Same Fault Code, Two Sites, One Truck: Which First?

Correct answer: C) Site B, because a stand-alone system has no second source: its loads are already down, and the deadline is whatever those loads can tolerate

The fault describes the inverter. It says nothing about what the inverter was holding up, and that is the whole question. A grid-tied array is a source sitting alongside another source. Take it away and the warehouse carries on from the utility exactly as before. What is lost is production, hour by hour, in a quantity you can calculate and that stops accruing the moment you arrive.

On the stand-alone site there is no second source, and the loads are not waiting for anything: they are off now. The pumps have stopped and the greenhouse has no climate control, and the deadline is set by what those loads tolerate. At altitude that can mean a single cold night, and a crop lost that way does not come back when you fix the inverter. There is no hourly rate to compare against the warehouse, because the loss is not accruing, it is waiting to happen all at once.

Note what the batteries do and do not do here. Storage is the reason a stand-alone system rides through a night, and it reaches the loads through the inverter. When the inverter is the thing that shut down, a full battery bank supplies nothing. Storage buys resilience against the sun going away, not against the single component every watt has to pass through.

The O&M point is that triage across a region is a job that only exists in service. An installation crew commissions one site at a time and finishes it. You get a morning with more faults than vehicles, and the ranking is not in the fault codes, the alarm priorities or the monitoring dashboard. It comes from knowing what type of system each one is and therefore what stops when it stops. The JTA lists the four system types as knowledge in their own right, and this is what that knowledge is for.

Why the other options are wrong

A) Site A, because 500 kW of lost production is worth far more per hour than a farm’s pumps and controls

This is the answer revenue produces, and revenue is the wrong axis this morning. The 500 kW figure is real, and every hour of it is just an hour of it: a loss that accrues at a steady rate and stops when you arrive. The farm does not work that way. Its loss is not accumulating at all right now, it is sitting at zero until a threshold is crossed and then arriving in full, which makes being an hour late on the wrong side of that threshold categorically different from being an hour late on a warehouse roof.

B) Site B, but only once the batteries are close to exhausted, since storage keeps the farm running until then

This reads storage as a buffer that is currently doing its job, and it is not. The batteries deliver through the inverter, so an inverter that has shut down leaves the loads dead with a full bank sitting behind it. Waiting for the batteries to discharge would be waiting for something that is not happening, while the greenhouse cools. It is worth carrying this correction beyond this question: a system with storage is not automatically a system that keeps running, and which component failed decides which of the two it is today.

D) Either — the fault is the same, so the work is the same and the order makes no practical difference

The technical work may well be identical, and the consequence of delay is not, which is what triage is for. Treating the two as interchangeable is the same error as reading the fault code and stopping there. It is also the answer that looks defensible in a dispatch log and indefensible afterwards, because the question the customer asks when the greenhouse is lost is not what the fault code was.

References

• NABCEP OMAT JTA v.2026.5 — Domain 2, Task 1: "Types of PV Systems", listing PV Direct, Stand-alone, Grid-tied and Multimode (i.e., grid-tied with energy storage). The correct answer rests on what "stand-alone" means: no utility connection, therefore no second source.
• No external standard is cited. The correct answer follows from the system type and from where the storage sits relative to the component that failed.