G. Mihalakakou

A Statistical Analysis of Wind Speed Distributions in the Area of Western Greece

The wind energy potential in Western Greece was evaluated from measurements of wind speed and direction at four weather stations. Data collected over a period of years were used to statistically analyze wind speed distributions. Weibull parameters, at the selected stations, were calculated using three different methods. The theoretical values calculated from the analysis of the collected data performed well with the measured ones. Finally, the correlation between Weibull parameters and the measured wind speed values was performed and analysed for each station.

Wind power potential assessment for seven buoys data collection stations in Aegean Sea using Weibull distribution function

This paper utilizes three hourly measured values of wind speed and direction from seven buoys data collection stations in Aegean Sea to study the wind speed and power characteristics applying the Weibull shape and scale parameters. Specifically, the site dependent, annual and monthly mean patterns of mean wind speed, Weibull parameters, frequency distribution, most probable wind speed, maximum energy carrying wind speed, wind power density and wind energy density characteristics have been studied. The Weibull distribution was found to represent the wind speed distribution with more than 90% accuracy in most of the cases. Slightly decreasing trends were observed in annual mean wind speed values at Lesvos and increasing at Mykonos. The mean values of wind speed, scale parameter, most probable wind speed, maximum energy carrying wind speed, wind power and wind energy density values showed higher values during winter time and lower in summer time. Mykonos was found to be the best site from wind power harnessi...

Wind power potential assessment for three buoys data collection stations in the Ionian Sea using Weibull distribution function

ABSTRACT The present article utilizes wind measurements from three buoys data collection stations in Ionian Sea to study the wind speed and power characteristics using the Weibull shape and scale parameters. Specifically, the site dependent, annual, and monthly mean patterns of mean wind speed, Weibull parameters, frequency distribution, most probable wind speed, maximum energy carrying wind speed, wind power density and wind energy density characteristics have been analyzed. The Weibull distribution was found to represent the wind speed distribution with more than 90% accuracy, in most of the cases. Moreover, the correlation between the percentages of times the wind speed was above cut-in-speed and the measured mean wind speed for the three selected sites, as the correlation between the aforementioned percentages and the scale parameter c were examined and were found linear. At all these sites, no definite increasing or decreasing trends in annual mean wind speed values could be detective over the data reporting period. The mean values of wind speed, scale parameter, most probable wind speed, maximum energy carrying wind speed, wind power and wind energy density values showed higher values during winter time and lower in summer time in Pylos and Zakynthos. Moreover, Pylos and Zakynthos were found to be the best sites from wind power harnessing point of view.

Cooling roofs through low temperature solar-heat transformations in hydrophilic porous materials

The principle of roofs cooling through the water vapor adsorption–desorption cycle in porous materials is presented. In order to study the effect, porous materials of natural origin or synthesized at our laboratory were characterized at the micro-scale with UV–VIS-NIR spectrometry, thermal and water vapor adsorption measurements and tested at the urban scale in a wind tunnel of controlled environmental conditions and simulated sun. In the later, the difference of temperature increase under simulated solar irradiation between a highly hydrophilic mesoporous sample and marble dust with comparable reflectance indicates that the low temperature solar heat transformation and evaporation cooling can be considered as an additional mechanism toward the reduction of building heat fluxes.

Moisture Sorption Properties of Modified Porous Clays for Roof Evaporative Cooling Applications

Abstract This research concentrates on evaporative cooling, a sustainable and alternative way to cool a roof surface by taking advantage of the properties of porous materials. During periods of rain or high humidity nights, water sorbents store moisture in their small pores inside their particles. During a warm sunny day, the latent heat released due to evaporation of moisture, maintains the surface temperature at low level. Lower roof temperatures contribute to smaller heat flow inside the building while reducing the cooling load. In this work, materials consisting of ordinary soil, montmorillonite and modified clays were used. Prior to moisture sorption experiments, materials were characterized by techniques including X–ray diffraction, X–ray fluorescence, thermogravimetric analysis and porosimetry. In order to determine the sorption isotherms, dry specimens were placed initially in desiccators above four different saturated salts in water solutions (32.8% to 93.6%). The modified clay was found to have the highest equilibrium state (10% after almost 4 days of sorption at high relative humidity). Also the moisture sorption rate of the modified clay was faster than the rest of the materials and equilibrium was attained in less than 12 hours. Moreover, a specific environment chamber was developed and tested for the evaporative cooling properties of the materials. The lower observed surface temperatures under simulating radiation of the modified clays in comparison to ordinary soil, indicated their significant potential for evaporative cooling applications.

An analysis of public attitudes towards renewable energy in Western Greece

Inputs to the planning and decision-making process addressing environmental and energy issues include expert opinions, public attitudes and perceptions. This research investigates the attitudes of local communities of Western Greece towards renewable energy and documents the existence of distinct household groups. Data were collected from 201 households via a questionnaire. Respondents were either young or around 40 to 50 years of age, mostly university or high school graduates, with a family income less than 5000 euros. Principal Components were extracted from household attitudes towards renewable energy projects. Cluster analysis revealed two clusters based on key demographic variables (age, years of education and average income) and principal component scores. The first cluster contained respondents who were older, less educated and economically weaker; the second contained younger, better educated and higher income respondents. Members of the better-off cluster thought that they were more aware of renewable energy, felt stronger about its future role in the energy mix and were more optimistic regarding its impacts; on the other hand, they were more cognizant of bureaucratic, economic and technical factors that could hinder its development.

Heat island phenomenon and cool roofs mitigation strategies in a small city of elevated temperatures

High urban temperatures are observed during the last 100 years due to the heat island phenomenon. The effect is intensively pronounced even in small-sized cities by temperature differences between rural and urban environment up to 6oC. In order to keep the phenomenon under control, mitigation strategies, especially concerning cool roofs have been established. Under hot and arid climates, roof temperatures reach almost 70oC and about 50% of heat enters into buildings through roof slab. The aim of this paper is to present the heat island phenomenon in a small city of Western Greece and to propose energy-saving techniques that improve the overall energy performance of building stock and are easy to be applied.