Emission Reduction Cost Research Articles

Carbon-Oriented Electricity Network Planning and Transformation

The acceleration of distributed energy resources and carbon pricing policies have compelled utilities to act and to prioritize carbon-constrained infrastructure augmentation in their capital programs. To implement various carbon emission reduction policies, power system transmission planning has become more challenging. The existing energy system will face massive retirement of coal-fired power plants (CFPPs), large scale integration of renewable energy and network expansion. In this paper, an electricity network planning and transformation roadmap, which has two milestones, is put forward. In the first stage, a mathematical model is proposed based on the average cost of carbon emission reduction to realize the cooperation of CFPPs retirement and renewable energy investment. It can help the network carry out the transition from a fossil-fuel dominated system to a low-carbon oriented system. Because of the promising prospect of power-to-gas (P2G) technology, in the second milestone, a method based on carbon emission flow (CEF) is employed to help the power-to-gas stations (P2GSes) to select the construction site and capacity. The gas network constraints are modeled to guarantee that P2GSes can work smoothly without energy flow congestion in both electricity and gas networks. According to the simulation results in case studies, our method can reach the emission reduction target more economically and effectively, and the P2GSes can produce and absorb clean energy.

Decisions in Power Supply Chain with Emission Reduction Effort of Coal-Fired Power Plant under the Power Market Reform

Sustainability in power supply chain has been supported by emission reduction of coal-fired power generation and increasing renewable energy power generation. Under the power market reform of direct power purchase transactions, this paper focuses on the channel selection and emission reduction decisions of power supply chain. From the theoretical perspective, this paper develops the decision-making models of centralized and decentralized power supply chain, which consist of one renewable energy power generation enterprise, one coal-fired power plant and one power grid enterprise. The optimal strategies of power quantities and profits for power supply chain members and their corresponding numerical experiments are analyzed in different cases. The results show that there are qA1Nc*<qA1Lc* for renewable energy power generation enterprise A, qB1Nc*>qB1Lc* and eBNc*>eBLc* for coal-fired power plant B, which indicate that the direct power purchase channel in the centralized scenario is conducive to promoting the transaction quantity of renewable energy power generation, as well as the on-grid power quantity and emission reduction efforts of coal-fired power plant B. Furthermore, the profit of whole power supply chain could be enhanced by the increasing on-grid power preference coefficient of coal-fired power generation, subsidy for renewable energy power generation and preference coefficient for clean production, and by the decreasing emission reduction cost coefficient of coal-fired power plant. Additionally, the emission reduction effort of coal-fired power plant is positively relevant with preference coefficient for clean production, whereas it is negatively relevant with power grid wheeling charge, emission reduction cost coefficient and subsidy for renewable energy power generation. Our findings can provide useful managerial insights for policymakers and enterprises in the sustainability of power supply chain.

EU Emission Targets of 2050: Costs and CO2 Emissions Comparison of Three Different Solar and Heat Pump-Based Community-Level District Heating Systems in Nordic Conditions

In Finland, old apartments (1980s) contribute toward emissions. The objective is to reduce CO2 emissions to reach Europe’s targets of 2050. Three different centralized solar-based district heating systems integrated either with non-renovated or renovated old buildings in the community were simulated and compared against the reference city-level district heating system. The three proposed centralized systems were: Case 1: photovoltaic (PV) with a ground source heat pump (GSHP); Case 2: PV with an air-water heat pump (A2WHP); and Case 3: PV with A2WHPs, seasonal storage, and GSHPs. TRNSYS simulation software was used for dynamic simulation of the systems. Life cycle cost (LCC), CO2 emissions and purchased electricity were calculated and compared. The results show that the community-level district heating system (Case 3) outperformed Case 1, Case 2, and the city-level district heating. With non-renovated buildings, the relative emissions reduction was 83% when the reference energy system was replaced with Case 3 and the emissions reduction cost was 3.74 €/kg.CO2/yr. The relative emissions reduction was 91% when the buildings were deep renovated and integrated with Case 3 when compared to the reference system with non-renovated buildings and the emission reduction cost was 11.9 €/kg.CO2/yr. Such district heating systems could help in meeting Europe’s emissions target for 2050.

An Air Pollutant Emission Reduction Path of China’s Power Industry

In China, as the major source of energy consumption and air pollutant emissions, the power industry is not only the principal force that bears the responsibility of national emission reduction targets but also a breakthrough that reflects the effectiveness of emission reduction. In this study, based on the integrated MARKAL-EFOM system (TIMES) model and scenario analysis method, a bottom-up energy system optimization model for the power industry was established, and four scenarios with different constraints were set up to predict and analyze the power demand and the energy consumption structure. Emission characteristics, emission reduction characteristics, and emission reduction cost of sulfur dioxide (SO2), nitrogen oxide (NOX), particulate matter 2.5 (PM2.5), and mercury (Hg) were quantitatively studied. Finally, for the environmentally friendly development and optimal adjustment of power production systems in China, the control path in the power industry that is conducive to the emission reduction of air pollutants was obtained, which is of great significance for the ultimate realization of climate friendliness. The results demonstrate that from 2020 to 2050, the power demand of the terminal departments will increase, with the composition significantly changed. The focus of power demand will change from industry to the service industry gradually. If no additional targeted emission reduction or adjustment policies are added in the power industry, the primary energy and air pollutant emissions will increase significantly, putting great pressure on resources and the environment. For the emission reduction of air pollutants, the promotion effect of emission reduction measures, such as the implementation and promotion of non-fossil fuels, is restricted. The power industry can introduce and maximize the best available technologies while optimizing the structure of energy consumption to realize efficient emission reduction of air pollutants and energy conservation. In 2030, emissions will reach peak values with reasonable emission reduction cost. This has the additional effect of abating energy consumption and preventing deterioration of the ecological environment, which is of profound significance for the ultimate realization of climate friendliness.

Carbon Emission Reduction Strategy for Energy Users in China

The Chinese government has made a commitment to control carbon emissions, and the deployment of renewable energy power generation is considered as an effective solution. In recent years, great effort has been exerted to support the development of renewable energy in China. While, due to fiscal pressures and changes in management policies, related subsidies are diminishing now and energy users are asked to pay for the cost. Regulations about carbon cap and renewable energy consumptions are issued to transfer the responsibility of consuming renewable energy and reducing carbon emissions to energy consumers. A national carbon trading system is set up in China and is under its growth stage. Therefore, this study lists the factors that should be considered by the energy users, analyzes the levelized cost of electricity generated by renewable energy in four cities in China, Beijing, Shanghai, Guangzhou, Wuhan, and compares the results with current carbon prices. Based on the research, under the current status, it is still more cost-efficient for enterprises to buy carbon credits than introduce renewable energies, and great differences among cities are shown due to different natural conditions. Besides, with diminishing subsidies and development of the carbon trading market, the carbon price will gradually reflect the actual value and carbon emission reduction costs will become an important part of enterprise expenditure. In the long term, enterprises should link more factors to carbon emissions, like social responsibility and brand image, instead of only the cost.

Day-Ahead Scheduling of Centralized Energy Storage System by Proposed Stochastic MINLP-Based Bi-Objective Optimization Approach

Recently, employing environmentally-friendly devices such as Energy Storage Systems (EESs) and Renewable Energy Resources (RERs) has been one of the remarkable ways to deal with the increasing trend of fossil fuel cost as well as environmental issues. Due to the stochastic nature of the RERs, especially wind farms and their effects on power system operation and planning, the ESS is used to alleviate output fluctuations of the renewable resources. The reduction of daily fuel cost is justified by the utilization of the ESS. In this research, the day-ahead scheduling of the ESS is concerned with reducing the fuel cost and the emission pollutants of thermal power plants considering load and wind speed uncertainties. The optimal day-ahead scheduling of the ESS has been obtained through using the proposed stochastic bi-objective optimization framework. Based on the proposed approach, the uncertainties are taken into account by the scenario-based decision-making technique as a time-efficient method. Pareto optimal solutions have been derived by the epsilon-constraint technique. Consequently, the fuzzy satisfying approach is employed to find the conservative decision based on the network planner’s perspective. The system under the study is IEEE 30 BUS system. In the presence of the uncertainties, it has been concluded that peak shifting and peak shaving can be achieved by the optimal scheduling of the ESS. Moreover, the ESS effects on the hourly electricity generation cost and the hourly emission pollutants have been discussed. Finally, the ESS has been used to simultaneous cost-emission reduction.

Profitable Decarbonization through E-Mobility

This paper focuses on the interdependent relationship of power generation, transportation and CO2 emissions to evaluate the impact of electric vehicle deployment on power generation and CO2 emissions. The value of this evaluation is in the employment of a large-scale, bottom-up, national energy modeling system that encompasses the complex relationships of producing, transforming, transmitting and supplying energy to meet the useful demand characteristics with great technological detail. One of such models employed in this analysis is the BUEMS model. The BUEMS model provides evidence of win-win policy options that lead to profitable decarbonization using Turkey’s data in BUEMS. Specifically, the result shows that a ban on diesel fueled vehicles reduces lifetime emissions as well as lifetime costs. Furthermore, model results highlight the cost-effective emission reduction potential of e-buses in urban transportation. More insights from the results indicate that the marginal cost of emission reduction through e-bus transportation is much lower than that through other policy measures such as carbon taxation in transport. This paper highlights the crucial role the electricity sector plays in the sustainability of e-mobility and the value of related policy prescriptions.

The Game Analysis of Low Carbon Supply Chain Emission Reduction Considering Channel Power under the Concern of Fairness

The emission reduction strategies of different channel power structures is studied under the fair, neutral and fair concerns of manufacturers, and compares the emission reduction levels, wholesale and retail prices, and the changes and differences in the profits of supply chain members under various circumstances. The research shows that the increase of emission reduction cost factor is not conducive to the improvement of emission reduction level, price and profit. The profit level of manufacturer under the manufacturer-led structure is not conducive to the manufacturer-led structure due to other structures, but is conducive to the improvement of the profit level of manufacturer under other structures. Manufacturer’s equity concern behaviour is beneficial to the improvement of manufacturer’s utility, in which the equity concern factor should be kept at a certain level under Nash vertical structure. Equity concerns and emission reduction strategies under decentralized decision-making are not conducive to the improvement of the overall supply chain effectiveness.

The low carbon development options for Russia

Russia is one of the largest carbon emitters in the world, possessing huge resources of both fossil fuels and zero-carbon energy sources. The Paris Agreement targets require substantial efforts to limit global warming to “well below 2 °C”. Energy-economic modeling provides sound conclusions that continuation of existing energy and climate policy will lead to stabilization of energy carbon emissions in Russia at the current level in 2010–2050 (about 30% below 1990). Stronger mitigation policies could gradually reduce domestic energy CO2 emissions by 61% from 2010 to 2050 (75% below 1990). Deep decarbonization policies with even more ambitious commitments could ensure an 83% reduction in energy CO2 emissions from 2010 levels (88% below 1990) by 2050. All key sectors (energy, industries, transport, and buildings) can play a substantial role in decarbonizing the national economy. However Russia’s historical reliance on domestic consumption and exports of fossil fuels creates strong barriers to decarbonization. Emission reduction costs are expected to be below 29 USD/tCO2 by 2030, 55 USD/tCO2 by 2040, and 82 USD/tCO2 by 2050 in the most ambitious decarbonization scenario. The results of this study provide insights into how Russia can enhance its ambitions to implement the Paris Agreement and contribute to global efforts toward building a climate-neutral economy by 2050.

Low-carbon development path research on China’s power industry based on synergistic emission reduction between CO2 and air pollutants

The compression of the industrialization process has forced China to confront the double pressure of greenhouse gas emissions and air pollution. This paper constructs an energy system optimization model for China’s power industry; establishes four energy consumption scenarios with different constraints; and forecasts and analyses the energy consumption structure, power consumption demand and production composition of China’s power industry from 2020 to 2050. Furthermore, based on synergistic effects, the emission characteristics, emission reduction potential and costs of CO2 and air pollutants are quantitatively analysed, and the obtained synergistic emission reduction effect and influencing factors are decomposed based on technical effect and structural effect. Finally, a low-carbon emission reduction path that can realize the synergistic control of CO2 and traditional air pollutants in China’s power industry is obtained. The results show that in the future, China’s power industry will continue to grow at a greater rate than primary energy consumption and the focus of power demand will gradually shift from industry to transportation and construction. The power industry can introduce and maximize the application of optimal control technologies while optimizing the energy consumption structure in order to realize synergistic emission reduction for CO2 and traditional air pollutants in China’s power industry. While saving energy, the corresponding cost of emission reduction will remain relatively low. After CO2 emissions peak in the power industry, the main way to reduce CO2 emissions will be to optimize the structure and upgrade the technology for CO2 self-governance. For the reduction of air pollutants, the promotion effect is limited only by the implementation and promotion of structural emission reduction measures focused on non-fossil energy.

Low carbon transition pathway of power sector with high penetration of renewable energy

The basic trend of low-carbon power sector transition is the expansion of non-fossil power, especially the power generation from renewable energy sources. With the higher penetration of renewable energy into the power system, the flexibility requirements and integration costs are important issues. The flexible generation of thermal power plants could serve as an effective solution to accommodating high share of variable renewable energy electricity. However, it brings about additional integration costs, which should be quantitatively assessed. In this paper, a long-term power generation expansion planning model incorporating integration costs for renewable energy penetration is proposed. This model is used to obtain the most cost-effective low carbon transition pathway of power sector with high penetration of renewable energy and analyze the impact of incorporating short-term integration costs on the long-term power generation planning. China is selected for a case study as it has the largest scale of thermal power plants in the world and urgent need for low carbon transition. The results indicate that thermal power plants gradually change from baseload providers to flexibility providers in the power system for higher penetration of renewable energy. The variable fuel consumption rate of thermal power plants should be taken into account otherwise the total carbon emissions and emission reduction cost would be underestimated.

ANALYSIS OF THE IMPACTS OF THE NDC SCENARIO ON ENERGY AND INDUSTRIAL STRUCTURE IN MAJOR COUNTRIES

The IAM model EMRICES was adopted to analyze the energy and industrial structure trends of the major countries in the world. In the aspect of energy consumption, the energy varieties are subdivided and a random shock model is introduced to depict the declining trend of energy intensity in different sectors. In the aspect of industrial structure, CGE model is used to describe the trend of economic growth. The NDC constraints would affect the total economic output and energy consumption of various industries according to the emission reduction cost function in EMRICES. The results show that the global temperature would be 2.61∘C by 2100 under NDC constraints, and it is still unable to achieve the target of 2∘C warming. The global carbon emission mitigation should be paid to more attention. In terms of energy consumption, the proportion of nonfossil energy and natural gas consumption will be greatly increased. The change of industrial competitive advantage represented by location quotient shows that China’s manufacturing competitiveness will decline, but its relative concentration and specialization level are still higher than the global average level. India’s manufacturing development will improve. In the financial sector, the United States would still be the leader.

Assessment of hybrid, firm renewable energy-based power plants: Application in the southernmost region of Thailand

The objective of this paper is to evaluate appropriate sites for Small Power Producers (SPP) hybrid, firm renewable energy-based power plants and their scenario suitability, focusing in the southernmost provinces of Thailand. The siting suitability of renewable SPP hybrid, firm power plants was assessed by employing the Analytical Hierarchy Process (AHP) in a Geographic Information System (GIS) environment. Para rubberwood distribution map, 1-km resolution Global Horizontal Irradiance (GHI) map, and high resolution (50 m) wind potential map are overlaid in possible regions for site selection. The inclusion of energy storage is also assessed in order to achieve the firm output of the optimized power plant, as per the requirement of the SPP policy. In total, 14 possible combinations of renewable SPP scenarios, ranging from 10 to 50 MW, were analyzed in order to identify an optimum scenario in terms of technical power potential, environmental suitability and socio-economic viability. The cost of each renewable SPP hybrid scenario was analyzed, as well as the annual energy production (AEP) for each scenario. The cost-benefit and the levelized cost of energy (LCOE) were analyzed using the Response Surface Methodology (RSM) in the ranking of all scenarios. Results show that the optimum scenario is a 40 MW solar PV power plant, complemented with a 10 MW biomass power plant and with a substantial energy storage system (ESS). This configuration has the highest generation capacity, at over 1,200 PWh/yr, the lowest LCOE, at 11.2 US cents/kWh, and avoiding CO2eq emissions of nearly 38 ktonnes per year. The methodology developed, based on a cost-benefit analysis, levelized cost of energy and greenhouse gas emission reductions, can also be applied in other jurisdictions characterized by the availability of biomass, solar and wind resources for electricity generation.

Assessing the costs of contributing to climate change targets in sub-Saharan Africa: The case of the Ghanaian electricity system

Ghana is one of the few countries within the sub-Saharan region which has been successful in reducing energy poverty. However, ensuring energy security, affordability, and environmental sustainability remains a significant challenge for the future development of the sub-region. Here, we examine how the electricity supply can evolve into the future to meet potential emission obligations for the period of 2020–2040. A generation expansion planning model which is able to incorporate the reality of fuel shortages and fuel switching typical of a developing country's power system is used. In doing so, we generate a range of emission reduction costs that provide important benchmarks for the relatively under-studied sub-Saharan region and identify drivers of these costs specific to developing countries. Results indicate that the total discounted cost in expanding generation to meet the demand for all scenarios range from 13–17 billion US$, while the expected emission ranges from 99–189 mtCO2. Subsequently, the cost of meeting different emission targets up to 2040 was quantified for each scenario ranging from 11–39 US$/tonne, which could be used as a benchmark for comparison in developed countries. We find that discount rates, representing Ghana's access to capital, are a particularly important variable for developing countries. We find that lower discount rates can lead to more investment in capital intensive renewable energy in the long run but can also lock in an additional conventional generation investment in the short term. Sensitivity analysis of demand growth reduction shows that with a 1% growth rate, the requirement of generation capacity could be reduced by 84%, providing initial evidence for the benefits of investing in demand-side measures. The study provides data and policy recommendations needed to inform decision-makers in developing countries as well as a comparison point for identifying decarbonization costs internationally.

Strategies for Capital Constrained Timber and Carbon Sink Supply Chain under the Cap-and-Trade Scheme

We consider a capital constrained timber and carbon sink supply chain under the cap-and-trade scheme, where the forest company produces timber and carbon sink. We consider two subsidy modes: financing subsidy to the carbon sink forests and financing subsidy to the manufacturer’s emission reductions. We apply a Stackelberg model and mainly consider the impact of subsidies on the profits and the strategies of the supply chain members. The results show that when the government gives a financing subsidy to the carbon sink forests, it is conducive to promoting the expansion of carbon sink forests, as well as the enhancement of the forest company’s profit. However, a larger supply of carbon sinks generates a lower price, which leads to the manufacturer reducing the technical emission reduction level and purchasing more carbon emission rights instead. On the other hand, when the manufacturer receives a financing subsidy for the technical emission reduction costs, its production becomes cleaner than before, and the profits of the forest company and the manufacturer increase.

Comparing negative emissions and high renewable scenarios for the European power system

Emerging literature highlights the essential role played by decarbonised electricity generation in future energy systems consistent with the Paris Climate Agreement. This analysis compares the impacts of high levels of renewable electricity and negative emissions technologies on exploratory visions of the future EU power system (2050) in terms of emissions reduction, technical operation and total system costs. The analysis shows that high renewable power system scenarios coupled with low levels of negative emissions technologies, such as biomass carbon capture and storage (< 2% of installed capacity), can deliver a net-negative European power system at lower comparable cost without breaching published sustainable biomass potentials in Europe (or requiring imports) or geological storage potentials while also contributing to power system inertia. Direct air capture has the capability to further decrease overall carbon emissions. While carbon capture and storage and power-to-gas must overcome market, regulatory and social acceptance challenges, given their potential benefits to emissions reduction, costs and system operation their role in a future power system should be further explored.

The Impact of Retailers’ Low-Carbon Investment on the Supply Chain under Carbon Tax and Carbon Trading Policies

In the current low-carbon economy, the government has adopted carbon taxes and carbon trading policies to control the carbon emissions of manufacturers. As consumers become increasingly aware of low-carbon, some retailers have also started investing in low-carbon to shape their public image and increase their competitiveness to attract more customers. In this paper, the Stackelberg game method is utilized to solve the model, and the graphs are used to analyze the benefits of retailers' low-carbon investment on the supply chain through numerical analysis. It is found that when the emission reduction cost coefficient of manufacturers is relatively low, manufacturers are willing to reduce carbon emissions. At this time, increasing carbon tax and the carbon emission permits price can effectively promote the emission reduction behavior of manufacturers, because it increases demand for products and the profit of manufacturers and retailers. However, when the emission reduction cost coefficient of the manufacturers is quite high, increasing carbon tax and carbon emission permits price cannot effectively promote the emission reduction behavior, because this situation of the emission reduction reduces the profit of manufacturers. The main contribution of this paper discovers that the green cost coefficient of retailers' low-carbon investment will adjust the impact of the carbon tax and the carbon trading price on the profits of retailers and manufacturers which proves that retailers’ low-carbon investment is beneficial to the supply chain. When the emission reduction cost coefficient is high and the green cost coefficient is low, increasing the carbon tax or carbon emission permits price can increase the profit of manufacturers and retailers. Finally, we design a supply chain coordination of comprehensive sharing contact for retailers and manufacturers. The result shows that this contract has economic and environmental benefits, and that it is beneficial for the environment and economy of sustainable development.

The Potential Contribution of Imported Biomass to Renewable Energy Targets in the EU–the Trade-off between Ambitious Greenhouse Gas Emission Reduction Targets and Cost Thresholds

Wood pellets could potentially contribute to bioenergy demand in the European Union (EU). Market cost constraints as well as greenhouse gas (GHG) emission savings thresholds imposed by the European Commission however limit the potential use of pellets. A spatially explicit assessment of import potentials of both pellets and torrefied pellets, based on the growing stock of forestry biomass in the US, Canada, Brazil, Russia and Baltic States, was combined with an analysis of supply chain costs and emissions in order to analyse potentials as limited by different levels of costs and emission constraints. Results show that in case of GHG savings thresholds of 70%, 80% and 85% the total import potential is reduced to 61 to 24 and 1 Mt, respectively. The potential for torrefied pellets is larger in all cases, 44 Mt in the case of an 80% limit. Import potentials at cost limits of 200, 175, 150 and 125 €/t are reduced from 58 Mt to 52, 38 and 9 Mt pellets, respectively, with little difference between pellets and torrefied pellets. This work shows that spatially explicit variation in feedstock availability and logistics has a significant impact on total import potentials and must therefore be included in any assessment of bioenergy potential and trade.

Cost-effective approaches for reducing carbon and air pollution emissions in the power industry in China

The power industry of China plays an important role in reducing the carbon dioxide (CO2) and air pollutant emissions. This paper focuses on synergistic CO2 and air pollution emission reduction by implementing technical and structural measures, and explores the processes aimed at achieving the co-benefits of carbon reduction and air pollution control effectively in the power industry at a local level. The results of the analysis show that the structural measures achieve overall co-benefits, and the technical measures have a good effect in reducing the air pollution, but simultaneously increase CO2 emissions because of the additional electricity used for running air pollution control devices (APCDs). Based on the analysis of the power generation incremental cost and pollutant emission reduction cost, cost-effective approaches to attain different emission reduction targets are proposed to the power industry in four case regions. These approaches can provide policy makers and stakeholders useful and relevant policy and operation recommendations to reduce CO2 and air pollution emissions cost-effectively and promote low carbon sustainability in the power industry of China.

On the feasibility of cropland and forest area expansions required to achieve long-term temperature targets

Biomass-based negative emission technologies (NETs) such as bioenergy with carbon capture and storage (BECCS) and afforestation/reforestation (AR) are regarded as important options to achieve the 2 °C and 1.5 °C targets stipulated in the Paris agreement, but the feasibility of their large-scale deployments remains very uncertain. This study focused on the speed of expansions of land-use area related to the biomass-based NETs and assessed the feasibility of climate change mitigation scenarios to achieve the temperature targets. Our model analysis shows that expansions at unprecedented speeds are required for total cropland area (including energy cropland) in Sub-Saharan Africa and for planted forest area for carbon sink in many regions in the next decades, under the assumption of global least-cost measures for CO2 emission reduction. On the other hand, when the speed of the land-use expansions is limited as observed in the real world, the CO2 emission reduction costs become unrealistically high around the middle of this century, particularly in scenarios for the 1.5 °C target; relatively low-cost measures such as BECCS in Sub-Saharan Africa and AR in many regions are limited in deployment due to the limited speed of the land-use expansion, and yet energy systems must be transformed to nearly net-zero/negative CO2 emissions for the 2 °C/1.5 °C target, which necessitates using other mitigation technologies of much higher costs. These results may cause concern over the feasibility of achieving the temperature targets, especially for the 1.5 °C target, and point to technical and scenario design aspects that will need further research for biomass-based NETs and their allowable expansion speed.