Numerical Optimization and Energetic Advantages of an Innovative Solar Power System Based on Scheffler Receiver Coupled with Volumetric Expanders

In the current context of increasing public awareness of the externalities of fossil fuel-based energy consumption, improvement in new technologies for energy-saving systems has become a crucial target to reduce both global warming and air pollution. Being motivated by such a critical matter, this study presents an innovative solar thermal plant based on volumetric expanders as work-producing devices coupled with Scheffler solar receivers as a thermal source. Nowadays, Scheffler receivers are well performing owing to high efficiency of the focal receiver which reduce heat losses. Simultaneously, screw expanders are volumetric machines which are able to convert thermal to mechanical power with acceptable efficiency also by expanding vapor-liquid blends at low operating pressures. The numerical model presented in this study evaluates the energetic benefits of the proposed solar power system for various operating situations. Parametric optimization of this solar power plant is then performed in a broad range of operating conditions: the optimum evaporation temperatures, together with the corresponding maximum global efficiencies, were so defined under various solar radiation intensities. The numerical results attained in this research prove that solar electricity generation systems based on screw expanders coupled with the Scheffler receivers are a promising technology.

Energy, Environmental, and Economic Analyses of a District Heating (DH) Network from Both Thermal Plant and End-Users’ Prospective: An Italian Case Study

District heating (DH) is an alternative technology to Individual Heating (IH) for satisfying end-user’s needs. This paper assesses the competitiveness of a DH network in the center of Italy from energy, environmental, and economic points of view considering both thermal power plant and end-users‘ sides. On the thermal power plant side, the energy analysis considers the Primary Energy Saving (PES) and the specific energy (Esp) of the fuel actually exploited in the thermal power plant compared to its Low Heating Value (LHV), while the environmental analysis considers the avoided CO2 and the economic analysis considers the Energy Efficiency Certificates (EECs). Results showed that the current thermal power plant configuration with two boilers and a Combined Heat and Power (CHP) unit reaches a yearly PES of 21.3% as well as 1099 tCO2 avoided. From the economic analysis of the thermal power plant side, 829 EECs with an economic return of 207,222€ are obtained, while from the end-users’ side the DH network is cheaper than IH in 84.7% of the cases. Further technologies are also studied to enhance the CHP unit flexibility.

Supercritical CO2 Binary Mixtures for Recompression Brayton s-CO2 Power Cycles Coupled to Solar Thermal Energy Plants

In this work, an evaluation and quantification of the impact of using mixtures based on supercritical carbon dioxide “s-CO2” (s-CO2/COS, s-CO2/H2S, s-CO2/NH3, s-CO2/SO2) are made as a working fluid in simple and complex recompression Brayton s-CO2 power cycle configurations that have pressure drops in their components. These cycles are coupled with a solar thermal plant with parabolic-trough collector (PTC) technology. The methodology used in the calculation performance is to establish values of the heat recuperator total conductance (UAtotal) between 5 and 25 MW/K. The main conclusion of this work is that the cycle’s efficiency has improved due to using s-CO2 mixtures as working fluid; this is significant compared to the results obtained using the standard fluid (pure s-CO2). Furthermore, a techno-economic analysis is carried out that compares each configuration’s costs using pure s-CO2 and a mixture of s-CO2/COS with a molar fraction (70/30), respectively, as working fluid where relevant results are obtained. These results show that the best configuration in terms of thermal efficiency and cost is the RCC-RH for pure sCO2 with values of 41.25% and 2811 $/kWe, while for the mixture sCO2/COS, the RCC-2RH configuration with values of 45.05% and 2621 $/kWe is optimal. Using the mixture costs 6.75% less than if it is used the standard fluid (s-CO2).

Pembangkit Listrik Tenaga Sampah: Antara Permasalahan Lingkungan dan Percepatan Pembangunan Energi Terbarukan

The government is trying to encourage the use of renewable energy, one of which is from waste to energy power plant. Efforts to accelerate the development of the plant are carried out through Presidential Regulation Number 35 of 2018. However, only one plant has been operating commercially since May 6th, 2021. This study aims to describe the development, the obstacles, and whether the plant is a solution to meet electricity needs or environmental problems. Through qualitative research, we found that the plant in Surabaya has been operating commercially; the plants in Surakarta and DKI Jakarta are in the construction stage; the plants in Palembang and Tangerang are in the stage of confirming the developer, and the rest are still on auction stage, Pre- Feasibility Study, Outline Business Case, or Final Business Case. The high tipping fee, limited local government budget, overestimation of potential for waste as electricity, limited competent human resources, the high selling price of the plant electricity, and no bankable guarantee for investment are obstacles to the plant development. The thermal plant is an instant solution for cities with above 1.000 ton/day waste and limited land for landfills. In the future, there should be regulatory support through the Renewable Energy Bill to overcome the obstacles. In addition, there should be a careful calculation of the energy potential of waste, a minimum budget allocation of 2–3% for waste management and preparing capable human resources, providing adequate waste collection and transportation infrastructure, and educating the public on sorting waste. AbstrakPemerintah berupaya mendorong pemanfaatan energi terbarukan, salah satunya dengan membangun Pembangkit Listrik Tenaga Sampah (PLTSa). Upaya mempercepat pembangunan PLTSa dilakukan melalui Peraturan Presiden Nomor 35 Tahun 2018. Namun, hingga 6 Mei 2021 hanya satu PLTSa telah beroperasi secara komersial. Penelitian ini bertujuan mendeskripsikan perkembangan pembangunan PLTSa, kendala-kendala dan permasalahan pengembangannya, dan apakah PLTSa solusi pemenuhan kebutuhan listrik atau mengatasi masalah lingkungan. Melalui penelitian kualitatif, diketahui 1 PLTSa sudah beroperasi secara komersial (di Surabaya), 2 PLTSa dalam tahap konstruksi (di Surakarta dan DKI Jakarta), 2 PLTSa dalam tahap sudah ada pengembang (di Palembang dan Tangerang), dan sisanya masih dalam tahap lelang, Pre-Feasibility Study, Outline Business Case, atau Final Business Case. Lambatnya pembangunan PLTSa terjadi karena tingginya tipping fee, anggaran pemerintah daerah terbatas, over estimasi potensi listrik dari sampah, keterbatasan sumber daya manusia yang kapabel, tingginya harga jual listrik PLTSa, tidak adanya insentif bagi pengembang, dan tidak adanya jaminan bankable untuk investasi. PLTSa termal merupakan solusi instan mengatasi permasalahan lingkungan untuk kota dengan produksi sampah di atas 1.000 ton/hari dan keterbatasan lahan untuk TPA. Untuk itu, perlu ada dukungan regulasi melalui RUU EBT mengenai harga jual listrik PLTSa yang bersaing, insentif bagi pengembang PLTSa, dan jaminan bankable untuk investasi PLTSa. Selain itu, perlu ada perhitungan secara cermat potensi energi dari sampah, alokasi APBD minimal 2–3% untuk pengelolaan sampah, dan menyiapkan sumber daya manusia yang kapabel, menyediakan sarana prasarana pengumpulan dan pengangkutan sampah yang memadai, dan mengedukasi masyarakat untuk memilah sampah.

Terrestrial Heat Repository for Months of Storage (THERMS): A Novel Radial Thermocline System

This paper describes a terrestrial thermocline storage system comprised of inexpensive rock, gravel, and/or sand-like materials to store high-temperature heat for days to months. The present system seeks to overcome past challenges of thermocline storage (cost and performance) by utilizing a confined radial-based thermocline storage system that can better control the flow and temperature distribution in a bed of porous materials with one or more layers or zones of different particle sizes, materials, and injection/extraction wells. Air is used as the heat-transfer fluid, and the storage bed can be heated or “trickle charged” by flowing hot air through multiple wells during periods of low electricity demand using electrical heating or heat from a solar thermal plant. This terrestrial-based storage system can provide low-cost, large-capacity energy storage for both high- (∼400–800°C) and low- (∼100–400°C) temperature applications. Bench-scale experiments were conducted, and computational fluid dynamics (CFD) simulations were performed to verify models and improve understanding of relevant features and processes that impact the performance of the radial thermocline storage system. Sensitivity studies were performed using the CFD model to investigate the impact of the air flow rate, porosity, particle thermal conductivity, and air-to-particle heat-transfer coefficient on temperature profiles. A preliminary technoeconomic analysis was also performed to estimate the levelized cost of storage for different storage durations and discharging scenarios.

An Enhanced Solar Hybrid Brayton and Rankine Cycles with Integrated Magnetohydrodynamic Conversion System for Electrical Power Generation

In many developing countries,the use of conventional power plants to generate electricity is not meeting the increasing demands. Therefore, it has become important to find sustainable alternatives. In the present study, a solar hybrid combined cycle power plant consisting of a solar thermal plant, large-scale gas and steam turbines, and a magnetohydrodynamic generator has been investigated under oxy-fuel combustion. The performance analysis of this system under fuel pressure rate varying from 10 to 25 bar was conducted using Cycle Tempo software. The analysis of the gas and steam combined cycle shows that the net powers and the net efficiencies obtained ranged from 98 MWe to 134 MWe and 30.5% to 40%, respectively. In addition, the integration of the magnetohydrodynamic generator to the combined cycle led to an increase in the overall power from 169 MWe to 205 MWe. Moreover, it is seen that the fuel mass rate (2.81 kg/s) obtained in the gas turbine system under oxy-fuel combustion is significantly reduced when compared to conventional systems. The incorporation of solar energy and oxy-fuel combustion in the gas turbine system has increased the combustor inlet and outlet temperature and reduced the fuel consumption. From these observations, the solar hybrid system proposed in this study does not only generates electric power but also reduce the turbine exhaust fumes and CO2 emissions, which is a key factor in minimizing environment pollution.

Short-Term Hydrothermal Scheduling using Imperialist Competitive Algorithm

In this study, the Imperialist Competitive Algorithm (ICA) is proposed to solve a multi-chain Short-Term Hydrothermal Scheduling problem (STHTS). It aims to minimize the generation cost of the thermal plants while satisfying the thermal and hydro plants constraints. In order to evaluate the effectiveness of the ICA, it has been tested on a system having a hydro plant with four-cascaded reservoir and a thermal plant. The results are compared with that obtained by other techniques. The ICA has the good convergence and the better results.

Performance of the Pressure Assisted Forward Osmosis-MSF Hybrid Desalination Plant

An osmotically driven membrane process was proposed for seawater pretreatment in a multi-stage flashing (MSF) thermal plant. Brine reject from the MSF plant was the draw solution (DS) in the forward osmosis (FO) process in order to reduce chemical use. The purpose of FO is the removal of divalent ions from seawater prior the thermal desalination. In this study, seawater at 80 g/L and 45 g/L concentrations were used as the brine reject and seawater, respectively. The temperature of the brine reject was 40 °C and of seawater was 25 °C. Commercial thin-film composite (TFC) and cellulose triacetate (CTA) membranes were evaluated for the pretreatment of seawater in the FO and the pressure-assisted FO (PAFO) processes. Experimental results showed 50% more permeation flux by increasing the feed pressure from 1 to 4 bar, and permeation flux reached 16.7 L/m2h in the PAFO process with a TFC membrane compared to 8.3 L/m2h in the PAFO process with CTA membrane. TFC membrane experienced up to 15% reduction in permeation flux after cleaning with DI water while permeation flux reduction in the CTA membrane was >6%. The maximum recovery rate was 11.5% and 8.8% in the PAFO process with TFC and CTA membrane, respectively. The maximum power consumption for the pretreatment of seawater was 0.06 kWh/m3 and 0.1 kWh/m3 for the PAFO process with a TFC and CTA membrane, respectively.

Experimental Investigation of Direct Steam Generation Dynamics in Solar Fresnel Collectors

Direct steam generation (DSG) is a technology used to produce steam from a solar concentrated thermal plant directly in the solar field without the use of an intermediate steam generator. This technology is attractive due to economic considerations but is technically challenging. In this brief, the results of an experimental study of DSG dynamics are presented. The study provides a detailed description of these effects supported by experimental results and suggests ways to coping with them.