Shariq Riaz

Evaluation of concentrated solar-thermal generation for provision of power system flexibility

Including a large amount of renewable energy sources (RES) in future power systems will not be possible without flexibility. Concentrated solar power (CSP) presents an excellent resource with inherent flexibility. This paper purposes aggregation of inflexible RES, such as utility-scale photovoltaic, with CSP to achieve the required flexibility. The aim is to keep in check the ramping stress induced on conventional generators due to the integration of RES. For this purpose, a Stackelberg game is used to capture the interaction between an independent system operator (ISO) and purposed RES aggregation (REA). In cost minimisation analysis, the ISO tries to minimise generation cost, whereas REA seeks to maximise revenue. In this setting optimising power dispatch from REA with total energy and ramp rate limitations is a challenging task. Case studies benchmark the effect of purposed REA against business as usual scenario for the Australian National Electricity Market.

Impact study of prosumers on loadability and voltage stability of future grids

Feed-in-tariffs (FiTs) have been reduced due to combinations of economic and technical reasons. So, existing and new rooftop-photovoltaic (PV) owners are left with the option to either concede the low value arrangement or to use battery storage to maximise their self-consumption, and so minimise their electricity cost. This paper explores the effect of increasing penetration of residential battery systems on balancing and voltage stability of future grid (FG) scenarios. For this purpose, a generic demand model based on a Stackelberg game is employed to capture the interaction between an independent system operator (ISO) and prosumers. In this arrangement, the ISO attempts to minimise the total generation cost, whereas the prosumers aim to maximise their self-consumption by reducing their feed-in power. As a case study, we use the Australian National Electricity Market (NEM) to explore the impact of increased penetration of residential battery system on performance of the grid in 2020.

A Framework for Assessing Renewable Integration Limits With Respect to Frequency Performance

The increasing penetration of nonsynchronous renewable energy sources (NS-RES) and demand side-technologies alter the dynamic characteristics, and particularly, the frequency behavior of a power system. Given this, we propose a framework for assessing renewable integration limits concerning power system frequency performance using a time-series scenario based approach. By considering a large number of future scenarios and their sensitivities with respect to different parameters, we can identify maximum nonsynchronous instantaneous penetration limits for a wide range of possible scenarios. Further, we derive a dynamic inertia constraint and incorporate it into the market dispatch model to reduce the detrimental impacts of high NS-RES penetration on the frequency performance. The results using the Australian future grid as a test case show that such an explicit inertia constraint ensures power system frequency stability for all credible contingencies. To improve the frequency performance, we assess and quantify the contribution of a wide range of technologies, including synchronous condensers, synthetic inertia from wind farms and a governor-like response from de-loaded wind farms. The results show that the last option is the most effective one.

Assessment of minimum inertia requirement for system frequency stability

The reduced amount of rotational kinetic energy in power systems has significant detrimental impacts on system frequency behaviour. To ensure system security, this issue must be addressed in a systematic way. Given this, we consider three different metrics, namely i) minimum power penetration from synchronous generators, ii) minimum rated power of synchronous generators, and iii) minimum synchronous kinetic energy, as frequency control constraints in the market dispatch model, and assess frequency behaviour of the system for these metrics. The results show that each metric has a different impact on market dispatch, and, accordingly, on the system frequency behaviour. It is shown that with high penetration of converter-based generation, we need to consider a minimum kinetic energy requirement as a frequency control security constraint in the market dispatch model to guarantee the frequency stability of power systems.

Comparing utility and residential battery storage for increasing flexibility of power systems

Evolution of the present-day grid from fossil fuel-based to green, sustainable generation is picking up pace due to environmental concerns and dwindling fossil fuel reserves. The era where renewable energy resources (RES) begin to significantly penetrate the power system has begun. In the future, this trend will be substantial, and RES contribution toward energy production will be significant, here this scenario is referred as the future grid (FG). The intermittent and stochastic nature of RES will introduce many new vulnerabilities in future power systems. This paper explores the merits and demerits of introducing photovoltaic (PV) battery system in FG scenario and discuss how utility and household storage can rectify some vulnerabilities. Here, flexibility in power systems is achieved by utilising the storage in contrast to demand response (DR) suggested in many works. Modified unit commitment (UC) model is used to study the effect of utility storage behaviours, and a bi-level optimisation approach is used to model household storage capability. The case study explores the effect of storage on Australian National Electricity Market (NEM) for the year 2020. For comparison and analysis, three scenarios are compared. Results demonstrate that storage can be used to achieve flexibility in FGs. Also, there exist a trade off for programs supporting large scale and distributed household storage. There is also some condition under which the behaviour and effect of both cases become very similar.

Computationally Efficient Market Simulation Tool for Future Grid Scenario Analysis

This paper proposes a computationally efficient electricity market simulation tool (MST) suitable for future grid scenario analysis. The market model is based on a unit commitment (UC) problem and takes into account the uptake of emerging technologies, like demand response, battery storage, concentrated solar thermal generation, and HVDC transmission. To allow for a subsequent stability assessment, the MST requires an explicit representation of the number of online generation units, which affects power system inertia and reactive power support capability. These requirements render a full-fledged UC model computationally intractable, so we propose unit clustering, a rolling horizon approach, and constraint clipping to increase the computational efficiency. To showcase the capability of the proposed tool, we use a simplified model of the Australian National Electricity Market with different penetrations of renewable generation. The results are verified by a comparison to a more expressive and computationally intensive binary UC, which confirm the validity of the approach for long term future grid studies.

Generic Demand Model Considering the Impact of Prosumers for Future Grid Scenario Analysis

The increasing uptake of residential PV-battery systems is bound to significantly change demand patterns of future power systems and, consequently, their dynamic performance. In this paper, we propose a generic demand model that captures the aggregated effect of a large population of price-responsive users equipped with small-scale PV-battery systems, called prosumers, for market simulation in future grid scenario analysis. The model is formulated as a bi-level program in which the upper-level unit commitment problem minimizes the total generation cost, and the lower-level problem maximizes prosumers’ aggregate self-consumption. Unlike in the existing bi-level optimization frameworks that focus on the interaction between the wholesale market and an aggregator, the coupling is through the prosumers’ demand, not through the electricity price. That renders the proposed model market structure agnostic, making it suitable for future grid studies where the market structure is potentially unknown. As a case study, we perform steady-state voltage stability analysis of a simplified model of the Australian National Electricity Market with a significant penetration of renewable generation. The simulation results show that a high prosumer penetration changes the demand profile in ways that significantly improve the system loadability, which confirms the suitability of the proposed model for future grid studies.