If you buy a solar system, you must buy an inverter. What is an inverter in a complete solar system? Solar cells produce a direct current that cannot be used in the home in this form. To convert direct current into usable alternating current, you need the inverter. Here you can find out everything about the function, the different types and the prices of an inverter.
The difference between direct and alternating current is simple: With a direct voltage, electrons flow in the same direction at the same speed. The AC voltage, on the other hand, causes electrons to flow in both directions. The speed of the electrons also varies. To transport electricity over long distances and to make it usable in the home, you need alternating currents.
Which functions does the inverter have exactly?
As the “heart” of the solar powered generator system, the inverter has many different tasks. Arguably the most important function is converting the DC power into usable AC power. However, there are also the following functions:
Network monitoring:
Because the power grid is very sensitive to changes in voltage or frequency, grid overload could quickly occur. To maintain stability, the inverter monitors these grid parameters. The inverter automatically disconnects the solar system from the power grid if a limit value is exceeded.
System monitoring:
Not only the network but also the system itself is monitored. The inverter constantly measures the solar system’s voltage, current and current output. In this way, faults and problems can be identified quickly. In addition, the data on performance and yield can be viewed so that self-use or feed-in can be optimized.
Performance maximization
Solar systems have a certain point at which the current generated and the respective voltage are optimal. This point is also called Maximum PowerPoint (MPP). The inverter constantly uses resistance changes to keep the MPP PV system in the MPP. This ensures maximum productivity.
Security
Because photovoltaic systems are connected directly to the power grid, craftsmen must be able to “switch off” the small solar panels for maintenance. Strictly speaking, there is no switch on the modules themselves, but instead, the inverter has a DC disconnect device. With the help of this switch, the DC supply is cut off, and the cables no longer have voltage. Without this step, repairs or maintenance would be impossible because of the hazard.
What types of inverters are there?
Module inverter:
Module inverters are occasionally used in smaller systems. A separate inverter then monitors each module. If the solar modules are aligned differently and have different outputs, module inverters can be useful. In this way, individual services can be compared and optimized. In addition, module inverters are installed directly on the module, saving up to 50% of the cables. However, because the efficiency of micro inverters is quite low, they are rarely recommended, even for small systems.
String inverter
Of all the types, the string inverter is the most commonly used. This inverter monitors an entire array of solar panels, also known as a string. Because each inverter has only one MPP tracker, the string inverter should only be used if all modules in the row have the same orientation, inclination and shading.
Otherwise, no attention would be paid to the individual situation of the modules. And with that, the potential for optimization is lost. In contrast to module inverters, string inverters are highly efficient. In addition, the maintenance of the inverters is simplified because they are located inside the house and not on the roof.
Multi-string inverter
Multi-string inverters have multiple MPP trackers, making monitoring and operating multiple strings possible. This means that the optimal operating setting can be selected for each row of modules. Multiple inclinations and module orientations are integrated into a single inverter. This type of inverter is often used in larger PV systems with different irradiation conditions.
Central inverter
This type of inverter is often only used in large photovoltaic systems from around 30 kWp. In addition, all solar modules must have the same irradiation conditions. If this condition is met, there is only one MPP for the entire plant that can be controlled centrally. This greatly simplifies both maintenance and handling.
What does an inverter cost?
All in all, the costs for inverters are around 10% to 15% of the total system costs. The average single-family house price is around $1,000 – $2,000.
It is often worth digging deeper into your pocket regarding inverters. Because if you’re only looking for the biggest bargain, the quality may suffer. As with so many others, the quality of the inverter goes hand in hand with the price. The higher the efficiency, power rating and several extra features, the more the inverter will cost. The pure sine wave inverter is the best inverter in the industry.
Good inverters have a high degree of efficiency (> 95%), a powerful cooling function and offer comprehensive protection for the system and the grid. The system performance and the number of MPP trackers also strongly impact the price. However, these features are not relevant to every house. The minimum requirements for your inverter depend on the size and location of your PV system.
What do you have to pay attention to when buying an inverter?
When you buy a complete photovoltaic system, the most suitable inverter is already included in the package, and you don’t have to worry about the selection. However, if you choose to assemble your components, it is important to consider the performance and quality factors. As mentioned above, quality factors are efficiency, reliable cooling function and protection.
The efficiency of an inverter works in the same way as a car’s fuel consumption. The less energy a car or an inverter needs for its function, the more efficient and the more money is saved. Because the efficiency indicates the relationship between supplied (solar) energy and usable electricity. The more the inverter consumes for monitoring, control and protection, the less is left for self-consumption or feed-in.
A good cooling function rarely comes alone but also depends on other factors. To avoid overheating, you must ensure that the inverter’s rated power is higher than your system’s maximum power. Because if your system should produce more electricity than your inverter can handle, even good cooling will no longer help to prevent overheating. The efficiency is also related to cooling. The more an inverter has to cool, the lower the efficiency.
On the other hand, efficient cooling is also noticeable in terms of efficiency. When cooling is fast, efficient and hassle-free, less energy is required, and efficiency is higher.
It is important to ensure that the inverter exactly meets your criteria. This includes, among other things, the right type, the minimum nominal power and the required number of MPP trackers.
The installation of the inverter
Make sure you choose the right location because a wrong location will negatively impact performance and lifespan.
Unless you buy microinverters installed directly on the system itself, your inverter should be installed in a location that is as cool and well-ventilated as possible. This helps in cooling and protection from overheating.
Cellars, utility rooms or garages are best suited for this purpose. Depending on the type, you must either attach your inverter to a wall or place it on a level surface.
What do you have to pay attention to when servicing an inverter?
The maintenance of the inverter should take place regularly. Among other things, it is important to check the DC connection and the cooling and clean them if necessary. A maintenance log from the manufacturer is also helpful. To recognize possible damage at an early stage, you should compare the yields with those of the previous year.
