Reading a system impact study in an afternoon, not a week
The structure of an ISO system impact study is the same every time. The parts an investor actually needs are small and predictable. A field guide for analysts on the investor side.
A system impact study (SIS, or in AEMO's language the 5.3.4A study) is a large document. Four hundred pages is not unusual. Most of it is boilerplate: study methodology, assumptions, load-flow base cases, short-circuit calculation traces, contingency lists. Every SIS from the same ISO reads the same until about page 180.
If you read it linearly you will spend a week. If you know the structure you can pull the parts an investment committee actually cares about in an afternoon. Here is where to look.
The only four sections that matter to an investor
1. Reactive power compensation requirements
This is always in the project-specific findings section, usually framed as 'additional reactive plant required for connection'. The number is a range of MVAr of STATCOM or synchronous condenser. Each unit is seven to eight figures of capex that was not on the project's original cost curve. If the study requires more than about 100 MVAr of compensation, the project's base-case IRR is probably off by 150 to 250 basis points.
2. Curtailment triggers
Look for 'network constraints' or 'binding constraints' in the findings. Every constraint listed is a scenario under which the project gets curtailed. What matters is how often the constraint binds in the ISO's load-flow base cases. One binding constraint that kicks in during the same dispatch window as the price signal you are being paid for is worth more thinking than ten that bind at 3 a.m.
3. Grid-code compliance gaps
There will be a table of grid-code requirements and the project's measured or simulated performance against each. A non-compliance flag is not always a deal-breaker. Read the mitigation column. 'Additional inverter tuning' is twelve months of engineering work. 'Additional synchronous plant on site' is capex you are going to wear.
4. Conditions of acceptance
The short list at the very end of the study. This is what the TNSP or ISO is actually going to write into the connection agreement. Everything earlier in the document is rationale. The conditions are the commitment. Read them, then go back and read the rationale only where the conditions surprise you.
What to ignore on a first read
The short-circuit calculation traces. The detailed load-flow base case printouts. The contingency list (unless the study flags a contingency as binding, in which case it has already surfaced in the findings). The assumed generator dispatch for the base case (unless you think it is materially wrong for your revenue model).
These sections matter to the project engineer. They do not matter to the investor on a first read. Every hour spent there is an hour not spent on a project that clears screening.
This is the read our red-flag engine does first on any new SIS ingested for a client. The methodology is not secret. It is just worth writing down.