What is the energy lost if I design a 2.64 kW system with a 6 kW inverter (SMA 6.0)?
My vague memory is the inverter - when under-loaded - performs low on the efficiency curve......
As opposed to a 3.8 kW.
Want to make it easy to add kW later for customer.
Interesting. So it sounds fine.
Although a 2.64 kW rated system will supply much less. Maybe averaging around just 1.5 kW. So maybe it is 25% loading the 6 kW inverter.
Make it easy to add to later by using micro-inverters. ...
That would be trusting that the micro manufacturer stays in business and makes things backwards compatible.
Well, using an oversized string inverter is trusting that one can get modules in the future that are compatible with the inverter and the existing modules. Got to trust something.
Adding to a micro-inverter system will not require backward compatibility. Maybe you might end up with two monitoring systems if the new micro-inverters can't talk to the existing monitoring system. But any micro-inverter is going to output standard AC that can be combined with any other AC and back-fed to the grid. I would recommend this over the oversizing of a string inverter that may or may not ever be added too.
For inverters in general, you are correct. Everything on the same power processing zone, requires either the same modules & source circuits, or "electrically close enough" for the second phase of construction.
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Another strategy is to use an inverter with multiple MPPT zones, and only connect one of the zones during construction phase 1. The remaining zone remains empty, until you are ready to come back and build construction phase 2.
Another strategy is to use an inverter with multiple MPPT zones, and only connect one of the zones during construction phase 1. The remaining zone remains empty, until you are ready to come back and build construction phase 2.
I've added a screenshot of the efficiency curve for a 6kW SMA 240V inverter from PVSyst to give you an idea where it rolls off.
Make it easy to add to later by using micro-inverters.
make sure your string lengths aren't too short