Maximising the light output of a Luminescent Solar Concentrator

Luminescent Solar Concentrators (LSC's) are currently being developed so that sunlight may be more fully utilised in place of conventional lighting sources. In order to optimise the light output of an LSC, various collector properties including fluorescent dye concentration, collector dimensions and matrix quality have been investigated. This study, involving measurement and computer modelling of the light transport in a single colour LSC, shows that luminous output is highly sensitive to weak extinction processes in the emission spectral band. These fine details in the loss spectrum play a key role in determining the output and efficiency of an LSC system. The separation of dye and matrix losses enables a quantitative study of the effect of matrix optical quality on performance.     

Performance investigation of a novel near-isothermal compressed air energy storage system with stable power output

As one of the grid-scale energy storage technologies, compressed air energy storage (CAES) is promising to facilitate the permeability of renewable energies. By integrating CAES into renewable sources, the fluctuation and intermittence of renewable energies could be effectively restrained. Among various CAES system configurations, isothermal CAES (I-CAES) is considered as a most competitive technology with expected high efficiency. However, most of the existing I-CAES systems have trouble in keeping a stable power output. To address this issue, a novel near-isothermal CAES system is proposed in this article to acquire a near stable power output. Imitating the concept of hydraulic accumulator, a two pressure vessels structure is employed to maintain the gas pressure stable during discharging. Besides, the turbine power output can be controlled by adjusting the liquid flow rate of the Pelton turbine under this near constant pressure condition. Based on the system transient model and economic model, the system components transient behavior, parametric analysis, off-design performance analysis and economic evaluation issues are also conducted. Results show that system round trip efficiency (RTE) with 61.42% and energy density (ED) with 0.2015 kWh/m³ can be achieved under design condition. In the discharge process, the gas pressure in vessel varies in a small range, from 68 to 72 bar, which is relatively stable. The power output from Pelton turbine can be maintained around 1 kW. Meanwhile, the initial pressure, the pipe diameter, and the spraying flow rates of circulating pumps have significant effects on system RTE and ED. Furthermore, the Pelton turbine power output level can be adjusted by adding jets number, and the higher storage pressure can make the power output unsteady.     

Maximising the working fluid flow as a way of increasing power output of geothermal power plant

This paper presents a method of increasing the power output of a geothermal power plant based on organic working fluid. The power is raised by increasing the flow of geothermal water supplied to the evaporator by means of returning the stream of geothermal water from downstream of the evaporator for a repeated passage through that heat exchanger. Such arrangement increases the flow of the working fluid in the circuit. Analyses have been conducted for a power plant using several types of organic fluids. The results obtained show that there is one optimum evaporation temperature of the working fluid, which depends on the quantity of the recycled geothermal water, at which the capacity of the Clausius–Rankine is the highest.     

空压机系统节能改造

介绍某铸造厂在空压机组节能改造方面的综合措施,通过变频控制和余热回收,降低了企业空压机系统的运行能耗,有利于提高其经济性。     

Improved photovoltaic energy output for cloudy conditions with a solar tracking system

This work describes measurements of the solar irradiance made during cloudy periods in order to improve the amount of solar energy captured during such periods. It is well-known that 2-axis tracking, in which solar modules are pointed at the sun, improves the overall capture of solar energy by a given area of modules by 30-50% versus modules with a fixed tilt. On sunny days the direct sunshine accounts for up to 90% of the total solar energy, with the other 10% from diffuse (scattered) solar energy. However, during overcast conditions nearly all of the solar irradiance is diffuse radiation that is isotropically-distributed over the whole sky. An analysis of our data shows that during overcast conditions, tilting a solar module or sensor away from the zenith reduces the irradiance relative to a horizontal configuration, in which the sensor or module is pointed toward the zenith (horizontal module tilt), and thus receives the highest amount of this isotropically-distributed sky radiation. This observation led to an improved tracking algorithm in which a solar array would track the sun during cloud-free periods using 2-axis tracking, when the solar disk is visible, but go to a horizontal configuration when the sky becomes overcast. During cloudy periods we show that a horizontal module orientation increases the solar energy capture by nearly 50% compared to 2-axis solar tracking during the same period. Improving the harvesting of solar energy on cloudy days is important to using solar energy on a daily basis for fueling fuel-cell electric vehicles or charging extended-range electric vehicles because it improves the energy capture on the days with the lowest hydrogen generation, which in turn reduces the system size and cost.     

An exergy analysis of a traditional compressed air energy storage system

压缩空气储能技术是具有较大发展前景的大规模储能技术之一,具有广阔的发展前景。使用Aspen Plus软件以传统压缩空气储能系统为例进行流程模拟,运用分析方法对模拟结果进行热力性能分析。分析结果表明,燃烧室的损失是系统各设备损失中最大的。同时还对压缩空气储能系统各个组成部件的运行效率与储能系统的损失之间的关系进行了敏感性分析,分析结果表明,对系统效率影响最大的参数为燃烧室效率,最小的参数为膨胀透平绝热效率。     

某铸造厂综合空调系统节能设计

从某铸造工厂综合空调系统的实际工程出发,在综合空调系统设计和控制系统设计的基础上,分别从自然冷却、冷冻水的能量能级利用、岗位空调技术、变频控制等方面论述该空调系统的节能措施。     

射流送风系统的能耗研究

射流送风能加强对工作区域的控制，提高空调舒适性和室内空气品质。文中对射流送风系统的能耗进行了实验研究，结果表明射流送风能有效地降低系统的总耗能。     

Technical principle of compressed air energy storage system

压缩空气储能被公认为是一种比较适合大规模系统的储能技术.本文对压缩空气储能的技术原理和发展现状进行了简要讲解,包括工作原理,工作过程,关键技术,发展现状,应用领域等.     

Net power and energy output of the German LWR nuclear power system

Net energy analysis is used to calculate the (annual) net energy output and the power and energy efficiencies of the German nuclear power system from the beginning of the construction program until 1982. For each individual power plant, actual construction time, start of operation and annual energy yield data are taken into account. The power expenditure data for construction, first core and reloading are taken from the literature on energy analysis, and the sensitivity of the results to the pertinent data uncertainties is shown. The problem of evaluation of thermal and electric forms of energy is also addressed. The results clearly show that an appreciable fraction of the power produced in the German nuclear power system is consumed within the nuclear industry, especially in the first period of expansion when small power plants are in operation and large ones under construction. This finding is contrary to what may be expected from the small payback time associated with individual power plants. However, nuclear power is not an energy sink. If the issue were to compare a nuclear power system with an alternative option such as an oil or coal-based technology, the same efficiency assessment would have to be carried out for the alternative system before a proper comparison can be made.     

空气调节二次回风系统的节能问题

讨论了二次回风系统在夏季工况下与一次回风系统相比的节能效果,以及在冬季工况如何更好降低能耗的问题,着重分析了冬季工况下机器露点对能耗的影响,并提出降低能耗的途径。     

Design, development and performance monitoring of a photovoltaic-thermal (PVT) air collector

The photovoltaic-thermal (PVT) systems allow the enhancement of the energy performance of photovoltaics, by removing thermal energy and subsequently decreasing the operating temperature of the cells. The possibility of the utilization of heat for climatization makes them attractive for the building integration. In order to diffuse this kind of solar systems it is necessary to translate the basic concepts into efficient and functional technological components and associated performance should be evaluated in a reliable manner. This paper presents the experimental and theoretical results of a research and development program carried out at the Politecnico di Milano on the design, development and performance monitoring of a hybrid PVT air collector. One of the main products of the research consists of a simulation model for performance prediction of the system. This R&D program led to the development of the TIS (tetto integrale solarizzato, i.e. integrated solar roof), an innovative technological system for building integration of hybrid PVT air collectors. The successful commercial application of the TIS in a research center building is also shown as a case study.     

基于液化空气储能的综合能源系统经济性分析

以园区为研究背景,基于"以热定电"、"以电定热"两种模式,对园区内的综合能源系统进行研究.针对夏季、冬季两个典型日设计了八种方案来对比系统配置液化空气储能与未配置液化空气储能时各子系统输出功率及总成本的变化.结果表明,在园区配置液化空气储能,采用"以热定电"模式运行时经济效益最高且能源损耗量最少.在大暑日,其总成本比未配置液化空气储能的系统降低6.1％.在大寒日,其总成本比未配置液化空气储能的系统总成本降低4.5％.同样配置液化空气储能的情况下,采用"以热定电"模式运行的系统要比"以电定热"模式总成本低.在大暑日总成本降低9.5％,在大寒日,总成本降低4.5％.     

Energy and exergy analysis of a micro-compressed air energy storage and air cycle heating and cooling system

Energy storage systems are becoming more important for load leveling, especially for widespread use of intermittent renewable energy. Compressed air energy storage (CAES) is a promising method for energy storage, but large scale CAES is dependent on suitable underground geology. Micro-CAES with man-made air vessels is a more adaptable solution for distributed future power networks. In this paper, energy and exergy analyses of a micro-CAES system are performed, and, to improve the efficiency of the system, some innovative ideas are introduced. The results show that a micro-CAES system could be a very effective system for distributed power networks as a combination that provides energy storage, generation with various heat sources, and an air-cycle heating and cooling system, with a energy density feasible for distributed energy storage and a good efficiency due to the multipurpose system. Especially, quasi-isothermal compression and expansion concepts result in the best exergy efficiencies.     

Fuzzy logic based energy saving technique for a central air conditioning system

In this paper a scheme has been proposed to maintain the temperature and the humidity, in each of the rooms served by a central Air Conditioner (AC) unit, close to the targeted values, and reduce the electrical energy intake of the AC compressor. The upper limits of the comfort zone, typically marked at a temperature of 25 °C and a relative humidity of 70%, are used as the targets. It should be noted that a conventional AC system controls humidity in its own way without giving the users any scope for changing the set point for the targeted humidity unlike the scope it offers to change the set point for the targeted temperature through a thermostat. But in this work this limitation has been taken into cognizance and overcome to a great extent using fuzzy logic to represent the intricate influences of temperature on the humidity of the space being cooled and correct the thermostat setting. In the developed scheme, the sensor captured temperature and humidity readings for each room are compared against the targets at the selected intervals of time, and the corresponding differences are fuzzified. These differences are used to decide the fuzzy qualifier, which is decoded into a crisp value that is the change required in the setting of the thermostat of the AC. As a result, each room will maintain a temperature near 25 °C and a relative humidity near 70% while the compressor will remain off for an appreciable period leading to a saving of energy. Though a thermostat with programmable setting for an AC unit dedicated to a single room has been reported in the literature, the same for a central AC unit that serves more than one room appears to have not yet been presented. The advantages of the scheme proposed for programming a thermostat under central air conditioning system are that it (i) requires for each room only a pair of input data i.e. the sensor captured temperature and humidity readings for each room, (ii) controls humidity indirectly and (iii) leads to a saving in energy consumption while maintaining a comfortable level of cooling in each of the rooms though their occupancy, size and the thermal conditions are different from one another.     

An analysis for the need of a battery energy storage system in tracking wind power schedule output

电池储能系统(battery energy storage system,BESS)在风储联合应用中具有多种功能,利用电池储能系统提高风电并网调度运行能力是当前研究的热点之一.文章基于我国北方某风电场历史运行数据与预测数据,依据预测误差评价指标和风电场预报考核指标的综合评价方法对风电场预测数据进行分析研究,归纳了预测误差的概率分布特征;提出利用电池储能系统提高风电跟踪计划出力能力,统计并量化出电池储能系统用于跟踪计划出力场合的作用范围;通过仿真验证电池储能系统在风储联合系统中提高风电跟踪计划出力控制策略的有效性和可行性.     

卷烟厂空调系统采用变风量运行的节能研究

根据卷烟厂空调系统定风量运行的缺点分析了其采用变风量运行的合理性。通过比较指出变频调速变风量运行是最为节能的运行方式,并以实例说明其经济可行性。     

The thermodynamic effect of thermal energy storage on compressed air energy storage system

With the increasing penetration of renewable energy into energy market, it is urgent to solve the problem of fluctuations of renewable energy sources (RES). Energy storage technology is regarded as one method to cope with the unstable nature of RES. One of these technologies is compressed air energy storage (CAES), which is a modification of the basic gas turbine technology. Electric power supplied by CAES can meet peak-load requirement of electric utility systems. Because there is heat waste in the existing CAES systems during compression process, fossil fuels are used to improve the expansion work to generate peak power. In order to avoid the use of fuels and keep high efficiency of system, CAES system with thermal energy storage (TES) is designed to capture and reuse the compressed air heat. This paper uses a thermodynamic model of a CAES system with TES to analyze the effect of TES on system efficiency. Besides, this paper evaluates the influence of temperature and pressure on the utilization of heat in TES. Results show that even when power efficiency reaches maximum, there is still a proportion of thermal energy left in TES for other use. Meanwhile, the utilization of heat in TES can be affected by pressure in the air storage chamber. With appropriate selection of pressure limits, the utilization of compressed air heat can be optimized.     

Detailed analysis of the energy yield of systems with covered sheet-and-tube PVT collectors

Solar cells have a typical efficiency in the range of 5-20%, implying that 80% or more of the incident solar energy can be harvested in the form of heat and applied for low-temperature heating. In a PVT collector one tries to collect this heat. In this work, the electrical and thermal yield of solar domestic hot water systems with one-cover sheet-and-tube PVT collectors were considered. Objectives of the work were to understand the mechanisms determining these yields, to investigate measures to improve these yields and to investigate the yield consequences if various solar cell technologies are being used. The work was carried out using numerical simulations.A detailed quantitative understanding of all loss mechanisms was obtained, especially of those being inherent to the use of PVT collectors instead of PV modules and conventional thermal collectors. The annual electrical efficiencies of the PVT systems investigated were up to 14% (relative) lower compared to pure PV systems and the annual thermal efficiencies up to 19% (relative) lower compared to pure thermal collector systems. The loss of electrical efficiency is mainly caused by the relatively high fluid temperature. The loss of thermal efficiency is caused both by the high emissivity of the absorber and the withdrawal of electrical energy. However, both the loss of electrical and thermal efficiency can be reduced further by the application of anti-reflective coatings. The thermal efficiency can be improved by the application of a low-emissivity coating on the absorber, however at the cost of a reduced electrical efficiency.     

空气压缩机供气系统的节能增效措施

该文通过对矿山空压机及供气系统存在的各种缺陷、浪费能源及常见多发性故障分析 ,比较系统全面地提出技术改进措施。对于减少设备故障、节约能源、降低生产成本、提高工作效率有实际意义