Two axis tracking system for solar concentrators

A two axis tracking system is described for the focussing of sunlight in paraboloid-type solar reflectors used in solar thermal devices like solar cookers. This system consists of wormgear drives and four bar type kinematic linkages for effortless and accurate focussing of reflectors at low cost.     

太阳能集能器自动跟踪装置

太阳能集能器自动跟踪装置是由传感器、方位角跟踪机构、高度角跟踪机构和自动控制装置组成。自动跟踪装置驱动太阳能集能器 ,使集能器的主光轴始终与太阳光线相平行。当太阳光线发生倾斜时 ,传感器输出倾斜信号 ,指示执行器动作调整太阳能集能器的角度 ,直到太阳能集能器对准太阳 ,实现自动跟踪太阳的目的。在阴天或太阳光辐照度低于工作照度时自动关机 ,太阳光辐照度达到工作照度时自动开机。该装置适用于聚光式太阳能集能器、太阳能电池等需要跟踪太阳的装置     

Synthesis of four bar linkages for solar tracking

A method is presented for the synthesis of four bar linkages to provide adequate tracking of solar collectors. The design procedure starts with the selection of a number of accuracy points on the altitude vs hour function to yield a first form of a four bar linkage. An optimization algorithm inproves on the original design for minimum error and optimum structural characteristics. Based on the method, mechanisms were design for a certain locality with negligible tracking error, acceptable even for focusing collectors. This design procedure can yield inexpensive, yet accurate enough tracking with very simple seasonal adjustment.     

太阳能跟踪装置风载荷的计算方法

风载荷是跟踪装置所承受的主要载荷,其大小直接影响整个系统的结构强度以及装置传动部件的选择。太阳能跟踪装置的常规形式属于非流线的可旋转平板结构,其风载荷主要与风力系数相关。文章详细分析了跟踪装置的风载荷,比较了3种不同风力系数的计算方法,结果表明:三维CFD数值计算方法与系统的实际试验结果更加吻合。     

Discrete two-positional tracking of solar collectors

Northern European regions, such as Estonia at 60° latitude, receive about 980 kWh m⁻² y⁻¹ of solar radiation. These low insolation levels motivate solar collectors to be equipped with a tracking mechanism for an increased yield. Classical active tracking is complicated and energy intensive, negating tracking benefits for PV modules and thermal flat-plate collectors. This paper describes mainly the performance of PV modules with daily two-positional tracking. The symmetrical and asymmetrical positions about the north–south axis are analyzed, corresponding to the positions of sun in the morning and in the afternoon. The tracking drive is simple and requires a minimum energy input during the brief daily triggering of movement. Results indicate that the seasonal energy yield is increased by 10–20% over the yield from a fixed south-facing collector tilted at an optimal angle. The results are based on long-term solar data measured at the Tartu-Tõravere Meteorological Station in Estonia, confirmed by experimental testing during summer 2004 and 2005 in Tallinn University of Technology.     

Different strategies for operation of flat-plate solar collectors

Three strategies for solar collector operation are defined. These involve keeping one of the following constant during the day:

1. (i) the average working fluid temperature,

2. (ii) the outlet temperature and

3. (iii) the inlet temperature.

A graphical and analytical method previously developed by the authors was generalized to analyse and compare these strategies. For a constant flow rate, the best strategy is to maintain a constant inlet temperature. A constant outlet temperature is recommended when flow-rate control is possible.     

Maximum-power-point tracking control of solar heating system

The present study developed a maximum-power point tracking control (MPPT) technology for solar heating system to minimize the pumping power consumption at an optimal heat collection. The net solar energy gain Q_net (=Q_s ? W_p/η_e) was experimentally found to be the cost function for MPPT with maximum point. The feedback tracking control system was developed to track the optimal Q_net (denoted Q_max). A tracking filter which was derived from the thermal analytical model of the solar heating system was used to determine the instantaneous tracking target Q_max(t). The system transfer-function model of solar heating system was also derived experimentally using a step response test and used in the design of tracking feedback control system. The PI controller was designed for a tracking target Q_max(t) with a quadratic time function. The MPPT control system was implemented using a microprocessor-based controller and the test results show good tracking performance with small tracking errors. It is seen that the average mass flow rate for the specific test periods in five different days is between 18.1 and 22.9 kg/min with average pumping power between 77 and 140 W, which is greatly reduced as compared to the standard flow rate at 31 kg/min and pumping power 450 W which is based on the flow rate 0.02 kg/s m² defined in the ANSI/ASHRAE 93-1986 Standard and the total collector area 25.9 m². The average net solar heat collected Q_net is between 8.62 and 14.1 kW depending on weather condition. The MPPT control of solar heating system has been verified to be able to minimize the pumping energy consumption with optimal solar heat collection.     

Simple nonlinear solar irradiation estimation model

A simple nonlinear model with three parameters is proposed for global solar irradiation estimation from sunshine duration ratio measurements. Two of the parameters have almost the same interpretations for extreme weather conditions as in the classical Angström model but the third parameter appears as the power of the sunshine duration ratio. This model reduces to the classical Angström equation when power is equal to one. It contains the possible nonlinear effects in solar irradiation and sunshine duration relationship as a first-order mathematical approximation to the linear Angström equation. Power values different than one imply nonlinear models. The model parameter estimates are achieved through the nonlinear least-squares analysis. The application of the methodology is performed for eight irradiation measurement stations in Turkey.     

太阳能电池自动实时逐日系统设计

采用非易失实时时钟芯片DS12C887配合SPA算法,精确获取所在地实时太阳方位;单片机根据光功率评估电池方位驱动后所获电能及驱动耗电,优化驱动的时间间隔;不驱动时,系统掉电。该方案具有断电重启方便,实时跟踪,太阳能电池效能高的优势,具有一定的应用价值。     

A novel prediction algorithm for solar angles using solar radiation and Differential Evolution for dual-axis sun tracking purposes

This paper deals with a dual-axis sun tracking system for a photovoltaic system. Its trajectories are determined by an optimization procedure. The optimization goal is the maximization of the electrical energy production within a photovoltaic system, by considering the tracking system consumption. The procedure used for determining the tilt angle and azimuth angle trajectories is described as a nonlinear and bounded optimization problem. Since an explicit form of the objective function is unavailable, a stochastic search algorithm called Differential Evolution is applied as the optimization tool. In order to evaluate the objective function, models for calculating the available solar radiation and tracking system consumption are applied together with the efficiencies of solar cells, a DC/DC converter and inverter. A new algorithm is introduced for the time dependent prediction of available solar radiation. It is based on the length of a sunbeam’s path through the atmosphere and the statistical data of a pyranometer measured total and diffuse solar radiation at a given location on the Earth. The optimization bounds are given in the form of angular speed, lower and upper bounds for both angles and angle quantization. The results presented in this paper show, that the optimal trajectories can help to increase the electrical energy production within photovoltaic systems by sun tracking.     

Simple thermal decomposition reactions for storage of solar thermal energy

Simple thermal decomposition reactions have been investigated for the purpose of solar thermal energy storage. Ten criteria regarding the thermodynamics and kinetics of the reaction and the physical properties of the components of the reaction have been established. One particular reaction, the decomposition of ammonium hydrogen sulfate, has been evaluated in a preliminary manner and appears to satisfy all of the established criteria. The efficiency of storage is high and the decomposition occurs in the vicinity of 500°C. Other compounds such as ammonium halides, alkali and alkaline earth metal hydroxides, carbonates, sulfates and oxides have also been examined.     

Adaptive neuro-fuzzy inference system-based maximum power point tracking of solar PV modules for fast varying solar radiations

This paper analyses the operation of an adaptive neuro-fuzzy inference system (ANFIS)-based maximum power point tracking (MPPT) for solar photovoltaic (SPV) energy generation system. The MPPT works on the principle of adjusting the voltage of the SPV modules by changing the duty ratio of the boost converter. The duty ratio of the boost converter is calculated for a given solar irradiance and temperature condition by a closed-loop control scheme. The ANFIS is trained to generate maximum power corresponding to the given solar irradiance level and temperature. The response of the ANFIS-based control system is highly precise and offers an extremely fast response. The response time is seen as nearly 1 ms for fast varying cell temperature and 6 ms for fast varying solar irradiance. The simulation is done for fast-changing solar irradiance and temperature conditions. The response of the proposed controller is also presented.     

主动式双轴太阳跟踪控制器

简要分析了太阳运动的基本规律,对主动式和被动式太阳跟踪方式进行了分析,在此基础之上,设计了一套主动式双轴太阳跟踪控制器.在西藏羊八井国家可再生能源实验基地的实地运行中,此太阳跟踪控制器表现出了良好的性能,与固定式光伏发电系统相比,发电量提高30%以上.     

Probabilistic modelling of hybrid solar/wind power system with solar tracking system

This paper presents a probabilistic model applied to a hybrid solar-wind power system (HSWPS), which is equipped with either a one-axis or a two-axis solar tracking system.Within the framework of a case study, the potential of the developed probabilistic approach is presented, and the effect of the solar tracking systems on the annual energy gain is discussed.Specifically, the impact of a tracking system on the probability density function (PDF) of the power produced by a photovoltaic system (PVS) is evaluated through the first four moments (mean, variance, skewness and kurtosis) of a PDF.Finally, to estimate the impact of a tracking system on HSWPS energy performance, a reliability analysis is performed using the energy index of reliability (EIR), which is directly related to energy expected not supplied (EENS), given different annual load scenarios.     

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 experimental comparison of operating strategies for solar water systems

Three identical DHW (Domestic Hot Water) solar energy systems are experimentally compared in terms of the amount of energy collected during two extended periods. The goal of the experiment is to compare three different modes of operating the systems: (1) a single-pass mode, in which the circulating fluid passes once and only once through the collector; (2) a conventional forced circulation multipass mode, in which storage contents passes many times through the collector during each day, and (3) a thermosyphon mode.It is shown that the single-pass system performs better than the other two, with the multipass system being the worst. The thermal advantage of the single-pass mode is specially significant on days with poor radiation and can be as high as 16%, in comparison with the multipass system, being on the average 7% better. The thermosyphon system is shown to perform slightly better than the multipass, although the 1.4% difference found is within the experimental errors.     

The realization of a simple solar tracking concentrator for university research applications

A tracking parabolic concentrator was built from easily available and affordable components. Simplicity and ease of assembly were prime considerations. Considerable experience was gained in the design, assembly and testing. The system performed reasonably well considering its simplicity and rapid assembly. As an educational tool, demonstrating both energy conversion and control, or for simple high temperature experiments and applications, any university could easily set up a similar working concentrator at a very low cost.     

Design factors of sensors for the optical tracking systems of solar concentrators

Basic diagrams for the sensors of the optical tracking systems of solar concentrators are considered, the design factors that determine their accuracy are analyzed, a new sensor design is suggested, and its optimal parameters are determined.