Okay, let's break down this inverter replacement project and find some suitable options.

Understanding the Requirements Existing System

3 x ABB TRIO 27.6 kW inverters (now FIMER) = 82.8 kW AC total.

Location

Rooftop wall (transformerless preferred, for weight and cost).

DC Input

297 SolarWorld 280W panels = 83.16 kW DC 5 strings per inverter, so ~99 panels per inverter. Max DC Voltage: 959V Max DC Current per String: 9.3A

AC Output

480VAC

Year Installed

2015 (so likely no RSD required)

RSD

None required (important for choosing appropriate inverters)

Preferences

direct replacement, transformerless

Key Considerations



Sizing

The existing inverter capacity is a good starting point (82.8 kW AC). We could potentially slightly undersize the inverter capacity to the DC array size, particularly since you may see some degradation in the existing array.

Voltage

Crucial to ensure the replacement inverters can handle the string voltage.

Current

Check the inverter's maximum input current per string.

MPPTs

Given 5 strings per original inverter, you'll want inverters with multiple MPPTs to handle the strings efficiently.

Warranty

Consider the warranty offered by the manufacturer.

Monitoring

How important is remote monitoring? Choose inverters with suitable communication options (Wi-Fi, Ethernet, etc.).

Availability and Cost

Check availability and pricing from your local suppliers.

Possible Inverter Replacements

Here are a few inverter options (depending on the number of inverters you want to replace the 3 existing units)

Option 1: 3 x Similar-Sized Inverters (Close to original system)
SolarEdge SE27.6K-US

27.6 kW AC output 480VAC Multiple MPPTs (designed to work with SolarEdge optimizers, but can be used without in simpler systems). Transformerless Considerations: Might be slightly oversized compared to the DC array capacity but are very close to the original inverter size. Benefit: Well-known brand, good monitoring capabilities.

SMA Sunny Tripower CORE1 33kW Considerations: slightly oversized compared to the DC array capacity, would be very close to the original inverter. Benefit: This unit has 6 MPPTs for over 6 strings.

Option 2: 2 x Larger Inverters SMA Sunny Tripower CORE2 110kW 110kW 480VAC 12 MPPTs Considerations: Significantly reduces the number of inverters. Cost savings for 2 units vs 3. Benefit: Well-known brand, good monitoring capabilities.

Option 3: 1 x Large Inverter SMA Sunny Tripower CORE2 110kW 110kW 480VAC 12 MPPTs Considerations: Might be slightly oversized compared to the DC array capacity Benefit: The unit has enough MPPTs for the number of strings.

Important Steps Before Final Selection


Detailed String Calculations

Perform detailed calculations for the voltage and current of your strings at the coldest expected temperature and hottest expected temperature. This is critical to ensure you stay within the inverter's operating range. Use online string sizing tools (many inverter manufacturers offer these) or consult with a PV design professional. Pay close attention to open-circuit voltage at cold temperatures.2.

Check Inverter Datasheets

Carefully review the datasheets for the specific inverter models you are considering. Verify: Maximum DC input voltage MPPT voltage range Maximum input current per MPPT or string input AC output voltage and current3.

Local Codes and Regulations

Ensure that any replacement inverters meet all applicable local codes and regulations.4.

Professional Installation

Engage a qualified and licensed solar installer to handle the installation and commissioning of the new inverters.5.

Talk to Distributors

Discuss your specific needs and system details with solar equipment distributors. They can often provide valuable insights and help you select the best inverter for your application.6.

Check NEC 690.4(B). Ensure compliance with rapid shutdown requirements if applicable.

In Summary:

Based on your requirements, a good starting point would be to investigate the SolarEdge SE27.6K-US and SMA Sunny Tripower CORE1 33kW. The best approach is to perform detailed string sizing calculations, review inverter datasheets, and consult with a qualified installer and distributor to ensure a safe and reliable system upgrade. Flag for review