The Geothermal Power Plants of Amiata Volcano, Italy: Impacts on Freshwater Aquifers, Seismicity and Air

Production of geothermal energy for electricity at Amiata Volcano uses flash-type power plants with cooling towers that evaporate much of the geothermal fluid to the atmosphere to condense the geothermal vapour extracted. Because the flash occurs also within the geothermal reservoir, it causes a significant depressurization within it that, in turns, results in a drop of the water table inside the volcano between 200 and 300 m. The flow rates of natural springs around the volcano have also substantially decreased or ceased since the start of geothermal energy exploitation. Continuous recording of aquifer conditions shows substantial increases in salinity (>20%) and temperature (>2°C) as the water table falls below about 755–750 m asl. In addition to hydrologic impacts, there are also a large numbers of induced earthquakes, among which the ML 3.9, April 1, 2000 earthquake that generated significant damage in the old villages and rural houses. Relevant impacts on air quality occur when emissions are considered on a per-MW basis. For example, CO2+CH4 emissions at Amiata are comparable to those of gas-fired power plants (1), while the acid-rain potential is about twice that of coal-fired power plants. Also, a significant emission of primary and secondary fine particles is associated with the cooling towers. These particles contain heavy metals and are enriched in sodium, vanadium, zinc, phosphorous, sulphur, tantalium, caesium, thallium, thorium, uranium, and arsenic relative to comparable aerosols collected in Florence and Arezzo (2). Measurements have shown that mercury emitted at Amiata comprises 42% of the mercury emitted from all Italian industries, while an additional comparable amount is emitted from the other geothermal power plants of Tuscany (3). We believe that the use of air coolers in place of the evaporative cooling towers, as suggested in 2010 by the local government of Tuscany (4), could have and can now drastically reduced the environmental impact on freshwater and air. On the opposite side of the coin, air-coolers would increase the amount of reinjection, increasing the risk of induced seismicity. We conclude that the use of deep borehole heat exchangers could perhaps be the only viable solution to the current geothermal energy environmental impacts.

Research on Trench Etching and Photolithography Process of SiC Trench MOSFET

In this paper, the development of trench etching process and photolithography process for 6-inch 4H-SiC trench-type power MOSFET devices is mainly studied. Among them, the etching process successfully solved the anisotropy of dry etching of SiC, the different etching rates of different crystal planes, the difficulty of controlling the angle of the trench sidewall, and the easy formation of micro-trenches at the corners, etc. Successfully realized trenches with etch depth greater than 1.2um and sidewall angle greater than 90° in SiC. Subsequently, the trench was filled with SiO2 to achieve no holes in the trench after filling, and then the photolithography process was studied. Photolithography process is resolved at the trench coating, exposing and developing the non-uniformity problem, achieve a full and uniform coating, self-aligned trench overlay and the overlay accuracy of less than 0.1um, and there is no residue of photoresist in the groove after development. This article uses scanning electron microscope (SEM) to measure the morphology of the trench after etching and photolithography to characterize the experimental results, and the results meet the process requirements. The successful development of this process will facilitate the research and development of deeper trench-type power MOSFET devices.

Recent Strategies for Automatic Generation Control of Power Systems With Diverse Energy Sources

This paper reveals Automatic Generation Control (AGC) strategies of power systems including diverse type power generating sources and comprehensive literature review is also presented. These diverse type energy sources considered conventional power sources like thermal, diesel, nuclear, etc. and Renewable Energy Sources (RESs). RESs are solar energy, wind energy, hydro energy, etc. A variety of AGC schemes based on hard, soft and artificial intelligent computation techniques is presented here. The benefits and their limitations of these energy generating units are also taken in this article. In the present scenario, deregulation, smart micro-grid and grid concept is also utilized with interconnection of the considered energy generating sources. The literature of this review article fulfills the gap of recent and previous decades research work and provides future exploration in AGC techniques.

Recent Strategies for Automatic Generation Control of Power Systems with Diverse Energy Sources

This paper reveals Automatic Generation Control (AGC) strategies of power systems including diverse type power generating sources and comprehensive literature review is also presented. These diverse type energy sources considered conventional power sources like thermal, diesel, nuclear, etc. and Renewable Energy Sources (RESs). RESs are solar energy, wind energy, hydro energy, etc. A variety of AGC schemes based on hard, soft and artificial intelligent computation techniques is presented here. The benefits and their limitations of these energy generating units are also taken in this article. In the present scenario, deregulation, smart micro-grid and grid concept is also utilized with interconnection of the considered energy generating sources. The literature of this review article fulfills the gap of recent and previous decades research work and provides future exploration in AGC techniques.

Promising Thermoelectric Performance in Two-Dimensional Semiconducting Boron Monolayer

A heavy element is a special character for high thermoelectric performance since it generally guarantees a low lattice thermal conductivity. Here, we unexpectedly found a promising thermoelectric performance in a two-dimensional semiconducting monolayer consisting of a light boron element. Using first-principles combined with the Boltzmann transport theory, we have shown that in contrast to graphene or black phosphorus, the boron monolayer has a low lattice thermal conductivity arising from its complex crystal of hexagonal vacancies. The conduction band with an intrinsic camelback shape leads to the high DOS and a high n-type Seebeck coefficient, while the highly degenerate valence band along with the small hole effective mass contributes to the high p-type power factor. As a result, we obtained the p-type thermoelectric figure of merit up to 0.96 at 300 K, indicating that the boron monolayer is a promising p-type thermoelectric material.

Comparison of the Thermal Performance of Mineral Oil and Natural Ester for Safer Eco-Friendly Power Transformers A Numerical and Experimental Approach

At present, most of the worldwide transformer fleet uses mineral oil as insulation fluid. However, the use of natural ester is playing an increasing role as safer and eco-friendly alternative to mineral oil. From the utilities’ perspective, the change in the mineral oil paradigm can be approached by replacing their assets by new eco-friendly transformers or refurbishing their assets, substituting only the insulating fluid. To make an informed decision, guidelines indicating how a transformer designed for mineral oil would behave when operating with natural ester, are of paramount importance. In the present research, temperature rise tests were carried out in a 15MVA ODAF core-type power transformer, under different operating conditions. Tests were run for mineral oil as insulating fluid and subsequently repeated for natural ester. To gain further insights on experimental results, thermal modelling of the transformer under the same test conditions was carried out, using Thermal-Hydraulic Network Models and Computational Fluid Dynamics techniques. From the present work it was found that the relationship between the thermal behaviour of the transformer using natural ester or mineral oil is not simple as it depends on the operating conditions of the transformer and on the geometry of the windings.