Inverter Output Exceeds Nominal Power

[Behzad]

Inverters usually have a nominal AC power (nameplate), and a maximum AC power. I need to limit the inverters so not to exceed the maximum AC power, but I don't have any success.

In this case, the inverter I am using is SMA Sunny Central 800CP-US. I have changed the maximum AC power from 880 kW to 800 kW, and also changed the maximum AC current to a value equal to Nominal AC current (which i 1283 A). But I still exceed the inverter output by 0.5 kW on many occasions during a year, and thus get higher MWh/year than expected.

I am aware that there is a power limitation option, and it is ticked in my case.

Any suggestions on how to overcome this issue?

Thanks

[André Mermoud]

The calculation involves curve approximations in some cases, and there may be some calculation artefact errors.

Now 0.5 kW/800 kW represents 0.06% error. If this arises, say, 100 times in the year, this will represent 50 kWh.

Your installation will probably produce around 1'000 MWh/year or more.

Does really an error of 0.005 % affect your financial balance ?

However I will analyze this situation when I will have some time.

[Behzad]

Hi Andre,

Thanks for your reply.

Financially, it does not make any impact. We are talking about $700 extra in $7m for a typical 8MW plant. But I have been asked to cap the inverter output, in this case to 800 kW. Thanks a lot for your help.

[lonav]

Dear Andre,

I have read the thread and I wonder if you came up with an explanation for this.

In my case, for a 200 MW plant, I am seeing the inverter I am simulating with exceeds the specified max AC power by 15 kW around 20 hours. Could you help me clarify why this happens?

Attached are two screenshots from the ond file so you can have enough information about my enquire.

Thank you in advance for your help.

Regards,

Lola.

Inverter OND specification_2

Inverter OND specification_1

[André Mermoud]

I don't know.

15 kW/200MW represents 0.0075%. This may be a rounding error somewhere.

[lonav]

Sorry, I didn't explain it the right way. It's not 15 kW in total; the software is giving 15 kW more per inverter (specification as per the jpg files attached before).

What other explanation could there be for it?

Regards,

[André Mermoud]

The nominal power of your inverters may be up to 1155 kW if the temperature around the inverter is less than 35°C. Please explain in detail how you observe an increase of 15 kW with respect to this value.

[lonav]

Hi,

according to the OND, maximum power should be delivered at 35°C so there should be no chance for higher power at the inverter output.

I have simulated a power block formed by 2 inverters as the one described before. When looking at EoutInv field on the hourly CSV export file from PVsyst I see the maximum value is 2339 kW, which will mean each inverter is producing ~1170 kW, when max. export power is 1155 kW.

[lonav]

Hello,

Any update on the topic? I am seeing the same issue with other inverters and sites. The programm is calculating around 1% more power 20 to 30 hours over the year. Could there be some default setting causing this?

Thank you in advance for your help.

[André Mermoud]

How do you define your "Maximum export power" ?

If it is a grid limitation, this is quite normal: when you have losses after the inverter, the inverter has to produce some energy more, for compensating the AC losses after the inverter and ensuring a specified power injected into the grid.

[dtarin]

This observation I think is independent of any grid limit, max export power, or AC losses. We're seeing production that is higher than what the inverter is defined to be able to output. Not only does the inverter report higher production than the defined maximum, it doesnt show clipping loss associated with these hours in example provided.