As a result of the huge uptake of grid-connected PV systems in South Australia, the Australian Energy Market Operator (AEMO) is projecting significant system security risks to the South Australian electricity supply network. As a result, the South Australian Government will be implementing some new requirements for PV systems, known as Regulatory Changes for Smarter Homes, from 28th September 2020.
Despite the reference to homes in its title, these changes apply to all grid-connected PV systems, residential or otherwise. In short, installers will be required to:
- Install inverters that have low voltage ride-through capabilities and are listed on an approved inverter list;
- Ensure the system owner appoints a Relevant Agent who can perform remote disconnection and reconnection of their grid-connected PV system; and
- Install inverters that have internet capability and an onboard communications port.
There will be additional requirements for dynamic export control which will require active control of the inverter. However, these requirements are still in development and will be implemented from July 2021.
These requirements have caught many in the industry by surprise, and as a result the list of approved inverters and agents is small. Some inverter manufacturers have already tested their inverters and proved compliance, and in other cases have simply ‘declared’ that they are compliant and will finish the testing later.
This technical article will summarise the implications of the new technical standards for grid-connected PV systems being installed on the network.
A list of approved inverters is available here.
A list of agents is available here.
In May 2020, in response to a request for information from the South Australian Government, AEMO released a report advising the minimum operational demand required to maintain a reliable electricity supply to the state and the analysed the supply disruption risk posed by lowering daytime demand due to the high level of solar generation.
Operational demand in a region is demand that is met by local power plants (including large-scale renewables) and imported generation. This excludes any demand that is met by small local generation e.g. rooftop solar.
The report highlighted that rooftop grid-connected PV installations are growing rapidly – more than 200 MW a year is being installed in the state, consistent with the AEMO’s high DER uptake scenario (Figure 1).
Figure 1: Actual and projected capacity of distributed PV in South Australia (Source: AEMO)
Under the high DER scenario, AEMO projects that operational demand could reach zero within 1-3 years. (Figure 2 & 3). Figure 3 takes the day with the lowest demand in 2019-20, 10th November 2019, projected forward with an annual growth rate in distributed PV of 219 MW with the increase in distributed PV, operational demand will be especially impacted during the middle of the day and that we can start seeing zero daytime operational demand by late 2022.
Figure 2: Minimum operational demand projections for South Australia (Source: AEMO)
Figure 3: Effect on South Australian operational demand from increasing distributed PV generation, average day (Source: AEMO)
Grid-connected PV systems effectively reduce the amount of operational demand due to their behind-the-meter nature. If there is no operational demand on the network, traditional dispatchable power stations cannot operate. This is problematic because these generators provide essential network services such as maintaining the power system strength, inertia, frequency and voltage. Distributed grid-connected PV systems do not provide these services.
Disconnecting of Distributed PV
A problem with the high level of distributed PV system penetration on the South Australian network is caused by a safety feature within these systems’ inverters, which shuts the system down when it senses grid disturbances such as very high or very low voltage from the grid. As the level of penetration of distributed PV systems is anticipated to increase, if a large number of PV systems are suddenly disconnected due to a voltage disturbance, it will significantly impact the stability of the power supply.
In the same report to the South Australian Government, AEMO conducted an analysis of distributed PV disconnection behaviour from historical voltage disturbances between 2016 to 2020. It found that voltage disturbances on the network can lead to tripping of PV systems. For example, a severe fault in the network near the Adelaide metro area, such as a power plant suddenly disconnecting, could lead to simultaneous tripping of up to half of the rooftop solar in South Australia, an estimated 200-400 MW of solar generation by the end of 2020. This means that a contingent power plant now needs to be much bigger to cover for loss of generation from both solar and the disconnected plant.
The disconnection of distributed PV was related to the severity of the voltage disturbance (Figure 4). In the most severe voltage disturbance analysed, disconnection of more than 40% of distributed PV in the region was observed.
Figure 4: Percentage of distributed PV sites in a region observed to disconnect following historical voltage disturbances (Source: AEMO)
Minimum load requirement
South Australia is electrically connected to Victoria and the rest of the National Electricity Market (NEM) via the Heywood interconnector. It is a critical element in maintaining frequency and helps balance variances in demand and supply in South Australia’s network. When the link is down, South Australia becomes islanded from the NEM and requires a minimum amount of load required to provide grid stability. Currently this is at around 550 MW, and is set to decrease to 450 MW by 2021 when additional synchronous condensers are installed.
To manage their power system security during high levels of distributed PV generation, AEMO recommended the implementation of a backstop mechanism to curtail distributed PV generation via South Australia Power Networks (SAPN) during abnormal system conditions. This mechanism was trialled in February 2020 during a disconnection of the Heywood Interconnector.
Following the advice from AEMO, the South Australian Government has introduced a range of new technical standards and requirements (under the Smarter Homes mandates) which come into effect in South Australia on 28 September 2020. These include the following:
- Voltage ride through standards for grid-connected inverters;
- Remote disconnection and reconnection requirements for distributed generating systems; and
- Export limit requirements for distributed generating systems.
Low Voltage Ride Through Requirements
This requirement applies to all new grid-connected PV inverters connected to the network. For existing systems, this requirement comes into effect if the current inverter is being replaced outside of the warranty.
The new technical standard specifies that all low voltage inverters must meet testing standards outlined in Appendix G.2 of AS/NZS 4777.2:2015 and a supplementary short duration undervoltage response test (VDRT) developed by AEMO.
Section 7.4 of AS/NZS 4777.2:2015 stipulates that an inverter must provide the following passive anti-islanding protection in response to undervoltage on the grid:
- Has a trip delay time of greater than 1 second if the voltage falls below 180 V;
- Remain in continuous and uninterrupted operation (i.e. ride through) for voltage variations under 1 second; and
- Provide anti-islanding measures beyond 1 second and before the maximum disconnection time of 2 seconds.
The current testing procedure in Appendix G.2 of AS/NZS 4777.2:2015 confirms that an inverter will trip after one second for incremental voltage reductions (in steps of less than 1 V from 182.5 V to 177.5 V, with a dwell time of 5 seconds for each voltage step).
However, AS/NZS 4777.2’s testing procedure only tests an inverter’s response to slow voltage sag and not during a short duration voltage step. It also does not sufficiently test whether an inverter can remain connected for faults with a duration of less than one second.
AEMO’s VDRT test tests that the inverter meets the 1 second trip delay requirement when the grid voltage drops suddenly below 180 V, and that it will ride through the low voltage (i.e. remain connected and operating) if the drop lasts less than the trip delay. The values are selected based on the distribution clearance times and potential transmission level events.
The test seeks to confirm two aspects of the inverter’s behaviour:
- The inverter remains connected during an event where the voltage reduces to 50 V and consequently returns above 180 V within 1 second (after 220 ms, to be precise); and
- The inverter stays connected for at least 1 second following a sudden event where the voltage remains below 180 V. Maximum disconnection time of 2 seconds still applies.
Smart Home Requirements
Responsibilities of system owners or operators
The owner or operator of the PV system must ensure that the inverter installed is featured on the approved inverter list.
Responsibilities of installers
Installers must install only inverters that are listed on the SA Govt’s approved inverters list. At this stage, 25 inverter brands comply, and more are expected to come soon.
For existing grid-connected PV systems, this requirement will come into effect when the existing inverter is being replaced, unless the inverter is being replaced under warranty.
For grid-connected PV systems that do not exceed 30 kW, like-for-like warranty replacement of inverters will not be required to be compliant with SAPN’s technical standard (TS129), unless the capability exists within the replacement inverter. If the capability exists, the inverter’s settings must be updated to the current standard (particularly the inverter’s power quality response settings). For grid-connected PV systems above 30 kW, all inverters must be compliant with SAPN’s technical standards.
Responsibilities of inverter manufacturers and importers
Manufacturers and their importers must complete and submit these test results to the SA Govt prior to 25 September 2020. The SA Govt is in the process of developing a list of compliant inverters that have undergone the VDRT test.
However, manufacturers and importers can also enter into a legally binding arrangement with the SA Govt to be provided with a transitional period to 31 March 2021 to complete the VDRT testing under a set of conditions. These conditions include:
- Must commit to complete the testing by the transitional period end date;
- Provide test reports showing that the inverters meet the VDRT test;
- Must commit to make good any inverter installed during the transitional period if the inverter fails the VDRT test, at no cost to the customer, installer or supplier.
The SA Govt will be frequently updating the approved list of compliant inverters.
Remote Disconnection and Reconnection Requirements
All new grid-connected PV systems installed after 28 September 2020 must be capable of being remotely disconnected and reconnected by an agent registered with the Technical Regulator (relevant agent). This requirement also applies to existing grid-connected PV systems if a grid-connected inverter or multimode inverter is being replaced outside of the warranty, or is relocated to a different building within the same electrical installation. If these components in an existing system are being repaired, replaced under warranty or relocated to another position on the same building, they are exempt from this requirement.
A relevant agent is a party authorised by the owner or operator of a grid-connected PV system. They remotely ramp down or disconnect and reconnect a grid-connected PV system only when legally directed by SAPN (in accordance with the grid-connection agreement) and AEMO. A list of relevant agents can be found on SA Govt’s website, and is frequently being updated.
For example, Solar Analytics is a listed relevant agent. One of their solutions uses the inverter’s internet connection (Wi-Fi, ethernet or 4G) to actively manage its export limit settings via the cloud (API). Solar Analytics will receive and act on the control signals from AEMO and SAPN, and will notify installers and solar owners during these event.
To be technology neutral, the SA Govt has released a range of deemed methods that can be utilised within a grid-connected PV system to facilitate disconnection and reconnection by a relevant agent. This includes the following:
- A device connecting to the DRM port of the inverter which asserts a DRM 0 or a DRM 5 signal; or
- The following list of devices under the condition that they can receive a signal from the relevant agent causing it to operate the disconnection device or limit the exported energy to zero:
- Direct communication channel to the inverter
- Electricity meter
- Central Protection Unit (CPU) or Network Protection Unit (NPU)
- Supervisory Control and Acquisition (SCADA) system
Relevant agents can also enter into a legally binding arrangement with the SA Govt to be provided with a transitional period to 31 December 2020 to complete preparation activities to enable remote connection and disconnection measures. Under this process, they must show that they have demonstrated these measures by 1 January 2020.
Relevant agents who apply after 31 December 2020, or who have no need of the transitional arrangement will be required to demonstrate their technology as part of the registration process.
Responsibilities of system owners or operators
The owner or operator of the grid-connected PV system must:
- Select a Relevant Agent, featured on the list of Relevant Agents;
- Authorise the relevant agent to perform the remote disconnection and reconnection; and
- Inform the relevant agent if ownership of the grid-connected PV system is going to change, e.g. when a house with solar is sold.
Responsibilities of installers
Installers need to ensure a relevant agent has been nominated for the installation. Installers should help the system owner to select a relevant agent who will limit their solar export if required by AEMO or SAPN. It should be double checked that the relevant agent is registered and approved prior to installation. The relevant agent needs to be nominated as the installer completes the Certificate of Compliance.
Installers are also responsible for installing a system that is capable of being remotely disconnected and reconnected from the distribution network by the relevant agent.
Responsibilities of relevant agents
When the relevant agent has received direction from SAPN or AEMO, they must activate the remote disconnect and reconnect capability of the grid-connected PV system.
Directions may require the relevant agent to disconnect or reconnect:
- Some or all of the grid-connected PV systems under their control;
- A specific grid-connected PV system;
- Multiple grid-connected PV systems (in terms of number or within specific locations of the SAPN distribution network); or
- A certain level of megawatts.
Relevant agents must be capable of undertaking the direction within 15 minutes of advisement and must be capable of doing so during daylight hours during the week. After completing these directions, they must inform the directing party (SAPN and/or AEMO).
Export Limit Requirements
In accordance with the National DER Connection Guidelines, SAPN had already introduced an export limits for grid-connected PV systems, whereby:
- As of 1 December 2017, single phase can export a maximum of 5kW; and
- As of April 2019, three phase systems can export a maximum of 5kW per phase.
Due to the expected growth in distributed PV systems, SAPN has recognised the use of dynamic export limits in their 2020-2025 regulatory proposal. In the plan, they have introduced a low voltage management business case which includes dynamic export limits. This new business case seeks aims to align with their ‘feed in management approach’ that has been developed for large embedded generators connected to the network. This approach is anticipated to involve publishing dynamic export limits to customers and DER aggregators, and the ongoing publication of dynamic export limits to small embedded generators, aggregators and virtual power plant operators.
To avoid grid stability issues caused by high levels of PV exports, the new technical standard requires remote updating of inverter export limits. From 28 September 2020, all inverters installed in new distributed PV systems must feature internet connection capability and possess an onboard communications port that can be used to connect to another device (e.g. via ethernet, USB and RS-232). The inverter may also communicate wirelessly (e.g. by providing a secure Application Programming Interface (API) over Wi-Fi) to another device in lieu of a physical communication port.
This requirement also applies to existing grid-connected PV systems where a grid-connected inverter or multimode inverter is being replaced outside of the warranty or intended to be relocated to a different building within the same electrical installation. If these components in an existing system are being repaired, replaced under warranty or relocated to another position on the same building, they are exempt from this requirement.
The additional requirements for dynamic export control are still being developed and will be implemented from 1 July 2021.
Responsibilities of installers
Installers must install inverters that have internet capability and an on-board communications port, so that is capable of dynamic export limitation.
Installers must only carry out work of connecting the grid-connected inverter (and submit the grid-connection application) if it complies with the technical standard.
Implications of these changes
While there is urgency in ensuring the distributed PV systems do not contribute to instability of the South Australian grid, the South Australian Government introduced these requirements on relatively short notice. Check with your supplier to see if the inverters you hold are being retested as an approved product, as non-approved products can only be used as replacement under warranty.
Installers will likely need to help their customer select an appropriate relevant agent for remote disconnection and install any additional components to ensure the agent can operate the system remotely. It is unclear still how often PV systems will be asked to ramp down or disconnect in the future or whether there will be further complications with this function, although as this capability is reserved for emergencies only, interruptions are likely to be limited.
AEMO Minimum operational demand thresholds in South Australia Technical Report:
South Australian Government Webpage on Regulatory Changes for Smarter Homes:
South Australian Power Network 2020-2025 Draft Plan: