氢能知识系列讲座(12)前景日益重要的氢能

一使用氢能是CO_2减排的最终方案2007年11月27日,联合国开发计划署(UNDP)在其发布的《2007～2008人类发展报告》中,以极其严厉的措辞警告气候变化会带来双重灾难:首先是贫困人口的发展倒退,接着是全人类长期遭受威     

High efficiency electric power generation: The environmental role

Electric power generation system development is reviewed with special attention to plant efficiency. It is generally understood that efficiency improvement that is consistent with high plant reliability and low cost of electricity is economically beneficial, but its effect upon reduction of all plant emissions without installation of additional environmental equipment, is less well appreciated. As CO₂ emission control is gaining increasing acceptance, efficiency improvement, as the only practical tool capable of reducing CO₂ emission from fossil fuel plant in the short term, has become a key concept for the choice of technology for new plant and upgrades of existing plant. Efficiency is also important for longer-term solutions of reducing CO₂ emission by carbon capture and sequestration (CCS); it is essential for the underlying plants to be highly efficient so as to mitigate the energy penalty of CCS technology application. Power generating options, including coal-fired Rankine cycle steam plants with advanced steam parameters, natural gas-fired gas turbine-steam, and coal gasification combined cycle plants are discussed and compared for their efficiency, cost and operational availability. Special attention is paid to the timeline of the various technologies for their development, demonstration and commercial availability for deployment.     

太阳能热发电的显热蓄热技术进展

介绍了太阳能热发电显热蓄热的3种技术:单一流体蓄热,直接接触蓄热和间接接触蓄热。单一流体蓄热,主要有导热油、熔融盐和蒸汽3种选择。直接接触蓄热,使用廉价材料作为蓄热介质,节约了成本。间接接触蓄热使模块化安装成为可能,进一步克服了直接接触蓄热的缺点,为蓄热技术发展提供了便利。     

Classical and minimum entropy generation analyses for steady state conduction with temperature dependent thermal conductivity and asymmetric thermal boundary conditions: Regular and functionally graded materials

Minimum entropy generation (MEG) temperature profiles are derived for steady conduction in a plane wall, a hollow cylinder and a hollow sphere and compared with the classical results. Cases of constant thermal conductivity, temperature dependent and location dependent thermal conductivities for each geometry are analyzed. Results are presented for the classical and the minimum entropy temperature profiles illustrating the effect of thermal asymmetry and variable thermal conductivity in each geometry. These results show that the difference between the classical and the MEG temperature profiles is largest when there is a strong thermal asymmetry. For all three geometries, the effect of temperature dependent thermal conductivity on the classical temperatures is moderate but its effect on the MEG temperatures is only small. Both the classical and minimum entropy generation rates, for each geometry, are found to be strong functions of thermal asymmetry and thermal conductivity variation parameter. Comparison of results for a hollow cylinder and a hollow sphere reveals that rate of entropy generation in a hollow sphere is much higher than in a hollow cylinder for the same thermal asymmetry and radius ratio.     

The environmental impact of decentralised generation in an overall system context

Decentralised-generation technologies are very likely to play an important role in our future energy supply. The operational behaviour of several decentralised-generation technologies, as well as their interaction with the central power system, are being discussed and reviewed. The outcome of this analysis is then used to make correct judgements on the global environmental performance of the concept of embedded generation. In order to assess the environmental impact of a massive installation of decentralised-generation units, simulations are being performed using the code PROMIX, a very accurate model of the generation units presently existing (and anticipating those planned in the future) in Belgium. Finally, the simulation results are being discussed and some important conclusions about the environmental impact of decentralised generation can be drawn.     

The value of solar: Prices and output from distributed photovoltaic generation in South Australia

The Australian government's Solar Cities Program sees great value in so-called “cost-reflective pricing”, code for valuing solar at pool prices. We test that proposition in South Australia where pool prices and insolation are often high and we show that there were few days in 2004 when the pool price gives better outcomes than if the solar is valued at the regulated and fixed, so-called standing contract price. We also find that the illustrative day used in the Solar Cities Program literature to promote the notion of cost-reflective pricing is highly atypical. Finally, we consider ways in which the incentive to install distributed photovoltaic generation might be improved.     

Does environmental regulation affect energy efficiency in China's thermal power generation? Empirical evidence from a slacks-based DEA model

Data envelopment analysis (DEA) has gained much popularity in performance measurement of power industry. This paper presents a slack-based measure approach to investigating the relationship between fossil fuel consumption and the environmental regulation of China's thermal power generation. We first calculate the total-factor energy efficiency without considering environmental constraints. An environmental performance indicator is proposed through decomposing the total-factor energy efficiency. The proposed approach is then employed to examine whether environmental regulation affects the energy efficiency of China's thermal power generation. We find that the environmental efficiency plays a significant role in affecting energy performance of China's thermal generation sector. Decreasing the discharge of major pollutants can improve both energy performance and environmental efficiency. Besides, we also have three main findings: (1) The energy efficiency and environmental efficiency were relatively low. (2) The energy and environmental efficiency scores show great variations among provinces. (3) Both energy efficiency and environmental efficiency are of obvious geographical characteristics. According to our findings, we suggest some policy implications.     

The vulnerability of hydroelectric generation in the Northeast of Brazil: The environmental and business risks for CHESF

The main objective of this study is to identify how global climate change may affect the internal and external variables of enterprises, and how strategic planning could include responses to potential performance threats. A case study was prepared using data from the São Francisco Hydroelectric Company (CHESF), the largest hydroelectric power generator in Brazil's Northeast region. It is essential to understand how the leading energy company in the region is preparing to address these problems involving economic impacts resulting from the environmental effects of climate change. Two prospective methodologies were used to select the variables and construct a SWOT matrix, and their respective scenarios: A Panel of Experts and the Delphi Method. The methodologies used allow for four (4) distinct scenarios to be inferred for CHESF up until 2050: Development, Growth, Survival and Decline. The analyses of these scenarios concluded that CHESF's main risk from climate change is the possible reduction of water flow and reservoir levels, which could threaten energy security throughout the country if certain preventative adaptations to climate change are not implemented.     

Effects of temperature dependent thermal conductivity on Nu number behavior in micro-tubes

The numerical modeling of the conjugate heat transfer and fluid flow through the micro-tube was presented in the paper. Three different fluids with temperature dependent fluid properties are considered: water and two dielectric fluids, HFE-7600 and FC-70. The diameter ratio of the micro-tube was D_i/D_o = 0.1/03 mm with a tube length L = 70 mm, geometry used in [D. Lelea, Nishio S., Takano K., The experimental research on microtube heat transfer and fluid flow of distilled water, International Journal of Heat and Mass Transfer 47 (2004) 2817–2830]. The laminar fluid flow regime is analyzed. Two different heat transfer conditions are considered: heating and cooling. The influence of the temperature dependent thermal conductivity on Nu number is analyzed for these two cases and compared with k = const.     

太阳能热发电储热材料研究进展

综述了太阳能热发电储热材料研究进展.分别介绍了浇注料、混凝土储热材料、液态显热储热、硝酸盐叠层相变储热、金属相变储热和氨热化学反应储热材料,分析了它们各自的优缺点,并展望了太阳能热发电储热材料的发展前景.     

The energy and environmental implications of UK more electric transition pathways: A whole systems perspective

Electricity generation contributes a large proportion of the total greenhouse gas emissions in the United Kingdom (UK), due to the predominant use of fossil fuel (coal and natural gas) inputs. Indeed, the various power sector technologies [fossil fuel plants with and without carbon capture and storage (CCS), nuclear power stations, and renewable energy technologies (available on a large and small {or domestic} scale)] all involve differing environmental impacts and other risks. Three transition pathways for a more electric future out to 2050 have therefore been evaluated in terms of their life-cycle energy and environmental performance within a broader sustainability framework. An integrated approach is used here to assess the impact of such pathways, employing both energy analysis and environmental life-cycle assessment (LCA), applied on a ‘whole systems’ basis: from ‘cradle-to-gate’. The present study highlights the significance of ‘upstream emissions’, in contrast to power plant operational or ‘stack’ emissions, and their (technological and policy) implications. Upstream environmental burdens arise from the need to expend energy resources in order to deliver, for example, fuel to a power station. They include the energy requirements for extraction, processing/refining, transport, and fabrication, as well as methane leakage that occurs in coal mining activities – a major cotribution – and from natural gas pipelines. The impact of upstream emissions on the carbon performance of various low carbon electricity generators [such as large-scale combined heat and power (CHP) plant and CCS] and the pathways distinguish the present findings from those of other UK analysts. It suggests that CCS is likely to deliver only a 70% reduction in carbon emissions on a whole system basis, in contrast to the normal presumption of a 90% reduction. Similar results applied to other power generators.     

Spectrally dependent photocurrent generation in aggregated MEH-PPV:PPDI donor–acceptor blends

Films of MEH-PPV and PPDI blends with weight ratio 1:2 have been prepared by spin-coating and annealing between 0 and 60 min at 95 °C. The films were characterized by absorption spectroscopy and atomic force microscopy (AFM). The main emphasis has been on the photon conversion efficiency in the photovoltaic cells as a function of excitation wavelength and applied voltage/electric field. Site selective excitation at wavelengths at which either non-aggregated bulk PPDI or dimers/aggregates of PPDI absorb prove that (i) the rate-limiting process for power conversion is the field-assisted escape of optically generated geminate electron–hole pairs from their mutual coulombic potential and (ii) the photogeneration yield depends on the donor–acceptor topology. A significant difference of the yield has been noted when alkoxy-pendent groups in MEH-PPV are replaced by phenyl-alkoxy groups.     

The effect of surface thermal radiation on entropy generation in an open cavity with natural convection

In this work, a numerical study on entropy generation in a square open cavity with natural convection and surface thermal radiation is presented. The overall continuity, momentum, and energy equations for the gas phase in the open cavity were solved numerically by means of the finite-volume method. Temperature-dependent fluid properties were considered. During the calculations, the values of the Rayleigh number (Ra) were set in the range of 10⁴–10⁶. The temperature difference between the hot wall and the bulk fluid (ΔT) was varied between 50 and 400 K, and was represented by a dimensionless temperature difference (φ) for the purpose of generalization of the present study. The results of this investigation indicate that surface thermal radiation increases the overall entropy generation rate between 33.52% and 560.87%, and thus cannot be neglected in the analysis of this type of system.     

Status of thermal power generation in India—Perspectives on capacity,generation and carbon dioxide emissions

India’s reliance on fossil-fuel based electricity generation has aggravated the problem of high carbon dioxide (CO₂) emissions from combustion of fossil fuels, primarily coal, in the country’s energy sector. The objective of this paper is to analyze thermal power generation in India for a four-year period and determine the net generation from thermal power stations and the total and specific CO₂ emissions. The installed generating capacity, net generation and CO₂ emissions figures for the plants have been compared and large generators, large emitters, fuel types and also plant vintage have been identified. Specific emissions and dates of commissioning of plants have been taken into account for assessing whether specific plants need to be modernized. The focus is to find out areas and stations which are contributing more to the total emissions from all thermal power generating stations in the country and identify the overall trends that are emerging.     

An economy-wide evaluation of new power generation in South Africa: The case of Medupi and Kusile

This paper investigates the role that the building of two new power stations, Medupi and Kusile, will play in facilitating future economic activity in South Africa. We use a dynamic computable general equilibrium (CGE) model to estimate the economy-wide effects of these new power stations. Our simulation results also provide insight into how much the local economy has lost due to inadequate electricity supply in the period leading up to the construction of Medupi and Kusile. We find that the decision to build additional power generation capacity was necessary and justified, and that the failure to sooner recognise the need for expansion of the country's electricity generation capacity and subsequent delays in commissioning Medupi and Kusile, likely cost the economy over R110bn in lost production. Additional analysis, in which a further two-year delay in the construction of Medupi and Kusile is simulated, shows that such an event will cause the economy to perform below baseline projections up to 2022.     

Solar thermal power generation in India: effect of potential incentives on unit cost of electricity

For large-scale dissemination of solar thermal power plants, in countries identified with huge potential, governments are offering various incentives. In an attempt towards studying the effectiveness of various incentives in reducing the levelised cost of electricity (LCOE) delivered by solar thermal power plants in India, this paper presents simple mathematical frameworks that facilitate the determination of the required level of an incentive so as to ensure that the LCOE is within a pre-specified limit. For example, for a 50?MW solar thermal power plant at Barmer (Rajasthan), LCOE of Rs. 9.75 per kWh can be achieved by providing 6.3% viability gap funding or an interest subsidy of 3% or provision of 32% investment tax credits to the equity investor or provision of production tax credits to the equity investor at the rate of Rs. 0.81 per kWh for first 10 years of operation of a plant.     

Less is more: Robust prediction for fueling processes on hydrogen refueling stations

The monitoring of hydrogen refueling stations (HRSs) ensures the safety of their operations as well as optimal fueling performance. For a H70-T40 dispenser, a fueling process is required to control the temperature to be below 85 °C; the pressure to be under 70 MPa; and the final state-of-charge (SOC) to be between 95% and 100%. Table-based or MC (total heat capacity) formula-based fueling protocols are traditionally used to achieve such control. In this paper, we propose using a machine learning model to predict the key parameters of fueling processes: the final SOC, the final temperature, and the final pressure in the vehicle tank. To handle outliers and noise in real operation, we adopt a two-stage method. In the first stage, after clustering fueling processes using soft dynamic time warping, a small number of fueling processes are selected from a large amount of historical data. In the second stage, based on initial and current operating conditions, the final SOC, temperature, and pressure of fueling processes are predicted using three models: least absolute shrinkage and selection operator (LASSO), Gaussian process regression (GPR), and robust regression. The experiments on real operational data collected from four hydrogen refueling stations show that the robust regression model achieves better performance than LASSO and GPR for three out of the four stations, and that the robust regression model captures the normal states of regular operation. The computational time of the robust regression model is also scalable for real-time operation. Our study provides a feasible machine learning model for predicting the key fueling parameters, which facilitates the optimization of HRS operation.     

Electrical power generation from ocean currents in the Straits of Florida: Some environmental considerations

Ocean currents contain a remarkable amount of kinetic energy and have potential worldwide capability. Initial tests to harness current power focus on the Straits of Florida where the Florida Current has a total flow capacity of about 30 × 10⁶ m³ s⁻¹. Generation of clean electricity from ocean currents off southeast Florida is based on a power extractor comprising open-center turbine technology. This innovative turbine provides safe passage for fish and other aquatic species. The water-column array of energy production units (EPUs) will have a 350 km² footprint, based on a 600 m (10 rotor diameters) downstream separation distance between EPUs with a lateral separation of 400 m. Water depths for the EPU field are in the range of 100–500 m. With such a large area of water column and benthic habitat utilized, environmental concerns must be overcome, including routing of transmission lines to shore. Risks and vulnerabilities of the proposed ocean current generated electricity include failure of individual EPUs and damage to sensitive coastal marine environments during installation.     

Barriers and strategies of hydrogen fuel cell power generation based on expert survey in South Korea

Recently, South Korea has become a pioneer in implementing hydrogen fuel cell energy production; however, sustainable development of hydrogen fuel cell as an energy source in South Korea remains limited. Hence, it is necessary to address these challenges that hinder such development. This study aims to identify the barriers to developing hydrogen fuel cell energy in South Korea and classify them. We used the combined qualitative methodology, which includes both expert Delphi surveys and Analytic Hierarchy Process techniques. Five factors were identified, each of which has three sub-factors derived for the Delphi survey. The results show that the most serious barriers are institutional and political factors; in addition, the cost of the unit and infrastructure of the fuel cell are significant barriers.