• Energy Research

Energy production from clean sources is mandatory to reduce pollutant emissions. Among different options for hidden hydropower potential exploitation, Pump-as-Turbine (PaT) represents a viable solution in pico- and micro-hydropower applications for its flexibility and low-cost. Pumps are widely available in the global market in terms of both sizes and spare parts. To date, there are several PaTs’ performance prediction models in the literature, but very few of them use optimization algorithms and only for specific and limited prediction goals. The present work proposes evolutionary Artificial Neural Networks (ANNs) based on JADE, which is a typology of differential evolution algorithm, to forecast Best Efficiency Point (BEP) and performance curves of a PaT starting from the pump operational data. In this model, JADE is employed as optimizer of basic ANNs to upgrade parameter values of the learning rate, weights, and biases. The accuracy of the proposed model is evaluated through experimental data available from the literature and compared to a basic ANN and two versions of the differential evolution algorithm. Results are also validated with experiments on a PaT showing that the proposed method can achieve an average R2-value of 0.97, which is 5% higher than the one obtained with a basic ANN.

Renewable power generation can help countries meet their sustainable development goals through provision of access to clean, secure, reliable and affordable energy. Concentrated Solar Power (CSP) is a power generation technology that uses mirrors or lenses to concentrate the sun's rays and, in most of today's CSP systems, to heat a fluid and produce steam. CSP technologies are not currently widely deployed. This paper present a possible solution for the implementation of the electronic control board for a CSP system.

Abstract: The hydropower sector is moving to the small-scale generation due to the exploitation of the majority water reservoirs with the aim of providing electrical energy in rural zones. Pump-as-Turbines (PaTs) is one of the most interesting technology due to their use for recovering energy in different industrial applications. Several studies aimed to study the performance of the tested PaTs and to describe their performance curves. The efficiency of these machines at their Best Efficiency Point (BEP) is comparable as much as the pump mode. In this work, a general analytical method for forecasting PaTs performance in turbine mode was investigated.

Abstract In this paper, the concept design of a small-scale CSP system for residential application is presented and by means of analytical simulations. The concept configuration consists of 48 hexagonal heliostats for a total reflecting surface area of 8.7 m2 and a nominal power of 5 kWth. The main objective of this work is to describe the design of a small-scale CSP system and to present an analytical simulation tool with the aim to assess the influence of different irradiance data on the performance of the system. Three different Italian locations have been considered: the city of Ghedi for the North of Italy, Roma for the Centre and Bari for the South. The simulations using the solar radiation data (SoDa) in 2005 and the mean year data of the Meteonorm database are analyzed and compared. Results disclose that the performance calculated using single year and mean year irradiance data for Roma and Bari differ less than 10%. Instead, in the case of Ghedi the difference is larger than 20%. In addition, the simulation tool allows to evaluate the thermal energy collected throughout the year: in Roma and Bari it is over 7721 kWh and 7647 kWh respectively, which is a consistent amount of energy that can be used for residential and civil applications; in Ghedi, only 5384 kWh are collected.

Abstract Internal combustion engines are well spread in traditional power-generation systems: given their reliability, low-cost and performance it is desirable to avoid their full substitution in the short term, but, rather, to rely on the reduction of their environmental impact. This can be achieved by implementing solutions that involve minor modifications on the devices, such as the use of different fuels. In this work, the fossil fuels replacement approach has been applied to a micro-cogeneration system based on a small water-cooled compression ignition engine. The effect of bioethanol introduction as a diesel substitute in six diesel-biodiesel blends has been studied in terms of performances of the whole energy-conversion system and of the exhaust gas emissions. Positive results have been obtained showing that with a small amount (3%) of bioethanol, enhancements can be fulfilled both on performances (with approximately an average 13%-boost of the electrical and thermal efficiency) and emissions (reaching nearly a 80% of smoke opacity reduction).

Abstract This work is an in-depth analysis of the performance behavior of a small scale single effect thermal desalination plant. The prototype, which refers to the distributed micro cogeneration field, consists of a 1 kWe Stirling engine coupled with a single effect thermal desalination plant for the simultaneous production of electricity and >150 L/day of fresh water. The prototype was able to work in two different operation modes: batch operation and continuous operation. In the former, the evaporator tank is initially filled with the salt water up to its maximum and the evaporation process ends as the salt water level reaches the top of the coil. In the latter, concentrate is continuously extracted and salt water is fed inside the evaporator tank in order to maintain brine salinity almost constant. In a previous work authors investigated the plant performance in batch operation mode finding a good agreement with the predicted results. In this work, plant performance is evaluated in continuous operation and compared to the batch operation mode. In both cases, fresh water production reached a maximum of about 7 L/h in the best operating conditions. However, despite the higher complexity of the plant, performance is worse in the continuous operation mode due to the negative effect of the continuous seawater flow. Indeed, the lower the salt content of the treated water, the lower the fresh water production due to process limits which will be extensively discussed in the paper. More precisely, the plant's average productivities were about 1.3 L/kWh and 1.16 L/kWh of thermal energy input in batch and continuous operation modes respectively. In any case, the apparatus exhibited a very good response to varying thermal power input thus confirming the opportunity to feed the desalination plant also with different forms of waste heat. Hence the proposed solution, studied for a coupling with a 1 kWe Stirling engine, can be easily applied also to the other micro-CHP technologies.

Fuelling micro-combined heat and power (micro-CHP) devices using renewable sources, such as biogas, can enhance the energy and environmental benefits associated with such devices. This paper presents a solution for increasing the electric efficiency of biogas-fed Stirling co-generators by recuperating the energy content of the combustion flue gas. When economically and energetically convenient for micro-CHP operation, the exhausts can be used to pre-heat fresh combustion air. It was assessed that, due to the introduction of a spiral gas-gas heat exchanger, whose main design parameters were identified, the electric efficiency of the Stirling unit can be raised to up to 22.5%. To determine the advantages of applying the system analysed over a traditional Stirling device, a specific algorithm for the optimal management of the micro-CHP unit was built and applied to a residential case study. The results demonstrate that the extra cost of the high-efficiency recuperator can be easily recovered in approximately two years of system operation, providing an additional advantage over a standard Stirling device in terms of primary energy consumption and an approximately 6% increase in economic savings.

Abstract This work refers to an innovative integrated system for the simultaneous production of fresh water and electricity. In particular, a 1 kWe Stirling engine coupled with a thermal desalination plant has been considered for the purpose. The prototype, which refers to the distributed micro cogeneration field, has the final aim of building and testing a single effect distillation plant with a fresh water production of about 150 L/d. Firstly, thermodynamic theories and numerical analysis have been carried out to define the final prototype configuration. Then, an experimental test phase has been carried out to evaluate the actual plant performance. The experimental analysis has been in good agreement with the predicted results. In particular, at nominal operating conditions (@50 °C) the maximum heat transfer rate was higher than the evaporator heat exchanger designed condition (5.5 kWt). Despite the non-ideal plant thermal insulation, fresh water production reached a maximum of about 7 L/h at best operating conditions, proving a good process efficiency. According to the behavior predicted by the model, fresh water production is strongly dependent on the temperature difference between the heating fluid and the salt water in the evaporator tank while it is weakly influenced by the salt content of the treated water. Moreover, the apparatus exhibited a very good response to varying thermal power input thus confirming the opportunity to feed the desalination plant also with different forms of waste heat. More precisely, the plant average efficiency was about 1.3 L/kWh of energy input with minimum and maximum values equal to 1.16 and 1.42 L/kWh. Definitely the proposed solution, studied for a coupling with a 1 kWe Stirling engine, can be easily applied also to the other micro-CHP technologies.

The environmental sustainability of agricultural and industrial vehicles, as well as of the transportation sector, represents one of the most critical challenges to the sustainable development of a nation. In recent decades, compression-ignition engines have been widely used in on-road and off-road vehicles due to their better fuel economy, autonomy, compactness, and mechanical performance (spec. the high torque values). Due to the consistent environmental impact of fossil fuels, scientists are searching for alternative energy sources while preserving the beneficial features of diesel engines. The utilization of blends of diesel fuel, biodiesel, and bioethanol fuel (referred to as “ternary blends”) is among the most promising solutions for replacing fossil fuels in the near term, allowing, at the same time, us to continue using existing vehicles until new technologies are developed, consolidated and adapted to the agricultural and industrial sector. These ternary blends can lower exhaust emissions without creating major problems for existing fuel-feeding systems, typically designed for low-viscosity fossil fuels. One of the concerns in using liquid biofuels, specifically biodiesel, is the high chemical affinity with conventional and bio-based lubricants, so the main parameters of lubricants can vary significantly after a long operation of the engine. The comprehensive literature review presented in this article delves into the technical challenges, the main research pathways, and the potential solutions associated with the utilization of biofuels. Additionally, it investigates the emerging application of nanoparticles as additives in lubricants and biofuels, highlighting their valuable potential. This study also discusses the potential implementation of bio-ethanol in ternary blends, offering a promising avenue for reducing reliance on fossil fuels while maintaining engine efficiency.