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Clipping occurs when solar modules produce more DC energy than the inverter can convert into usable AC energy. The excess energy is ‘clipped’ and therefore wasted.
Example: A 425W module paired with a 325W microinverter will clip 100W of potential energy output at peak performance. This is illustrated in Figure 5.
Clipping is easily spotted in solar system output graphs. When clipping occurs, the graph shows a flattened peak, indicating that the system is producing less power than it could. A quick scan of reddit/r/solar for clipping will show numerous examples of homeowners wondering why their energy production is capped. Some of the comments highlight how homeowners are increasingly aware of clipping and concerned about its impact on the performance of their systems.
Given the prevalence of microinverters paired with modules of greater capacity, clipping is not a rare phenomenon. In many cases, the module-microinverter mismatch is justified by not spending more money for higher wattage microinverters. However, the small losses all add up.
Just 3% annual clipping can cost $10,724 in lifetime savings for a residential 15kW solar installation (19% capacity factor, $0.30/kWh, 5% electricity rate escalator, 25 years). Using the same assumptions, 2% clipping reduces savings by $7,149, and 1% reduces it by $3,575.
In Figure 7, a performance analysis by a leading microinverter supplier shows that clipping amounts vary by the quality of solar conditions (different for each city identified) and the wattage of the modules.
Year 1 production losses from clipping by module wattage and location with a 300W microinverter
String inverter systems can clip too if the combined module wattage exceeds the string inverter wattage. This can happen anytime DC:AC ratios are greater than 1, which is common.
But string inverters in a system with DC architecture have a special feature: when paired with a DC-coupled battery, energy production beyond the inverter nameplate can be used to charge the battery.
Figure 8 illustrates the difference between DC-coupled inverter performance and microinverter performance on a day when solar production exceeds the inverter max (AC) capacity.
With a DC-coupled battery, excess solar can charge the battery. With an AC-coupled battery or microinverter system, the excess energy is clipped.
Installers that do not currently deploy batteries often think there is no clipping difference between string systems and microinverter systems if the DC:AC ratios are the same. But there is.
Bottom line: even with no battery and similar DC:AC ratios, a string inverter will clip less than microinverters. Because this topic is more complex and nuanced than described here, a chapter with a specific example and details can be found here: Bonus: Clipping showdown: MLPE vs. Optimizers.
Microinverters and optimizers are usually grouped into a technology category called Module-Level Power Electronics (MLPE). But since optimizers have the advantage of being DC-coupled, they perform less work and energy from the module can go to the battery without incurring the usual clipping and roundtrip conversion losses. One of the reasons MLPE has become popular is that they provide module level optimization, monitoring, and rapid shutdown – features that installers and homeowners want and ask for. Optimizers, like the TS4-A-O and TS4-X-O from Tigo (rated for up to 700W and 800W, respectively) provide those in-demand features while also accommodating high-performance solar modules.
Clipping is a hot topic with homeowners and installers in part because the flat top of the production curve is so noticeable. A brief look at a solar message board quickly uncovers concerned homeowners posting clipping graphs. These posts usually get one of the following responses:
“Don’t worry, it’ll go down over time”
It’s true that microinverter clipping will likely decrease over time. But it’s probably less than what’s being advertised. Many users will point to the Enphase tech brief on clipping as evidence. However, the brief assumes a 0.4% degradation rate after year 1. REC modules – which represented the largest share of quotes in the EnergySage 1H24 report, include a guaranteed performance degradation rate of less than 0.25% after year 1 in their warranty. The warranty guarantees “by the end of the 25th year, an actual output of at least 92% of the nameplate power output.” So, a 450W module is still guaranteed to produce 414W or more; that’s the maximum performance degradation, not average. In addition, the Enphase brief does not mention any degradation of microinverter max output despite there being no performance guarantees in its microinverter warranty. It would be difficult to name an electronic device subject to daily runtimes and thermal cycling that does not suffer performance impacts over decades of operation.
“It’s not worth the investment to upgrade to higher wattage microinverters.”
This is a reasonable statement to make if someone is comparing microinverter to microinverter; higher wattage microinverters are more expensive. But the real (and neutral) comparison to avoid clipping should be between a microinverter and a string inverter.
“It’s actually more efficient”
This statement is usually in reference to inverter efficiency curves, which demonstrate that inverters operate more efficiently when they are close to their maximum capacity. In addition, higher wattage microinverters typically have higher startup voltages. Upgrading to a higher wattage microinverter, therefore, means the system ‘wakes up’ later than a lower wattage one and would miss out on low light hours of production. This can be seen in Figure 9.
In addition to the cost increase that comes with upgrading to a higher wattage microinverter, there is a potential negative impact on efficiency and the number of operating hours. This is a real trade-off to consider. But again, this statement compares microinverters to microinverters. A Tigo string inverter, by contrast, starts producing at 80V across all the modules in a string, which means that production begins when just one string of modules operating at the low end of the production spectrum – as little as 10V each for a string of 8 modules.
“String inverters will clip too”
This topic is covered above, and a deep dive is available here: Bonus: Clipping showdown: MLPE vs. Optimizers
As module wattages rise, the cost of clipping rises. This ‘clipping tax’ can cost up to $10,724 over the lifetime of a solar project, but it’s avoidable. When batteries are paired with a DC-coupled inverter, excess solar production can charge the battery, avoiding clipping altogether. Thankfully, batteries are rapidly becoming the norm.
Furthermore, batteries introduce additional losses for microinverters, which we’ll detail in the next chapter - Conversion Tax: The hidden cost of AC-coupled batteries.
Webinar: On April 15 (Tax day in the US), we're hosting a webinar that will dive into the details of the Microinverter Tax series. Sign up for the webinar here.
Below is a full list of chapters included in this series (links will be added as chapters are published):
