Part Three: AC Losses
Inverter Clipping & Losses
The two common types of AC losses are inverter losses and inverter clipping. These losses occur at the inverter when the DC power from the solar panels is converted to AC power to be used in the home and on the grid.
AC Losses
Inverter Losses
Inverter efficiency describes how well a solar inverter converts DC energy into AC energy. Most inverter spec sheets have two numbers you should be aware of:
- Maximum efficiency - The inverter’s top efficiency under ideal conditions.
- Weighted efficiency - The inverter’s performance over a range of conditions.
It’s important to look at the weighted efficiency because an inverter’s efficiency will change based on the capacity it’s carrying. Most inverters peak around 20% load and fall slightly as the load reaches the maximum input rating.
Note: Your exact inverter efficiency will change based on the system that it’s installed on. For example, a system with an oversized inverter will operate at higher efficiencies more often than a smaller inverter.
This difference in performance is often small, so it’s not always cost effective to add the largest inverter possible. Balancing inverter capacity vs. cost is something you can only learn with experience, but in the beginning, you can remove the risk by choosing a slightly larger inverter.
AC Losses
Inverter Clipping
Inverter clipping is the total amount of kWh production lost (or “clipped”) by the inverter’s sub-optimal production compared to what the system would have produced. Typically, this happens at the height of sunny, cloudless days when the DC output from the panels is greater than the amount of DC power the inverter can convert.
There are scenarios where inverter clipping is acceptable, like when you’re trying to increase energy output during morning and afternoon hours, reducing inverter costs, or providing a more level energy output during intermittent clouds.
If you’re trying to design a system to minimize inverter clipping, Aurora’s PV simulations and loss diagram, and code-compliant NEC Validation Report can make the process much easier.
Further reading: Choosing the Right Size Inverter for Your Solar Design: A Primer on Inverter Clipping–a deep dive on inverter clipping on the Aurora Solar blog.
