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UK Inverter over grid voltage fault

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I have a Solis 3.6 KW inverter which works well until it exceeds about 2000W when it shows "over grid voltage" and shuts down. This does not happen if something is switched on in the house which draws a large amount of current such as the immersion heater. I have a voltage meter in the house which can be showing around 240V, but as soon as the inverter starts up, the voltage climbs until it reaches around 258V. As soon as the inverter shuts down, the voltage returns to normal. The company who installed the inverter insist this is a grid problem and there is nothing that can be done about it. Perhaps they are right, but the 6mm cable which connects the inverter to the consumer unit is about 30 metres long and is about 40 years old. Could this be adding to the problem, or indeed causing it? The cable can't be shortened, but would a thicker cable be able to absorb more volatage and stop the overload?
 
That sounds like a problem with the inverter to me, if the grid voltah is sitting at 240V then rises to 258V when the inverters turns on then the cause is logically going to be the inverter.

No, cable does not absorb voltage and no this is not an overload, it is an overvoltage.
 
If you have a good solid connection to the grid, a small inverter will not be able to push the voltage up.
 
While comments true, to be fair to the OP, there's logic in the question if the 258V was being measured at the inverter.
E.g. if the inverter ran flat out at 3.6kw, say 15A output, a fault in the 30m cable of about 1.2 ohms would result in an 18 volt drop, back to 240V at the incoming supply.

Or if there was a 1.2 ohm resistance in the incoming supply (I can't believe that can be true!) you would see this effect.
 
That sounds like a problem with the inverter to me, if the grid voltah is sitting at 240V then rises to 258V when the inverters turns on then the cause is logically going to be the inverter.

No, cable does not absorb voltage and no this is not an overload, it is an overvoltage.
Photovoltaic grid-tie or on-grid inverters, which are connected to the grid do not regulate voltage but rather the current injected into the grid based on local voltage sampling.
To inject the generated power into the electrical grid, there must be a potential difference (voltage) between the inverter terminals and the grid connection point; without this difference, there is no current flow from the inverter to the utility's electrical grid. However, the voltage increase must not occur uncontrollably.
To avoid unwanted stoppages due to overvoltage alarms, it is essential to analyze the voltage level provided by the utility, local generation and demand, cable sizing, and checking for faulty connectors or improper use. In addition, overvoltage can be caused by issues related to the internal grid of the photovoltaic system, such as inadequate conductor sizes, poorly made or defective connections, or by the utility's grid itself, especially in rural areas with few nearby consumer units to absorb the excess generation - called weak grids.


In these cases, where the utility's grid is considered weak, it is crucial to contact the utility so they can make the necessary improvements to the electrical grid, thus ensuring the proper operation of the photovoltaic system and avoiding generation stoppages due to overvoltage.
 
We had a similar call out and the issue was with the grid (which they admitted). Voltage was too high.
 
This thread hasn't been replied to for 14 days, so replying to this one may not get a response. Post a new thread instead.

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