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In the framework of a scenario with an always increasing share of generation from variable renewable sources, the need for systems able to store energy or to convert the excess generation into useful goods is becoming of paramount...
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In the framework of a scenario with an always increasing share of generation from variable renewable sources, the need for systems able to store energy or to convert the excess generation into useful goods is becoming of paramount importance. While several projects and pilot plants deal with direct energy storage or with the conversion of the excess generation into other energetic goods (hydrogen or methane) often overlooking economic considerations, this paper proposes a cost-effective approach in which liquified methane and oxygen are produced and sold on their specific markets, which represents one of the first profitable Power-to-X applications at current market values. The paper presents the completely new and never investigated before idea of coupling the plant with a freely available source of pure carbon dioxide from a geothermal unit, thus making it possible to produce synthetic methane to be liquefied, stored and then used in other sectors of the society. The carbon dioxide coming with the geothermal fluid is no longer released in the environment as it currently naturally happens even when not going through the geothermal facility. Detailed models of the main system components were created, and an optimization procedure was carried out. Interestingly, the revenues from the sale of liquefied oxygen are well above those coming from synthetic methane and turn the system profitable. With a proper operation planning, bidding on the electricity day-ahead-market, a large hydrogen storage system proved to be unnecessary. The results of the system optimization clearly show that this kind of systems, although conceived in a very favourable condition, can become profitable only if the energy storage function is coupled with the production of other goods services. Assuming an average electricity price of 52 Euro/MWh, the plant profitability is achieved for an LNG selling price of 0.45 (sic)/kg and an LOx price around 0.30 (sic)/kg. These figures will rapidly decrease in the near future as lower electricity prices are forecasted.
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The paper proposes an innovative scheme exploiting oxygen liquefaction as a means for storing excess electricity generation from renewable sources. Liquid oxygen is then used in an oxy-combustion process with LNG to generate elect...
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The paper proposes an innovative scheme exploiting oxygen liquefaction as a means for storing excess electricity generation from renewable sources. Liquid oxygen is then used in an oxy-combustion process with LNG to generate electricity when renewable energy generation is below the demand. An equivalent round trip efficiency is defined to make it possible comparing the system performances with hybrid plants including conventional generation and storage. The proposed scheme exhibits very high equivalent round trip efficiency, giving the system operators the opportunity to integrate more and more renewable energy generation inside power systems. Liquefied carbon dioxide and water are byproducts of the process. The size of the plant and of the storage tanks needed for a 4 TWh yearly demand with a peak around 800 MW is compatible with state-of-the-art systems used for LNG storage in similar size gas power plants.
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Power generation systems recovering waste heat, such as Organic Rankine Cycles (ORC), cannot work efficiently when the highest temperature ranges between 100 degrees C and 85 degrees C. For this reason, upgrading and recycling the...
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Power generation systems recovering waste heat, such as Organic Rankine Cycles (ORC), cannot work efficiently when the highest temperature ranges between 100 degrees C and 85 degrees C. For this reason, upgrading and recycling the low-grade waste heat is very interesting in this temperature range. High temperature heat pumps can upgrade the waste heat raising the temperature up to 150 degrees C, which is adequate for some productive process in the food, paper, chemical and tobacco industries. Despite the intense research effort, even focusing solely on the vapour compression heat pumps, selecting the most suitable working fluid for these applications is not trivial. The selection of a fluid for a high temperature heat pump is limited by several technical constraints and a trade-of between a high efficiency and a large volume flow rate is necessary. Since the recommended fluid may change for different combinations of heat source and heat sink temperatures, a systematic investigation of the heat pump performance with different fluids working at different operational conditions has been carried out. The effect of different technical limitations has been discussed, and the most suited fluids both with respect to the highest efficiency and optimal volume flow rate have been recommended.
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Biomass is becoming a more and more interesting option to replace conventional fossil fuels for heat and power generation. Small plants able to use solid biomass, collected in the plant neighborhoods, are having a growing diffusio...
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Biomass is becoming a more and more interesting option to replace conventional fossil fuels for heat and power generation. Small plants able to use solid biomass, collected in the plant neighborhoods, are having a growing diffusion: University of Pisa jointly with some local manufactures has designed, built and tested an externally fired micro gas turbine (EFMGT) supplying 70 kW of electricity as Well, as 200 -250 kW of useful heat. The present paper focuses on the development of a dynamic simulator of the plant. A mathematical model was implemented for the physical and chemical behavior of the biomass combustion process, as well as for heat transfer mechanisms and turbine behavior to assess the plant operating Variables in both steady state and transient operating conditions. Comparison between model results and data gathered on a test plant shows a good matching (with deviation below 5%) of the main and most critical variables in a wide range of operating conditions which makes the model suitable for synthesize a closed-loop control system able to ensure the highest performances in power production. (C) 2015 Elsevier Ltd. All rights reserved.
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The current increase in the deployment of new renewable electricity generation systems is creating new challenges in balancing electric grids. Solutions including energy storage at small and large scales are becoming of paramount ...
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The current increase in the deployment of new renewable electricity generation systems is creating new challenges in balancing electric grids. Solutions including energy storage at small and large scales are becoming of paramount importance to guarantee and secure a stable supply of electricity. This paper presents a study about a hybrid solution including a large scale energy storage system coupled with power generation and fast responding energy storage systems. The hybrid plant is able to deliver the energy previously stored by using an air liquefaction process either with or without the contribution of additional energy from combustion. The paper also highlights how such hybrid plants may offer the chance of providing the grid with fast control services.
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Biogas plants are an interesting solution for production of clean energy. Biogas produced in an anaerobic digester can be used locally to produce electric energy in an internal combustion engine or in a micro-gas turbine. A portio...
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Biogas plants are an interesting solution for production of clean energy. Biogas produced in an anaerobic digester can be used locally to produce electric energy in an internal combustion engine or in a micro-gas turbine. A portion of the waste heat is used to keep the digester at a constant temperature which is a necessary condition for a correct operation of the digester. Generally, waste heat overcomes that necessary to keep the digester at the desired temperature and a big portion of this thermal energy is dissipated. Many solutions exist to increase the amount of heat recovered. In this study, the use of an absorption chiller to decrease the inlet temperature of a micro-gas turbine operating with biogas was considered. The advantage of this solution relies in a more stable operation of the micro gas turbine and an increase in the power output. The integration of the absorber chiller in the biogas plant and the effect of the ambient conditions were investigated in detail. The study was based on an existing plant operating near Pisa (Italy). A model of the system has been developed in AMESim and a numerical simulation has been performed. The effects of different temperature profiles, corresponding to different climate conditions, have been investigated both from the energy and economic points of view. The results showed that local climate conditions strongly influence the effectiveness and the profitability of the inlet turbine air cooling technique. In those climates where the temperatures are constantly high over the year, this technique may lead to interesting benefits and profitability.
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Designing off-grid microgrids is a costly and risky activity, especially for newly electrified communities in developing countries. Private developers and researcher have been using several economic indicators to value the profita...
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Designing off-grid microgrids is a costly and risky activity, especially for newly electrified communities in developing countries. Private developers and researcher have been using several economic indicators to value the profitability of an investment, such as Net Present Value, Discounted Payback Period, Levelized Cost of Electricity; however, each index has its advantages and specific limitations. Selecting a single objective may lead the developer to misestimate the profitability of a project, because a single index cannot accommodate the variety of requirements of the business process. Acknowledging this, this study proposes a wide analysis for highlighting the effects of different indicators onto the optimal design of an off-grid system. A multi-objective approach that optimizes together different economic indicators is proposed, based on the results of a preliminary analysis on single-objective formulations. A sensitivity analysis with respect to the electricity price, the load curtailment cost and the dispatching strategy is also performed. A numerical case study is proposed for a possible off-grid microgrid in Soroti, Uganda, which well represents a hard environment for business development. Results suggest that the proposed multi objective approach provides intermediate configurations that are a good compromise between multiple objectives, thus satisfying the difficult environment developers are enduring. (C) 2020 Elsevier Ltd. All rights reserved.
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In this work a novel approach is presented for topology optimization of electromagnetic devices. In particular a surrogate model based on Deep Neural Networks with encoder-decoder architecture is introduced. A first autoencoder le...
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In this work a novel approach is presented for topology optimization of electromagnetic devices. In particular a surrogate model based on Deep Neural Networks with encoder-decoder architecture is introduced. A first autoencoder learns to represent the input images that describe the topology, i.e., geometry and materials. The novel idea is to use the low dimensional latent space (i.e., the output space of the encoder) as the search space of the optimization algorithm, instead of using the higher dimensional space represented by the input images. A second neural network learns the relationship between the encoder outputs and the objective function (i.e., an electromagnetic quantity that is crucial for the design of the device) which is calculated by means of a numerical analysis. The calculation time for the optimization is greatly improved by reducing the dimensionality of the search space, and by introducing the surrogate model, whereas the quality of the result is slightly affected.
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Reaching universal access to electricity by 2030 requires a massive deployment of mini-grids in rural areas of developing countries. Among the many challenges hindering this process, there are the high uncertainties in assessing d...
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Reaching universal access to electricity by 2030 requires a massive deployment of mini-grids in rural areas of developing countries. Among the many challenges hindering this process, there are the high uncertainties in assessing demand patterns in rural communities, the costs of field survey campaigns, and the absence of ample and reliable datasets coming from existing projects. This paper tries to address these issues by presenting and discussing a database of load profiles from sixty-one off-grid mini-grids from developing countries worldwide, gathered from the literature, private developers and fieldworks, and reported with technical, socio-economic and geographical characterization factors. A clustering procedure led to the identification of five archetypal load profile clusters, which are presented and analyzed together with their load duration curves. Subsequently, the distribution among the clusters of the various characterization factors selected is studied. The proposed approach allows to widen the range of load profiles usually considered, and to seek correlations between the load profile shapes, the peak power and average energy consumption per connection, the number of customers, the age of measurement, geographical position, operator model, type of tariff and generation technologies present. This work establishes a first step in the creation of a shared database for load profiles of rural mini-grids, helping to overcome the lack of available data and difficulties of demand assessment, proposing original insights for researchers to understand load patterns, and contributing to reduce risks and uncertainties for mini-grid developers. (C) 2020 International Energy Initiative. Published by Elsevier Inc. All rights reserved.
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Italy has experienced a revolution in the electricity production mix in the years 2008-2015, when a large scale deployment of intermittent renewables caused a high volatility of electricity prices, stopped the investments in both ...
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Italy has experienced a revolution in the electricity production mix in the years 2008-2015, when a large scale deployment of intermittent renewables caused a high volatility of electricity prices, stopped the investments in both fossil and renewable power plants and caused a high degree of uncertainty in matching electricity demand and supply.
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