Projects:2018s1-140 Energy Storage Requirements for the SA Grid

Introduction

Project Title: 140 - Investigation of storage optimization strategies for the National Electricity Market, with emphasis on South Australia.

Team Members

• Julius Bullas

• Paul Citti

Supervisors

• Derek Abbott

• David Vowles

Advisors

• Holger Maier

• Angus Simpson

• Wen Soong

Abstract

SA obtains approximately 45% of its electrical energy from renewable sources – large scale wind and small scale solar PV. To reliably integrate these intermittent sources into the grid will increasingly require energy storage in a variety of forms such as pumped-hydro and batteries together with virtual energy storage in the form of demand side management. The storage requirement will progressively increase as controllable fossil fuel generation sources are withdrawn from the system. The objective of this project is to develop tools to assess the energy storage requirements to ensure reliable supply with high levels of intermittent generation. This project commenced in 2017 and the two honours students involved did a very fine job in achieving several early objectives. Much work remains to be done, including the following:

• (1) Serve the time-series data via the web so that it can be analysed and graphically displayed in various ways online.

• (2) Extend the data analysis and graphical display toolbox to allow the user to rapidly identify and display interesting features and periods within the data.

• (3) Extend the storage optimization approaches to consider alternative optimization objectives and future scenarios.

• (4) To estimate storage requirements for Australia as a whole assuming a hypothetical 100% renewable scenario and hypothetical interconnected Australia.

(There are a number of similarities but also critical differences with the water storage problem. In this aspect of the project we will draw on the considerable experience in Civil Engineering in the area of water network optimization.)

The 2018 Project

Today’s world faces challenges with the way energy is being made and produced. This stems from the increasing use of renewable energy sources, instigated by global action to climate change and decreasing manufacturing and installation costs. However, these benefits incur the issue of the intermittent nature of renewables which presents reliability and unserved energy concerns in the South Australian grid.

This thesis documents the energy storage requirements for the South Australian grid. The Initial Problem involves the development of a supply-demand balance model of the state, given a set amount of energy storage. It aims to minimise a cost function that matches to the maximum controllable generation, whilst ensuring 100% reliability for a set period. The tool developed could potentially be utilised to form retirement strategies for fossil fuelled generation as more renewables come online.

Genetic Algorithms will be used to optimise the Initial Problem. Previously been applied by the 2017 iteration of the project and to water distribution problems in the civil space, this technique incorporates the Darwinian concepts of natural selection and survival to the fittest. A simple genetic algorithm program has been developed on MATLAB which is to be later expanded and integrated into the initial problem.

Motivation

RESs have become evidently popular but this rapid development incurs several challenges. A major issue is intermittent electricity, energy that is not readily available. Wind and solar are intermittent in nature, they only produce energy when the wind is blowing, or the sun is shining i.e. generation is largely dependent on weather conditions. This in contrast with controlled and synchronous generation that utilise fossil fuels. [5]

Although RES can be predicted, it cannot be dispatched to meet the electricity demand. [7] Therefore, during times of high demand (e.g. during the summer period), RES presents challenges to the power system in terms of reliability, power quality and system security. Security in the context of a power system is operating within the defined technical limits and parameters such as voltage, frequency and network loading. [4] To illustrate, renewable sources do not provide inertia as a by-product of generation due to the being connected to power electronics. This leads to issues related to the rate of change of frequency (RoCoF) and hence maintaining the balance between the demand and supply. [4]

Another set of dilemmas are associated during periods of low demand and high generation. For instance, large energy flow from rooftop PV systems back to the distribution network can result in damage to transformers. This is due to the inherent design of the power system network that has catered to one-way flow. To avoid this, generation from RES are curtailed – restricting excess energy into the system. Overall, the intermittent characteristic of renewables poses a threat to both the power system security and reliability which only increases as more come online.

The issue of intermittency in apparent South Australia. A key evidence of intermittency is the demand variation of RES. Figure 5 indicates that for recent years, the variation distribution has become wider and flatter. [7] This implies more frequent and larger changes in output between five-minute intervals. The curve also emphasises the greater variability in residual demand changes as more renewables come online. Therefore, this must be managed to maintain power system standards. The residual demand is met by other sources of generation or from power flow of the Heywood and Murraylink interconnectors. [7]

Figure 5: South Australian residual demand (variation distribution)

The potential effects of intermittency are becoming more recognised. It has made managing the power system challenging by introducing a heightened risk that involves unserved energy (USE), and the National Electricity Market (NEM) standard not being met. [8] AEMO forecasts that for during the 2017-18 period, the South Australian and Victorian power system will be at most risk to USE. Figure 6 conveys that during this period, USE is 0.0025% of the total demand. This exceeds the 0.0020% NEM reliability standard. Thus, if USE occurs it will be for two to four hours. [4] USE and reliability issues due to intermittency is therefore a clear threat to the reliability of the South Australian power system.

To alleviate the intermittent nature of RES and its potential threats to the power system, energy storage is considered as a viable option. Utilising energy storage allows capacity firming which is maintaining the power output at a committed level for a period. [9] Power can be immediately dispatched to the grid to meet demand while also be charged at times of low demand. Additionally, energy storage eliminates the need to have generation capacity for the predicted highest demand and stabilises the effects of withdrawn controlled generation.

Grid Energy Storage, a document produced by the United States Department of Energy (DOE) exemplifies the challenges associated with the U.S electric system and how the integration of energy storage can meet those challenges. [10] The main issue presented is the need for an electricity grid that is robust and reliable to meet the inevitable increase in electricity demand. The DOE summarises that modernising the electric system along with employing energy storage improves the operating capabilities of the grid, lower costs and ensure high reliability along with deferring and reducing infrastructure investments. [10]

Energy storage can also provide immediate response to emergencies by supplying backup power and stabilising the electric grid. [10] In conjunction with these functions, different types of energy storage technologies provide multiple applications including energy management, load levelling, frequency regulation and voltage support. Hence, this offers flexibility in terms of applying a specific technology to meet requirements. [10] For example, large flywheel installations combined with power monitoring software ensures intermittent sources and variable load demands are maintained at nominal frequency. They can provide spinning reserve or curtailment which could reduce greenhouse gas emissions and improve the efficiency of infrastructure with industrial plant processes. [10]

The report further details the challenges involved in the deployment of energy storage. These are costs in manufacturing and installation, validated reliability and safety, equitable regulatory environment and industry acceptance. [10] Understanding these challenges and the strategies to tackle them is vital in supporting the commercial viability of energy storage. Table 2 summarises how the DOE will address these challenges. [10]

Table 2: Strategy summary to address the challenges/goals of energy storage

Effectively, the report establishes potential options to improve energy storage as well as actions to further encourage and maintain both scientific advancements and a pipeline of project deployments. [10]

Objectives and Project Significance

With the increasing integration of intermittent electricity sources in the South Australian grid and the clear requirement of energy storage application, it is appropriate to quantify the amount of storage. It is necessary to first formulate a problem and then identify an objective to accomplish. This can include ensuring reliability standard is met, reducing carbon emissions to a set level or even to reduce the cost of electricity.

The main challenge of implementing energy storage in South Australia is the uniqueness of the grid - both its distribution and transmission networks. The distribution network covers a large area of 178,000 km squared while the transmission network operates the interconnectors that allow for energy flow from/to New South Wales and Victoria. [14] There is also the concern of different forecasted levels of solar and wind penetration in different regions, further emphasising the issue of intermittency. This presents the problem of quantifying renewable energy generation and hence the storage required. In addition, it also involves the assessment of costs of extending or upgrading the existing infrastructure to ensure safe and reliable operation.

AEMO retains useful data that can be used to determine the energy storage requirements for a predetermined objective. These data include the interconnector flow, electricity demand and dispatchable generation from both non-renewable and renewable sources. However, the limitation is that they are only forecasts and therefore does not reflect the actual situation of the electricity grid. This presents a challenge to the problem, particularly in emergencies, where it a priority to restore the system to a stable and secure state. Nevertheless, the data is beneficial in providing a starting point to be modified in the project investigations.

This project endeavours to parametrise the amount of energy storage required for several objectives and deliver a solution that combats the challenges previously mentioned. The initial investigation aims to optimally utilise a given amount of storage to minimise the reserve generation capacity that is required to supply the system load, whilst ensuring 100% reliability for a set period. The results of this study provide information on the impact of using a certain amount of storage capacity and highlights the issues involved in this transition phase of the Australian energy system. It will formulate a relationship between storage capacity and installed reserve generation capacity, building a foundation to undertaking more complex problems.

The industrial significance of this investigation is that the tool developed can be used to assist in developing retirement strategies for fossil fuelled generators in the National Electricity System (NES) while meeting the NEM reliability standard. For instance, it can potentially avoid a state-wide catastrophe such as the SA State Blackout in September 2016. [15] A controversial opinion is that this could have been avoided if the Port Augusta coal-powered power station was kept online. [16] Furthermore, it can help the NES to transition to increasing amounts of renewable energy and become less reliant on fossil-fuelled generation capacity. Ultimately, this promotes reducing CO2 emissions and assists in attaining the Federal Government’s RET of 33,000 GWh by 2020.