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Small decentralized power generation units (DG) are politically promoted because of their potential to reduce GHG-emissions and the existing dependency on fossil fuels. A long term goal of this promotion should be the creation of a level playing field for DG and conventional power generation. Due to the impact of DG on the electricity grid infrastructure, future regulation should consider the costs and benefits of the integration of decentralized energy generation units. Without an adequate consideration, the overall costs of the electricity generation system will be unnecessarily high. The present paper analyses, based on detailed modelling of decentralized demand and supply as well as of the overall system, the marginal costs or savings resulting from decentralized production. Thereby particular focus is laid on taking adequately into account the stochasticity both of energy demand and energy supply. An efficient grid pricing system should then remunerate long-term grid cost savings to operators of decentralized energy production or/and charge long-term additional grid costs to these operators. With detailed models of decentralized demand and supply as well as the overall system, the marginal costs or savings resulting from decentralized production are determined and their dependency on characteristics of the grid and of the decentralized supply are discussed.

Sewage sludge handling is becoming a concern in Europe due to its increasing amount and the presence of contaminants, such as heavy metals and pharmaceutical and personal care products (PPCPs). Currently, over 70% of sludge in Europe is treated thermally by incineration or used as fertilizer in agriculture. New thermochemical methods are under development and are expected to be implemented in the near future. This paper considers the life cycle environmental impacts of the following five alternatives for sludge handling, taking into account the presence of heavy metals and PPCPs: i) agricultural application of anaerobically digested sludge; ii) agricultural application of composted sludge; iii) incineration; iv) pyrolysis; and v) wet air oxidation. The results suggest that anaerobic digestion with recovery of nutrients and electricity has the lowest environmental impacts in 11 out of 18 categories considered. For the mean to maximum resource recovery, composting is the worst alternative, followed by pyrolysis with lower recovery rates. Agricultural application of anaerobically digested sludge has the highest freshwater ecotoxicity due to heavy metals, unless their concentration is in the lowest range, as found in some European sewage sludge applied on land. Therefore, stricter control of heavy metals in the sludge is needed for this option to limit freshwater ecotoxicity to the levels comparable with the thermal processes. The results also indicate that PPCPs have a negligible contribution to freshwater ecotoxicity when compared to heavy metals in the anaerobically digested sludge. Since thermal processes are currently drawing attention due to their potential benefits, the findings of this work suggest that their adoption is environmentally beneficial only if high resource recovery rates can be achieved.

AbstractHydrothermal carbonization (HTC) is an emerging path to give a new life to organic waste and residual biomass. Fulfilling the principles of the circular economy, through HTC “unpleasant” organics can be transformed into useful materials and possibly energy carriers. The potential applications of HTC are tremendous and the recent literature is full of investigations. In this context, models capable to predict, simulate and optimize the HTC process, reactors, and plants are engineering tools that can significantly shift HTC research towards innovation by boosting the development of novel enterprises based on HTC technology. This review paper addresses such key-issue: where do we stand regarding the development of these tools? The literature presents many and simplified models to describe the reaction kinetics, some dealing with the process simulation, while few focused on the heart of an HTC system, the reactor. Statistical investigations and some life cycle assessment analyses also appear in the current state of the art. This work examines and analyzes these predicting tools, highlighting their potentialities and limits. Overall, the current models suffer from many aspects, from the lack of data to the intrinsic complexity of HTC reactions and HTC systems. Therefore, the emphasis is given to what is still necessary to make the HTC process duly simulated and therefore implementable on an industrial scale with sufficient predictive margins.Graphic Abstract

Although renewable energy production is widely accepted as clean, it is not necessarily environmental neutral since, for example, wind turbines kill large numbers of airborne animals such as bats. Consequently, stakeholders involved in the planning and operation of wind turbines are often in conflict when trying to reconcile both goals, namely, promoting wind energy production and protecting bats. We report the responses to an online questionnaire sent out to stakeholders to assess this conflict. More than 80% of stakeholders acknowledged the conflict between bat conservation and wind energy production; yet, the majority was confident about solutions and all desired an ecologically sustainable energy transition. All groups, except members of the wind energy sector, disagreed with the statements that wind energy production is of higher priority than biodiversity protection and that global warming is more critical than the biodiversity crisis. All groups agreed that more measures have to be taken to make wind energy production ecologically sustainable and that the society should be included to pay for the implementation of these measures. All stakeholders except for members of the wind energy sector agreed on that revenue losses from wind energy production and delays in the transition process should be acceptable to resolve the green–green dilemma. Among offered choices, most stakeholders suggested engaging in more research, improving the efficiency of energy use and implementing context dependent cut-in speed during wind turbine operation. The suggestion to weaken the legal protection of wildlife species was dismissed by all, underlining the consensus to protect biodiversity.

Abstract The Heatpipe Reformer provides an allothermal gasification process for the generation of a hydrogen-rich synthesis gas. Heat pipes transport the heat from a fluidized bed furnace to the steam-blown fluidized bed gasification reactor. The goal of our institute is the generation of hydrogen from the synthesis gas by means of membrane separation in the fluidized bed reactor. The major requirement to ensure a high cold gas efficiency of the Heatpipe Reformer is a high efficiency of the combustor, which is determined by the used heat exchanger and the air–fuel ratio of the combustion. State-of-the-art is a cold gas efficiency of 70% with a combustor efficiency of 60–70%. For that reason the combustion chamber developed at our institute comprises of an efficient heat exchanger to internally recuperate the heat from the flue gas and ensure a high temperature of the primary and secondary air. Another consideration is the design of the secondary air inlet in order to allow a complete combustion of the fuel and low CO emissions. The paper describes the impact of the combustion chamber on the efficiency of the gasifiers cold gas efficiencies. It presents the current state-of-the-art of the heat pipe reformer as well as the current state of the construction of the 100 kW pilot at the Institute of energy process engineering (FAU-EVT). The paper shows experiments on the combustor discussing CO emissions and combustor efficiency in order to calculate a prospected cold gas efficiency of the whole system. Both, biomass and coal can be used as feedstock for the gasification system and results from combustor operation using lignite and wood pellets are shown. The combustion chamber provided CO emissions below 30 mg/m 3 . The internal air-preheater achieved temperatures of more than 500 °C. An analysis of heat losses finally indicates potentials for optimization of the Heatpipe Reformers cold gas efficiencies in the commercial scale.

The building and construction sector is a large contributor to anthropogenic greenhouse gas emissions and consumes vast natural resources. Improvements in this sector are of fundamental importance for national and global targets to combat climate change. In this context, vertical greenery systems (VGS) in buildings have become popular in urban areas to restore green space in cities and be an adaptation strategy for challenges such as climate change. However, only a small amount of knowledge is available on the different VGS environmental impacts. This paper discusses a comparative life cycle assessment (LCA) between a building with green walls, a building with green facades and a reference building without any greenery system in the continental Mediterranean climate. This life cycle assessment is carried according to ISO 14040/44 using ReCiPe and GWP indicators. Moreover, this study fills this gap by thoroughly tracking and quantifying all impacts in all phases of the building life cycle related to the manufacturing and construction stage, maintenance, use stage (operational energy use experimentally tested), and final disposal. The adopted functional unit is the square meter of the facade. Results showed that the operational stage had the highest impact contributing by up to 90% of the total environmental impacts during its 50 years life cycle. Moreover, when considering VGS, there is an annual reduction of about 1% in the environmental burdens. However, in summer, the reduction is almost 50%. Finally, if the use stage is excluded, the manufacturing and the maintenance stage are the most significant contributors, especially in the green wall system.

The search for energy efficient construction solutions is still pending in the agro-food industry, in which a large amount of energy is often consumed unnecessarily when storing products. The main objective of this research is to promote high energy efficiency built environments, which aim to reduce energy consumption in this sector. We analyze the suitability of using the thermal inertia of the ground to provide an adequate environment for the storage and conservation of agro-food products. This research compares different construction solutions based on the use of ground thermal properties, analyzing their effectiveness to decrease annual outdoor variations and provide adequate indoor conditions. The analysis undertaken is based on over five million pieces of data, obtained from an uninterrupted four year monitoring process of various constructions with different levels of thermal mass, ranging from high volume constructions to others lacking this resource. It has been proven that constructive solutions based on the use of ground thermal inertia are more effective than other solutions when reducing the effects of outdoor conditions, even when these have air conditioning systems. It is possible to reach optimal conditions to preserve agro-food products such as wine, with a good design and an adequate amount of terrain, without having to use air conditioning systems. The results of this investigation could be of great use to the agro-food industry, becoming a reference when it comes to the design of energy efficient constructions.

SummaryThe production of liquid biofuels to blend with gasoline is of worldwide importance to secure the energy supply while reducing the use of fossil fuels, supporting the development of rural technology with knowledge‐based jobs and mitigating greenhouse gas emissions. Today, engineering for plant construction is accessible and new processes using agricultural residues and municipal solid wastes have reached a good degree of maturity and high conversion yields (almost 90% of polysaccharides are converted into monosaccharides ready for fermentation). For the complete success of the 2G technology, it is still necessary to overcome a number of limitations that prevent a first‐of‐a‐kind plant from operating at nominal capacity. We also claim that the triumph of 2G technology requires the development of favourable logistics to guarantee biomass supply and make all actors (farmers, investors, industrial entrepreneurs, government, others) aware that success relies on agreement advances. The growth of ethanol production for 2020 seems to be secured with a number of 2G plants, but public/private investments are still necessary to enable 2G technology to move on ahead from its very early stages to a more mature consolidated technology.