Hold point testing is how AEMO and the network service provider (NSP) release a new solar farm or battery to full output in steps. The plant runs at a capped output level, completes an agreed set of tests, submits the results, and only moves to the next level once AEMO and the NSP have reviewed them and released the hold point.
These are grid hold points, not construction hold points. A construction ITP hold point stops work until an inspector signs off a trench or a termination. An AEMO hold point stops the plant at an output limit until it has proven, with measured data, that it behaves the way its generator performance standards (GPS) and power system models say it will.
Where Hold Points Come From
Hold points are not a fixed national schedule. They are written into the commissioning program for each project, which the developer prepares and agrees with AEMO and the connecting NSP before energisation.
That program is built from three inputs:
- The agreed GPS. Every performance standard that needs on-site evidence, such as reactive capability, voltage control, frequency response and active power control, has to be tested somewhere in the sequence.
- The R1 model package. The tests are chosen so that measured responses can be compared against the PSS/E and PSCAD models AEMO and the NSP approved. If you need a refresher on that package, our guide to R0, R1 and R2 model submissions covers it.
- Network conditions at the connection point. Weak grid areas, local constraints and outage availability all shape how cautious the step-up needs to be.
The result is a project-specific document listing each output level, the tests to be performed at it, the data to be recorded, who needs notice, and what the release criteria are. When that document is agreed late, the hold points tend to be discovered rather than planned, which is one of the patterns we describe in why commissioning runs late.
Typical Stages and Tests
The number of hold points and the output level at each one vary by project. The table below is an example of how a utility-scale solar or BESS program is often structured. Treat the output steps as illustrative, not as AEMO rules. Your commissioning program sets the actual limits.
| Stage | Example output limit | Typical tests and evidence |
|---|---|---|
| First energisation | Zero export, plant energised | Protection and SCADA checks, metering, communications to AEMO and the NSP, plant controller in service, setpoint and status points verified |
| Low-output hold point | A small fraction of rated output, e.g. 10 to 30% | Voltage setpoint step tests, reactive power steps, power factor and Q control mode checks, active power ramp rate and setpoint tests |
| Intermediate hold point(s) | Mid-range output, e.g. around 50 to 70% | Reactive capability at higher active power, frequency response (droop) tests, repeat of voltage control steps, runback and curtailment response |
| Full output | Rated output | Full reactive capability across the operating range, remaining frequency and voltage tests, any disturbance or fault response evidence captured from real network events |
Voltage and Reactive Power Tests
Voltage control is usually the backbone of the early hold points. The plant controller is given step changes in voltage setpoint, and the recorded rise time, settling time and overshoot are compared with the GPS and the model. Reactive capability is tested in steps across the active power range, so capability at low output and near rated output are both demonstrated.
Frequency Response Tests
Frequency response is commonly tested by injecting a simulated frequency deviation into the plant controller rather than waiting for the grid to move. The measured active power response, deadband and droop are then compared with the agreed settings and the model.
Disturbance Evidence
Fault ride-through cannot be tested on demand at a connection point. Evidence tends to come from simulations using the validated model, factory test data, and any genuine network disturbances recorded by high-speed monitoring during commissioning. That is why high-resolution recorders need to be installed and time-synchronised before first export, not added later.
What Goes in a Hold Point Report
At each hold point the developer, usually through the OEM and the power systems consultant, compiles a report and submits it to AEMO and the NSP. A report that clears quickly normally contains:
- The test procedure as performed, with any deviations from the commissioning program explained
- Plant configuration at the time of test: firmware versions, controller settings, number of inverters or PCS units in service
- Raw and processed measurement data, with sample rates and time references stated
- Overlays of measured response against simulated response from the R1 model, run at the same conditions
- An assessment of each result against the relevant GPS clause
- Any non-conformances, their cause, and the proposed fix
AEMO and the NSP both review it. The NSP is generally focused on the connection point and its own network, while AEMO looks at compliance with the GPS and at how well the model matches the plant. Either can raise questions, ask for repeat tests, or hold the plant at its current level.
How R2 Model Validation Ties In
Hold point testing is not only about proving compliance. It is also how the R2 model is built.
The R1 model is what the plant was expected to do. The R2 package is the model updated and confirmed against what the plant actually did on site. Each set of hold point test results is used to check the model's response, and where it diverges, the model parameters or the plant settings are adjusted until the two agree within the tolerances in AEMO's model guidelines.
That means the test design matters. A voltage step that is too small, recorded at too low a sample rate, or taken with half the inverters offline without that being documented, produces data that cannot be used for model validation. The test then has to be repeated at a later window.
The R2 model package and validation report follow the final commissioning tests. If you are planning the modelling side, our article on PSS/E and PSCAD modelling for renewables explains how those models are built and benchmarked.
BESS Differences
A battery goes through the same broad sequence, but there are two practical differences that catch teams out.
Charge and Discharge Are Both Tested
A BESS operates in both directions, so the GPS and the model cover both. Voltage control, reactive capability and frequency response generally need to be demonstrated while charging and while discharging, and sometimes around zero active power. That roughly doubles the number of test points at each hold point compared with a solar farm of the same rating.
State of Charge Has to Be Planned
A test sequence that discharges the battery for an hour cannot start with the battery at 20%. Test days need a state-of-charge plan: which tests run first, how much energy each consumes or absorbs, and when the battery is recharged or discharged between blocks. If market registration is not yet complete, the options for cycling energy are more limited, so this planning has to happen with the commissioning program, not on the morning of the test.
Frequency response tests on a battery also deserve care, because a BESS can move its full output very quickly. Ramp limits and droop settings in the plant controller need to match what was modelled, or the measured response will not line up with the R1 model.
Why Hold Points Stall
Most plants reach full output eventually. The question is how many weeks are lost between steps. The delays usually trace back to a small number of causes.
Data Quality
Missing channels, unsynchronised recorders, unclear plant configuration and sample rates too low to see the response are the most common reasons a report comes back. Each one costs a repeat test, which may mean waiting for the right network conditions or another outage window.
Plant Controller Tuning
The plant controller sits between the grid and dozens of inverters. If its gains, deadbands or ramp limits differ from the values in the submitted model, step responses will not match. Sometimes the fix is a setting change. Sometimes it is a vendor model update, which then needs to be re-run and re-accepted. A firmware change mid-commissioning can unsettle results that were already accepted.
Review Turnaround
AEMO and the NSP review reports alongside many other projects. A clear, complete report with model overlays already included gets through faster than one that leaves the reviewer to reconstruct what happened. Agreeing the report format with both reviewers before the first hold point removes a lot of back and forth.
Before Your First Hold Point
- Commissioning program agreed with AEMO and the NSP, with release criteria for each stage
- Test procedures written against specific GPS clauses
- High-speed recorders installed, time-synchronised and checked
- Plant controller settings and firmware match the R1 model
- Simulated responses prepared for each planned test
- BESS state-of-charge plan for every test day
- Report template agreed with both reviewers
Get GPS and Commissioning Support
Hold point testing is where the GPS, the models and the physical plant all have to agree. When they do, the step-up to full output is a matter of weeks. When they don't, the plant can sit at a capped level while a modelling or tuning issue is worked out.
ElectraGlobe prepares hold point test simulations, reviews test results against the GPS and the R1 model, and takes non-conformances through to close-out as part of our AEMO GPS applications service. For smaller distribution-connected plant, our guide to commissioning a 5 MW solar farm covers the DNSP pathway. If you are approaching commissioning, contact our team to talk through your program.
Frequently Asked Questions
What is a hold point in AEMO commissioning?
A hold point is an agreed stage in the commissioning program where the plant is held at a capped output level. The developer runs the specified tests, submits the results, and waits for AEMO and the NSP to review them before the next output level is released. It is a grid compliance step, separate from construction inspection hold points.
How long does each hold point take to clear?
It varies with the project, the quality of the data and the reviewers' workload. A well-prepared hold point with clean data can clear in days to a couple of weeks. One that needs repeat tests or a model update can take considerably longer, so the overall step-up to full output can range from a few weeks to several months.
What is the difference between R1 and R2 data?
R1 is the model package submitted before commissioning, describing how the plant is expected to perform. R2 is the package confirmed after commissioning, validated against measured test results from the hold points. The R2 model is what AEMO and the NSP rely on for future studies of the network.
Do DNSP-connected solar farms have AEMO hold points?
Not always. Smaller embedded generators can be exempt from AEMO registration, in which case commissioning is approved by the DNSP under its own process, as with the 5 MW solar farms we commission. Where the line falls depends on the plant's size and classification, so check AEMO's registration and exemption guidance early. Registered plant, whether connected to a DNSP or a TNSP, goes through an AEMO-agreed commissioning program with hold points.