Micro Inverters

[kolp180]

Hi guys,

I am currently analyzing the advantages of having a micro inverter instead of a central inverter for Solar farms.

Our current design consist of central inverters feeding into national grid.

As i understand, the dc cables (from solar cells to Inverter) will be replaced with ac cables (solar cells to grid).

My question is
[ul]
[li][/li]
[/ul]How to determine if the cable swap is worth it?

[ul]
[li][/li]
[/ul]How big a scale it needs to be for it to be more cost effective?
[ul]
[li][/li]
[/ul]Are there any factors i should consider?

Would appreciate any assistance rendered.

 

[davidbeach]

You just need to run the numbers. If the big inverter guy is hungrier that will be the cheaper solution but if the micro inverter guy is hungrier then that will be the cheaper option. Cells are less likely to fail than inverters. If you lose a single large inverter you lose a bunch of capacity, but if yo have 300 or 1000 times as many inverters how often do you think you'll be running without a failed inverter?

 

[kolp180]

Having a faulty PV cell would greatly reduce the power output from a string of cells.
The advantage of micro inverter would be to isolate each failure of PV cells.
I do agree that micro-inverters have a higher likely hood to fail than PV cells(after reading several reviews of early adopters). I believe the failure rate can be reduced as micro-inverters is still a relatively new concept.

Assuming non of the micro-inverters fail, would the losses from DC cables or AC cables be higher? given the same length? or are they negligible?

Also what would you mean by hungrier?

 

[davidbeach]

Hungrier = Willing to make less profit in order to make the sale.

Consider that there is no reactance in a DC circuit, only resistance. So there is less voltage drop in a DC circuit if current and wire size are the same. On the other hand you don't have the option of three phase with DC.

 

[cranky108]

I would also assume the microinverters would boost the voltage to above 100 V, so the currents should be less than using DC.

The problem with microinverters is on a large farm, someone would be chasing bad inverters often. However, the knoledge needed to replace microinverters, versis having an expert arive on site to fix a large inverter might weigh out as a lower cost. The on-site person actually sounds like a good way to find and fix problems not related to the power production, things such as painting, fence, homeless people, etc.

 

[PHovnanian]

Cable swap?

If your micro inverters put out a higher (but not too high) voltage, you might not need to swap all the cable. Possibly some re-wiring at each end. Unless you have something special installed, quite a bit of wiring is good for 600V. If this is the case, leave it in place. The inverter outputs will have lower currents, so ampacity will be a non-issue.