• Energy Research

Abstract With a potential geothermal generation of 610 GWt, Spain constitutes a promising EU-28 country for geothermal direct heating systems and binary cycle electricity production. Spain has a need to reduce energy consumption in buildings and in the secondary sector in order to comply with the Spanish Energy Plan 2011–2020, which establishes an objective of 50 MWe of electricity generation from geothermal energy and 66 MWt for direct heating use. Geothermal pumps are admissible in low and medium temperature heating schemes, but to achieve these energy savings targets, the most interesting way to generate energy is by using a CHP production from binary cycle plants. An analysis determining the energy consumption for Spanish dwellings shows that with a low-temperature design concept for district heating distribution, an organic Rankine cycle plant of 15 MWt with a geothermal temperature supply of 105 °C and a vector transportation fluid mass of 100 kg/s can cover 3% of the expected targets of electricity from geothermal sources and 15% of that expected for direct heating.

Energy efficiency is becoming one of the key research topics in the energy field and has, therefore, attracted extensive attention in recent research [...]

Abstract Electricity generation costs are typically higher on islands than in mainland regions, primarily due to the costs associated with conventional primary energy transportation. However, at the same time, islands are commonly granted with significant renewable energy potential in terms of wind, solar radiation and marine energy, among others, varying by case. This article is focused on the impact that the grid regulatory framework has had on several islands from both the technical and economical points of view, with respect to renewable energy development. A comparison among the studied islands is carried out. Additionally, the possible differences between each island (or archipelago) and the rest of the corresponding country on the mainland are analysed to determine to what extent the peculiarities of the islands have been taken into account in the regulations. Our objective is to analyse whether the renewable energy developments on certain islands have taken place because of certain favourable scenarios or by promoting specific actuations, which could be applicable on other islands to promote similar developments. As a result of the study, strategic key ideas are identified to increase the renewable energy percentage of the electricity generation and energy consumption mix on islands.

The energy flows of the double skin, glass-glass façades have been analysed, establishing a mathematical model to determine the energy savings provided by this construction solution in 10 cities in Spain. It has been found that the two climatological variables that most influence energy savings are outdoor temperature, as it is directly related to the demand for heating, and solar irradiation, as it is the source of energy from which savings are extracted. Energy savings in winter vary between 11.1% and 20.5%, depending on the weather. A linear relationship between the annual average outdoor temperature and the useful energy provided by the double- skin façade has been determined. It was verified that the maximum energy saving occurs when the façade is offset a few degrees to the east from the pure south orientation. It deviates further east, the higher the annual average temperature. A linear relationship has been established between the outside temperature and the azimuth of the façade with which the maximum energy saving occurs. To obtain savings percentages greater than 20%, the ratio between the double-skin façade surface and the total heated surface of the building must be less than 7.

Abstract A triple-state LiCl–H 2 O absorption system with a power of 10 kW that is fully driven by solar thermal energy has been designed and installed in a detached house in Spain. The system dissipates heat through a swimming pool, avoiding the need for a cooling tower. The system is fed using a solar thermal system with an area of 35.54 m 2 . The behavior of the system was monitored for a full year. The design and the calculations for the thermal requirements are presented, and the values of the coefficient of performance (COP) and the expected temperatures are compared with those obtained experimentally. This paper demonstrates that the actual values are slightly lower than the simulated values. The experiment has validated the possibility of using a swimming pool as a sink for heat dissipation. The economic analysis shows that the internal rate of return (IRR) reaches 12.45% while achieving a 68% reduction in greenhouse gasses GHG emissions. The results show that this approach can add great value to solar thermal energy systems while avoiding problems due to high temperatures during the summer months.

The current EU 2020 reference framework has set a 20% goal for energy coming from non-exhaustive resources. In general, it can be said that the national action plans for renewable energy sources and the biennial control provided in Directive 2009/28/EC, regarding the promotion of the use of energy from renewable sources, have been adequate in encouraging clarity for venture capitalists and other stakeholders and, thus, have favored a rapid development of renewable energy from 10.4% in 2007 to 17% in 2015. Between 2005 and 2013, the Spanish government implemented a renewable aid plan that induced an important boost in the number of wind energy projects facilitated by companies. This scheme was modified in 2013, resulting in a drastic decrease in the investments on wind energy capacity. The reason that this regime was modified not only because of the worldwide economic downturn since 2010 but also owing to the shortcomings of this scheme. The expected venture capitalist behavior with respect to the current energy regime is still uncertain. Given the limited support provided by the Spanish government, any remarkable development seems unlikely. This research suggests that a sudden change in the decreased investments on wind energy capacity is unlikely and the wind energy targets for 2020 will not be achieved if no new policies are implemented. 3,632 12,11 Q1 Q1 SCIE

Abstract The purpose of this paper is to prove as possible the improvement of the efficiency of a photovoltaic power plant, if it could be installed on top of a water canal, and how this facility could at the same time improve the efficiency of the water canal. The Tajo-Segura water transfer located in Spain has been chosen as the scenario for this research paper. The use of a water canal for this type of photovoltaic facility involves several problems. For example, it is very important that under no circumstance should any change on the canal structure affect the main end-use purpose of the hydraulic infrastructure (to channel water). Moreover, these facilities are strongly linear structures, so there is a problem connecting the electricity to the network. Nevertheless, these problems could be solved or minimized by applying different technical solutions, and if optimal synergies between infrastructures were obtained. It should be taken into account that the water facilities, which are already on service, save a significant quantity of water, and that these savings are achieved while avoiding the evaporation produced by direct solar radiation. The facility in this study can increase its efficiency, thanks not only to the optimal positioning to avoid the shadow between panels but also because panels can be cooled with the water that the canal contains. Focusing on these improvements, different types of technology implementation have been studied, concluding that the best option is the fixed system technology. A special methodology to geometrically place the photovoltaic panels has been developed. A proposal for novel cooling is also included in this work. The results of this study show that the project could be developed with an investment of 248 M€. Through the power generation and the savings in canal water resources, the investment could be repaid in approximately 15 years. The contribution of this work is the demonstration of the technical and economic interest of the optimal configuration analyzed.

Abstract Very low enthalpy geothermal systems have been traditionally associated to the use of electricity as primary energy heat pumps supply. Gas engine heat pumps (GEHP) have been recently introduced in the current market. In this research, the electric heat pumps (EHP) as well as the GEHPs (considering natural gas and biogas as combustibles) have been analysed. The calculation of the ground source heat pump (GSHP) system has been made for a building placed in three different areas. Results reveal the influence of the heat pump configuration on the whole geothermal design. This research finally considers the European policies whose aim is a sustainable low-carbon economy by 2020. According to the existing Energy Efficiency Directive, energy requirements are defined for new and existing residential and non-residential buildings in the Member States. Based on these standards, the research compares the geothermal heat pump scenarios and a traditional one to determine if they would meet the regulation. Final results show that the Directive is a highly-demanding regulation that can only be respected by using EHP in one of the areas. The rest of geothermal heat pumps scenarios are much closer to meeting the energy standards than the traditional fossil heating sources.

Abstract Energy needs increases day by day in those areas of the world where the electrical distribution lines are not available. This situation limits the industrial and economic development of these areas as well as the establishment of the population, so that it facilitates the exodus and the uprooting of people. At the moment the electrical energy supply in remote areas is based on solutions with generator sets, consuming great amounts of fuel with a great environmental damage. The technological development of renewable energies and the new concepts for their management, make possible proposing off-grid generation solutions for providing great amount of energy with high quality and reliability. Along this paper, a smart-grid configuration is proposed which is developed with products of proved reliability and which uses renewable energies as main generation source. This configuration allows having “standard” grid services anywhere, without the need of connection to the traditional grid. Environmental, economic and operation benefits of using these technologies against traditional solutions are also presented in this paper. This proposed solution allows the economical development and exploitation of areas where due to the lack of energy or to the energy cost it has not been possible until now.