Primary Frequency Response Requirements for Solar and Wind Farms Australia
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ustralia, in line with the World’s drive towards sustainable development and cleaner energy sources, has set a target of achieving 82% renewable energy target by 2030 and is working committedly towards achieving that with 2023 seeing almost 35% in the energy mix being attributed to renewable sources, even among that the share of solar power was the highest approximately 16%, followed by wind energy at 12%.
As Australia moves towards generating a large part of its energy through renewable sources, integrating these into the existing grid may sometimes pose a challenge, especially when it comes to maintaining the stability of the grid and handling fluctuations, etc., this is where Primary Frequency Response, or PFR comes into play.
This article will explore the Primary Frequency Response Requirements for the Solar and Wind Sector in Australia, the sector’s evolution, challenges, etc.,
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Table of Contents
What is Primary Frequency Response(PFR):
The Australian Energy Market Commission(AEMC), defines Primary Frequency Response as “the first stage in frequency in a power system. It is the response of generating systems and loads to arrest and correct locally detected changes in frequency by changing their active power output or consumption. PFR is automatic; it is not driven by a centralized system of control and begins immediately when a frequency change beyond a specified level is detected.” In simple words, it is a mechanism that responds to frequency changes in the AC-power Grid System for maintaining grid reliability and stability.
How does PFR work for conventional power grid systems?
The Common frequency at which all the coal and gas-fired generators in the National Energy Market jurisdiction in Australia work is 50,000Hz, which means that the speed is 50 cycles per second or 3,000 RPM. Now, if there are fluctuations within the grid, which could either be when supply exceeds demand or vice-versa, there exists a simple mechanism to balance things out and maintain the stability of the grid.
If the supply of energy suddenly starts exceeding the demand, it is regulated by an increase in the frequency of rotation of the machinery(i.e., generators) which are phase-locked to the grid frequency. This leads to the absorption of the increased energy supply and continues till the time a supply-demand equilibrium is achieved.
On the other hand, if demand exceeds supply, the extra energy demand required is met by the slowing down of the rotational generators connected to the grid for drawing out the required energy.
While this change in the power generation system(usually coal and gas-powered generators) is driven by the nature and size of the energy imbalance what also comes into play is the “inertia” of the rotating machines, their resistance to a change in speed, being a function of how much energy is absorbed in accelerating their spin by a given amount, this plays a vital role in regulating the system and frequency control. While inherently a part of the conventional energy generation mechanisms and plants powering the grid, the newer, “inverter-connected” generation methods like wind and solar do not naturally provide the inertia required for frequency control.
Diagrammatic Representation of PFR in conventional grid systems(source: AEMO)
Current PFR Requirements in the Australian National Energy Market(NEM)
Stable Frequency is a very important part of operating a safe and reliable power system, in line with this the AEMC(Australian Market Energy Commission) in March, 2020 issued a directive that made it mandatory for all scheduled and semi-scheduled generators in the NEM to be able to respond automatically to frequency changes. Further changes in the rule, overlooking compliance and exemptions have been entrusted to the AEMO(Australian Energy Market Operator).
Some Specific PFR standards set by the AEMO are:
- Frequency Control Ancillary Services(FCAS):
A process used by the energy market operator to maintain the frequency of the system at 50 cycles per second, is a requirement for all generators under the NEM and includes both contingency FCAS and regulation FCAS.
- Response Time:
It is instrumental for the generators to respond to frequency deviations within specified time frames, which is approximately 5-10 seconds
- Effectiveness:
Various parameters like response time stability and accuracy determine the effectiveness of the PFR of a system.
PFR requirements for Renewable Energy Systems
PFR requirements might be slightly different for Renewable Energy Systems because they lack the inherent inertia that helps traditional fossil-fuel-powered generators to fulfill their PFR requirements.
Solar PV Systems: Usually equipped with inverters, even Solar PV systems are required to fulfill particular standards when it comes to the PFR, which has been set at AS/NZS 4777.2 by the AEMO.
Wind Turbines: Wind Energy Systems are also required to adhere to PFR standards and are usually designed with advanced control systems for frequency regulation, which can, however, vary depending on the grid connection configuration.
While both these systems are increasingly being equipped with mechanisms that fulfill PFR, the current developments provide limited capacity for RES to regulate frequencies.
Challenges in Renewable Energy Systems that impede PFR:
- Intermittent and Weather-dependant: Solar and Wind Energy fall into the category of RE technology that is affected by short-term weather conditions, particularly, the intensity of the sunlight and wind speeds, respectively. These typically use inverters to connect to the power grid(Invertor Based Resources-IBR)
- Diurnal Mismatch: Solar Generation peaks during daylight hours, whereas in many areas, wind power generation is seen to be higher at night. This creates inconsistencies between the power output and the demand during the peak hours, thus disturbing the supply-demand balance. In addition to a diurnal mismatch, solar and wind energy systems could also prove to be inadequate as they are also prone to seasonal mismatches in demand and supply of energy.
- Limited ability of Inverter-Based Resources(IBRs): As mentioned above, RE systems like wind and solar usually rely on inverters and battery storage, which are limited in their scope to manage frequency regulations as compared to the synchronous AC generators which are generally connected to conventional turbine-based energy production. IBRs usually exhibit a limited capacity to supply large amounts of current under fault conditions, which can lead to an unreliable grid supply if integrated on a large scale.
Solutions and Future Scope
To be as reliable as the conventional generator run grid-supply, handling fluctuations, the Inverter Based Resources like Solar and Wind need to have the following standard features:
- Frequency Stability– responding automatically to frequency deviations.
- Voltage Stability- maintaining voltage within safe limits.
- Rotor Angle Stability- Refers to the ability of synchronous machines to remain synschronised even after disturbances
- Power System Stability- Ability to withstand faults and conditions like overcurrent and short-circuit, etc.,
- Voltage Control- Ability to form and regulate a 50Hz Waveform at the appropriate voltage at multiple points on the power system.
- Black Start- Restarting the system after a power outage.
Achieving inverter systems with all the above-mentioned functions is still ahead of us in the future, however, international as well as region-specific studies when it comes to RE integration into the grid have proposed solutions like-
- Shiftable load and demand response: This requires an incentivized shift of existing and new loads via responsive demand. For instance, EVs which have low utilization and availability during daylight hours, could charge with low-value renewable generation at night.
- Transmission: Although time-consuming and politically challenging, transmission could increase access to low-cost RE Resources
- Storage solutions: One way to counter the diurnal supply/demand mismatch is through storage solutions that are already popular in the market and are used for individual and commercial projects. Currently, the most popular form of batteries is the Li-ion batteries, other forms and types in the market including thermal storage, have been increasing the scope of storage solutions.
- Lowering the Cost of Generators: This can lead to cost-competitive deployment of supply via RE sources, even with a curtailment of the energy supplied, this will lower the Levelized Cost of Energy(LCOE).
The AEMO has also been on the path to introduce changes with the latest directive in August 2024 also suggesting that batteries enabled for FCAS also provide PFR, which would not only support power system stability but also economic efficiency.
Summing Up
The energy goals of Australia which would require a large-scale integration of the Renewable Power Systems into the national grid are replete with certain challenges, one of which remains the Primary Frequency Response, which forms the backbone of power security and reliability in the NEM. The existing PFR Requirements and the subsequent modifications, developments, and innovations to successfully incorporate the Inverter-based-resources like solar and wind into the grid would truly help establish a future run on green energy!
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