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The reliability of power systems, in terms of uninterrupted electricity supplies, is dependent on the reliability of the system's elements, especially the generation sources and transmission lines. The reliability of a coal-fired power unit's operation is essentially affected by the unit's main components, i.e. the turbine, the boiler and the generator. According to the statistics, the boiler is the most failure-prone element of the power unit. Therefore, efforts aimed at improving the reliability must include actions that enable early diagnostics of the state of the individual devices. In this paper it has been proposed that the optimal time to perform diagnostic testing of boiler tubes should be determined using risk analysis. Using the net present value (NPV) discounted cash flow index and the avoided risk criterion, a procedure has been put forward that optimizes the time when diagnostic tests should be carried out. The method has been applied to optimize diagnostic testing of boiler tubes, where corrosion is the principal cause of damage. Methods have also been given to determine the probability of the failure of such elements. • Maintenance planning based on criteria of avoided risk value and NPV index. • Optimization of periods of performing diagnostic tests. • Evaluation of the risk of corrosion damage to boiler tubes. [ABSTRACT FROM AUTHOR]

The consumption of fossil fuels, which are not economically and environmentally sustainable, can be reduced by producing biofuels, such as bioethanol. This study presents a reproducible model of the ethanol production process developed with Aspen Plus® software. The work's goal is to enhance the amount of ethanol produced per tonne of biomass and, therefore, the carbon yield of the process. The main steps of the process are the gasification of the pretreated switchgrass, the cleaning of the syngas obtained, the fermentation of the syngas to ethanol and its purification. The parameters relating to gasification were set to produce syngas with an optimal composition for the fermenter. A discounted cash flow analysis was used to determine the minimum ethanol selling price for different plant scales and H 2 prices. By enriching the syngas with green H 2 and adopting an optimal bioreactor, a remarkable ethanol yield of 1015.04 L/t of switchgrass can be obtained. Considering a plant size of 750,000 t/y of switchgrass, the minimum ethanol selling price is 1.07 $/L for the base scenario and is further lowered to 0.77 $/L for the 2050 H 2 scenario. The potential savings of building more plants were also assessed thanks to the learning effects. [Display omitted] • Gasification set to produce an optimal syngas composition for the fermenter. • Considerable ethanol yield of 1015.04 L/t switchgrass. • Adding green hydrogen to the syngas increase the process carbon yield of 23%. • Minimum ethanol selling price of 1.07 $/L processing 750000 t/y of switchgrass. • Reduction of almost 30% of the ethanol price considering 2050 green H 2 scenario. [ABSTRACT FROM AUTHOR]

The power generation from renewable sources is an interesting alternative to the diversification of the energy matrix of a country. This paper presents a probabilistic valuation method for power generation projects from renewable sources. It focuses on biomass plants that use sugarcane bagasse. The main objective is to bring a wider knowledge surrounding projects for investors that participate in energy auctions. Therefore, the highlight is for the net present value that allows us to analyze the financial viability of projects. Two stochastic variables are involved in the problem, the power generation and the energy price in the short-term market. Monte Carlo Simulation and Discounted Cash Flow methods are employed. A case study is carried out for a biomass plant. Sensitivity analysis is presented for different values of investment, bid, and minimum attractive rate of return. For each simulated scenario, the probability distribution of the net present value, the average net present value, and the internal rate of return are calculated. For the analyzed case study, the return of the project is more sensible to the bid value than the investment cost. The proposed method can be used as a tool to assist investors in energy auctions from renewable sources. [ABSTRACT FROM AUTHOR]

As the deployment of renewable energies increases, the development of power sources needed to adjust the supply–demand balance plays an important role. This study investigates a solid oxide fuel cell combined cycle (SOFC-CC) system with carbon dioxide capture, utilization, and storage (CCUS) that adopts green hydrogen methanation of stored CO 2. The proposed system has high power generation efficiency and does not contribute to global warming because the CO 2 emitted during operation is captured after separation, stored in carbon capture and storage, and converted into a synthetic fuel by methanation. However, because the economic feasibility of SOFC-CC with CCUS is unknown, the discounted cash flow method, which is used in the Projected Cost of Generating Electricity report, is used in this study. For a scenario with a 750 MW rated output, 25 MW photovoltaic capacity, and 3% discount rate at a unit electricity sales price of 0.36 USD/kWh, the simple integration balance, net present value, and dynamic payback periods are 9, 10, and 12 years, respectively. Therefore, the proposed system is economically viable. • An SOFC-CC with CCUS and green hydrogen methanation of stored CO 2 is proposed. • CO 2 emitted from operation is stored and converted into methane for use in SOFC. • The system is efficient, environmentally friendly, and economically viable. • The technology helps promote balance between renewable energy supply and demand. [ABSTRACT FROM AUTHOR]

Herein a novel path is analysed for its economic viability to synergize the production of biomethane and dimethyl ether from biogas. We conduct a profitability analysis based on the discounted cash flow method. The results revealed an unprofitable process with high cost/revenues ratios. Profitable scenarios would be reached by setting prohibitive DME prices (1983–5566 €/t) or very high feed-in tariffs subsidies (95.22 €/MWh in the best case scenario). From the cost reduction side, the analysis revealed the need of reducing investment costs. For this purpose, we propose a percentage of investment as incentive scheme. Although the size increase benefits cost/revenues ratio, only the 1000 m3/h biogas plant size will reach profitability if 90% of the investment is subsidized. A sensitivity analysis to check the influence of some important economical parameters is also included. Overall this study evidences the big challenge that our society faces in the way towards a circular economy. • Novel alternative for synergizing bio-methane and dimethyl ether production. • Profitability analysis for four different plant sizes. • The effect of dimethyl ether price and subsidies is studied. • The analysis revealed a technically viable but financially unprofitable process. • Evidence of the need of a strong green policy-making strategy. [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) systems transform solar irradiation into electricity, thereby substituting for traditional energy sources and reducing environmental pollution. The present work evaluates a developed market (Italy) in which subsidies have been re-introduced for PV plants with a nominal capacity above 20 kW through the FER1 (renewable energy sources) Decree. The discounted cash flow (DCF) methodology is applied to several cases of PV plants in public buildings, in order to determine the value of several critical variables (i.e. level of insolation, plant size, share of self-consumption, investment cost, electricity purchase price). In particular, differences in net present value (NPV) and discounted payback time (DPBT) between subsidy and no-subsidy scenarios are quantified. Break-even point (BEP) analysis is used to define the share of self-consumed energy for which NPV is positive. This share is found to range from 9 to 28% in 105 kW plants and from 10 to 35% in 25 kW plants. In addition, the results verify profitability in almost all of the baseline case studies and only half of the alternative scenarios (involving no subsidies). The estimated profits are consistent with investments aimed at increasing the share of self-consumed energy. • The proposed economic model supports public decision makers. • The economic model is based on both baseline and alternative scenarios. • PV systems realized on public buildings can be economically viable. • PV plant profitability is not verified in half of the cases without subsidies. • Share of self-consumed energy is the key variable in the economic assessment. [ABSTRACT FROM AUTHOR]