An application of Markov potential theory to Markovian decision processes

The aim of this paper is to identify the denumerable stochastic systems which have an optimal strategy, namely, to give general sufficient conditions of the existence of an optimal strategy for denumerable Markovian decision processes. The aim is accomplished by using Markov potential theory and showing the range of the validity of a method to find an optimal strategy called Howard's technique. Since Markov potential theory helps to characterize the properties of evaluations of strategies on such processes, it plays an important role to find the sufficient conditions mentioned above

For Markov potential theory, new concepts are introduced such as absorbable chains, quasi-potentials, etc., and using them, sufficient conditions for the existence of a solution of the equation x = f+Px are generalized to the one's for cyclic chains and multi-chains

The results obtained in this paper are as follows : if a system represents a strong Markov chain for any strategy, then there exists an optimal strategy with respect to the total or the mean expected earnings, and for any stochastic system there exists an optimal strategy with respect to the discounted total expected earnings.     

Prediction of wind speed for the estimation of wind turbine power output from site climatological data using artificial neural network

In this paper, the wind speeds of Noupoort in the Western Cape region of South Africa are forecasted from the site climatological data using feed forward artificial neural network (ANN) with the back propagation training method. Different architectural designs are tested with different combinations of climatological data to obtain the most suitable ANN for predicting the wind speed of the site. The predicted wind speeds are compared with the actual measured wind speeds and the results are evaluated using mean absolute error (MAE), mean absolute percentage error (MAPE), root mean square error (RMSE) and correlation coefficient (R). Some of the key results show that combination of temperature, wind direction and time of the day (TEM?+?WD?+?T) could effectively predict wind speed of Noupoort. The forecasted wind speed shows a strong agreement with the measured wind speed with R, RMSE, MAPE and MAE of 0.96, 0.56, 6.64% and 0.44, respectively.     

On mathematical models of adaptive systems

The aim of this paper is to present a mathematical model for a system to control an object favourably which is unknown for the system—an adaptive system. We make the concept of adaptiveness precise first and consider systems as stochastic sequential machines (SSM's) to answer the question : what kind of logical structure is necessary and sufficient for a SSM to be adaptive. Some necessary conditions for a SSM to be adaptive are shown, and for a specified class of SSM's, the necessary and sufficient conditions to be adaptive are given. Furthermore, some examples of adaptive SSM's are shown.     

Off-grid hybrid renewable energy system with hydrogen storage for South African rural community health clinic

Most inhabitants of rural communities in Africa lack access to clean and reliable electricity. This has deprived the rural dwellers access to modern healthcare delivery. In this paper, an off-grid renewable energy system consisting of solar PV and wind turbine with hydrogen storage scheme has been explored to meet the electrical energy demands of a health clinic. The health clinic proposed is a group II with 10 beds located in a typical village in South Africa. First, the wind and solar energy resources of the village were analysed. Thereafter, the microgrid architecture that would meet the energy demand of the clinic (18.67 kWh/day) was determined. Some of the key results reveal that the average annual wind speed at 60 m anemometer height and solar irradiation of the village are 7.9 m/s and 4.779 kWh/m²/day, respectively. The required architecture for the clinic composes of 40 kW solar PV system, 3 numbers of 10 kW wind turbines, 8.6 kW fuel cell, 25 kW electrolyser and 40 kg hydrogen tank capacity. The capital cost of the microgrid was found to be $177,600 with a net present cost of $206,323. The levelised cost of energy of the system was determined to be 2.34 $/kWh. The project has a breakeven grid extension distance of 8.81 km. Since this distance is less than the nearest grid extension distance of 21.35 km, it is established that the proposed renewable energy microgrid with a hydrogen storage system is a viable option for the rural community health clinic.     

Assessment of turbulence intensity of local wind regimes

This paper analyses the turbulence intensity of seven different sites in the coastal region of South Africa. The study is based on 12 months, 10-minute average wind speed measurement. The turbulence intensity is calculated using mean wind speed and the standard deviation method. Some of the key results show that generalised extreme value distribution gives the best fit to the turbulence intensity in the entire sites. The annual shape parameter of the distribution ranges from 0.11 at site WM06 to 0.3 at site WM05. The scale parameter varies from 3.55 at site WM04 to 6.06 at site WM02, while the location parameters span between 7.07 at site WM04 and 10.65 at site WM01. The annual turbulence intensity varies from 9.6% at site WM04 to 15.9% at site WM03. The result also reveals that sites with higher turbulence intensity have lower wind power potential and hence are less attractive for wind power application.     

Performance assessment of empirical models for prediction of daily and monthly average global solar radiation: the case study of Ibadan,Nigeria

In this study, the performance assessment of empirical models for modelling global solar radiation in Ibadan is presented. The empirical models are derived from the three basic models: Angstrom–Prescott model, Garcia model and Hargreaves–Sammani model. The data used in the analysis consist of daily average global solar radiation, daily average sunshine hours, daily average maximum temperature and daily average minimum temperature collected over a period of nine years (2000–2008). Regression constants are determined for each of the model for each months of the year. The study reveals that Garcia Quadratic model puts up the best overall performance. The model can predict the daily average global solar irradiation with Mean Absolute Error of 1.86?MJ?m^?2?day^?1, Root Mean Square Error of 2.7?MJ?m^?2?day^?1, Mean Absolute Percentage Error 9.34% and Coefficient of Determination (R²) of 0.68.     

Bearing Resistance of Wind Turbine Generator System

The vertical axis wind turbine generator is mainly used for small size wind turbine applications, and is independent of wind direction. Its rotating part (shaft unit) should be rotated by an extremely small torque so as to increase the generation efficiency. However, commercially available bearings are not necessarily suitable for the shaft unit because their static and dynamic load ratings are frequently larger than those required for the vertical axis wind turbine. As a result, the frictional force and the rotating torque of commercially available bearings are too large for the shaft unit to rotate lightly. In this study, through an experiment with an actual vertical axis wind turbine, the bearings used for the shaft unit are reviewed in accordance with IEC61400‐2. Design of a shaft unit with the bearings having the most suitable load rating and frictional force for the vertical axis wind turbine is attempted. The newly designed shaft unit will be applied to the vertical axis wind turbine and will be tested.     

MICROBIOLOGICAL QUALITY OF SELECTED STREET FOODS IN PORT HARCOURT, NIGERIA

The microbiological quality of selected ready‐to‐eat foods sold on the streets of Port Harcourt, Nigeria, was evaluated. Twenty to twenty‐eight samples each of 10 different types of foods were analyzed. About 50% of the foods were deep fat fried, 20% were baked, 10% each were either boiled, pasteurized and frozen, or fermented and chilled products. Methods of food preparation and handling practices influenced the shelf lives of the foods, and their implications on microbiological quality and safety are discussed. The heterotrophic counts were highest for yogurt and ice cream and lowest for chin‐chin and buns. Bacterial counts for pancake, moi moi, cake, meat pie and egg roll on McConkey agar gave comparable results with counts obtained on Deoxycholate agar. Eleven bacteria genera were isolated. Bacillus spp. and Klebsiella spp. occurred in most of the foods, followed by Staphylococcus spp. and Micrococcus spp., while other species exhibited a random distribution. Generally, the foods were microbiologically safe despite defective handling practices.     

Optimum selection of photovoltaic modules using probabilistic approach based on capacity factor estimation

In this paper, the optimum selection of photovoltaic module using probabilistic techniques based on capacity factor estimation is proposed. The approach entails modelling the solar irradiance characteristics of the site by fitting probability distributions to the irradiance data for different hours of a typical day in each month of the year. The parameters of the probability distribution that best fits the solar irradiance data for a particular hour are thereafter used to estimate the capacity factor of different designs of PV modules. The module with the highest average capacity factor across all the months is identified as the best suited module for the given site. The proposed technique is investigated using 5 years data (2008–2012) of solar irradiance and temperature. The choice of the year of observation of the data was due to accuracy and completeness of the data for the period. The data sheets of 10 commercially available PV modules were also obtained from different manufacturers. The proposed method is simple, easy to use, and can be applied to any solar regimes around the world.