https://hdl.handle.net/1721.1/92237 Sat, 04 Apr 2026 19:02:56 GMT 2026-04-04T19:02:56Z https://hdl.handle.net/1721.1/130632 Interplay of Gas and Electricity Systems at Distribution Level Tapia-Ahumada, Karen; Duenas, Pablo Distributed energy resources for space conditioning comprise a set of varied technologies, ranging from mature well established systems such as furnaces, boilers, and air-conditioning (AC) units to emerging ones such as micro combined heat and power (micro-CHPs), reversible heat pumps, and hybrid gas-electricity conditioning systems. Micro-CHP systems, for instance, will have different prime movers depending on the underlying conversion process. Therefore, reciprocating engines, microturbines, and fuel cells-based CHPs have different technological characteristics and dissimilar market maturity levels, which make them attractive for a variety of applications at various scales. Depending on the quality of the thermal energy contained in the exhaust gas and cooling systems, this can be used to produce hot water, low- to medium-pressure steam, and heating and cooling for space conditioning. This paper looks into the relative value of using gas- and electricity-based systems for space conditioning for residential consumers. The profitability of these technologies is the key metric for comparison, as it is what consumers mostly consider when deciding to adopt one technology over another. Performance characteristics such as efficiency and heat-to-power ratio, as well as economic characteristics such as capital and operational costs, energy prices and their associated tariff structure are expected to have a major impact not only in their profitability, but also on how they compete each other to meet the consumers’ energy needs. Motivated by this, the specific question we explore in this case study is: “What would the costs and benefits be of gas and electricity DERs used for space conditioning under different market and climatic conditions?” The structure of the paper is a follows. In the first half of this document, we concisely describe the salient features of these gas- and electricity-based systems for space conditioning. In the second half of this paper, we assess the relative value of using gas- and electricity-based systems for space conditioning for residential consumers, looking at the primary energy, their profitability and annual energy costs savings under several scenarios. Wed, 14 Dec 2016 00:00:00 GMT https://hdl.handle.net/1721.1/130632 2016-12-14T00:00:00Z https://hdl.handle.net/1721.1/130631 Cybersecurity White Paper Draffin, Cyril Information and communications technologies are rapidly decreasing in cost and becoming ubiquitous, enabling more flexible and efficient consumption of electricity, improved visibility of network use, and enhanced control of power systems. These technologies are being deployed amidst several broad drivers of change in power systems, including growth in the use of variable renewable energy sources such as wind and solar energy; efforts to decarbonize the energy system as part of global climate change mitigation efforts; and the increasing interconnectedness of electricity grids and other critical infrastructure, such as communications, transportation, and natural gas networks. Widespread connection of distributed energy resources (DERs) (e.g., demand response, generation including from wind and solar, energy storage, and energy control devices) will increase digital complexity and attack surfaces, and therefore require more intensive cybersecurity protection. A multi-pronged approach to cybersecurity preparedness is required. System operators must have the capacity to operate, maintain, and recover a system that will never be fully protected from cyber-attacks. Relevant issues that need to be addressed include cloud security, machine-to-machine information sharing, advanced cybersecurity technologies, outcome-based regulation to avoid prolonged outages and increase system resilience, and international approaches to cybersecurity. Widespread connection of distributed energy resources, smart appliances, and more complex electricity markets increases the importance of cybersecurity and heightens privacy concerns. • Robust regulatory standards for cybersecurity and privacy are needed for all components of an interconnected electricity network. • To keep pace with rapidly evolving cybersecurity threats against large and complex electric power systems, electric utilities, vendors, law enforcement authorities, and governments should share current cyber threat information and solutions quickly and effectively. Maintaining a data hub or data exchange would serve several purposes: securely storing metered data on customer usage, telemetry data on network operation and constraints, and other relevant information; allowing non-discriminatory access to this data to registered market participants; and providing end consumers with timely and useful access to data on their own usage of electricity services. Responsibility for this function should also be carefully assigned, with priority given to data security and consumer privacy considerations. Utilities will need resilience and will need to be prepared to contain and minimize the consequences of cyber incidents. Future power systems with high penetration of DERs are envisioned to have features that are favorable for their resilient operation. For instance, microgrids, with DERs, are helpful for resilience, and with “islanding” operations can assist in “black-start” or continued operations if the broader grid goes down due to a cyber or physical incident. Privacy is also a growing concern, as ever expanding private personal and corporate information is gathered and stored by utilities and their affiliated companies. With expanding connection of electric and telecommunications devices, vastly more information will become available. Data analytics and the opportunity for outside organizations to have access to large quantities of data will increase the amount of information held by electric utilities and their affiliated partners. If electric utility companies expand their services beyond just delivering electricity, by interacting with DER aggregators, for example, specific procedures to protect data breaches and exfiltration of information will be needed. In summary, key points to consider: • Industry needs to adopt cybersecurity best practices and develop a risk management culture; cybersecurity regulations are important, but because there is a delay in developing and implementing them, regulations lag behind evolving threats • Important to rapidly share information about cyber threats, while respecting privacy guidelines • Good cybersecurity requires skilled teams to understand baseline operations, detect and respond to anomalous cyber activity, reduce the “dwell time” of cyber attackers, and implement layered cyber defenses • Need to understand and increase system resilience to avoid prolonged outages and recover from cyber attacks • In the future, utilize advanced cybersecurity technologies, international approaches to cybersecurity, and machine-to-machine information sharing so response to cyber incidents is in milliseconds and not in months Mon, 02 Jan 2017 00:00:00 GMT https://hdl.handle.net/1721.1/130631 2017-01-02T00:00:00Z https://hdl.handle.net/1721.1/130619 Machine learning from schools about energy efficiency Knittel, Christopher; Burlig, Fiona; Rapson, David; Reguant, Mar; Wolfram, Catherine In the United States, consumers invest billions of dollars annually in energy efficiency, often on the assumption that these investments will pay for themselves via future energy cost reductions. We study energy efficiency upgrades in K-12 schools in California. We develop and implement a novel machine learning approach for estimating treatment effects using high-frequency panel data, and demonstrate that this method outperforms standard panel fixed effects approaches. We find that energy efficiency upgrades reduce electricity consumption by 3 percent, but that these reductions total only 24 percent of ex ante expected savings. HVAC and lighting upgrades perform better, but still deliver less than half of what was expected. Finally, beyond location, school characteristics that are readily available to policymakers do not appear to predict realization rates across schools, suggesting that improving realization rates via targeting may prove challenging. Wed, 27 Sep 2017 00:00:00 GMT https://hdl.handle.net/1721.1/130619 2017-09-27T00:00:00Z https://hdl.handle.net/1721.1/130590 Energy Storage for the Grid: Policy Options for Sustaining Innovation Hart, David M.; Bonvillian, William B.; Austin, Nathaniel The electric power sector must be transformed in the twenty-first century. The threat of climate change, and the difficulty of reducing carbon emissions from other sources, means that power sector emissions must fall to near zero. Grid-scale energy storage has the potential to make this challenging transformation easier, quicker, and cheaper than it would be otherwise. A wide array of possibilities that could realize this potential have been put forward by the science and technology community. Grid-scale storage has become a major focus for public research and development (R&D) investment around the world. The public sector has also played a crucial role in moving some of these ideas from the laboratory into practice. In the United States, federal investments pushed storage technologies forward in the early 2010s, and state and regional initiatives provided a pull as the federal push slackened in the last few years. The shift from federal push policies to regional and state pull policies coincided with the consolidation of the grid-scale energy storage market around lithium-ion (Li-ion) batteries. This technology now accounts for more than 90% of the global and domestic markets. It is relatively mature, compared to the battery alternatives, and benefits from large-scale use in electronics and, more recently, electric vehicles (EVs). These qualities have enabled rapid price-cutting for grid-scale applications. Most projections suggest that Li-ion batteries will dominate the grid-scale market as that market grows rapidly in the coming years. This emerging situation runs the risk of technology “lock-in,” a characteristic pattern in the history of technology in which one “dominant design” drives out alternatives that would perform the same function. Lock-in may be beneficial because it accelerates process innovation and drives down costs for the dominant technology, which in turn expands adoption. In the case of energy storage, Li-ion batteries have begun to break through an older “legacy sector” paradigm that has hindered innovation in the electric power sector. What is needed now, in this interpretation, is to focus innovative effort on the dominant design and use it to transform the entire sector. An alternative interpretation is that the risks of technology lock-in in grid-scale energy storage outweigh the benefits. One risk is excessive market concentration, which commonly follows the establishment of a dominant design. East Asian producers, notably recent Chinese entrants backed by government policies, are the most likely to consolidate control, especially if supply runs ahead of demand for an extended period. An even more worrisome risk is that innovations that could improve on the dominant design become “stranded” and never fully mature. Li-ion batteries are well-suited to transportation applications, but not necessarily ideal for the grid. Lock-in on Li-ion batteries is already making it difficult for producers of alternative storage technologies to survive, much less continue to innovate and scale up. Public policy-makers should take action to build on the opportunities and mitigate the risks identified by these two interpretations of the near future of grid-scale energy storage. The objectives of such action should include growing the grid-scale energy storage market overall, creating niches within the market in which a range of technologies have opportunities to establish their cost and value characteristics, and ensuring that R&D continues in order to expand the portfolio of technology options. The evolving roles of the states, regions, and federal government create new opportunities to realize these objectives, but also complicate policy development and implementation. We argue that the federal government should expand funding for R&D, create tax incentives that focus on emerging technologies, support national and international processes that will lead to open standards, and counter unfair international trade practices. Policies that make sense for the states as well as the federal government include expanding support for demonstration projects and early deployment and providing financial assistance to help grid-scale energy storage hardware innovators overcome barriers to scaling up. Important state policy options to accelerate grid-scale energy storage innovation include setting smart and ambitious overall targets for deployment while also setting subtargets that are reserved for alternatives to Li-ion batteries. States along with regional organizations, including regional transmission organizations (RTOs) as well as groupings of states, should revise their rules so that storage assets can participate fully in electricity markets, implement regulations that allow storage asset owners to receive compensation through multiple value streams, explore the development of market signals that reward the unique performance characteristics of alternatives to Li-ion batteries, oversee integrated resource plans and approve rate designs that encourage storage innovation and deployment, establish regional storage innovation and purchasing consortia, and form expert advisory systems to stay informed about storage technology options. Sun, 01 Apr 2018 00:00:00 GMT https://hdl.handle.net/1721.1/130590 2018-04-01T00:00:00Z https://hdl.handle.net/1721.1/130589 Enhanced Decision Support for a Changing Electricity Landscape: The GenX Configurable Electricity Resource Capacity Expansion Model Jenkins, Jesse D.; Sepulveda, Nestor A. The electric power sector is currently undergoing several important transitions, which individually and collectively have the potential to transform the design, operation, and characteristics of electricity systems, including: decarbonization of electricity supplies; increased adoption of variable renewable energy and distributed energy resources; digitization of power systems; and electrification of greater shares of heating, transportation, and industry. In the face of these transformations, many conventional electricity resource capacity expansion models are no longer adequate for rigorous decision support and policy analysis. This working paper describes the formulation of “GenX," a highly-configurable electricity resource capacity expansion model that incorporates several state-of-the-art improvements in electricity system modeling to offer improved decision support for a changing electricity landscape. GenX is a constrained optimization model that determines the mix of electricity generation, storage, and demand-side resource investments and operational decisions to meet electricity demand in a future planning year at lowest cost subject to a variety of power system operational constraints and specified policy constraints, such as CO2 emissions limits. The appropriate level of model resolution with regards to chronological variability of electricity demand and renewable energy availability, power system operational detail and unit commitment constraints, and transmission and distribution network representation each vary for a given planning problem or policy question. As such, the GenX model is designed to be highly configurable, with several different degrees of resolution possible on each of these three key dimensions. The model is capable of representing a full range of conventional and novel electricity resources, including thermal generators, variable renewable resources (wind and solar), run-of-river, reservoir and pumped-storage hydroelectric generators, energy storage devices, demand-side flexibility, and several advanced technologies such as high temperature nuclear reactors and carbon capture and storage. Two optional modules also allow modeling of heat storage, industrial heat demand, and co-generation of heat and power; and distributed energy resources deployed at distribution voltages. The model has been implemented in Julia Language. Mon, 27 Nov 2017 00:00:00 GMT https://hdl.handle.net/1721.1/130589 2017-11-27T00:00:00Z https://hdl.handle.net/1721.1/130578 Assessing the potential of electrification concessions for universal energy access: Towards integrated distribution frameworks Jacquot, Grégoire; Pérez-Arriaga, Ignacio; Stoner, Robert J.; Nagpal, Dyviam The situation of energy access in Sub-Saharan Africa remains critical. According to the 2019 Tracking SDG 7: The Energy Progress Report, about 573 million people lacked access to electricity in 2017. Despite the proclaimed UN’s Sustainable Development Goal #7 (SDG 7) of a global energy access by 2030, the Agency forecasts that nearly 600 million Africans will still live in the dark. As a matter of fact, Sub-Saharan Africa has demonstrated limited progress in energy access over the past decade. Less than a third of the region experienced electrification rates faster than 1% per year due to ailing electrification policies and rampant demographic pressure, and World Bank estimates suggest that the continent may not be in a position to achieve universal energy access with the next 50 years under current policy scenarios. While various governance and financial models have been attempted over the past decades in order to foster private investments in energy access, sustainable and replicable business models for universal energy access remain elusive. As national utilities still struggle to escape financially unsustainable business models and cycles of regular bankruptcy and bailouts, the new momentum in the energy access sector has sparked growing interest in the development of innovative governance models to restructure the distribution sector and accelerate electrification. An estimated $52 billion of investment is needed per year to reach universal electricity access by 2030 – a figure that far exceeds the $30 billion committed in 2015-16 and that is out of reach for public agencies. As a result, increased attention is being paid to business models that can attract private capital under socially, politically and economically sustainable terms. Concession agreements, in which “the government grants a private company the right to extend a specific service under conditions of significant market power,” offer an interesting middle ground between traditional State-owned approaches to distribution and entirely private sector-driven strategies. While this model has already been tested in a number of Latin American, Asian and mostly African countries with mixed results, recent technological breakthroughs and the large experience derived from past experiences in the design and implementation of concessions may now pave the way for bright prospects for universal energy access. This study aims at demonstrating that properly designed and implemented concession agreements designed at the utility-level may lead to significant breakthroughs in reviving ailing utilities and reaching universal energy access. Building on a brief historical overview of past electrification attempts, the authors of this paper argue that tailored electrification models will be needed to reach universal energy access on the African continent. In practice, a review of past concession experiences demonstrate that national utility-scale concessions may hold the most potential provided that such agreement entail well-defined financial sustainability and energy access-specific clauses open to periodic revision. This paper concludes by proposing an actionable approach to implement concessions to accelerate electrification. It elaborates on the concept of Integrated Distribution Framework, whereby an entity is granted with a well-designed territorial concession and adequate incentives with the mandate of achieving full electrification under stringent quality of service requirements. Sun, 01 Sep 2019 00:00:00 GMT https://hdl.handle.net/1721.1/130578 2019-09-01T00:00:00Z https://hdl.handle.net/1721.1/130577 Two-Way Trade in Green Electrons: Deep Decarbonization of the Northeastern U.S. and the Role of Canadian Hydropower Dimanchev, Emil; Hodge, Joshua; Parsons, John Meeting climate policy targets in the U.S. Northeast will likely require the nearly complete decarbonization of electricity generation. To that end, consideration is being given to expanding imports of hydropower from neighboring Quebec, Canada. We use a capacity expansion and dispatch optimization model to analyze the role Canadian hydro might play, and the economic trade-offs involved. We find that, in a low-carbon future, it is optimal to shift the utilization of the existing hydro and transmission assets away from facilitating one-way export of electricity from Canada to the U.S. and toward a two-way trading of electricity to balance intermittent U.S. wind and solar generation. Doing so reduces power system cost by 5-6% depending on the level of decarbonization. In a cost-optimal low-carbon power system, transmission assets are used to flow power to Quebec in hours of excess wind and solar generation and to flow power to the U.S. in hours of scarcity. Therefore, the cost-optimal use of Canadian hydropower is as a complement, rather than a substitute, to deploying low-carbon technologies in the U.S. Expanding transmission capacity enables greater utilization of existing hydro reservoirs as a balancing resource, which facilitates a greater and more e fficient use of wind and solar energy. New transmission also reduces the costs of deep decarbonization. Adding 4 GW of transmission between New England and Quebec is estimated to lower the costs of a zero-emission power system across New England and Quebec by 17-28%. Wed, 12 Feb 2020 00:00:00 GMT https://hdl.handle.net/1721.1/130577 2020-02-12T00:00:00Z https://hdl.handle.net/1721.1/130576 System implications of continued cost declines for wind and solar on driving power sector decarbonization Mallapragada, Dharik S.; Diaz Pilas, Diego; Gonzalez Fernandez, Pilar; Delgado Martín, Agustín Global efforts on confronting climate change through reducing energy-related greenhouse gas (GHG) emissions have seen the most success in the electric power sector through the continued growth in variable renewable energy (VRE) generation, as well as fuel switching from coal to natural gas (NG) in some regions. For example, between 2009 and 2018, global capacity installations of wind and solar increased by a factor of ~3 and ~20 respectively, enabled by continued technology cost declines and policy support1. In some regions, like the U.S., this trend has been complemented by the displacement of generation from coal with gas, leading to U.S. power sector CO2 emissions declining by 28% since 20052. Despite these promising trends, deep decarbonization of the power sector remains a daunting challenge, as reflected by the fact that VRE sources accounted for only 9% of global electricity generation in 2018, while generation from coal, the most carbon-intensive fossil fuel, accounted for 38% of total generation and continues to grow in some regions (e.g., India)3. Several studies project that global electricity consumption could grow by as much as 45-50%4 by 2050, driven by rapid growth of electricity use for services such as air-conditioning in currently under-served regions, electrification of other end uses like heat and transport, as well as increased digitization and associated proliferation of data centers to support cloud computing needs. This suggests that in order to ensure that power sector GHG emissions approach net-zero by mid-century, the rate of power sector decarbonization needs to be significantly accelerated. Given the long lifetimes of infrastructure investments in the power sector, the next 2-3 decades are likely to be pivotal in defining the longer-term GHG emission trends of the sector and the ability to achieve end-of-century climate stabilization goals. The timely availability of low- or zero-carbon technologies that are also cost-competitive is a crucial lever for enabling the transition toward a more sustainable energy system. This document explores the potential for power sector decarbonization based on the cost-competitive addition of wind and solar technologies in the absence of any supporting policy, as per current technology cost and performance trends, as well as projected cost and performance in 2030. Additionally, the appendix provides an industry perspective5 on the potential technology roadmap and opportunity for cost reductions achievable for VRE generation and energy storage technology by 2030. Sun, 01 Mar 2020 00:00:00 GMT https://hdl.handle.net/1721.1/130576 2020-03-01T00:00:00Z https://hdl.handle.net/1721.1/130564 Reaching universal energy access in Morocco: A successful experience in solar concessions Jacquot, Grégoire; Pérez-Arriaga, Ignacio; Nagpal, Divyam; Stoner, Robert J. Ten years after the conclusion of its universal energy access program, Morocco has now become one of the best examples of successful integrated utility-led electrification programs. In less than fifteen years, rural electrification rates in the kingdom skyrocketed from a bottom low of 18% in 1990 to nearly 100% presently. Around 10% of the country’s population, or 200,000 households living in remote rural areas, were electrified through solar home systems. Morocco is currently Africa’s only success story in scaling up solar-driven electrification programs wherever grid extension programs were not feasible—not a small feat when one considers that it was not until the late 2000s that solar finally gained traction continent-wide with the emergence of so-called “pay-as-you-go” business models. Three key factors have underpinned the dramatic success of the Moroccan experience with solar. First, a strong political support in favor of solar systems, which translated into ambitious agendas and adequate public resources to achieve government objectives. Second, the ability of local stakeholders to design and implement solar concessions and attract capable international solar developers on the basis of extensive pre-feasibility analyses that match demand estimates with various possible supply options through solar systems. Third, the ability of the national utility and solar concessionaires to leverage all possible sources of funding available for energy access around a transparent and financially sustainable private sector-driven model, from cross-subsidies to direct public subsidies and international debt. The Moroccan case demonstrates that solar systems hold potential in closing the electrification gap and electrifying the last percent of unelectrified households on reasonable financial terms. However, several factors call for prudence as one may be tempted to generalize key success factors for universal energy access in African contexts. Morocco started out with a rural electrification level which was far below those of its comparable neighboring countries. It had—and seized—the opportunity to exploit a high level of cross-subsidization from urban consumers and greatly benefited from an economic development level far exceeding that of most Sub-Saharan African countries. While the Moroccan experience may then well confirm the potential of solar to reach universal energy access, it seems important not to relate the dramatic increase in electrification to the implementation model alone and to rather contextualize the Moroccan experience in the light of the specific challenges that faced the country throughout its electrification process. Sat, 01 May 2021 00:00:00 GMT https://hdl.handle.net/1721.1/130564 2021-05-01T00:00:00Z https://hdl.handle.net/1721.1/130562 Plausible Energy Futures: A Framework for Evaluating Options, Impacts, and National Energy Choices. Arbabzadeh, Maryam; Gençer, Emre; Morris, Jennifer F.; Paltsev, Sergey; Armstrong, Robert C. The global energy system is undergoing major transformations. The world faces a dual challenge of meeting increasing energy demand while reducing greenhouse gas emissions. This change is characterized by the convergence of power, transportation, industrial, and building sectors, and the surge of multi-sectoral integration. Such transformation of energy systems requires a combination of technology selection and policy choices to ensure providing reliable and clean energy. Understanding the implications of these dynamics is challenging and requires a holistic approach to provide systems level insights. In this working paper, we provide an overview of energy transformation analysis and projection tools and discuss the use of quantitative methods to examine possible future energy pathways. This is done to facilitate achieving decarbonization goals by providing thought leaders and policy makers with a robust framework in which energy choices and decarbonization goals can be made based on lifecycle analyses. We synthetize our findings applicable to modeling tools based on discussions with colleagues in other academic institutions and government labs and provide a summary of a wide range of lifecycle assessment (LCA) and energy modeling tools. Our assessment shows that although there is considerable related research work emerging, there is a lack of readily available or generally accepted quantitative models and tools that consider a broad and robust lifecycle analysis approach for a range of plausible energy futures at regional and national levels. Such a tool is needed to help policy makers, industry, investors, and the financial sector to better understand and make decisions on energy choices and energy transitions, and avoid narrowly framed and advocacy-driven pathways. We at MIT have substantial experience in building and maintaining energy system assessment tools: i) A comprehensive system-level and pathway-level lifecycle assessment model, which is called the Sustainable Energy Systems Analysis Modeling Environment (SESAME). SESAME is a publicly available, open access model with multi-sector representation. ii) The Integrated Global System Modeling framework (IGSM), which combines an economy-wide, multi-sector, multi-region computable general equilibrium (CGE) model (The MIT Economic Projection and Policy Analysis model, EPPA) with a natural systems component (The MIT Earth System model, MESM). The IGSM is an integrated assessment model (IAM). To quantify additional environmental impact categories such as air pollutants and water footprint, we develop an expanded SESAME platform. For an economy-wide scenario analysis, we use the MITEI Energy Choice Program Working Paper 3 modeling results from our EPPA model. The expanded SESAME version will be a publicly available technology options and scenario analysis tool that can use input information from any economy-wide system (or use the default settings that represent our base-case values). The tool will evaluate options, impacts, and national energy choices for exploring the impacts of relevant technological, operational, temporal, and geospatial characteristics of the evolving energy system. It focuses on lifecycle analysis with high technology resolution (linked with the existing MIT energy-economic models) that provides economic information and quantifies lifecycle GHG emissions, as well as impacts related to criteria pollutants and water. Such analysis highlights how effective policy choices and technology selection can reduce such environmental impacts Wed, 30 Oct 2019 00:00:00 GMT https://hdl.handle.net/1721.1/130562 2019-10-30T00:00:00Z https://hdl.handle.net/1721.1/130560 Energy Storage Investment and Operation in Efficient Electric Power Systems Junge, Cristian; Mallapragada, Dharik; Richard, Schmalensee We consider welfare-optimal investment in and operation of electric power systems with constant returns to scale in multiple available generation and storage technologies under perfect foresight. We extend a number of classic results on generation, derive conditions for investment and operations of storage technologies described by seven cost/performance parameters, and develop insights on power systems with multiple storage technologies. Simulation of a deeply decarbonized “Texas-like” power system with two available storage technologies shows both the non-existence of simple “merit-order” rules for storage operation and the value of frequency domain analysis to describe efficient operation. Our analysis points to the critical role of the capital cost of energy storage capacity in influencing efficient storage operation. Tue, 05 Jan 2021 00:00:00 GMT https://hdl.handle.net/1721.1/130560 2021-01-05T00:00:00Z