String inverters

A string inverter is a central component in photovoltaic systems. It converts the direct current (DC) generated by solar panels into alternating current (AC), which can then be fed into the home power grid or used directly by household appliances.

How it works:

1. Connection of the modules: Solar modules are connected in series and form a so-called “string”. The number of modules per string depends on the power of the modules and the inverter type.
2. DC conversion: The string inverter receives the direct current from the string. Inside the inverter there are electronic components that convert the direct current into alternating current.
3. Optimization of performance: An important component of the string inverter is the so-called Maximum Power Point Tracker (MPPT). This MPPT determines the optimal operating point (Maximum Power Point - MPP) of the solar modules and ensures that the modules deliver their maximum power.
4. Adaptation to the power grid: The alternating current generated by the string inverter must have certain properties in order to be fed into the power grid. The inverter therefore adapts the voltage, frequency and current of the alternating current to the grid specifications.
5. Monitoring and security: Modern string inverters have integrated monitoring functions. These functions are used to monitor the operation of the solar system and detect errors.

Advantages of string inverters:

• Cost-effective: String inverters are usually the cheapest variant among the inverter types.
• Easy Installation: Installing a string inverter is relatively easy and can be carried out by a professional in just a few hours.
• Proven: String inverters are a mature technology and have been in use for many years.

Disadvantages of string inverters:

• Losses due to shading: If a module in the string is shaded, the performance of the entire string decreases. This can lead to reduced yields.
• No module monitoring: String inverters do not provide any information about the performance of individual modules.
• Less flexible: Compared to other types of inverters, string inverters offer less flexibility in system planning.

Conclusion:

String inverters are a good choice for price-conscious homeowners looking for a simple and reliable solution for their photovoltaic system. However, it is important to note that string inverters can cause losses when shaded and do not provide information about the performance of individual modules.

String inverters are the most commonly used inverter technology in photovoltaic systems. They offer some significant advantages over other types of inverters:

Cost-effective: String inverters are usually the cheapest variant among the inverter types. This is due, on the one hand, to the simple construction and, on the other hand, to the large number of pieces produced by manufacturers.

Easy Installation: Installing a string inverter is relatively easy and can be done by a professional in just a few hours. The cabling is straightforward because the modules are connected in series.

Proven: String inverters are a mature technology and have been in use for many years. There is therefore a wide range of models from different manufacturers, and installation and maintenance are well established.

High overall efficiency: When the solar modules are illuminated evenly, string inverters achieve high levels of efficiency. Modern devices achieve efficiencies of over 97%.

Low maintenance: String inverters are low-maintenance devices. As a rule, only an annual visual inspection is required.

Other advantages:

• String inverters are insensitive to errors in individual modules.
• They offer good protection against overvoltage and short circuits.
• Many models have integrated functions for monitoring the system.

Disadvantages of string inverters:

• Losses due to shading: If a module in the string is shaded, the performance of the entire string decreases. This can lead to reduced yields.
• No module monitoring: String inverters do not provide any information about the performance of individual modules.
• Less flexible: Compared to other types of inverters, string inverters offer less flexibility in system planning.

Conclusion:

String inverters are a good choice for price-conscious homeowners looking for a simple, reliable and efficient solution for their photovoltaic system. However, it is important to note that string inverters can cause losses when shaded and do not provide information about the performance of individual modules. For more complex systems or when using bifacial modules, other inverter types may be more suitable.

String inverters can be categorized according to various criteria:

1. According to their topology:

• Centralized string inverters: This variant is the most common and cost-effective. The inverter is located in a central location in the system and receives the direct current from all strings.
• Decentralized string inverters: In this variant, several smaller inverters are distributed across the system. This can offer advantages in installation and maintenance, but is usually more expensive.

2. According to their performance:

• Low-power string inverters: These devices are designed for small photovoltaic systems with an output of up to 5 kWp.
• Mid-range string inverters: These inverters are suitable for systems with an output of 5 to 20 kWp.
• High-performance string inverters: These devices are designed for large photovoltaic systems with an output of over 20 kWp.

3. According to their additional functions:

• Standard string inverters: These devices provide the basic functions of converting direct current to alternating current and adapting to the power grid.
• String inverter with integrated data logger: These devices also record data on the performance of the system.
• String inverters with integrated shadow management: These devices can optimize the performance of individual modules when there is shade.
• String inverters for grid-connected and grid-parallel systems: These devices can be used in both grid-connected and grid-parallel systems.

4. According to their protection class:

• Indoor string inverters: These devices are intended for indoor installation.
• String inverters for outdoor areas: These devices are designed for outdoor installation and have a degree of protection against weather influences.

When selecting a string inverter, various factors should be taken into account, such as: B. the size and performance of the photovoltaic system, the budget, the desired functions and the installation environment.

It is important to choose an inverter from a reputable manufacturer and have the installation carried out by a qualified professional.

The correct size of a string inverter is crucial for the optimal performance and efficiency of a photovoltaic system. An inverter that is too small can lead to overloads and reduced yields, while an inverter that is too large is unnecessarily expensive and can cause energy losses.

The most important factors when dimensioning a string inverter are:

• The power of the solar modules: The total power of the solar modules in the system (in kWp) is the most important factor. The inverter should have at least the same power as the solar modules,> but it is better to choose a little more power to compensate for possible losses due to shading or low temperatures.
• The string current: The string current is the current that flows from the individual string. The inverter must be designed for the maximum string current of the system.
• The voltage range: The voltage range of the solar modules must be compatible with the voltage range of the inverter.
• Ambient conditions: The ambient temperature and humidity can affect the performance of the inverter. You should therefore choose an inverter that is designed for the expected conditions.
• The efficiency: The efficiency of the inverter indicates how efficiently it converts the direct current into alternating current. High efficiency is important to minimize energy losses.
• The number of strings: Most string inverters can connect multiple strings. The number of strings should be taken into account when selecting the inverter.
• Additional functions: Some string inverters have additional functions such as: B. an integrated data logger or shadow management. These functions can increase the price of the inverter, but also improve the utility of the system.

Rule of thumb:

The following rule of thumb can be used as a rough guide:

Inverter power (kVA) = 0.9 x total module peak power (kWp)

Example:

A photovoltaic system has a total output of 10 kWp. The string inverter should therefore have an output of at least 9 kVA.

However, it is important to consider this rule of thumb only as a guide. The exact dimensioning of the inverter should be carried out by a specialist based on the factors mentioned above.

It should also be noted that most inverters have a certain power range. This means that they can operate modules with a slightly higher power than the rated power of the inverter. This may be useful in some cases, e.g. B. if the system is to be expanded in the future.

Conclusion:

The correct dimensioning of a string inverter is important for the optimal performance and efficiency of a photovoltaic system. Various factors should be taken into account such as: B. the power of the solar modules, the string current, the voltage range, the ambient conditions, the efficiency, the number of strings and the desired additional functions. The exact dimensioning should be carried out by a specialist.

Choosing the right string inverter is crucial for the optimal performance and efficiency of a photovoltaic system. There are several factors that should be considered when choosing an inverter:

1. Performance and sizing:

• Total power of the solar modules: The inverter should have at least the same power as the solar modules, preferably a little more to compensate for any losses.
• String current: The inverter must be designed for the maximum string current of the system.
• Voltage range: The voltage range of the modules must be compatible with that of the inverter.

2. Environmental Conditions:

• Ambient temperature: The inverter should be designed for the expected temperatures.
• Humidity: The inverter should be designed for the expected humidity.

3. Technical characteristics:

• Efficiency: A high level of efficiency minimizes energy losses.
• Number of strings: The inverter should be suitable for the number of strings in the system.
• Protection class: The inverter should be protected against weather influences, if it is installed outdoors.
• Additional functions: Integrated functions such as data loggers or shadow management can increase the benefit of the system.

4. Other criteria:

• Manufacturer and quality: Choose a reputable manufacturer with a good warranty.
• Price: Set a budget and compare offers from different manufacturers.
• Maintenance: Find out about the inverter's maintenance requirements.
• Certifications: Make sure that the inverter meets the relevant standards and certifications.

Recommendation:

The exact dimensioning and selection of the inverter should always be carried out by a specialist. This can take the individual requirements of the system into account and recommend the optimal inverter.

The costs for a string inverter vary depending on various factors, such as: E.g.:

• Power of the inverter: The higher the power, the higher the price.
• Manufacturer and quality: Renowned manufacturers with good guarantees usually charge more money.
• Additional functions: Integrated functions such as data loggers or shadow management can increase the price.
• Procurement route: Online retailers often offer cheaper prices than local specialist retailers.

Please note:

• The prices generally do not include assembly and installation.
• Additional costs may apply for accessories such as: B. Cables and connections are created.

Conclusion:

The costs for a string inverter can vary greatly depending on the performance, manufacturer, functions and procurement route. It is important to obtain various offers and consider the total costs including assembly and installation.

The installation of a string inverter should only be carried out by qualified specialists. Incorrect installations can lead to serious damage to the system and safety risks.

Below you will find a general overview of the steps that need to be taken into account when installing a string inverter:

Preparation:

1. Read the installation instructions of the inverter and solar panels carefully. Make sure you have all necessary tools and materials.
2. Choose a suitable installation location for the inverter. The location should be dry, well ventilated and protected from direct sunlight.
3. Install the wall mount for the inverter according to the manufacturer's instructions.
4. Lay the cables from the solar modules to the inverter. Pay attention to the correct polarity and the use of suitable cables.
5. Connect the cables to the inverter and the solar modules. Follow the manufacturer's instructions exactly.

Installation:

1. Attach the inverter to the wall bracket.
2. Ground the inverter according to local regulations.
3. Connect the inverter to the power grid.
4. Configure the inverter using the included software or display.
5. Start up the system and check its functionality.

Further information:

• Wear appropriate safety equipment when installing the inverter.
• Always switch off the power supply before working on the system.
• Follow all manufacturer safety instructions.
• If in doubt, contact a qualified specialist.

Recommendation:

Installing a string inverter is a complex task that requires specialist knowledge and experience. Therefore, you should always have the installation carried out by a certified electrician or photovoltaic installer. This will ensure that the system is installed professionally and that all safety regulations are adhered to.

String inverters are indispensable components in photovoltaic systems and convert the direct current generated by solar modules into grid-compliant alternating current. In order to ensure optimal performance and service life of the system, regular maintenance of the inverter is essential.

Maintenance Frequency:

The frequency of maintenance depends on the specific inverter model and the manufacturer's recommendations. As a rule, an annual inspection by a specialist is advisable. For some models, a maintenance interval of up to two years may be sufficient.

Maintenance tasks:

The most important tasks when maintaining a string inverter include:

1. Visual inspection: The inverter and its surroundings are checked for damage, contamination or corrosion.
2. Functional test: The function of the inverter is checked using special software or measuring devices. Among other things, the power, efficiency and voltage values are checked.
3. Cleaning: The fans and cooling channels of the inverter are freed from dust and dirt.
4. Update of the firmware: If necessary, the firmware of the inverter is updated to the latest version.

Additional tasks:

Depending on the inverter model, additional maintenance tasks may be added, such as: B. replacing filters or checking the connections.

Recommendation:

Maintenance of a string inverter should always be carried out by a qualified specialist. This person has the necessary specialist knowledge and tools to carry out maintenance safely and effectively.

Benefits of regular maintenance:

• Increased service life of the inverter: Through regular maintenance, signs of wear and tear are detected and remedied at an early stage, which can significantly extend the service life of the inverter.
• Optimal performance: A well-maintained system works more efficiently and generates more electricity.
• Avoiding failures: Regular maintenance minimizes the risk of unexpected failures and system downtimes.
• Increased security: Regular checks reduce security risks such as: B. Short circuits or fires can be detected early and prevented.

Conclusion:

The maintenance of a string inverter is an important part of the maintenance of a photovoltaic system. It contributes to optimizing performance, extending the service life and increasing the safety of the system. Therefore, you should always have maintenance carried out by a specialist.

1. Isolate errors:

• Visual check: Check the inverter for damage, such as burn marks or water penetration.
• Noise development: Pay attention to unusual noises from the device.
• LED display: Pay attention to the error codes or messages on the inverter's LED display.
• Power measurement: Check whether the photovoltaic modules generate electricity and whether the inverter feeds it into the power grid.

2. Security:

• Switch off the inverter: Operate the DC isolator and the fuses on the inverter to avoid voltages.
• Securing the system: Make sure that the photovoltaic modules are protected against short circuits and overvoltage.

3. Get help:

• Contact the installer: The installer of your photovoltaic system can usually quickly diagnose and correct the error.
• Inverter manufacturer: Contact the inverter manufacturer's customer service if the installer cannot be reached or if the problem seems too complex.
• Online forums: In online forums about photovoltaics you can find help and reports from other owners of solar systems.

4. Possible solutions:

• Reset: Sometimes simply resetting the inverter by switching it off and on helps.
• Troubleshooting: The installer or customer service can resolve the error based on error codes or measurements.
• Repair: In some cases the inverter can be repaired.
• Replacement: If repair is not possible or uneconomical, the inverter must be replaced.

5. Tips:

• Regular maintenance: Have your photovoltaic system regularly serviced by a specialist in order to identify and correct errors at an early stage.
• Guarantee: Check the guarantee conditions of your inverter and the photovoltaic modules.
• Insurance: Photovoltaic insurance can cover financial damage in the event of a defect in the inverter.

Important: Never work on a defective inverter yourself. There is a danger to life due to high voltage!

The efficiency of string inverters today is 96 to 98%, with modern devices often achieve over 98%.

Efficiency describes the ratio of energy used to usable energy. With an efficiency of 98%, this means that for every 100 kWh of energy fed into the photovoltaic modules, 98 kWh reaches the power grid in the form of alternating current. The remaining 2 kWh are lost as power loss in the form of heat.

Factors affecting efficiency:

• Efficiency of the inverter: The higher the efficiency of the inverter, the less energy is lost.
• Partial shading: If individual modules in the string are shaded, the performance of the entire string drops. Modern inverters have MPP tracking to minimize this effect.
• Temperature: At high temperatures, the efficiency of the inverter decreases.
• Age: Over time, the efficiency of the inverter may decrease slightly.

Transformerless inverters usually achieve a higher efficiency.

In summary, string inverters are now very efficient devices. However, choosing the right inverter can influence the overall performance of your photovoltaic system.