Why does too much sun shut down a PV system?
On especially sunny days, installers often receive the following question from customers: “Our solar energy system sometimes shuts down when the sun is shining. Why does this happen and what can I do to prevent it?” To clarify this issue, we’ll explain exactly how it works below.
Why does too much sun shut down a PV system?
To begin with, every inverter includes a built-in protection mechanism that ensures it automatically disconnects from the grid when it exceeds the so-called “grid parameters.” These parameters include voltage, current, frequency, and grid impedance (loop resistance between phase and neutral). Of these, the most important are grid voltage and frequency.
Normally, the grid frequency in Europe is set at 50 Hertz, although the grid voltage can vary by country. For instance, in the Netherlands, the low-voltage grid is 230 Volts, with an allowable tolerance range typically between 207 and 253 Volts.
Furthermore, the threshold values at which an inverter must disconnect from the grid are legally defined and vary per country. In the Netherlands, these limits are set by the NEN EN 50438 standard for small installations, and by the Dutch Netcode Elektriciteit for larger systems.
Grid voltage and inverters
One of the most critical thresholds is the upper voltage limit of 253 V. If the inverter detects a grid voltage above this level, it will disconnect automatically. This happens because an inverter feeding power back into the grid always causes the voltage to rise. In contrast, household appliances (such as a washing machine) tend to lower the voltage.
As a result, on a sunny day, the inverter may try to deliver a large amount of power to the grid while electricity consumption in the household is low. Consequently, the grid voltage increases, eventually reaching the upper limit. At that point, the inverter shuts down. However, once the voltage drops back within the acceptable range, the inverter restarts automatically.
In short, the sun may be shining at full strength, yet the solar power system doesn’t perform optimally because the inverter repeatedly shuts down.
What can be done about this?
Fortunately, there are several things you can do to mitigate this issue. First of all, it often happens that multiple solar installations in the same neighborhood are connected to the same phase of the power grid. This may lead to one phase experiencing higher voltage than the other two. If technically possible, connecting the inverter to a different phase can help reduce this imbalance. In addition, during periods of high solar irradiance, it’s a good idea to switch on several household appliances. This will increase local energy usage and help prevent the grid voltage from rising too much. Another possible cause is the use of an AC cable that’s too long or too thin. In such cases, we recommend limiting the voltage drop across the AC cable to a maximum of 1%. Refer to NPR 5310, chapter 712 for detailed guidelines.
Lastly, you can also connect a battery to the solar energy system. The battery charges during peak production times, which helps lower the grid voltage. Later in the day, you can use the stored energy, improving both efficiency and self-consumption.