• Energy Research
• Restricted close
• ES close
• EU close
• UA close

Artículos en revistas This paper presents the principles of a centralized underfrequency load-shedding (UFLS) scheme based on a frequency stability boundary curve suitable for small isolated power systems. The centralized UFLS scheme is illustrated in case of two small isolated Spanish power systems. info:eu-repo/semantics/publishedVersion

Shallow Geothermal Systems (SGS) are widely used to provide low-cost heating and cooling of residential and commercial buildings. SGS can be an economically-viable solution even for commercial buildings, where controlled temperature is fundamental for the production processes. To assess the thermal resistance of the soil and the performance of a SGS, Thermal Response Tests (TRT) must be performed. TRT machines are today designed mainly for short term monitoring, for relatively deep SGS (up to 200 m) and for being used by expert operators. Lightweight, low-cost machines for both fast and long term, reliable and unattended TRT for very Shallow Geothermal Systems (vSGS) are not available today. This paper describes the design of a micro-TRT machine (mTRT) for vSGS, which is gaining interest in the civil engineering, environmental, energy and food chain sectors. The paper describes the features of the wireless monitoring system, the design choices to achieve the required accuracy and the software developed for adding remote control capability. Experimental validation in a real test field demonstrates the quality of measurements collected for analysing the TRT data.

Common hornbeam (Carpinus betulus) is one of the most important spring pollen allergens widespread in the Czech Republic. This study evaluates the changes in Carpinus betulus flowering and the length of the blooming period in the Czech Republic during 1991-2020. Temporal and spatial evaluations in the timing of the flowering and the length of the blooming period were investigated at different altitudinal levels. Moreover, the changes in mean air temperature and precipitation total in spring months (March-April-May) were assessed, including the correlation with phenological data. Geographic Information System methods, the Mann-Kendall test and Pearson's correlation coefficient were used for processing. The flowering of Carpinus betulus changed significantly over time during the 1991-2020 period. The linear models predicted early flowering in Carpinus betulus at different altitudes (27 days at > 701 m 18 days at 501-700 m and 13 days at 301-500 m) significantly (p<0.001) over the last three decades. Furthermore, the length of the blooming period of Carpinus betulus has been shortened (4 days) at the 301-500 m a.s.l. altitudinal level significantly (p<0.05). The strongest correlation was predominantly observed between flowering and the mean air temperature (March-April-May).

Nordhaus (1973) has in his seminal contribution addressed two emerging questions in the field of energy economics. First, how do current market prices of natural resources reflect true scarcity fro...

Although hydrothermal carbonization of biomass components is known to be mainly governed by reaction temperature, consistent reports on the effect and statistical significance of process conditions on hydrochar properties are still lacking. The objective of this research was to determine the importance and significance of reaction temperature, retention time and solid load on the properties of hydrochar produced from an industrial lignocellulosic sludge residue. According to the results, reaction temperature and retention time had a statistically significant effect on hydrochar ash content, solid yield, carbon content, O/C-ratio, energy densification and energy yield as reactor solid load was statistically insignificant for all acquired models within the design range. Although statistically significant, the effect of retention time was 3-7 times lower than that of reaction temperature. Predicted dry ash-free solid yields of attained hydrochar decreased to approximately 40% due to the dissolution of biomass components at higher reaction temperatures, as respective oxygen contents were comparable to subbituminous coal. Significant increases in the carbon contents of hydrochar led to predicted energy densification ratios of 1-1.5 with respective energy yields of 60-100%. Estimated theoretical energy requirements of carbonization were dependent on the literature method used and mainly controlled by reaction temperature and reactor solid load. The attained results enable future prediction of hydrochar properties from this feedstock and help to understand the effect of process conditions on hydrothermal treatment of lignocellulosic biomass.

Artículos en revistas This work develops a stochastic optimization model for the creation of a bidding strategy for a generator in an energy call option auction similar to Brazil's, i.e., where the bidder can offer both the premium and the strike price. The objective of the model is to maximize the bidder's competitiveness while ensuring that the project's target rate of return is achieved with a given probability, for example 95%. The problem's complexity is compounded by uncertainties in fuel supply and the need to switch between fuels. The generators face the conundrum of bidding a single strike price to cover the expenses generated by using multiple types of fuels. We address the problem of finding bidding strategies which, taking into account uncertainty in fuel supply and risk constraints, set the combination of strike price and option premium that ensure a desired risk-adjusted return for greenfield dual-fuel thermal plants. info:eu-repo/semantics/publishedVersion

Abstract Water transport control is the major issue of direct methanol fuel cell. High water flow rates through the fuel cell imply extra water feeding at the anode and flooding at the cathode. In the present work, water transport and flooding in the direct methanol fuel cell are investigated through both experimental and modeling analyses and an interpretation of such phenomena is proposed. The model is validated on the experimental data of two different fuel cells in an extensive range of operating conditions. The analysis elucidates that water transport through the cathode diffusion layer is determined by vapor diffusion, slightly affected by current density, and by liquid water permeation proportional to current density, that occurs when liquid pressure in the electrode exceeds a threshold value. To simulate the effects of cathode diffusion layer flooding two mechanisms must be considered simultaneously: superficial pore obstruction, proportional to liquid water concentration in cathode channel, and bulk pore obstruction, proportional to liquid water permeation. The modeling analysis proposes the correlations to reproduce the effects of cathode flooding and permits to discuss the onset and magnitude of such phenomenon and the influence of micro-porous layer.

Capítulos en libros This paper proposes a simplified approach to design power system stabilizers (PSSs) aimed at damping low frequency inter-area oscillations when only limited information of the power system is available. The proposed method uses a simplified two-machine test system and a robust-PSS-design method based on eigenvalue sensitivities. The proposed approach has been used to evaluate the contribution of a number of PSSs installed in Spanish generators to the damping of 0.15 Hz inter-area mode of the European system. info:eu-repo/semantics/publishedVersion