Feeding solar power into the grid: voltage goes up

Solar panels produce direct current (DC), which is converted into alternating current (AC) by the inverter. The power is injected into the grid through the inverter. The grid absorbs all the incoming electricity and redistributes it to other consumers.

If a large amount of electricity (measured in amperes) is injected into the grid at a time when there is little demand, the voltage (measured in volts) will start to rise. You can compare this to the pressure in a water pipe system, where water is introduced at different points. As long as water is being drawn from other points, the pressure remains stable. However, when a lot of water is added while little is being drawn, and the pipes are not large enough to carry the water further away, the pressure increases. In an electrical network, voltage (in volts) can be seen as a form of pressure. Normally, the grid voltage is around 230 volts, but when a lot of power is pushed in and can't escape properly, the voltage gradually rises.

This is generally not a problem, as the voltage always fluctuates a little. At times when everyone switches on their lights and coffee machines at once, the voltage drops slightly. Conversely, when everyone in offices or factories goes home at the same time and switches off their devices, the voltage rises again.

What Do Grid Operators Do?

Grid operators ensure that the voltage in the grid stays around 230 volts. They do this by ensuring that transformer stations across the country have enough capacity to draw energy from the high-voltage lines and push it into the low-voltage grid. However, with the introduction of solar panels, the system has changed slightly: the power no longer only comes from high-voltage lines to homes but now also comes from the homes themselves. This means that in some areas, at certain times, the voltage can rise.

Grid operators are required to ensure that the voltage does not exceed 10% above the normal voltage. For 230 volts, this means 230 x 1.10 = 253 volts. If the voltage gets too high, certain electrical devices can wear out a bit faster. However, this usually happens only when high voltage is applied to devices over an extended period.

Inverters that feed power back into the grid measure the grid voltage. When the grid voltage measured by the inverter exceeds 253 volts, the inverter immediately stops feeding power and goes into a fault state. Technically, the inverter could still work at higher grid voltages, but the device's settings cause it to stop. The value of 253 volts is defined in the Electricity Grid Code.

We often see problems with grid voltage occurring at specific times: for example, on sunny Sundays, when nearby shops, offices, and factories do not consume power, while the panels produce a lot.

How can you recognise the issue?

This graph clearly shows that the inverter briefly stopped working around noon: typical behavior in cases of high grid voltage

A solar power system that suffers from high mains voltage will temporarily fail, as long as the mains voltage remains too high. When the voltage drops again, the inverter will automatically reconnect. You can recognise the behaviour by a yield graph with one or more 'gaps' as in the picture above. The gaps mainly occur around noon, when a lot of power is produced. In the installation logbook you will see messages such as 'warning: grid overvoltage'.

How Can We Prevent Problems?

Zonnefabriek is fully aware of the grid voltage problems in some areas. Initially, one thing that can be done is to ensure that there is as little resistance as possible between the inverter and the distribution board: make sure the electrical cable between the inverter and the board is thick enough to transport the power easily. The further away the inverter is from the distribution board, the thicker the cable needs to be.

Additionally, it is important that the grid operator is aware of the problem. Grid operators can install extra (thicker) cables and transformers in areas with many solar panels to stabilize the voltage.

For homeowners, there is not much that can be done to prevent problems, except to ensure that electricity is consumed when it is being produced: when devices like washing machines and dishwashers are running, the voltage drops slightly. Installing a home battery with smart control also helps: such a system directs the excess solar power towards the battery instead of towards the grid, so that the grid voltage doesn't increase any further. A smart system takes the weather forecast into account, and only starts charging when it makes the most sense.

In exceptional cases, the inverter's settings can be adjusted: the voltage at which the inverter shuts off can be set a few volts higher than 253 volts. However, this requires permission from the grid operator, as it would mean the inverter is no longer set according to the standards in place in the Netherlands.