Abstract--Power systems have traditionally been designed to provide flexibility in a context where demand is met by bulk generation. The integration of variable and uncertain renewable generation sources, such as wind, increases the flexibility needed to maintain the load-generation balance. This paper aims to provide a systematic approach to evaluate the flexibility level and investigate the role of flexibility in generation planning and market operation. An 'offline' index is proposed to estimate the technical ability of both the individual generators and the generation mix to provide the required flexibility. A dedicated unit construction and commitment (UCC) algorithm, able to consider plant investment and operation costs, is developed to determine the optimal investments in flexible generating units. Market simulation models are then implemented to determine the profits obtained from providing flexibility in different market designs. An adapted RTS-96 system is used to test the proposed models and the flexibility metric. Results demonstrate the validity of the UCC algorithm and the coherence of the proposed flexibility index. The analysis of the profits of flexibility shows that the market design plays an important role in the efficient deployment and subsequent profitability of flexibility resources.Index Terms-Flexibility index, wind power, unit commitment and construction, market design, profitability, day-ahead market, balancing market, rolling clearing.
Abstract--Power systems have traditionally been designed to provide flexibility in a context where demand is met by bulk generation. The integration of variable and uncertain renewable generation sources, such as wind, increases the flexibility needed to maintain the load-generation balance. This paper aims to provide a systematic approach to evaluate the flexibility level and investigate the role of flexibility in generation planning and market operation. An 'offline' index is proposed to estimate the technical ability of both the individual generators and the generation mix to provide the required flexibility. A dedicated unit construction and commitment (UCC) algorithm, able to consider plant investment and operation costs, is developed to determine the optimal investments in flexible generating units. Market simulation models are then implemented to determine the profits obtained from providing flexibility in different market designs. An adapted RTS-96 system is used to test the proposed models and the flexibility metric. Results demonstrate the validity of the UCC algorithm and the coherence of the proposed flexibility index. The analysis of the profits of flexibility shows that the market design plays an important role in the efficient deployment and subsequent profitability of flexibility resources.Index Terms-Flexibility index, wind power, unit commitment and construction, market design, profitability, day-ahead market, balancing market, rolling clearing.
The uncertainties resulting from the integration of a large amount of wind and other stochastic forms of renewable generation affect the reliability of the power system. While it is generally agreed that coping with this uncertainty will require a more flexible system, not enough work has been done to provide dependable estimates of the amount of "flexibility" needed. This paper discusses a technique to determine the optimal amount of flexibility that a generation portfolio should provide for different levels of wind penetration. This optimization must bridge the gap between long-term investment decisions on the type of plants to be built and short-term operational decisions on how these plants are scheduled to meet the load and provide sufficient reserve. To achieve this goal, the unit commitment (UC) problem has been extended to consider not only whether a particular generating unit should be committed at a given time but also whether building this unit would reduce the sum of the operational and investment costs. A proper assessment of the balance between these two costs must take into account the seasonal variations in the load profile and must therefore consider an optimization horizon representative of a year. This paper describes the techniques that have been developed to make such calculations both accurate and achievable with a reasonable amount of computing resources. Test results based on the IEEE RTS system are presented and demonstrate how different amounts of wind generation capacity and reserve requirements affect the need for flexibility.
Within a year after its emergence, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has infected over 100 million people worldwide with a death toll over 2 million. Vaccination remains the best hope to ultimately put this pandemic to an end. Here, using Trimer-Tag technology, we produced both wild-type (WT) and furin site mutant (MT) S-Trimers for COVID-19 vaccine studies. Cryo-EM structures of the WT and MT S-Trimers, determined at 3.2 Å and 2.6 Å respectively, revealed that both antigens adopt a tightly closed conformation and their structures are essentially identical to that of the previously solved full-length WT S protein in detergent. The tightly closed conformation is stabilized by fatty acid and polysorbate 80 binding at the receptor binding domains (RBDs) and the N terminal domains (NTDs) respectively. Additionally, we identified an important pH switch in the WT S-Trimer that shows dramatic conformational change and accounts for its increased stability at lower pH. These results validate Trimer-Tag as a platform technology in production of metastable WT S-Trimer as a candidate for COVID-19 subunit vaccine. IMPORTANCE Effective vaccine against SARS-CoV-2 is critical to end the COVID-19 pandemic. Here, using Trimer-Tag technology, we are able to produce stable and large quantities of WT S-Trimer, a subunit vaccine candidate for COVID-19 with high safety and efficacy from animal and Phase 1 clinical trial studies. Cryo-EM structures of the S-Trimer subunit vaccine candidate show that it predominately adopts tightly closed pre-fusion state, and resembles that of the native and full-length spike in detergent, confirming its structural integrity. WT S-Trimer is currently being evaluated in global Phase 2/3 clinical trial. Combining with published structures of the S protein, we also propose a model to dissect the conformation change of the spike protein before receptor binding.
Abstract--The increasing penetration of renewable energy sources, particularly wind power, raises concerns about the level of flexibility needed to cope with the inherent variability and uncertainty affecting these sources of energy. Departing from the common conception of providing flexibility using fossil-fuelled generators with fast ramp rates, this paper explores the use of demand-side resources. A technique to optimize the balance between the flexibility provided by fast generating units and the flexibility achievable from demand side management (DSM) is presented. This methodology is based on an extended unit commitment optimization that considers both short-and longterm aspects, i.e. operational and investment costs. The methodology is applied to the IEEE RTS (RTS-96), using actual demand and wind profiles from central Scotland.Index Terms--Flexibility, demand side management, integration of wind generation, long-term unit commitment, reserve requirements.
-The stochastic nature of renewable energy sources such as wind and sun introduces a new form of uncertainty in power system operation. The standard answer to the concerns that this increase in uncertainty raises is that the system should become more "flexible". However, there is as yet no agreement on exactly how much flexibility is needed or even a commonly accepted measure of flexibility. There is agreement however on the fact that flexibility has a cost and that this cost should be minimized in a way that does not affect reliability to facilitate the integration of these renewable energy sources. This presentation will explore how flexibility from demandside resources compares with the flexibility that fast ramping generating units can provide. In order to take into account the associated investment costs, this comparison relies on an extended unit commitment optimization that considers both short-and long-term aspects.Index Terms--Flexibility, demand side management, integration of wind generation, long-term unit commitment, reserve requirements.
Less than a year after its emergence, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has infected over 22 million people worldwide with a death toll approaching 1 million. Vaccination remains the best hope to ultimately put this pandemic to an end. Here, using Trimer-Tag technology, we produced both wild-type (WT) and furin site mutant (MT) S-Trimers for COVID-19 vaccine studies. Cryo-EM structures of the WT and MT S-Trimers, determined at 3.2 Å and 2.6 Å respectively, revealed that both antigens adopt a tightly closed conformation and their structures are essentially identical to that of the previously solved full-length WT S protein in detergent. These results validate Trimer-Tag as a platform technology in production of metastable WT S-Trimer as a candidate for COVID-19 subunit vaccine.
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