Capping solar panels often raises questions. What exactly is it? Why do you sometimes deliberately choose a system that does not use the maximum peak power? And is energy loss due to capping acceptable? In this blog, you will read in detail what capping an inverter, or solar panels, entails. We also tell you why it can be wise and how to make the best choices for your system installation.
What is capping solar panels?
The term capping solar panels means limiting the peak power your inverter can deliver. Solar panels have a rated capacity, called the Watt peak (Wp), measured under ideal conditions of 1,000 W/m² of solar irradiation at 25°C. Those conditions rarely occur in the Netherlands, usually the actual efficiency is around 80% of Wp power.
An inverter that capped is actually under- or over-dimensioned relative to the panel power. Simply put, you are coupling more panel power than the inverter can handle. On sunny peak days, the output reaches the inverter’s limit and “tops off. At first glance, this seems like waste, but in practice it actually yields more over an entire year.
The terms capping solar panels and capping the inverter are often used interchangeably, but technically there is a difference. Capping the inverter involves deliberately choosing an inverter with a lower capacity than the peak power of the solar panels. As a result, the inverter does not process some of the power at sunny times. This results in the so-called capping of solar panels: the panels then deliver more, but this is not fully utilized. In fact, therefore, the limitation takes place at the inverter, not at the solar panels themselves.
Why capping an inverter can be smart
Capping your inverter can be a smart idea. For example, a smaller inverter tends to be more active on days with less sunlight. That’s because it turns on earlier during morning or evening sunlight and stays active later than a heavier model. Thus, you utilize more hours of energy output. In addition, you reduce the risk of grid congestion by limiting the peak capacity of the inverter. This is especially relevant with limited grid infrastructure, but also applies to households with dynamic energy contracts. After all, less feed-in means lower return costs. Finally, a smaller inverter is usually cheaper. In addition, you avoid the need for a heavier grid connection, which saves installation costs. Viewed over an entire year, this outweighs the modest yield you miss on peak days.
How do you decide the right ratio when capping solar panels?
When installing solar panels, look at the Wp capacity of the panels and the AC capacity of the inverter. In the Netherlands, an inverter with 10-30% less power than the panel power is often chosen. For example: with 4 200 Wp panels, a 3 600 W inverter is common. You top off a maximum of 600 Wp at sunny times. This has several advantages. For example, the inverter may start earlier in the morning and shut down later. In addition, there is less downtime on gray days, thanks to higher efficiency at low power levels. Also, you have a smaller chance of feed-in when you run out of space for storage or direct consumption yourself.
Seasonal effects on capping your inverter
In spring, when the air is clear and the temperature is still low, solar panels perform quite optimally. So your solar panels produce the most energy in the spring. This is precisely when the inverter peaks. This is often evidenced by flat tops in your yield graph. This is a sign that the inverter is reaching its maximum capacity. This is not a problem, however, because the extra yield you realize in the morning and evening hours weighs more heavily in the annual score. You even lose a little at peak times, but this is more than compensated by extra yield at other times.
7 helpful tips for capping your solar panel system
We have collected a few more tips for you. That way you can get started efficiently with (having) capping your inverter.
- Calculate ratios: it is smart to calculate the ideal ratio of panel power to inverter. Keep in mind ± 20% difference.
- Recognize flat tops: you can check these through your yield chart and they are a sign of capping. Do not see this as disturbing, but as normality.
- Choose the right inverter: pay attention to inverter specifications about efficiency at low load. For example, that it turns off when it falls below 8% power.
- Choose the right dynamic limiting: if your inverter supports dynamic limiting, make sure you choose the right one. This way, grid load is variably controlled.
- Keep an eye on the grid connection: lower capacity prevents additional costs for grid reinforcement.
- Assess feed-in charges with your energy supplier: in fact, less peak supply means less charges.
- Schedule maintenance and monitoring: trends in yield graphs help you determine if the system is still functioning optimally.
Capping your solar panels is therefore not a bad choice, but rather a smart one. By deliberately choosing an inverter with slightly less capacity than your panel power, you will benefit from several advantages. For example, you will have more yield on cloudy days by starting earlier and stopping later. You also have less peak load on peak days, reducing grid charges for feed-in tariffs. And you have the opportunity to save on inverter and grid costs. On your annual report, you will find that a system that taps occasionally ends up producing more than one that runs right on peak all day, especially in the Netherlands.
Hopefully you now have a clear answer to the question “what is capping solar panels? In any case, make sure the design, choices and your monitoring are done professionally. That way you will maximize the benefits. Also feel free to get good advice and contact an installer or energy consultant. In this way you can avoid wasting energy on sunny days and reap the benefits of days with less sun. Isn’t that what everyone wants?
