Can I run a 100kW inverter off a 1MW busbar?

Can I run a 100kW inverter off a 1MW busbar?

I think this question means can you connect 1MWp PV array to a 100kVA inverter input.

This would give you a 10:1 DC:AC ratio. In C&I installations, a 1.2:1 is about average in the UK (subject to site-specifc considerations, which can cause considerable variation); in utility scale that ratio is nowadays often 1.6:1 or even edging towards 2:1 at the extreme. So this is a long way off piste.

Inverters normally operate with a limit from the AC output current, which, by and large, is where the inverter nominal power rating comes from. The MPPT algorithm operates by adjusting the DC bus voltage; normally this will be to maximise power (hence the MP of MPPT) but if it cannot due to excess power it will adjust the voltage along the IV curve, causing the array to operate less efficiently but within a range the inverter can convert. If it cannot get to an acceptable operting regime within the MPPT range, the inverter will shut down (going open circuit) due to overpower.

The same applies if you took a normal inverter configuration and limit the output through control parameters (e.g. G100)

Sara Helin said:

If there is a single input (not multiple strings) what happens?

As it's all on one DC bus into a single MPPT, it makes no difference how the downstream DC side is arranged. All the inverter "sees" (acts on) is one IV curve being the sum of the subarray.

Sara Helin said:

Can you operate a grid-forming inverter of this type without a battery?

Yes in principle, with ideal components.

However, with such an extreme oversizing, three extra considerations in practice are

• It is quite likely that the DC Isc will exceed the inverter's rated maximum, which is driven by busbar thermal ratings, switcgear capacity etc. This is an important safety consideration
• With such high oversizing you will probably invalidate the manufacturer's warranty. I have never seen a manufacturer cover such a high ratio
  • The MPPT will be forced to operate at a higher voltage more frequently than usual which could create greater stress on the components
  • The DC-DC conversion will require PWM switching a greater Isc than designed, and with a greater capacitance, which will again stress the components
• You will likely struggle with the cable terminations and/or overcurrent protection
• Due to the overpower shutdown, you will get far less energy out than you would expect. You'll probably get more by reducing the array size to something a bit more sensible

These considerations would also apply if there was a battery though!

This being the case it's probably a bad idea!

Can I run a 100kW inverter off a 1MW busbar?

I think this question means can you connect 1MWp PV array to a 100kVA inverter input.

This would give you a 10:1 DC:AC ratio. In C&I installations, a 1.2:1 is about average in the UK (subject to site-specifc considerations, which can cause considerable variation); in utility scale that ratio is nowadays often 1.6:1 or even edging towards 2:1 at the extreme. So this is a long way off piste.

Inverters normally operate with a limit from the AC output current, which, by and large, is where the inverter nominal power rating comes from. The MPPT algorithm operates by adjusting the DC bus voltage; normally this will be to maximise power (hence the MP of MPPT) but if it cannot due to excess power it will adjust the voltage along the IV curve, causing the array to operate less efficiently but within a range the inverter can convert. If it cannot get to an acceptable operting regime within the MPPT range, the inverter will shut down (going open circuit) due to overpower.

The same applies if you took a normal inverter configuration and limit the output through control parameters (e.g. G100)

Sara Helin said:

If there is a single input (not multiple strings) what happens?

As it's all on one DC bus into a single MPPT, it makes no difference how the downstream DC side is arranged. All the inverter "sees" (acts on) is one IV curve being the sum of the subarray.

Sara Helin said:

Can you operate a grid-forming inverter of this type without a battery?

Yes in principle, with ideal components.

However, with such an extreme oversizing, three extra considerations in practice are

• It is quite likely that the DC Isc will exceed the inverter's rated maximum, which is driven by busbar thermal ratings, switcgear capacity etc. This is an important safety consideration
• With such high oversizing you will probably invalidate the manufacturer's warranty. I have never seen a manufacturer cover such a high ratio
  • The MPPT will be forced to operate at a higher voltage more frequently than usual which could create greater stress on the components
  • The DC-DC conversion will require PWM switching a greater Isc than designed, and with a greater capacitance, which will again stress the components
• You will likely struggle with the cable terminations and/or overcurrent protection
• Due to the overpower shutdown, you will get far less energy out than you would expect. You'll probably get more by reducing the array size to something a bit more sensible

These considerations would also apply if there was a battery though!

This being the case it's probably a bad idea!