

MPPT – what is it?

The art of assembling a photovoltaic system says that each module that forms a chain of connections must be identical. This means that the combined photovoltaic panels must come from the same manufacturer, have the same power and be of the same type. But that is not all. Each panel should also have a similar position and an equal slope. All these requirements are important, because only then can we be sure that the MPPT tracking system will be used optimally.

How does the MPPTT work? In a great simplification, it allows to increase the amount of energy obtained even by several percent. How is it possible? It is quite simple. The modules available on the market do not have a fixed maximum power point, it is variable and depends on the radiation that is produced. The aforementioned system tracks where such a point occurs (MPP maximum power point) and adjusts to its new value. This results in increased energy production. Today every modern investor has at least one such system.

Types of investors

There are several types of inverters available in the market. We distinguish between them:

• single-phase or three  – phase – single-phase is used for low power, for higher power requirements three-phase solutions are used. However, if we have to choose between a low-power single-phase inverter and a low-power three-phase inverter, the latter is worth considering as it can significantly affect the stability of the local grid, result in less voltage fluctuations, and require lower cable cross sections;
• no need for a transformer  – if one of the poles of the installation needs to be grounded, an inverter with a transformer must be reached, as it provides galvanic isolation between the constant input voltage and the power grid. However, if we do not need to use the galvanic isolation provided by the transformer, we can choose transformerless solutions, which -although they are lighter and smaller- are sometimes more expensive due to the protection systems used, but in the long term it is a good one. choice;
• String or central inverters – string inverters can work with several series of modules and are designed for installations of various sizes of lower power. Central inverters are dedicated to solar farms and are unlikely to be used in a home installation;
• micro inverters  – they are adapted to work with a single photovoltaic cell;
• Grid inverters  – are divided into two types, depending on whether they are connected to the grid or not. The island’s inverter is not synchronized with the grid, so it cannot supply power to the grid, but it has the ability to charge the batteries in case of surpluses. The grid inverter allows synchronization with the public grid, but is not capable of charging the batteries.

How to choose the optimal solar inverter?

What inverter for photovoltaic energy? There are two options to choose from: either match the solar modules with the solar inverter, or match the inverter with the photovoltaic panels.

For maximum efficiency, you should choose an inverter that can handle  90-110%  of the installation. Other sources say this is between 85 and 125%. Specifically, this means that a 3 kWp solar panel installation requires a 2.7 kWp to 3.3 kWp inverter. Why? It all comes from the formula for calculating the inverter power factor – IR. This formula is the following:

inverter power factor IR = module field strength [Wp] * inverter efficiency [%] / inverter maximum AC power [W]

We can obtain three results that show us if the inverter is underloaded, with minimal power or overloaded.

IR <100%, the inverter is underloaded
IR = 100%, the inverter loaded with the rated power
IR> 100%, the inverter was overloaded on the DC side

However, the optimal value must be calculated for each installation. This is because it depends on many geoatmospheric factors and the type and orientation of the photovoltaic modules and how they are connected to the inverter.

The selection of an inverter for the photovoltaic installation is not the easiest task. Request free estimates for photovoltaic installations and you will receive several detailed offers from specialists. With the knowledge of this article you will be able to evaluate them better. We generally recommend using this option.

What is the efficiency of a photovoltaic inverter?

The efficiency of an inverter is nothing more than the ratio between the effective output power of alternating current and the electrical input power of direct current and its normalized form (Euro-η efficiency also known as European weighted efficiency). It is defined by a formula:

η = PAC output power / PDC input power

However, it must be remembered that although it would be worth having maximum values, the investor will not perform at its maximum value or will do so occasionally. This is because the final energy value is influenced by many more parameters. These are, among others, the brand (and consequently the quality), the adaptation speed of the MPPT device. It also means that efficiency is not an absolute parameter, and a more efficient inverter will not always guarantee higher energy production.

System operation monitoring

The installation of the solar panels along with all the necessary components and cables is part of the whole process. During use, it is important to monitor all parameters of photovoltaic systems. This ensures that the optimal energy input is obtained and that irregularities can be reacted.

The easiest way is, of course, to read the data from the screen, which is equipped with practically all the inverters available on the market. However, these data are not always sufficient and complete. For this reason, many manufacturers and service providers have decided to turn to additional solutions and special software.

This allows us not only to analyze but also to record the input and output parameters of the investor, collect historical data and process them. All this with the help of universal access to the network. Advanced PV inverters can be connected to the grid, allowing automatic data transfer to the data collection and processing center. The investor owner can view this data through a dedicated website or app.

Quality

There are many companies on the market that deal with the installation of photovoltaic panels. When deciding on a solution, let’s not just be guided by price, but also by other criteria. The parameters of the panels, the investor, as well as the support it receives from its local representative must be important to the clients. It is worth seeking out vendors in your area to ensure that in crisis situations the response to the request is fast enough.

The most important parameters of a solar inverter, to which we must pay attention, are:

• how fast it finds and maintains the maximum power point MPP,
• the efficiency of the inverter at part load,
• how reliable the device is,
• what is the temperature range in which the device can operate – those that can operate without problems in the range (-25 ° C to + 60 ° C) are recommended,
• how easy it is to operate and control the device, if you have a remote panel and access to historical data,
• that meets all quality and safety standards,
• If the service is located on site or at a distance that can be easily reached or that can be covered by a service team, it is also important that the service is located in our country.

Inverters are tested for reliability by the PVEL institute – we have included the results of the latest research.

There are many investors from different companies on the market. Among the reputable brands, it is worth mentioning:

• SMA  (Germany)
• SolarEdge (Israel)
• Enphase (United States)
• Fronius (Austria)
• Schneider (France)
• ABB (Sweden / Switzerland)
• Huawei (China)
• Delta (Taiwan)

Price

Investors differ in many parameters and also in price. Many panel installers trust  SMA  because they are good value for money in the industry. The models of this company are characterized by their efficiency and reliability. However, in recent years the SolarEdge brand has also jumped onto this top shelf. However, other products cannot be said to be much worse. Each brand has its own premium models, which will appeal to demanding users.

How much money does it take to buy an investor? On average, prices start at around € 700, but you can buy inverters, which cost three thousand and more. It all depends on the parameters of the device, and whether it is equipped with additional functionalities such as memory, the Wi-Fi module or a web server that collects the data from the files.

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It is worth taking advantage of the help of specialists

If we do not know which solution is optimal for our home or business, it is not worth risking and it is better to trust experts who are always ready to help and share their knowledge. Ask  our service for a  free estimate and you will see the savings you can achieve by installing the right panels, as well as the best inverter.