Volume 21 - 2019

Due to the intermittent and fluctuating nature of wind and other renewable energy sources, their integration into electricity systems requires large-scale and flexible storage systems to ensure uninterrupted power supply and to reduce the percentage of produced energy that is discarded or curtailed. Storage of large quantities of electricity in the form of dynamic energy of water masses by means of coupled reservoirs has been globally recognized as a mature, competitive and reliable technology; it is particularly useful in countries with mountainous terrain, such as Greece. Its application may increase the total energy output (and profit) of coupled wind-hydroelectric systems, without affecting the availability of water resources. Optimization of such renewable energy systems is a very complex, multi-dimensional, non-linear, multi modal, nonconvex and dynamic problem, as the reservoirs, besides hydroelectric power generation, serve many other objectives such as water supply, irrigation and flood mitigation. Moreover, their function should observe constraints such as environmental flow. In this paper we developed a combined simulation and optimization model to maximize the total benefits by integrating wind energy production into a pumped-storage multi-reservoir system, operating either in closed-loop or in open-loop mode. In this process, we have used genetic algorithms as the optimization tool. Our results show that when the operation of the reservoir system is coordinated with the wind farm, the hydroelectricity generation decreases drastically, but the total economical revenue of the system increases by 7.02% when operating in closed-loop and by 7.16% when operating in open-loop mode. We conclude that the hydro-wind coordination can achieve high wind energy penetration to the electricity grid, resulting in increase of the total benefits of the system. Moreover, the open-loop pumped-storage multi-reservoir system seems to have better performance, ability and flexibility to absorb the wind energy decreasing to a lesser extent the hydroelectricity generation, than the closed-loop.

Organic solvent extracts of three cyanobacterial species (Anabaena oryzae, Oscillatoria sp. and Stigonema ocellatum) were tested for antimicrobial activity against human pathogenic fungal and bacterial strains as well as for antioxidant and cytotoxic activity against human breast adenocarcinoma (MCF-7). The acetone extract of Anabaena oryzae was found to be the most active one against tested fungal and bacterial strains. It showed a maximum antimicrobial activity against Serratia marcescens and Candida albicans. The methanol extract of Oscillatoria sp. exhibited the best total antioxidant capacity compared to the other solvents and algal species. Acetone and methanol extracts of Anabaena oryzae exhibited high toxicity against MCF-7 cell line with IC50 of 45.1 and 44.4 µg/L, respectively. Acetone was the best solvent for extracting the active material. The acetone extracts were characterized by Gas Chromatography Mass Spectrophotometer (GC–MS) to identify the compounds responsible for such activities. Pharmaceutical important compounds in the acetone extract of cyanobacterial species like diacetone alcohol, acetic acid butyl ester mesityl oxide and heptadecane were present as a major component. These results indicate that extracts of studied cyanobacterial species exhibited appreciable antimicrobial, antioxidant and cytotoxic activity and could be a source of valuable bioactive materials for health products.

This study focuses on the impact of climate change on rainfall-runoff pattern, and to assess the surface runoff and groundwater recharge potential from the intensified rainfall for the effective management of surface and groundwater resources in Tirunelveli city. The rainfall contribution is consistent, dependent, maximum and intensified during the month of November followed by October and December. The intensified rainfall in these months causes a temperature decrease and the climate becomes more and more colder than ever. The indices SPI and DI clear show that there is a change in climatic pattern. Landuse Landcover (LULC) analysis shows that the residential area and mining area is on the increasing trend, Village area is slightly increasing, agricultural area and dense scrub area is on the decreasing trend. The present capacity of the storage tanks available in Tirunelveli city is less than the maximum runoff generated during the month of November. The increase in residential area in LULC reflects the direct linear relation with the population increase of the city. The impact of urbanization leads to LULC change with the loss of agricultural land and water bodies.

This study investigates the effectiveness of fly ash-based geopolymer concrete was conducted to be used as an alternative material to replace the normal concrete. The concrete mixture was prepared by mixing fly ash, fine aggregate, nano-slag, and SP in Na2SiO3/NaOH solution. The mixture was divided into three different groups, with constant water to fly ash ratio of 0.1, and different alkaline content: 0.4, 0.45, and 0.5 of fly ash rather than two curing techniques (moist and autoclave). Several hardeness properties of concrete like compressive strength, density; and splitting tensile strength were examined after 28 d. The microstructural development of geopolymer concrete was monitored using X-Ray Diffractometer. Based on the results of this investigation, it is recommended to cure the geopolymer concrete by autoclaving rather than the traditional moist technique, especially at lower alkaline dosage. However, the partial addition of nano slag by weight of FA had a positive effect on both curing techniques.