Inverter Clipping: What to Know
WHAT IS INVERTER CLIPPING?
In a solar PV system, the inverters are responsible for converting the DC electricity produced by the solar panels into AC electricity that can be used in the home or exported to the grid. Inverters can sometimes become a bottleneck in the system when the power output of the solar panels exceeds the maximum capacity of the inverter. This can result in solar clipping, where the excess energy produced by the panels is not used and is effectively wasted.
There are two types of inverters commonly used in solar PV systems: string inverters and microinverters. A string inverter is a centralized inverter that is typically located in a central location in the system, while microinverters are located on each individual solar panel.
In a system with a string inverter, the maximum capacity of the inverter is determined by the maximum power output of the solar panels in the system. If the total power output of the solar panels exceeds the maximum capacity of the inverter, solar clipping can occur. For example, if a system has 19 solar panels, each with a capacity of 400 watts, the total capacity of the system would be 7.6 kW. If a SolarEdge SE7600H inverter with a capacity of 7.6 kW is used, there will be no solar clipping because the capacity of the inverter matches the capacity of the solar panels.
However, if a smaller inverter is used, such as a SolarEdge SE5000H with a capacity of 5 kW, solar clipping will occur because the power output of the solar panels exceeds the maximum capacity of the inverter. In this case, the system would generate a maximum of 7.6 kW of power, but the inverter would only be able to handle 5 kW of power. As a result, the excess power generated by the panels would be lost.
When using individual inverters or microinverters, the maximum power output is limited by the capacity of each inverter. As a result, each panel may not be able to operate at its full capacity, which can result in a higher level of clipping. For example, in a system with 19 modules that are 400 watts each, if Enphase microinverters with a maximum output of 349 watts per microinverter are used, the maximum output of each panel will be limited to 349 watts, resulting in a maximum clipping rate under STC of 51 watts per panel, or roughly 969 watts for the entire system.
HOW DOES AZIMUTH (PANEL ORIENTATION) COME INTO PLAY?
Azimuth angle is one of the key factors that determine the overall power output of a solar panel system. Azimuth angle refers to the direction that the panels face and is measured in degrees from true south. A solar panel that is oriented directly south will receive the most direct sunlight throughout the day and will be able to generate the most power. However, if the panels are not oriented directly south, the amount of sunlight they receive will be reduced, resulting in a lower overall power output.
For a solar panel system that is fixed and not able to track the sun, such as on your roof, the azimuth angle is fixed and cannot be changed. In this case, the optimal azimuth angle depends on the location of the system. In the northern hemisphere, the optimal azimuth angle for a solar panel system is typically south-facing. In the southern hemisphere, it is typically north-facing. However, other factors, such as shading, may need to be considered when determining the optimal azimuth angle.
In addition to the optimal azimuth angle, the actual azimuth angle of a solar panel system can also have a significant impact on its real-world production. For example, a system that is facing east will receive more sunlight in the morning, while a system facing west will receive more sunlight in the afternoon. This means that the actual azimuth angle of a system can impact the timing and amount of power it produces throughout the day. For more on how this helps with Time of Use (TOU) or Peak Demand, we have another blog post that goes over the topic more in depth.
When panels are placed on eastern and western facets, the solar access is less, resulting in less production per panel and reducing the maximum output of the panels. This can also result in reduced inverter clipping. Inverter clipping occurs when the maximum power output of the panels exceeds the maximum power capacity of the inverter. This can happen when the panels are generating more power than the inverter can handle and can result in a significant loss of power production.
In systems where the panels are placed on eastern and western facets, the power production is more spread out over the day, which can help to reduces the likelihood of inverter clipping. In addition, systems with microinverters or DC power optimizers can be effective at mitigating inverter clipping, as the bottleneck is at the individual panel level rather than at the inverter level.
For example, suppose a solar panel system is designed with 20 panels, each with a maximum output of 300 watts, and is paired with a string inverter that has a maximum output of 5,000 watts. If the panels are all oriented directly south, the maximum power output of the system could be 6,000 watts, which would exceed the maximum output of the inverter, resulting in inverter clipping. However, if the panels are placed on eastern and western facets, the maximum power output of the system would be less, reducing the likelihood of inverter clipping.
In conclusion, the azimuth angle of a solar panel system is an important factor that impacts its real-world production. By placing panels on eastern and western facets, the peak power output can be reduced, resulting in less overall clipping. This means a system of 7.6kW might see zero real world clipped kWh production on an annual basis even if the inverter was downsized from a 7600 to a 6000. This is important, because the larger the inverter, the more upfront cost. At Progreen Solar, our energy assistant’s assess every project to identify solutions that will provide the best overall value to you as a customer, so they are taking close looks at what the clip-to-cost ratio is so you end up with the optimal system for your home or business.
SO DOES THAT MEAN A STRING INVERTER IS ALWAYS BETTER THAN A MICROINVERTER SINCE THEY CLIP EVERY PANEL, WHILE STRING INVERTERS ARE ONLY SYSTEM WIDE?
When it comes to choosing between a string inverter and a microinverter, there is no clear-cut answer that fits every project. The decision should be made based on a careful assessment of each project's unique characteristics.
It's important to note that panels rarely achieve their maximum output, which is determined by their STC rating, due to a variety of factors such as shading, temperature, and soiling. As a result, clipping isn't typically an issue unless the panels are directly south-facing and at optimal angles for your latitude or longitude. Therefore, microinverters aren't necessarily inferior to string inverters just because they clip each panel individually.
Choosing between a string inverter and a microinverter depends on a range of factors, such as the number of panels in the array, the orientation and tilt of the panels, and the presence of shading or other obstructions. In some cases, a string inverter may be a better choice, as it allows for greater flexibility in system design and can be more cost-effective. On the other hand, microinverters may be more appropriate in situations where shading or other factors limit the performance of individual panels.
Ultimately, the decision of which type of inverter to use should be made based on a careful assessment of the specific project's needs and requirements. At Progreen Solar, our energy experts are equipped with some of the world’s most sophisticated software and tools, combined with the individual knowledge and expertise necessary to evaluate each project on an individual basis and recommend the most appropriate inverter solution to maximize both production and value for our customers.
In summary, there is no one-size-fits-all answer when it comes to choosing between a string inverter and a microinverter. The decision should be based on careful evaluation of the project's unique characteristics and requirements, with the goal of maximizing energy production and overall value. At Progreen Solar, our experienced energy experts will work closely with you to develop a customized solar solution that meets your specific needs and delivers the best possible results.