Inverter sizing - What do I lose by oversizing?

[rmk9785e]

I'm considering a 5.1 kW (320Wx16) PV system and debating between SE7600 and SE5000 inverters with P320 optimizers. My understanding is that the price difference between the two models in nominal and there may be some efficiency drop by using the SE7600 but not a whole lot. I'm thinking of the larger inverter to have enough headroom for capacity increase in case our power utilization goes up. What do the experts think about it?
(RANT] Tried calling SolarEdge corporate to ask the same. The sales line for the western region always goes to voice mail. Tech support line says wait time of about 45 minutes and gives option for a call back after that time. There is no call back even hours later. Is this the kind of company to do business with?[/RANT}

[inetdog]

I'm considering a 5.1 kW (320Wx16) PV system and debating between SE7600 and SE5000 inverters with P320 optimizers. My understanding is that the price difference between the two models in nominal and there may be some efficiency drop by using the SE7600 but not a whole lot. I'm thinking of the larger inverter to have enough headroom for capacity increase in case our power utilization goes up. What do the experts think about it?
(RANT] Tried calling SolarEdge corporate to ask the same. The sales line for the western region always goes to voice mail. Tech support line says wait time of about 45 minutes and gives option for a call back after that time. There is no call back even hours later. Is this the kind of company to do business with?[/RANT}

The usual penalty for an oversized inverter is reduced efficiency when operating at partial load. But GTIs may not exhibit that behavior and may even be more efficient at lower power. The biggest downside is usually the extra cost for hardware you do not need, but apparently the costs you are being quoted are pretty close.

Having headroom in the inverter for adding panels is great, but adding panels may still involve a new building permit, inspection, and POCO interconnect agreement, so getting your system size right at the start is important.

One major consideration if you have any interest in adding a PowerWall battery (Tesla) is that the 7600 includes support for adding the battery pack and the 5000 does not.

[SunEagle]

Another point to consider would be that the circuit breaker for the solar connection in the main panel will be sized based on the inverter wattage not on the panel wattage.

[solarix]

Even though it is industry practice to make array's 10% or so larger than the inverter, we are putting in oversized inverters more and more these days to allow for future growth and better reliability.

btw, If you are considering which brand of inverter to go with, try calling their techline phone and see what kind of service you can expect. That alone will tell you a lot about how the company is doing.

[bcroe]

A larger inverter costs more; MAYBE it will last a bit longer to compensate. I don't think generally the inverter efficiency
varies enough to be a factor at reduced load, for an incremental size step. Here Fronius use multiple inverters internally
so that the most efficient combination is continuously selected for power available.

But a larger inverter will take a larger support plant and a different grid tie agreement. Here the rules change if you move
into a higher category. The larger plant will probably increase your efficiency (larger conductors) at a given power. Bruce Roe

[adoublee]

Operating voltage of strings has been the efficiency driver in the past, and being over-conservative on maximum possible voltage often caused strings to operate in the lower end of the spectrum which is generally less efficient. SolarEdge establishes the desired voltage at the optimizer though, so voltage conversion at the inverter can be optimized no matter what the wattage of panels works out too.