Inverter Clipping: High Wattage Panels with Lower Wattage Microinverters

At first glance, Project Solar's pairing of a solar panel rated at 350W-400W with a microinverter rated at 300W can raise some questions--for example: "Wouldn't it be more efficient to match the wattage of the two pieces of equipment?"

This policy is intentional, though. This article seeks to explain the answer to this question, and explain why we design our systems this way.

Converting DC to AC with Microinverters

For more information on string inverters, microinverters, and DC/AC energy, check out our article titled "Microinverters vs. String Inverters"!

Solar panels produce direct current (DC) energy, which must be converted to alternating current (AC) energy before it can be used. This is the inverter's job.

With microinverter systems, each panel has an inverter to regulate and process energy. This means that each panel and each microinverter can be directly compared to each other based on their rating.

Inverter Clipping 

When matched with a 300W-rated microinverter, a panel with a 360W rating would be limited to a maximum of 300W of usable power produced at a time. 

This is called inverter clipping, and initially it can ring alarm bells for some customers--however, it's completely normal, and happens much less than you would think.

Solar panels don't produce at their full capacity at all times: their wattage rating is listed for "STC", or "Standard Test Conditions". This means that they are tested to produce their full capacity in controlled ideal temperature and sunlight conditions.

Due to weather and other variables, these ideal test conditions don't happen very often in the natural world. This means that most of the time, the solar panel will produce at least slightly less energy than it is rated for--about 10-15%.

An Enphase microinverter, on the other hand, is tested in much more rigorous conditions with many variables, and must pass these tests while performing at or above its rating.

An example of ideal inverter clipping

Enphase describes a microinverter's rating as "a minimum hurdle which the inverter must be able to consistently and continuously clear when operating in the field." Due to these rigorous tests, microinverters are able to surpass their rating by 4-5% in some cases.

These different factors all translate to less clipping.

Planning for Panel Degradation

Inverter clipping can also be a useful tool to help plan for panel degradation.
Inverter Clipping and Panel Degradation.png
Solar module performance typically degrades about 0.5% each year, while microinverters do not degrade over time. Essentially, while the panel rating begins to decline, the microinverter will continue to funnel power through at a consistent level.

We can illustrate this with our previous example--if the 360W panel degrades by 5% over 10 years to a maximum capacity of 342W, the 300W microinverter is not affected. There's just less clipping, and the inverter will still convert ~300W of power.

Thus, the system as a whole is only minimally affected.

Options & Recommendations

At Project Solar, we have found the sweet spot between panel and microinverter ratings. Our combination of higher wattage panels with more mid-level microinverter ratings translates to better overall system performance, and most importantly means better solar savings.

In some areas, we can source higher-rated microinverters, but these will come with a premium. Generally, our standard equipment will always be the best bang for your buck.

Currently, we're sourcing Enphase IQ8+ microinverters in most areas. We use a few different panel options with these inverters, depending on location and availability; for a full list, see this link

If you're more interested in upgrading your microinverters to a slightly higher-wattage model (such as the IQ8M or IQ8A), just ask our Customer Experience Team and they will let you know which options are available for your project. 

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