Generic Market Modelling for Future Grid Scenario Analysis

Power systems worldwide are moving away from being dominated by large-scale synchronous generation and passive consumers. Instead, in the future, new actors on both the generation and the load side will play an increasingly significant role. On the generation side, there are renewable energy resources (RES) such as wind generation (WG), photovoltaic (PV) and concentrated solar thermal (CST). On the load side, there are demand response (DR), energy storage and price responsive users equipped with a small-scale PV-battery system (called prosumers). The two sides will together shape future grids. However, if connected at a large scale without proper consideration of their effect, they can also jeopardise the reliability and security of electricity supply. For example, the addition of non-synchronous RES will jeopardise the frequency response of the future grids, while the intermittency and variability of RES threats the existing model of electricity supply (supply following demand), complicating balancing and stressing future grids’ ramping capabilities. On the other hand, the inclusion of DR, prosumers and storage without proper consideration of the implications can cause significant changes to the demand profiles and may result in new stresses such as secondary peaks or excessive ramps. In summary, balancing, stability (frequency, voltage, transient) and ultimately reliability are affected by the changes introduced to the future grids’ technology mix. Given that the lifespan of power system assets is well over fifty years, laying out a roadmap to future grid development in an economical fashion without risking its security is a challenging task. The uncertainty of cost, availability and quality of new technologies requires power system planners and policy-makers to evaluate the feasibility and viability of future grids for a diverse range of technology options. To this end, a rigorous and systematic approach is developed in this dissertation to analyse the implications of prosumers, storage and CST on the balancing and stability of future grids. The best features of all these approaches are combined and presented in a single coherent framework. Computation time improvement techniques are then deployed to improve the computational efficiency and solution accuracy. Taken as a whole, the tool will fill the gap to explore the validity of emerging technologies to tackle balancing, stability, security and reliability issues, over a diverse scope of uncertain premises. The tool is developed for an approach to future grids studies called scenario analysis. Traditionally, power systems are planned based on a handful of the most critical scenarios with an aim to find an optimal generation and/or transmission plan. In contradistinction, scenario analysis involves analysing possible evolutionary pathways to facilitate informed decision making by policy-makers and system planners. Specifically, the primary aim of future grids studies is to deal with the uncertainty of long-term decision making and providing outcomes that are technically possible, although explicit costing might be considered. To this end, for any future grids stability framework, the market model is a critical bottleneck. Existing future grids studies mostly look at simple balancing, ignore network constraints and include most of the emerging technologies in an ad hoc fashion. These simplifications are made to combat the high computation time requirement of accurate approaches. Against this backdrop, this dissertation presents: i) a novel optimisation-based models to capture the effects of prosumers (Chapter 2, 3); ii) co-optimise dispatch of PV and CST aggregation to reduce ramping stress on the conventional generators (Chapter 4); iii) efficiently implemented market-based dispatch (Chapter 5); iv) framework for frequency performance assessment of future grids (Chapter 6). In more detail, first, Chapter 2 and 3 develop a novel approach to explicitly model prosumers’ demand in market dispatch (production cost) models. The key novelty of the method is its ability to capture the impact of prosumers without going into specific market structure or control mechanisms, which are computationally expensive. The model is formulated as a bi-level program in which the upper-level unit commitment (UC) problem minimises the total generation cost and the lower-level problem maximises prosumers’ aggregate self-consumption. Unlike the existing bi-level optimisation 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 grids studies where the market structure is potentially unknown. This model addresses some critical questions such as, How much flexibility can prosumer provide to help with large-scale RES integration? Flexibility is the key to achieve a high RES penetration. One of the major problem in the integration of RES is their intermittent and variable nature. Concentrated solar thermal (CST) presents an excellent resource with inherent flexibility. In contrast to Chapter 2 and 3 (exploring flexibility through DSM), Chapter 4 examines flexibility options from a generation end. In particular, it proposes an RES aggregation (REA) scheme aiming to co-optimise the dispatch of intermittent and dispatchable RES. The principal aim is to keep in check the ramping stress imposed on the conventional generators due to the RES integration. A Stackelberg game is used to capture the interaction between an independent system operator (ISO) and the REA when the ISO tries to minimise the generation cost, while REA seeks to maximise its revenue. This approach also highlights the potential of a ramping market, as proposed by some US studies. In Chapter 5, the utility storage proposed in Chapter 2, prosumers model proposed in Chapter 3, the dispatch model of CST developed in Chapter 4 and inertia constraint detailed in Chapter 6 are combined into a single coherent framework. The addition of these emerging technologies in the energy market model significantly increases the computation burden. Also, to allow for a subsequent stability assessment, an accurate representation of the number of online generation units is required, which affects the power system inertia and the reactive power support capability. This renders a fully-fledged market model computationally intractable, so in Chapter 5 we deploy unit clustering, a rolling-horizon optimisation approach and constraint clipping to improve the computational efficiency. Together, these comprise a computationally efficient market simulation tool (MST) suitable for future grid stability analysis. Finally, developed MST is used in Chapter 6 for a comprehensive frequency performance assessment of the Australian National Electricity Market (NEM). First, an assessment of minimum inertia requirements is presented, followed by a framework for frequency performance assessment of future grids. The maximum non-synchronous instantaneous range from a frequency performance point of view is established for the NEM. Also, to alleviate the deteriorating effects of the high RES penetration on frequency performance, different technical solutions are proposed and discussed. These efforts will empower policy-makers and system planners with the information on safe penetration levels of different technologies while ensuring reliability and security of future grids

On Feasibility and Flexibility Operating Regions of Virtual Power Plants and TSO/DSO interfaces

Distributed energy resources are an ideal candidate for the provision of additional flexibility required by power system to support the increasing penetration of renewable energy sources. The integrating large number of resources in the existing market structure, particularly in the light of providing flexibility services, is envisioned through the concept of virtual power plant (VPP). To this end, it is crucial to establish a clear methodology for VPP flexibility modelling. In this context, this paper first puts forward the need to clarify the difference between feasibility and flexibility potential of a VPP, and then propose a methodology for the evaluation of relevant operating regions. Similar concepts can also be used to modelling TSO/DSO interface operation. Several case studies are designed to reflect the distinct information conveyed by feasibility and flexibility operating regions in the presence of "slow" and "fast" responding resources for a VPP partaking in provision of energy and grid support services. The results also highlight the impact of flexible load and importantly network topology on the VPP feasibility (FOR) and flexibility (FXOR) operating regions

Visual and treatment outcomes of tubercular uveitis: a prospective case series from a referral hospital in Pakistan

Objective: Pakistan is the fifth highest TB burden country. Tuberculous uveitis (TbU) is a form of extrapulmonary TB, that is not uncommon in high burden country but very limited data is available on its outcome. The aim of the study is to assess the outcome of TbU with anti-tuberculous treatment (ATT). Results: A prospective study was conducted at Jinnah Medical College Hospital (JMCH) Karachi, Pakistan from July to December 2017. Patients with suspected TbU were started on standard ATT chemotherapy for 12 months. Their response was assessed via slit lamp examination and visual acuity at 1, 3, 6 and 12 months of treatment. Forty patients with probable TbU were treated with ATT, mean age was 36 ± 3 years and 24 (60%) were females. Around 26 (65%) had Monteux test of 15 mm or more. History of TB contact was positive in 24 (60%) and 12 (30%) had previous history of TB. All patients complained for blurring of vision and floaters. Posterior uveitis seen in 36 (90%) of patients. Complete response achieved in 32 (80%) after ATT while 6 (14%) had changed in inflammation and 2 (6%) had no benefit

Concurrent adult pulmonary tuberculosis prevalence survey using digital radiography and Xpert MTB/RIF Ultra and child interferon-gamma release assay Mycobacterium tuberculosis infection survey in Karachi, Pakistan: a study protocol.

Background: Assessment of the effectiveness of tuberculosis control strategies requires the periodic measurement of M. tuberculosis transmission in populations, which is notoriously difficult. One well-established method is to measure the prevalence of infectious pulmonary tuberculosis in the population which is then repeated at a second time point after a period of 'intervention', such as scale up of the Search-Treat-Prevent strategy of the Zero TB Cities initiative, allowing for a 'before and after' comparison.  Protocol: The concurrent adult pulmonary tuberculosis prevalence survey (using digital radiography and Xpert MTB/RIF Ultra) and child M. tuberculosis infection survey (using QuantiFERON-TB® Gold Plus) will primarily provide a baseline measure of the burden of adult infectious tuberculosis in Karachi and assess whether a large-scale interferon gamma release assay survey in children aged 2 to 4 years is feasible. The target population for the prevalence survey is comprised of a stratified random sample of all adults aged 15 years and above and all children aged 2 to 4 years resident in four districts in Karachi. The survey procedures and analyses to estimate pulmonary tuberculosis prevalence are based on the World Health Organization methodology for tuberculosis prevalence surveys. Ethics and dissemination: The study protocol has been approved by the Interactive Research Development / The Indus Hospital Research Centre Research Ethics Committee in Karachi, Pakistan and the London School of Hygiene & Tropical Medicine Research Ethics Committee. Due to non-representative sampling in this setting, where a large proportion of the population are illiterate and are reluctant to provide fingerprints due to concerns about personal security, verbal informed consent will be obtained from each eligible participant or guardian. Results will be submitted to international peer-reviewed journals, presented at international conferences and shared with participating communities and with the Provincial and National TB programme

Insights into tuberculosis burden in Karachi, Pakistan: A concurrent adult tuberculosis prevalence and child Mycobacterium tuberculosis infection survey.

Pakistan is one of the five highest tuberculosis burden countries globally. We estimated prevalence of adult bacteriologically confirmed pulmonary tuberculosis and annual risk of Mycobacterium tuberculosis (M. tuberculosis) infection in children aged 2-4 years in Karachi, Pakistan. The survey design enabled exploration of tuberculosis burden by whether the population had previously been exposed to widespread tuberculosis active case-finding (ACF) activities or not. We conducted a concurrent adult pulmonary tuberculosis prevalence survey and a child M. tuberculosis infection survey using interferon gamma release assays in four districts (Korangi, South, West and Central). A cluster-based unequal probability random sampling method was employed with the a priori plan to oversample Korangi district which had been the focus of tuberculosis ACF activities since 2011. We defined Korangi district as the 'prior ACF' zone and remaining districts as the 'no prior ACF' zone. Between March 2018 and May 2019, 34,962 adults (78·5% of those eligible) and 1,505 children (59·9%) participated. Overall estimated prevalence of bacteriologically confirmed pulmonary tuberculosis was 387 cases per 100,000 population (95% CI 276-498) with a prevalence of 421 cases [95% CI 276-567] per 100,000 in the 'no prior ACF' and 279 cases [95% CI 155-403] per 100,000 in the 'prior ACF' zone. We estimated the annual risk of M. tuberculosis infection in children to be 1·1% (95% CI 0·7-1·5) in the 'no prior ACF' zone and 0·6% (95% CI 0·3-1·1) in the 'prior ACF' zone. We observed consistent differences in the population distribution of tuberculosis between the 'prior ACF' and 'no prior' ACF zones with a trend towards lower estimates of burden and M. tuberculosis transmission in the 'prior ACF' zone. A plausible explanation is that intensive ACF activities that have been ongoing in Korangi district for the preceding years have noticeably reduced the burden of tuberculosis and transmission

Mapping local patterns of childhood overweight and wasting in low- and middle-income countries between 2000 and 2017

A double burden of malnutrition occurs when individuals, household members or communities experience both undernutrition and overweight. Here, we show geospatial estimates of overweight and wasting prevalence among children under 5 years of age in 105 low- and middle-income countries (LMICs) from 2000 to 2017 and aggregate these to policy-relevant administrative units. Wasting decreased overall across LMICs between 2000 and 2017, from 8.4% (62.3 (55.1–70.8) million) to 6.4% (58.3 (47.6–70.7) million), but is predicted to remain above the World Health Organization’s Global Nutrition Target of <5% in over half of LMICs by 2025. Prevalence of overweight increased from 5.2% (30 (22.8–38.5) million) in 2000 to 6.0% (55.5 (44.8–67.9) million) children aged under 5 years in 2017. Areas most affected by double burden of malnutrition were located in Indonesia, Thailand, southeastern China, Botswana, Cameroon and central Nigeria. Our estimates provide a new perspective to researchers, policy makers and public health agencies in their efforts to address this global childhood syndemic