Performance of a solar ejector cooling-system in the southern region of Turkey

Performance variations of a solar-powered ejector cooling-system (SECS) using an evacuated-tube collector are presented for Antalya, Aydin, Konya and Urfa cities located in the southern region of Turkey by means of hourly and monthly average ambient temperature and solar radiation meteorological data. A SECS, based on a constant-area ejector flow model and using R-123, was considered. The cooling season and period were taken into account for the 6 months (May–October) and the hours 8:00–17:00, respectively. It was found that the evacuated-tube collector efficiency depending upon the ambient temperature and solar radiation within the day was remarkably varied. However, for all the cities, the cooling capacities of the SECS were very similar. When generator, condenser, and evaporator temperatures were taken, namely, 85 °C, 30 °C and 12 °C, the maximum overall coefficient of performance and the cooling capacity were obtained as 0.197 and 178.26 W/m², respectively, at 12:00 in August for Aydin. The evacuated-tube collector area per ton cooling was found to be around 21 m² at noontime in August for all the cities. Furthermore, at the off-design conditions, a performance map of the system was derived and discussed. It was determined that the SECS could be used for office-cooling purposes during the hours (8:00–15:00) in the southern region of Turkey.     

Short–mid-term solar power prediction by using artificial neural networks

Solar irradiation is one of the major renewable energy sources and technologies related with this source have reached to high level applications. Prediction of solar irradiation shows some uncertainties depending on atmospheric parameters such as temperature, cloud amount, dust and relative humidity. These conditions add new uncertainties to the prediction of this astronomical parameter. In this case, prediction of generated electricity by photovoltaic or other solar technologies could be better than directly solar irradiation.In this paper, firstly, Artificial Neural Networks (ANNs) methodology is applied to data obtained from a 750 W power capacity of solar PV panel. The main objective of this paper is to determine time horizon having the highest representative for generated electricity prediction of small scale solar power system applications. It is seen that 5 min time horizon gives the best solar power prediction for short term and 35 min could be used for medium terms in April. In addition, these time horizons have increased to 3 and 40 min for very short time and medium time prediction respectively during August. During April and August Root Mean Square Errors (RMSEs) between measured and testing values changed between 33–55 W and 37–63 W ranges respectively. Especially, during August for solar irradiation, stationary conditions are observed and these situations let ANN predict easily generated electricity from 30 to 300 min ahead.     

Assessment of forecasting techniques for solar power production with no exogenous inputs

We evaluate and compare several forecasting techniques using no exogenous inputs for predicting the solar power output of a 1 MWp, single-axis tracking, photovoltaic power plant operating in Merced, California. The production data used in this work corresponds to hourly averaged power collected from November 2009 to August 2011. Data prior to January 2011 is used to train the several forecasting models for the 1 and 2 h-ahead hourly averaged power output. The methods studied in this work are: Persistent model, Auto-Regressive Integrated Moving Average (ARIMA), k-Nearest-Neighbors (kNNs), Artificial Neural Networks (ANNs), and ANNs optimized by Genetic Algorithms (GAs/ANN). The accuracy of the models is determined by computing error statistics such as mean absolute error (MAE), mean bias error (MBE), and the coefficient of correlation (R²) for the differences between the forecasted values and the measured values for the period from January to August of 2011. This work also addresses the accuracy of the different methods as a function of the variability of the power output, which depends strongly on seasonal conditions. The findings show that the ANN-based forecasting models perform better than the other forecasting techniques, that substantial improvements can be achieved with a GA optimization of the ANN parameters, and that the accuracy of all models depends strongly on seasonal characteristics of solar variability.     

Consequences of a carbon tax on household electricity use and cost,carbon emissions,and economics of household solar and wind

The study was conducted to determine the consequences of a carbon tax, equal to an estimated social cost of carbon of $37.2/Mg, on household electricity cost, and to determine if a carbon tax would be sufficient to incentivize households to install either a grid-tied solar or wind system. U.S. Department of Energy hourly residential profiles for five locations, 20 years of hourly weather data, prevailing electricity pricing rate schedules, and purchase prices and solar panel and wind turbine power output response functions, were used to address the objectives. Two commercially available household solar panels (4 kW, 12 kW), two wind turbines (6 kW, 12 kW), and two price rate structures (traditional meter, smart meter) were considered. Averaged across the five households, the carbon tax is expected to reduce annual consumption by 4.4% (552 kWh/year) for traditional meter households and by 4.9% (611 kWh/year) for households charged smart meter rates. The carbon tax increases electricity cost by 19% ($202/year). For a household cost of $202/year the carbon tax is expected to reduce social costs by $11. Annual carbon tax collections of $234/household are expected. Adding the carbon tax was found to be insufficient to incentivize households to install either a solar panel or wind turbine system. Installation of a 4 kW solar system would increase the annual cost by $1546 (247%) and decrease CO₂ emissions by 38% (2526 kg) valued at $94/household. The consequence of a carbon tax would depend largely on how the proceeds of the tax are used.     

Testing and modelling of a variable speed scroll compressor

Variable speed compressors offer continuous control, low noise level, reduced vibration, low-start current, rapid temperature control, by operating the compressor at higher speeds initially, and better COPs than the conventional on/off control. However, there exist some drawbacks concerning the inverter efficiency, the effect of the inverter on the induction motor and the effect of variable speed on the compressor isentropic and volumetric efficiencies. This study gives some experimental results as to inverter and compressor performances: it can be observed that the inverter efficiency varies between 95% and 98% for compressor electrical power varying between 1.5 and 6.5 kW ; and that compressor efficiencies are not enormously influenced by compressor supply frequency, but depend mainly on compressor pressure ratio, except the tests developed at 35 Hz and one test at 40 Hz, for which the difference is attributed to the compressor internal leakages due to a lack of lubrication at low speeds. At 75 Hz there was also observed a slight degradation that can be attributed to the electromechanical losses that increase with compressor speed. A maximal isentropic efficiency of 0.65 for a pressure ratio of the order of 2.2 is obtained. The volumetric efficiency decreases linearly from 0.98 for a pressure ratio of 1.5 to 0.83 for a pressure ratio of 5.6. In spite of the test conditions (condensing and evaporating pressures up to 40 and 20 bar, respectively), the compressor performance stays unchanged. The experimental results obtained at 50 Hz are used to identify six parameters of a semi-empirical model which is then used to simulate the different tests developed at different compressor speeds. The simulated results are in very good agreement with those measured with averages errors of ?0.5 K; +3 g s^?1 and ?24 W for the exhaust temperature, the refrigerant flow rate and the compressor electrical power, respectively. The results show that motor losses induced by the inverter are negligible.     

Evaluation of optimal power options for base transceiver stations of Mobile Telephone Networks Cameroon

Photovoltaic hybrid systems (PVHS) with 2 days of energy autonomy are shown to be optimal options for the supply of the daily energy demands of 33 base transceiver stations of MTN Cameroon. PVHS were computed for all sites using the technical data for a 150 Wp mono-crystalline module, the site specific hourly load data, the average monthly solar radiation and temperature. Hourly solar radiation data for all sites were downloaded using the solar resource module of HOMER and geographical coordinates of the selected sites. The 3-hourly temperature data available on a website maintained NASA was used to generate average monthly hourly temperatures needed in the calculation of the output of solar modules. The energy costs and breakeven grid distances for possible power options were computed using the Net Present Value Technique and financial data for selected power system components. The results with a PV module cost of 7.5 €/Wp, a remote diesel price of 1.12 €/l, a general inflation rate of 5% and a fuel escalation of 10% showed that the annual operational times of the diesel generator were in the range 3–356 h/year with renewable energy fractions in the range 0.89–1.00. However, only 22 PVHS had two parallel battery strings as stipulated in the request for proposal launched by MTN Cameroon in 2008. The PV array sizes evaluated for the 22 PVHS were found to be the range 2.4–10.8 kWp corresponding to daily energy demands in the range 7.31–31.79 kW h/d. The energy costs and breakeven grid distances determined were in the ranges 0.81–1.32 €/kW h and 10.75–32.00 km respectively.     

Characterization of a scroll compressor under extended operating conditions

Refrigeration and air-conditioning compressors are designed to work under well-defined conditions. In some applications it is interesting to observe their performances beyond these conditions, for example in the case of a high temperature two-stage heat pump or of a cooling system working at high temperature.In this study a compressor is characterized experimentally with refrigerant R134a and through 118 tests at condensing pressures varying from 8.6 up to 40.4 bar (t_sat = 33.9 °C to t_sat = 100.8 °C) and evaporating pressures varying from 1.6 up to 17.8 bar (t_sat = ?15.6 °C to t_sat = 62.4 °C). Under these conditions the compressor motor was pushed at its maximal current in several tests.This compressor’s performance is mainly characterized by its isentropic and volumetric efficiencies. It presents a maximal isentropic efficiency of 72%, corresponding to a pressure ratio of around 2.5–2.6. The volumetric efficiency decreases linearly from almost 1.0 (for a pressure ratio of 1.3) to 0.83 (for a pressure ratio of 9.7). A slight degradation of the isentropic and volumetric efficiencies is observed when the compressor supply and exhaust pressures are increased for a given pressure ratio; this could be due to an internal leakage.The compressor tests are used to identify the six parameters of a semi-empirical simulation model. After parameter identification, experimental and simulated results are in very good agreement, except for some points at high compressor power where the compressor is pushed at its maximal current.     

Modelling and experimental verification of the operating current of mono-crystalline photovoltaic modules using four- and five-parameter models

This article presents the modelling and experimental verification of the operating current of a 120 W of mono-crystalline photovoltaic module using four- and five-parameter analytical models. The southern part of Turkey, where the experimental system is mounted, is particularly well suited to photovoltaic installations. The operating current of the photovoltaic module, calculated from the models, is validated based on a series of experimental measurements. As well as the current and voltage of the photovoltaic module, the environmental variables such as ambient temperature and solar irradiance were measured and used for validation of the operating current. The photovoltaic cell models considered in this article are drawn from the equivalent electrical circuit that includes light-generated current, diode reverse saturation current, and series and shunt resistances. The simplified four-parameter model assumes the shunt resistance as infinite and thus neglects it. After determining the model parameters, the operating current is calculated using both models and compared to the measured current produced by the photovoltaic module. It is shown that the complete five-parameter model predicts the operating current better than the simplified four-parameter model, especially around solar noon, when most of the power is produced.     

Economic analysis of power generation from floating solar chimney power plant

Solar chimney thermal power technology that has a long life span is a promising large-scale solar power generating technology. This paper performs economic analysis of power generation from floating solar chimney power plant (FSCPP) by analyzing cash flows during the whole service period of a 100 MW plant. Cash flows are influenced by many factors including investment, operation and maintenance cost, life span, payback period, inflation rate, minimum attractive rate of return, non-returnable subsidy rate, interest rate of loans, sale price of electricity, income tax rate and whether additional revenue generated by carbon credits is included or not. Financial incentives and additional revenue generated by carbon credits can accelerate the development of the FSCPP. Sensitivity analysis to examine the effects of the factors on cash flows of a 100 MW FSCPP is performed in detail. The results show that the minimum price for obtaining minimum attractive rate of return (MARR) of 8% reaches 0.83 yuan (kWh)^?1 under financial incentives including loans at a low interest rate of 2% and free income tax. Comparisons of economics of the FSCPP and reinforced concrete solar chimney power plant or solar photovoltaic plant are also performed by analyzing their cash flows. It is concluded that FSCPP is in reality more economical than reinforced concrete solar chimney power plant (RCSCPP) or solar photovoltaic plant (SPVP) with the same power capacity.     

Viability of solar photovoltaics as an electricity generation source for Jordan

Viability of solar photovoltaics as an electricity generation source for Jordan was assessed utilizing a proposed 5 MW grid-connected solar photovoltaic power plant. Long-term (1994–2003) monthly average daily global solar radiation and sunshine duration data for 24 locations – distributed all over the country – were studied and analyzed to assess the distribution of radiation and sunshine duration over Jordan, and formed an input data for evaluation and analysis of the proposed plant's electricity production and economic feasibility. It was found that – depending on the geographical location – the global solar radiation on horizontal surface varied between 1.51 and 2.46 MWh/m²/year with an overall mean value of 2.01 MWh/m²/year for Jordan. The sunshine duration was found to vary – according to the location – between 8.47 and 9.68 h/day, with a mean value of 9.07 h/day and about 3311 sunshine hours annually for Jordan. The annual electricity production of the proposed plant varied depending on the location between 6.886 and 11.919 GWh/year, with a mean value of 9.46 GWh/year. The specific yield varied between 340.9 and 196.9 kWh/m², while the mean value was 270.59 kWh/m². Analysis of the annual electricity production of the plant, the specific yield, besides the economic indicators i.e., internal rate of return, simple payback period, years– to- positive cash flow, net present value, annual life cycle saving, benefit–cost ratio, and cost of energy – for all sites – showed that Tafila and Karak are the most suitable sites for the solar photovoltaic power plant's development and Wadi Yabis is the worst. The results also showed that an average of 7414.9 tons of greenhouse gases can be avoided annually utilizing the proposed plant for electricity generation at any part of Jordan.     

MODERGIS application: Integrated simulation platform to promote and develop renewable sustainable energy plans,Colombian case study

This research presents the MODERGIS Integrated Simulation's Platform as a tool to promote and develop renewable energy plans under sustainability criteria, in order to increment the participation of renewable technologies in the national “energy mix” and shows an application to Colombia as a case study. Potential zones of solar and wind energy and productive areas were determined for bio-energies, by means of a geographical information system which simulated energy scenarios influenced by climatic phenomena up to the year 2030. Results yield potentials of 26,600 MW in wind energy and 350,000 MW in solar energy. Bioenergy potentiates in a sustainable way of 366,310 km per biomass, 291,486 km in African palm, 9,667 km in sugar cane. These scenarios were simulated in a supply/demand with time horizons up until 2030, including an analysis of the effects on the energy systems of the El Niño Southern Oscillation atmospheric component (ENSO). Finally, in order to obtain an appropriate mix of renewable sources that could be introduced in the national energy mix, the Multi-Criteria Analysis method VIKOR was used, allowing to perform performing 5151 possible combinations of renewable projects; the optimal selection corresponds to 600 MW from wind power, 740 MW solar photovoltaic and 660 MW solar thermoelectric. Giving these results to the new scene allowed for incrementing the participation of renewable technologies up to a 0.23% in the current year and up to a 7% of the “energy mix” in the year 2030.     

Situation and outlook of solar energy utilization in Tibet,China

The near-exponential rise in tourist numbers and accelerating economic growth have challenged Tibetan energy supply and threaten its peculiar environment and valuable ecosystem. Exploitation of pollution free solar power may medicate this demand for energy. Here we shall provide a review of solar power development in Tibet. This region has a near inexhaustible source of solar energy due to its average annual radiation intensity of 6000–8000 MJ/m², ranking it first in China and second after the Sahara worldwide. Currently, Tibet has 400 photovoltaic power stations with a total capacity of nearly 9 MW. In addition, 260,000 solar energy stoves, passive solar house heating covering 3 million square meters, and 400,000 m² of passive solar water heaters are currently in use in Tibet. Although Tibet places first in applying solar energy in China, solar energy faces big challenges from hydroelectric power and the absence of local know-how. The new power generation capacity in Tibet's “11th Five-Year (2006–2010)” Plan focuses primarily on hydropower, PV power stations being relegated to a secondary role as supplementary to hydropower. Here it will be argued that this emphasis is incorrect and that solar energy should take first place in Tibet's energy development, as it is crucial in striving for a balance between economic development, booming tourism, and environmental protection.     

A probabilistic method for calculating the usefulness of a store with finite energy capacity for smoothing electricity generation from wind and solar power

This paper describes a novel method of modelling an energy store used to match the power output from a wind turbine and a solar PV array to a varying electrical load. The model estimates the fraction of time that an energy store spends full or empty. It can also estimate the power curtailed when the store is full and the unsatisfied demand when the store is empty. The new modelling method has been validated against time–stepping methods and shows generally good agreement over a wide range of store power ratings, store efficiencies, wind turbine capacities and solar PV capacities.Example results are presented for a system with 1 MW of wind power capacity, 2 MW of photovoltaic capacity, an energy store of 75% efficiency and a range of loads from 0 to 3 MW average.     

Hydropower for sustainable energy development in Turkey: The small hydropower case of the Eastern Black Sea Region

Turkey is a rich country from the point of variety and potential of renewable energy resources. Hydros, winds, biomass, solar and geothermal are important renewable and environmentally friendly sources for energy in Turkey. Turkey produces large amount of hydropower with a total gross hydropower potential of 433 TW h/yr, which is equal to 13.8% of the total hydropower potential of Europe. Technically useable potential is 216 TW h/yr and economic potential is 140 TW h/yr. The main aim of the present study is to investigate hydropower potential of Turkey and small hydropower plants in Eastern Black Sea Region for sustainable energy development in Turkey. The geography of Turkey especially, Eastern Black Sea Region supports and suitable the development of the small hydro plants to increase the energy generation and utilization of available water sources in Turkey. Besides, the paper deals with hydropower policies to meet ever increasing energy demand for sustainable development of Turkey.     

Influence of the superheat associated to a semihermetic compressor of a transcritical CO2 refrigeration plant

This work evaluates, from an energetic point of view, the effects of the superheat caused in the refrigerant by the electric motor cooling (SH_SC) in a semihermetic compressor installed in an experimental refrigerating plant, which operates with CO₂ as the working fluid in transcritical conditions. The analysis is based on 84 experimental tests which cover a wide range of operating conditions of the plant: three evaporating levels (0, ?10, ?17 °C) at four compressor speeds (1150, 1300, 1450, 1600 rpm) over a range of discharge pressures from 74.2 to 104.9 bar.The paper presents the empirical model of the compressor and its validation with the experimental measurements, which allows the behaviour of the facility to be calculated with prediction errors below 5%. With the model, the effect of the SH_SC on the energy efficiency of the plant is evaluated by comparing the actual performance of the facility with the simulated behaviour of the plant without considering the SH_SC produced by the semihermetic compressor. The maximum estimated reductions, due to the SH_SC of the compressor, are a 20% in cooling capacity and a 23% in COP.     

Development of the high concentration III-V photovoltaic system at INER,Taiwan

The 100 kW high concentration photovoltaic (HCPV) system has been constructed in October 2007 at the Institute of Nuclear Energy Research (INER), Taiwan. The maximum module efficiency with a geometrical concentration ratio of 476× is about 26.1% under 850 W/m² DNI and passive cooling conditions [Cherng-Tsong Kuo. The project of demonstrating MW high concentration photovoltaic (HCPV) system. Science and technology yearbook of Taiwan. ROC; 2008]. The 100 kW HCPV system consists of 14 sets of pillar-stand 5 kW systems and 21 sets of roof-top 1.5 kW systems. Each 5 kW system and 1.5 kW are comprised of 40 modules and 12 modules respectively. Each module was integrated with 40 solar cells with 35% conversion efficiency each, manufactured by Spectrolab Company, the highest III-V solar cell conversion efficiency record keeper. This project is the pioneer for the establishment of one MW HCPV demonstration system in 2008.     

Technical and economic assessment of grid-independent hybrid photovoltaic–diesel–battery power systems for commercial loads in desert environments

Solar photovoltaic (PV) hybrid system technology is a hot topic for R&D since it promises lot of challenges and opportunities for developed and developing countries. The Kingdom of Saudi Arabia (KSA) being endowed with fairly high degree of solar radiation is a potential candidate for deployment of PV systems for power generation. Literature indicates that commercial/residential buildings in KSA consume an estimated 10–45% of the total electric energy generated. In the present study, solar radiation data of Dhahran (East-Coast, KSA) have been analyzed to assess the techno-economic viability of utilizing hybrid PV–diesel–battery power systems to meet the load requirements of a typical commercial building (with annual electrical energy demand of 620,000 kW h). The monthly average daily solar global radiation ranges from 3.61 to 7.96 kW h/m². NREL's HOMER software has been used to carry out the techno-economic viability. The simulation results indicate that for a hybrid system comprising of 80 kWp PV system together with 175 kW diesel system and a battery storage of 3 h of autonomy (equivalent to 3 h of average load), the PV penetration is 26%. The cost of generating energy (COE, US$/kW h) from the above hybrid system has been found to be 0.149 $/kW h (assuming diesel fuel price of 0.1 $/L). The study exhibits that for a given hybrid configuration, the operational hours of diesel generators decrease with increase in PV capacity. The investigation also examines the effect of PV/battery penetration on COE, operational hours of diesel gensets for a given hybrid system. Emphasis has also been placed on unmet load, excess electricity generation, percentage fuel savings and reduction in carbon emissions (for different scenarios such as PV–diesel without storage, PV–diesel with storage, as compared to diesel-only situation), cost of PV–diesel–battery systems, COE of different hybrid systems, etc.     

Projections of future changes in solar radiation in China based on CMIP5 climate models

Surface solar radiation research is important for understanding future climate change and the application of large-scale photovoltaic systems. We used the coupled model intercomparison project phase 5 (CMIP5) under the RCP8.5 scenario to project potential changes in surface solar radiation, surface temperatures, and cloud fractions between 2006 and 2049 in China, as well as how these changes may affect photovoltaic power generation. The results show that the following. (1) For surface temperatures, the median trends of all considered models show warming in China of 0.05 K/year. The maximum positive trends for all-sky radiation appear in the southeast of China, reaching 0.4 W/m²/year. Cloud cover exhibits a mainly decreasing trend in the overall region of China. (2) The all-sky radiation of most selected regions shows a decreasing trend. The maximum negative value (− 0.08 W/m²/year) appears in Qinghai. (3) Compared with the average photovoltaic power output from 2006 to 2015, the photovoltaic power output in western China will decrease by − 0.04 %/ year, while photovoltaic power output in southeastern China will increase by 0.06–0.1%/year.     

Fabrication and characterisations of n-CdS/p-PbS heterojunction solar cells using microwave-assisted chemical bath deposition

n-CdS/p-PbS heterojunction solar cells were prepared via microwave-assisted chemical bath deposition method. A cadmium sulfide (CdS) window layer (340 nm thickness) was deposited on an indium tin oxide (ITO) glass. A lead sulfide (PbS) absorber layer (985–1380 nm thickness) with different molar concentrations (0.02, 0.05, 0.075, and 0.1 M) was then grown on ITO/CdS to fabricate a p–n junction. The effects of changing molar concentration of the absorber layer on structural and optical properties of the corresponding PbS thin films and solar cells were investigated. The optical band gap of the films decreased as the molarity increased. The photovoltaic properties (J–V characteristics, short circuit current, open circuit voltage, fill factor, and efficiency) of the CdS/PbS heterostructure cells were examined under 30 mW/cm² solar radiation. Interestingly, changing molar concentration improved the photovoltaic cells performances, the solar cell exhibited its highest efficiency (1.68%) at 0.1 M molar concentration.