Performance evaluation of hybrid (wind/solar/diesel) power systems

Depleting oil and gas reserves, combined with the growing concerns of global warming, have made it inevitable to seek alternative/renewable energy sources. The integration of renewables such as solar and wind energy is becoming increasingly attractive and is being used widely, for substitution of oil-produced energy, and eventually to minimize atmospheric degradation. The literature shows that commercial/residential buildings in Saudi Arabia consume an estimated 10–40% of the total electric energy generated. In the present investigation, hourly wind-speed and solar radiation measurements made at the solar radiation and meteorological monitoring station, Dhahran (26°32′ N, 50°13′ E), Saudi Arabia, have been analyzed to investigate the feasibility of using hybrid (wind+solar+diesel) energy conversion systems at Dhahran to meet the energy needs of twenty 2-bedroom houses. The monthly average wind speeds for Dhahran range from 4.1 to 6.4 m/s. The monthly average daily values of solar radiation for Dhahran range from 3.6 kWh/m² to 7.96 kWh/m². The performance of hybrid systems consisting of different rated power wind farms, photovoltaic (PV) areas, and storage capacities together with a diesel back-up are presented. The monthly average daily energy generated from the above hybrid system configuration has been presented. The deficit energy generated from the back-up diesel generator and the number of operational hours of the diesel system to meet a specific annual electrical energy demand of 702,358 kWh have also been presented.     

Analytical model as a tool for the sizing of a hydrogen production system based on renewable energy: The Mexican Caribbean as a case of study

The main advantage of the hybrid system compared with separate array solar photovoltaic and stand-alone wind turbine is the possibility of the surplus energy storage by transforming it to hydrogen that can be use in fuel cells. However the design and sizing of this kind of technologies need to meet the local microclimate in order to reach higher efficacies. A tool based on an analytical model to sizing, analyze and assess the feasibility of the hybrid wind/photovoltaic/H₂ energy conversion systems using real weather data is presented in this work. The model considers an energy balance analysis and electrical variables of the system components; the tool calculates the subsystems efficacy and proposes the improvements to increase the efficiency of the use in surplus energy produced by the hybrid system. To validate the analytical model, simulation based on wind speed and solar radiation measurements from meteorological monitoring station in a Mexican Caribbean City is discussed.     

Wind characterization analysis incorporating genetic algorithm: A case study in Taiwan Strait

In this paper, the genetic algorithm (GA) is originally applied to compute the Weibull parameters for wind characterization analysis, in which an objective function required in GA for searching optimization solution has been first defined as well. Wind data analyzed are observed at a wind farm in the Taiwan Strait from 2006 to 2008. To accurately describe wind speed distribution three kinds of probability density functions are compared, i.e. the Weibull, logistic and lognormal functions. Statistical parameters including the max error in the Kolmogorov-Smirnov test, root mean square error, Chi-square error and relative error of wind power density are considered as judgment criterions. The results show that GA is a useful method, there is about 33% time saving when compared with conventional iteration method. Weibull function describes best the wind distribution, regardless of time periods. Accordingly, wind power density, availability factor and electrical energy output from an ideal turbine are assessed using the Weibull parameters; utilization rate of wind energy for the currently used turbine is discussed. Further the wind energy compensates very well with solar energy; when solar radiation is down in winter and spring, the wind power becomes greater; energy ratios for each month are calculated lastly.     

A wind–PV-battery hybrid power system at Sitakunda in Bangladesh

The measured wind data of Local Government Engineering Department (LGED) for 2006 at 30 m height shows a good prospect for wind energy extraction at the site. For a few months and hours the speed is below the cut in speeds of the available turbines in the market. The predicted solar radiation data from directly related measured cloud cover and sunshine duration data of Bangladesh Meteorological Department (BMD) for 1992–2003 indicates that a reliable power system can be developed over the year if the solar energy technology is merged with the wind energy technologies for this site. This research work has studied on optimization of a wind–photovoltaic-battery hybrid system and its performance for a typical community load. The assessment shows that least cost of energy (COE) is about USD 0.363/kWh for a community using 169 kWh/day with 61 kW peak and having minimum amount of access or unused energy. Moreover, compared to the existing fossil fuel-based electricity supply, such an environment friendly system can mitigate about 25 t CO₂/yr. The analysis also indicates that wind–PV-battery is economically viable as a replacement for conventional grid energy supply for a community at a minimum distance of about 17 km from grid.     

Assessing complementarity of wind and solar resources for energy production in Italy. A Monte Carlo approach

Wind and solar energy are expected to play a major role in the current decade to help Europe reaching the renewable energy penetration targets fixed by Directive 2009/28/EC. However, it is difficult to predict the actual production profiles of wind and solar energy as they depend heavily on variable meteorological features of solar radiation and wind speed. In an ideal system, wind and solar electricity are both injected in a fast reacting grid instantaneously matching supply and demand. In such a system wind and solar electricity production profiles should complement each other as much as possible in order to minimise the need of storage and additional capacity. In the present paper the complementarity of wind and solar resources is assessed for a test year in Italy.To achieve this goal we employ data at high spatial and temporal resolution data for both solar radiation and wind speed in Italy obtained from running two state of the art models (PVGIS and MINNI). Hourly profiles for solar and wind energy produced are compared in each 4 × 4 km² grid cell in Italy for 2005, and hourly, daily and monthly correlation coefficients are computed in order to assess the local complementarity of the two resources. A Monte Carlo approach is also developed to estimate how large-scale wind and solar energy productions could be potentially involved to complement each other in a scenario with up to 100 production sites across Italy. The results show how local complementarity can be very interesting with monthly correlation coefficients reaching values lower than −0.8 in several areas. Large-scale complementarity is also relevant with nation-wide monthly correlation coefficients showing values between −0.65 and −0.6. These model results indicate that in this sample year of 2005, wind and solar energy potential production have shown complementary time behaviour complementary, favourably supporting their integration in the energy system.     

Parametric study of hybrid (wind + solar + diesel) power generating systems

The combined utilization of renewables such as solar and wind energy is becoming increasingly attractive and is being widely used for substitution of oil-produced energy, and eventually to reduce air pollution. In the present investigation, hourly wind-speed and solar radiation measurements made at the solar radiation and meteorological monitoring station, Dhahran (26°32′N, 50°13′E), Saudi Arabia, have been analyzed to study the impact of key parameters such as photovoltaic (PV) array area, number of wind machines, and battery storage capacity on the operation of hybrid (wind + solar + diesel) energy conversion systems, while satisfying a specific annual load of 41,500 kWh. The monthly average wind speeds for Dhahran range from 4.1 to 6.4 m/s. The monthly average daily values of solar radiation for Dhahran range from 3.6 to 7.96 kWh/m². Parametric analysis indicates that with two 10 kW wind machines together with three days of battery storage and photovoltaic deployment of 30 m², the diesel back-up system has to provide about 23% of the load demand. However, with elimination of battery storage, about 48% of the load needs to be provided by diesel system.     

太阳能烟囱发电新技术

介绍了一种太阳能烟囱发电新技术。太阳光辐射透过太阳能集热棚，加热集热棚下面的地面，被加热的地面与集热棚内的空气进行热量交换，使其温度上升，被加热的空气上升并进入与集热棚中部相连的烟囱，在烟囱内上升气流推动涡轮发电机旋转、发电。整个太阳能烟囱发电技术的能量转化以及效率可以从三个部分来分析：通过集热棚太阳能转化为空气热能，通过烟囱将热能转化为动能，通过涡轮发电机将动能转化为电能。另外，总结了太阳能烟囱发电技术的优缺点，指出它是一种适合于我国西部地区的一种能源开发新途径。     

Wind energy potential assessment at four typical locations in Ethiopia

The wind energy potential at four different sites in Ethiopia – Addis Ababa (09:02N, 38:42E), Mekele (13:33N, 39:30E), Nazret (08:32N, 39:22E), and Debrezeit (8:44N, 39:02E) – has been investigated by compiling data from different sources and analyzing it using a software tool. The results relating to wind energy potential are given in terms of the monthly average wind speed, wind speed probability density function (PDF), wind speed cumulative density function (CDF), and wind speed duration curve (DC) for all four selected sites. In brief, for measurements taken at a height of 10 m, the results show that for three of the four locations the wind energy potential is reasonable, with average wind speeds of approximately 4 m/s. For the fourth site, the mean wind speed is less than 3 m/s. This study is the first stage in a longer project and will be followed by an analysis of solar energy potential and finally the design of a hybrid standalone electric energy supply system that includes a wind turbine, PV, diesel generator and battery.     

Investigation of the potential of wind–waves as a renewable energy resource: by the example of Cesme—Turkey

There are opinions claiming that 70% of the world energy consumption could be provided from renewable resources by the year 2050. These resources are needed, because fossil fuels both cause pollution of the environment and will be depleted in the near future. In this regard, the objective of this study was to determine the wave energy potential and the costs associated with its application to Turkish waters. To this goal, the wave energy potential in Cesme–Izmir was investigated. Cesme is known to have abundant wind, which plays the primary role in the formation of sea waves. For this purpose, the Solar Energy Institute of Ege University carried out wind velocity measurements within the period from 05.11.1998 to 05.11.1999 at an altitude of 10 m in Cesme. The measured values were regarded as if they were taken at an altitude of 19.5 m from seawater level. With this approach, the Pierson–Moskowitz wave energy spectrum was constructed. Through this wave energy spectrum, wave energy that is to be obtained at the measurement area within one year was determined. The variation of wave energy according to each month was evaluated. Hence, the unit cost of electricity to be produced by a turbine (with a width of 1 m), assumed to be installed at the area of measurements, was calculated.     

Solar balloons as mixed solar–wind power systems

Solar balloons, in which solar radiation is used to heat directly the air in a hot-air flying balloon, can be used as a mixed power system that exploits both solar radiation and high-altitude winds. If the balloon is heated at ground level and then released, the upward drift due to solar energy and the lateral drift due to wind can both be used to generate energy. At high altitude, the balloon is completely deflated (except for a small Helium-filled chamber, which prevents the balloon from falling) and pulled to the ground: the aerodynamical drag is now strongly reduced with respect to the ascent. A production cycle is simulated for balloons of different sizes and in different working conditions, assessing the feasibility of such a system, calculating the energy output and the solar/wind proportion of the produced energy. Simulation results show that such a system can produce energy with non-negligible solar-to-electricity efficiency (up to 5%). Moreover, while this is primarily a solar-based system, wind can yield a significant amount of additional energy for wind velocities greater than 15 m/s.     

Design of a new three-degree of freedom spherical motor for photovoltaic-tracking systems

Photovoltaic (PV) panels directly convert the solar energy to electrical energy. The amount of electrical energy converted by PV panels mainly depends on incident solar radiation. Sun tracking systems can be used to maximize energy production since they ensure keeping the photovoltaic panels perpendicular to the incoming solar radiation. Spherical motors, which have the linear and circular movement ability in three independent dimensions, can be used for precisely tracking the sun as a solution. In this study, a spherical motor controlled by a micro-controller is designed for a PV-tracking system with the ability to move on two axes. Performance of PV-tracking system over a fixed tilted one is evaluated for the climate condition of Denizli, Turkey. The designed sun tracking system is observed to be improving this performance apparently using the output voltages obtained for one day.     

Performance of unglazed solar ventilation air pre-heaters for broiler barns

Solar radiation is an interesting heat source for applications requiring a limited amount of energy, such as pre-heating cold fresh air used in venting livestock barns. The objective of this study was to evaluate the energy recovery efficiency of a solar air pre-heater consisting of an unglazed perforated black corrugated siding where the incoming fresh ventilation air picks up heat from its face and back. Installed on the southeast wall of two broiler barns located 40 km east of Montreal, Canada, the performance of solar air pre-heaters was monitored over 2 years. Sensors inside the barns monitored the temperature of the ambient air, that pre-heated by the solar collector and that exhausted by one of the three operating fans. An on-site weather station measured ambient air temperature, wind direction and velocity and radiation energy absorbed on a vertical plane parallel to the unglazed solar air pre-heaters. The measured vertical solar radiation value was used to evaluate the heat recovery efficiency of the unglazed solar air pre-heaters. Using data from the Varennes Environment Canada weather station located 30 km northwest, the solar sensors were found to measure the absorbed solar radiation with a maximum error of 7%, including differences in exterior air moisture. Unglazed, the efficiency of the solar air pre-heaters reached 65% for wind velocities under 2 m/s, but dropped below 25% for wind velocities exceeding 7 m/s. Nevertheless, the unglazed solar air pre-heaters were able to reduce the heating load especially in March of both years. Over a period starting in November and ending in March, the solar air heaters recovered an energy value equivalent to an annual return on investment of 4.7%.     

An investigation on wind power potential of Nurda ı-Gaziantep, Turkey

Turkey is one of the developing countries. The production of electricity in Turkey is basically focused on hydro-power and thermal-power. On the other hand, measurements show that Turkey has a reasonable wind potential but this potential was not being used for many years due to government policies which supported the use of petroleum, coal, and hydro power as energy sources. In recent years there is an increasing interest in using wind energy as one of the energy sources. This paper briefly introduces a study of the determination of wind power potential of Nurda ı/Gaziantep district where is on the south of Turkey for future wind power generation projects. Evaluation of wind data; taken by Turkish Electrical Power Resources Development Administration at the foot of the mountain, Nurda ı, shows that the district has a mean wind speed of 7.3 m/s at 10 m height and observed highest value wind speed is 23.3 m/s. Mean power density of the site is found as 222 W/m² and the results suggest that the site encourages investors especially since the terrain is a grassy plain on the side of the mountain and the measurements are taken at 10 m height.     

Analytical model for predicting the performance of photovoltaic array coupled with a wind turbine in a stand-alone renewable energy system based on hydrogen

We present the results of an analysis of the performance of a photovoltaic array that complement the power output of a wind turbine generator in a stand-alone renewable energy system based on hydrogen production for long-term energy storage. The procedure for estimating hourly solar radiation, for a clear sunny day, from the daily average solar insolation is also given. The photovoltaic array power output and its effective contribution to the load as well as to the energy storage have been determined by using the solar radiation usability concept. The excess and deficit of electrical energy produced from the renewable energy sources, with respect to the load, govern the effective energy management of the system and dictate the operation of an electrolyser and a fuel cell generator. This performance analysis is necessary to determine the effective contribution from the photovoltaic array and the wind turbine generator and their contribution to the load as well as for energy storage.     

New development in the theory of heat and mass transfer in solar stills

A single basin solar still with basin area of 0.98 × 0.98 m was constructed from galvanized iron sheets and an inclined glass cover. The still was provided with 525 W electrical heating tapes, fixed under the still basin for indoor steady state operation. The variation of basin temperature, glass temperature and evaporation rate were measured during both indoor and outdoor operation. The hourly variation of solar radiation, ambient temperature, and wind velocity were also taken during the outdoor measurements. Transient analysis of the still requires the evaluation of evaporative, convective and radiative heat transfer coefficients. The Dunkle model, which has been widely used for the prediction of the evaporative coefficient, was found to overpredict evaporation rates. The models developed in this work were found to provide better prediction for the evaporation rate measured in this work and in some previous works.     

V-trough concentrator on a photovoltaic full tracking system in a hot desert climate

A V-trough concentrator with a two-axis tracker system to increase the performance of photovoltaics was designed by the authors and installed on the roof-top of the building of the National Research Institute of Astronomy and Geophysics at Helwan in South Cairo. The V-trough concentrator system comprises two flat mirrors with dimensions 50 cm × 18 cm. They are fixed with the reflecting surfaces facing each other with a separation of about 11 cm, on a wooden table of 50 cm axis length. A sample of polycrystalline and amorphous silicon solar cells were fixed into the system, and similar solar cells of each type were fixed separate to the system, to estimate the electrical gain. The measurements were performed daily at different air masses for one complete year. The temperature of the solar cells in and out of the system were measured for comparison. Also, measurements for beam and global solar radiation and other meteorological conditions were recorded. The optical losses of the system were analyzed and details of collectable energy calculations are presented. The energy gain from the isolated contribution of the V-trough concentrators is also evaluated.     

Evaluation of distributed building thermal energy storage in conjunction with wind and solar electric power generation

Energy storage is often seen as necessary for the electric utility systems with large amounts of solar or wind power generation to compensate for the inability to schedule these facilities to match power demand. This study looks at the potential to use building thermal energy storage as a load shifting technology rather than traditional electric energy storage. Analyses are conducted using hourly electric load, temperature, wind speed, and solar radiation data for a 5-state central U.S. region in conjunction with simple computer simulations and economic models to evaluate the economic benefit of distributed building thermal energy storage (TES). The value of the TES is investigated as wind and solar power generation penetration increases. In addition, building side and smart grid enabled utility side storage management strategies are explored and compared. For a relative point of comparison, batteries are simulated and compared to TES. It is found that cooling TES value remains approximately constant as wind penetration increases, but generally decreases with increasing solar penetration. It is also clearly shown that the storage management strategy is vitally important to the economic value of TES; utility side operating methods perform with at least 75% greater value as compared to building side management strategies. In addition, TES compares fairly well against batteries, obtaining nearly 90% of the battery value in the base case; this result is significant considering TES can only impact building thermal loads, whereas batteries can impact any electrical load. Surprisingly, the value of energy storage does not increase substantially with increased wind and solar penetration and in some cases it decreases. This result is true for both TES and batteries and suggests that the tie between load shifting energy storage and renewable electric power generation may not be nearly as strong as typically thought.     

Performance of low temperature solar rankine power generation system

The overall performance of a solar thermal electrical power generation system is governed by the performance of the energy collection system and the power conversion unit. Any system operating under given meteorological and solar radiation conditions has a unique energy collection temperature for which the electrical output of the system will be a maximum. An engineering analysis of the system was carried out to obtain general correlations which can be used for determining such an optimum temperature. Factual experience on the design and operation of a Rankine system, using flat plate collectors and the climatological data, was used to obtain numerical estimates for the net energy conversion capability of such systems operating in Kuwait.     

Promoting applications of hybrid (wind+photovoltaic+diesel+battery) power systems in hot regions

Depleting oil and gas reserves, combined with growing concerns of atmospheric pollution/degradation, have made the search for energy from renewable sources of energy, such as solar and wind, inevitable. Literature indicates that commercial/residential buildings in Saudi Arabia consume an estimated 10–40% of the total electric energy generated. In the present study, hourly mean wind-speed and solar radiation data for the period 1986–1997 recorded at the solar radiation and meteorological monitoring station, Dhahran (26°32′ N, 50°13′ E), Saudi Arabia, have been analyzed to investigate the potential of utilizing hybrid (wind+solar) energy conversion systems to meet the load requirements of a typical commercial building (with annual electrical energy demand of 620 000 kWh). The monthly average wind speeds for Dhahran range from 4.1 to 6.4 m/s. The monthly average daily values of solar radiation for Dhahran range from 3.6 kWh/m² to 7.96 kWh/m². The hybrid systems considered in the present analysis consist of different combinations of commercial 10 kW wind energy conversion systems (WECS), photovoltaic (PV) panels supplemented with battery storage unit and diesel back-up. The study shows that with 30 10-kW WECS together with 150 m² PV, and 3 days of battery storage, the diesel back-up system has to provide 17% of the load demand. However, in the absence of battery storage, about 38% of the load needs to be provided by the diesel system.