Inverter response to the grid variation

[Kunaifi]

Hi. I am looking at the specification of a 60 kW SMA inverter and am having questions about the dynamic relationship between the grid and inverter, particularly in situation where the grid is not very stable. For example, the Inverter out voltage range: 360-530 V at nominal voltage of 400-480V with 10% plus-minus. Inverter freq range: 54-65 Hz at grid freq. of 60 Hz. My questions are: if the grid voltage and freq. gone beyond the inverter specification above, what would the inverter do? Are there any other situations that would cause the inverter stop sending power to the grid?
Thanks. Kun.

[Mike90250]

When the Grid voltage or frequency exceed the limits programmed into the inverter, the inverter shuts down, and waits till the Grid has been in spec for 5 minutes.
While the inverter is shutdown, the PV panels and inverter are in a harmless idle state.

[Sunking]

What UL 1741 requires it to do. Shut Down to protect itself, equipment and personnel. It is to remain shut off until th egrid stabilizes for 5 minutes before turning back on.

[Kunaifi]

Thanks Mike. If the inverter is programmed to work with wide range of grid voltage and frequency, since the grid is so variable, would it cause any negative effect to both the inverter and the grid?

[Mike90250]

Thanks Mike. If the inverter is programmed to work with wide range of grid voltage and frequency, since the grid is so variable, would it cause any negative effect to both the inverter and the grid?

Well, there has to be some sensible limit for your area, you don't want to damage the inverter if it's trying to hold up the entire grid in your area. The factory setpoints are a suggested starting point, some inverters have adjustable set points, but you don't want to get to far off of nominal.

[jflorey2]

Hi. I am looking at the specification of a 60 kW SMA inverter and am having questions about the dynamic relationship between the grid and inverter, particularly in situation where the grid is not very stable. For example, the Inverter out voltage range: 360-530 V at nominal voltage of 400-480V with 10% plus-minus. Inverter freq range: 54-65 Hz at grid freq. of 60 Hz. My questions are: if the grid voltage and freq. gone beyond the inverter specification above, what would the inverter do?

Depends on what specs the inverter is designed to. Most inverters are designed to UL1741 and will trip off-line if anything unusual happens. Inverters built under Rule 21 (often called "smart inverters") are a lot more resilient and will tend to try longer to hold the grid up even if it sags or frequency changes.

[Kunaifi]

Hi Mike, Sunking, Jflorey2.
Thanks for your response. They were so helpful. So, can I conclude that even some issues need to consider, but no need to worry too much to connect a PV system to an unstable grid?

[jflorey2]

Hi Mike, Sunking, Jflorey2.
Thanks for your response. They were so helpful. So, can I conclude that even some issues need to consider, but no need to worry too much to connect a PV system to an unstable grid?

If the grid is truly unstable, conventional inverters will not work well. You will be tripping off-line very frequently. To find out you really need to monitor grid quality - frequency and voltage primarily. A relatively cheap meter will give you those two, although monitoring them will be annoying (you have to watch it constantly.) A power analyzer is ideal but is $$$.

[smily03]

Or, you could build your own like I did -- specs and code available for free from https://openenergymonitor.org/emon/ . It's quite nice

[SunEagle]

If the grid is truly unstable, conventional inverters will not work well. You will be tripping off-line very frequently. To find out you really need to monitor grid quality - frequency and voltage primarily. A relatively cheap meter will give you those two, although monitoring them will be annoying (you have to watch it constantly.) A power analyzer is ideal but is $$$.

Some commercial and industrial complexes install auto transformers and filters between the solar inverters and the grid power. This provides some voltage & frequency stabilization but does not solve all of the problems that can cause the inverter to shut down and isolate itself.

[Sunking]

Solar and small electrical systems do not play well together. Hawaii small communities and island countries are learning this quickly.

[SunEagle]

Solar and small electrical systems do not play well together. Hawaii small communities and island countries are learning this quickly.

Yep. It is like the tail wagging the dog. Not a pretty picture.

[Sunking]

Yep. It is like the tail wagging the dog. Not a pretty picture.

Solar does not play well with Dynamic loads.

[Kunaifi]

So, it is important to study further on how solar may contribute better in working with such a dynamic grid. Perhaps the concept of resilience is interesting above the reliability.

[SunEagle]

So, it is important to study further on how solar may contribute better in working with such a dynamic grid. Perhaps the concept of resilience is interesting above the reliability.

The best way to utilize solar with a dynamic grid would be to have a dynamic "buffer" in between. The could be an energy storage system like a battery. They are very fast and resilient but also very costly.

[Kunaifi]

There was a study from Spain that adding battery to pv could potentially reduce LCOE up to 1.51 $/MWh. However more study needed by PV plant owners whether pv+battery remain economically viable or not.