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Organic Rankine cycle (ORC) turbogenerators are the most viable option to convert sustainable energy sources in the low-to-medium power output range (from tens of kWe to several MWe). The design of efficient ORC turbines is particularly challenging due to their inherent unsteady nature (high expansion ratios and low speed of sound of organic compounds) and to the fact that the expansion encompasses thermodynamic states in the dense vapor region, where the ideal gas assumption does not hold. This work investigates the unsteady nonideal fluid dynamics and performance of a high expansion ratio ORC turbine by means of detailed Reynolds-averaged Navier–Stokes (RANS) simulations. The complex shock interactions resulting from the supersonic flow (M ≈ 2.8 at the vanes exit) are related to the blade loading, which can fluctuate up to 60% of the time-averaged value. A detailed loss analysis shows that shock-induced boundary layer separation on the suction side of the rotor blades is responsible for most of the losses in the rotor, and that further significant contributions are given by the boundary layer in the diverging part of the stator and by trailing edge losses. Efficiency loss due to unsteady interactions is quantified in 1.4% in absolute percentage points at design rotational speed. Thermophysical properties are found to feature large variations due to temperature even after the strong expansion in the nozzle vanes, thus supporting the use of accurate fluid models in the whole turbine stage.

The growth in biofuels’ investment brings with it concerns about the social and environmental impacts of the sector. Several tools and frameworks have been used to address these concerns, including the Responsible Research and Innovation (RRI) framework. This paper analyzes whether this framework can be applied in contexts where local culture and values shape differently the freedom of speech and engagement, such as in developing countries in which biofuel innovation projects are often implemented. A literature review focused on eight case studies of other authors was used to explore the role of “participation” as a structural element of the RRI framework and the impact of its absence where effective participation in the innovation development process is not possible. In conclusion, we highlight how this inspirational normative framework, designed to influence innovation, is misused to judge its impacts. More than that, the conclusions of such misused applications reflect more the difficulties involved in applying guidelines than the responsible character of the innovation, whose impacts are usually defined upfront materially and measurably.

Low voltage distribution networks incorporating solar photovoltaic (PV) panels experience overvoltage and voltage unbalance during periods of low load and high PV generation. Resolving overvoltage by active power curtailment (APC) is an effective and cost-efficient solution. However, current APC techniques result in excessive and unfair power curtailment for prosumers at the sensitive parts of the grid that might induce neutral current. In this work, an analytical approach for fair APC and Reactive Power Control is presented for voltage regulation along with neutral current compensation. The desired power quality is maintained by controlling each phase of the PV inverter independently. The proposed algorithm regulates the voltage at the point of common coupling (PCC) within grid limits, eliminates neutral current, and reduces the grid unbalance. Furthermore, the results demonstrate that reducing the neutral current reduces the voltage at the PCC and consequently decreases the power curtailment required for overvoltage regulation.

In this paper we investigate the prospects for the large-scale use of low-emission energy technologies in Africa. Many African countries have recently experienced substantial economic growth and aim at fulfilling much of the energy needs associated with continuing along paths of economic expansion by exploiting their large domestic potentials of renewable forms of energy. Important benefits of the abundant renewable energy resources in Africa are that they allow for stimulating economic development, increasing energy access and alleviating poverty, while simultaneously avoiding emissions of greenhouse gases. In this study we analyse what the likely energy demand in Africa could be until 2050, and inspect multiple scenarios for the concomitant levels of greenhouse gas emissions and emission intensities. We use the TIAM-ECN model for our study, which enawbbles detailed energy systems research through a technology-rich cost-minimisation procedure. The results from our analysis fully support an Africa-led effort to substantially enhance the use of the continent's renewable energy potential. But they suggest that the current aim of achieving 300 GW of additional renewable electricity generation capacity by 2030 is perhaps unrealistic, even given high GDP and population growth: we find figures that are close to half this level. On the other hand, we find evidence for leap-frogging opportunities, by which renewable energy options rather than fossil fuels could constitute the cost-optimal solution to fulfil most of Africa's growing energy requirements. An important benefit of leap-frogging is that it avoids an ultimately expensive fossil fuels lock-in that would fix the carbon footprint of the continent until at least the middle of the century.

A preliminary bottom-up analysis of the energy use in the chemical industry has been performed, using a model containing datasets on production processes for 52 of the most important bulk chemicals as well as production volumes for these chemicals. The processes analysed are shown to cover between 70% and 100% of the total energy use in the chemical sector. Energy use and the heat effects of the reactions taking place are separately quantified. The processes are also compared with energetically-ideal processes following the stoichometric reactions. The comparison shows that there is significant room for process improvements, both in the direction of more selective processes and in the direction of further energy-savings.

This paper proposes a Cognitive Stochastic Approximation (CSA)-based optimization method for charging an EV (electric vehicle) fleet, using a single, aggregate battery model. The charging station can either utilize the batteries of the parked vehicles to charge the vehicles before they leave, or can use power from the grid. The objective is to optimize the charging task with minimum energy costs, possibly taking into account price variations in the electricity price. The main advantage of the proposed approach is that it provides a nearly to optimal solution in the presence of uncertain charging/discharging dynamics. The method is evaluated through a numerical model of a grid-connected charging station. Four scenarios with different electricity price models are studied. The CSA optimization results are compared with the results obtained by a rule-based charging algorithm and by an open-loop optimal control algorithm: the results illustrate the advantages of the proposed CSA algorithm in minimizing the charging cost, satisfying the aggregate battery charge sustaining conditions and providing robust solutions in the presence of time-varying vehicle schedules.

AbstractCurrently it is standard practice to use Airy linear wave theory combined with Morison's formula for the calculation of fatigue loads for offshore wind turbines. However, offshore wind turbines are typically placed in relatively shallow water depths of 5–25 m where linear wave theory has limited accuracy and where ideally waves generated with the Navier–Stokes approach should be used. This article examines the differences in fatigue for some representative offshore wind turbines that are found if first‐order, second‐order and fully non‐linear waves are used. The offshore wind turbines near Blyth are located in an area where non‐linear wave effects are common. Measurements of these waves from the OWTES project are used to compare the different wave models with the real world in spectral form. Some attention is paid to whether the shape of a higher‐order wave height spectrum (modified JONSWAP) corresponds to reality for other places in the North Sea, and which values for the drag and inertia coefficients should be used. Copyright © 2004 John Wiley & Sons, Ltd.

Recently, many reviews on pre-combustion CO2 capture (CCS) in an IGCC plant have been focused on the techno-economic performance of palladium-based membrane reactor modules downstream of conventional steam reforming or shift reactors. Although the determination and minimisation of the amount of palladium necessary for a specific power production capacity has been the target of many research studies, surprisingly little attention has been paid in the open literature to the availability of this metal in the large quantities required for large scale applications. To fill this gap, the scope of this work was to compare the amount of palladium needed for pre-combustion CCS with Pd-membranes and the available production capacity of palladium. Two specific techno-economic studies with a different net IGCC power output were selected from the literature. In each case, the amount of palladium that is necessary for the plant to be in operation was compared with the world supply and demand for palladium. The results show that even for a power plant of "only" 1 GWe net electricity production utilizing membranes with the best reported performance, a relatively large (~0.7%) amount of palladium is required compared to the total world supply. Considering the total worldwide electricity production from fossil fuels (14,455 TWh in 2010) a tremendous increase in the world supply of Palladium would be required to redirect from the traditional IGCC power plants without CO2 capture units to the new membrane technology. We conclude that large scale pre-combustion capture of CO2 using palladium membranes seems to be unfeasible and research on Pd-based membrane reactors should focus on small(er) scale applications.