Let's break down what's happening in the panel and address your concerns. You're right to be cautious; these installations can be tricky and easily violate the NEC.

Understanding the Existing Panel Configuration 200A Panel

This is the main service panel. Its busbar likely has a rating of 200A.

150A Breaker

This breaker appears to be backfed into the main panel. This setup is highly suspect and almost certainly violates the NEC.

Why This Setup Is (Likely) Wrong

Here's the problem: A breaker is designed to protect the circuit downstream from it. In this configuration, the 150A breaker is protecting... what? It's certainly not protecting the 200A panel, because the panel's busbar could be overloaded beyond 150A. More importantly, it's also not backfeeding the utility source. There is a very high likelihood this is feeding some sort of load.

Possible Scenarios & NEC Violations1. The 150A Breaker is feeding a subpanel. This scenario is the most likely explanation for this panel configuration. If this is the case, then you are very likely limited by the 200A OCPD, which is not the same as the 200A busbar rating for the panel. In this case, the subpanel is allowed to carry up to 200A total for your load, and you will need to do a 20% rule calculation to see how much PV you can add without upgrading your service. NEC Violation(s)

This scenario is not inherently wrong if the subpanel is properly sized to not exceed the rating of the 200A OCPD.2.

Illegal Interconnection

The 150A breaker might be connected to another source (like a generator) without proper interlock protection. This is extremely dangerous.

NEC Violation(s)

This violates Article 702 (Optional Standby Systems) and potentially other sections depending on the source. Interlock requirements are strict to prevent backfeeding onto the utility grid.

Why a Supply-Side Tap Feels "Off" Here

Your hesitation about a supply-side tap is valid. Supply-side taps are very common in PV, but they come with specific requirements and considerations. Given the already questionable existing configuration, adding to it makes things even more complicated. NEC 230.82 allows for this configuration, as long as it is properly done. If the 150A breaker is backfeeding a subpanel, then you would likely need to move the subpanel to another location, and then add a supply side tap for your PV.

What You MUST Do1. Investigate the 150A Breaker

You absolutely must determine what that 150A breaker is feeding. This is non-negotiable. Trace the wires. Ask the homeowner. Without this information, you cannot proceed safely or legally. Document your findings.2.

Load Calculation

Perform a thorough load calculation on the existing service panel. This will tell you the existing demand and the available capacity for PV.3.

Consult with a Qualified Electrician

Given the complexities and potential code violations, a licensed electrician experienced with PV installations must* be involved. They can assess the situation on-site, verify the connections, and ensure code compliance.

In summary, this panel setup requires a much closer look. Do not proceed with any PV design or installation until you understand the existing configuration and ensure it is safe and compliant with the NEC. Involve a qualified electrician immediately.

I hope this helps! Let me know what you find out about the 150A breaker, and we can discuss the PV integration options further. Flag for review