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Hydrogen generation from water using solar energy has grown into a promising approach for sustainable energy production. Over the last years, graphitic carbon nitrides (g-C3N4, CN), polymers based on the heptazine-group, have been widely applied as photocatalysts for H2 evolution. The poor charge separation efficiency of CN is considered the major drawback. Here, we investigated the effect of coupling CN with different types of carbon nanotubes on the charge transfer properties and the photocatalytic H2 evolution. We used carbon nanotubes (CNTs) of different wall number (single (SWCNTs), double (DWCNTs) and multi-walled (MWCNTs) CNTs) for the development of full-organic CN based composite photocatalysts. Photoactivity was drastically affected by the content but more importantly by the nature of the CNTs. The SWCNTs functionalized CN composites were the most active presenting approximately 2-5 times higher H2 evolution than the corresponding DWCNTs and MWCNTs functionalized CN under both solar and pure visible light irradiation. Photoactivity was primarily controlled by the improved electronic properties linked with the abundance and stability of photogenerated charges as evidenced by electron paramagnetic resonance spectroscopy. Transient absorption spectroscopy verified the transfer of reactive electrons from CN to CNTs. CNTs functioned as electron acceptors improving charge separation. The data suggest that charge transfer is inversely proportional to the wall number of the CNTs and that photoactivity is directly controlled by the size at the nanoscale of the CNTs used. In the CNTs/CN nanocomposites, photogenerated electrons are transferred more efficiently from CN when SWCNTs are used, providing more available electrons for H2 production.

AbstractProjections show that biomass will remain important for reaching future EU renewable energy targets. In addition to using domestic biomass, European bioenergy markets will also partly rely on imports of biomass, in particular in trade‐oriented EU member states like the United Kingdom, the Netherlands, Belgium, and Denmark. There has been a lot of debate on the sustainability of (imported) biomass and how policy should deal with this. In this research, therefore, we defined long‐term strategies for sustainable biomass imports in European bioenergy markets. We used the input of different stakeholders in our approach through focus‐group discussions and a global survey, focusing on the following aspects: key principles of sustainable biomass trade, risks and opportunities of biomass trade, both for import regions (EU countries) and for sourcing regions, and practical barriers for trade. Overall we conclude that policies should be stable and consistent within a long‐term vision. An overall sustainability assurance framework of biomass production and use is key, but should ultimately apply to all end uses of biomass. Furthermore, the mobilization of biomass should be supported, as well as commoditization, considering the large diversity of biomass. Side impacts of biomass use should be monitored. Reducing investors’ risk perception is crucial for future developments in the biobased economy, and a clear policy to phase out fossil fuels, e.g. through a carbon tax, needs to be implemented. The results of this research are of interest for policy makers when deciding on long‐term strategies concerning sustainable bioenergy markets. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd

Feedbacks between land carbon pools and climate provide one of the largest sources of uncertainty in our predictions of global climate. Estimates of the sensitivity of the terrestrial carbon budget to climate anomalies in the tropics and the identification of the mechanisms responsible for feedback effects remain uncertain. The Amazon basin stores a vast amount of carbon, and has experienced increasingly higher temperatures and more frequent floods and droughts over the past two decades. Here we report seasonal and annual carbon balances across the Amazon basin, based on carbon dioxide and carbon monoxide measurements for the anomalously dry and wet years 2010 and 2011, respectively. We find that the Amazon basin lost 0.48 ± 0.18 petagrams of carbon per year (Pg C yr(-1)) during the dry year but was carbon neutral (0.06 ± 0.1 Pg C yr(-1)) during the wet year. Taking into account carbon losses from fire by using carbon monoxide measurements, we derived the basin net biome exchange (that is, the carbon flux between the non-burned forest and the atmosphere) revealing that during the dry year, vegetation was carbon neutral. During the wet year, vegetation was a net carbon sink of 0.25 ± 0.14 Pg C yr(-1), which is roughly consistent with the mean long-term intact-forest biomass sink of 0.39 ± 0.10 Pg C yr(-1) previously estimated from forest censuses. Observations from Amazonian forest plots suggest the suppression of photosynthesis during drought as the primary cause for the 2010 sink neutralization. Overall, our results suggest that moisture has an important role in determining the Amazonian carbon balance. If the recent trend of increasing precipitation extremes persists, the Amazon may become an increasing carbon source as a result of both emissions from fires and the suppression of net biome exchange by drought.

Central solar heating plants with seasonal storage (CSHPSS) are among the most promising technologies to save energy in the industrial and residential-commercial building sectors. This work introduces a systematic approach to optimize these systems according to economic and environmental criteria. Our method, which combines the TRNSYS 17 simulation software with life cycle assessment and multi-objective optimization, identifies optimal CSHPSS designs for any climatic condition and heating demand profile considering economic and environmental criteria simultaneously. The capabilities of this approach are illustrated through its application to a case study of a CSHPSS located in Barcelona (Spain), which satisfies a heating demand for a neighborhood of 1120 dwellings. Numerical results show that the CSHPSS plant leads to significant environmental and economic improvements compared to the use of a conventional natural gas heating system. Our tool can guide engineers and architects in the transition towards a more sustainable residential sector.

The database presents the scenario results of an exploratory research, carried out at the International Institute for Applied Systems Analysis (IIASA): the Low Energy Demand (LED) study (Grubler et al. 2018). The LED scenario explored how far transformative changes that combine technological changes, end-use efficiency, and new business models for energy service provision can lead for lowering energy demand, and how these changes could drive deep decarbonisation in the long-term. The scenario development methodology included a bottom-up analysis of how currently existing, though often embryonic, social, institutional, and technological trends could become mainstream with resulting step-changes in efficiency and resulting lowered energy demand. The bottom-up demand estimations were then further explored for their supply side and emissions and climate implications with a top-down modeling framework drawing on the Shared Socioeconomic Pathways (SSP) framework (Riahi et al. 2017). The results show that global final energy demands can be drastically reduced in 2050, to around 245 EJ/yr, or 40% lower than today, whilst significantly expanding human welfare and reducing global development inequalities. According to the knowledge of the authors, LED is the lowest long-term global energy demand scenario ever published. The LED scenario meets the 1.5°C climate target in 2100 without overshoot and keeps the global mean temperature increase below 1.5°C with a probability of more than 60%, without requiring controversial negative emission technologies, such as bioenergy with carbon capture and storage (BECCS), that figure prominently in the emission scenario literature (Rogelj et al. 2015, Anderson and Peters 2016, Creutzig et al. 2016, Smith et al. 2016). Furthermore, the beneficial impacts of the LED scenario on a range of other sustainable development goals are also shown, demonstrating that efficiency of energy services provision plays a critical role in reaching low-energy futures without compromising increased living standards in the Global South, while at the same time reducing adverse social and environmental impacts of climate mitigation strategies that focus predominantly on large-scale supply-side transformations. The research is published in a peer-reviewed article in Nature Energy (Grubler et al. 2018) with ample supplementary information. Water consumption and withdrawal data are published in Parkinson et al. (2018). The data is available for download from the LED Database. The content of the LED database and any derived analysis may only be used for non-commercial scientific publications, articles, educational purposes, figures and data tables provided that the source reference pursuant to section 'Required citation' is included and all relevant publications are correctly cited. Partial reproductions of the database content may be stored in online repositories, if this is necessary to comply with a journal's data archiving and access requirements. Such reproductions must be limited to the scope of the manuscript in question, and must include a hyperlink to the source database hosted at https://db1.ene.iiasa.ac.at/LEDDB and the download date from the source database. However, any wholesale duplication, translation, reworking, processing, arrangement, transformation, or reproduction through the internet or any other channels, of the https://db1.ene.iiasa.ac.at/LEDDEB for commercial or non-commercial purposes is not permitted without the explicit written approval of IIASA.

In Europe the demand of biomass for the whole bioeconomy is increasing year by year. In some cases, this biomass come from non-European countries. The EU is already a net importer of biomass for bioenergy and imports could be even more relevant in the near future. Therefore, it is important to guarantee that this biomass supply from outside the EU is being done in a sustainable way and that negative environmental and socio-economic impacts are minimised. The project BioTrade2020plus has the aim of providing guidelines for the development of a European Bioenergy Trade Strategy for 2020 and beyond. It has analyzed in depth the role of lignocellulosic biomass (woody resources, agricultural residues and cellulosic crops) imports from six selected sourcing regions: North America (Southeast United States), South America (Brazil, Colombia), East Europe (Ukraine), Southeast Asia (Indonesia) and East Africa (Kenya). It has considered availability and sustainability constrains as well as existing strategies in these sourcing regions. All this info is being integrated in an interactive tool available on the BioTrade2020plus webpage. Proceedings of the 24th European Biomass Conference and Exhibition, 6-9 June 2016, Amsterdam, The Netherlands, pp. 1356-1363

The beneficial results of the exponential expansion of photovoltaic installations in Germany and Italy are discussed. Remarkable falls in the peak price of electricity have been observed in both countries. The reasons are discussed in the light of the data from the Kombikraftwerk project. This has demonstrated, in a scaled, real-time experiment, how the demand on the German grid can be met by photovoltaics and wind with back-up from biogas and (pumped hydro) storage. We discuss the implications of the fall in price of photovoltaic cells particularly for 3rd generation technology. Using the specific example of the UK, we demonstrate the advantages of the complementary nature of wind and photovoltaic resources. We demonstrate that the wind and photovoltaic capacity targets for an all renewably powered UK are likely to be significantly lower than in Germany. We conclude by summarising the evidence in favour of a moratorium on all new electricity generation other than by the renewables.

We analyze global elemental phosphorus flows in 2009 for (1) mining to products, (2) animal and human manure flows, (3) crop harvests and animal production, (4) food production, (5) soil erosion, (6) and crop uptake. Informed by the flow assessment the potential and cost of phosphorus usage reduction and recycling measures are quantified, and fed into a constructed phosphorus supply-demand model with reserve assessment to assess the impact of these measures on phosphate rock resource availability. According to our results in 2009 globally 21.4 Mt elemental phosphorus from rock phosphate was consumed in products of which 17.6 Mt used as fertilizers, fully able to cover erosion losses and outputs in agriculture in aggregate, but insufficient from the perspective of bio-available phosphorus in soils. We find substantial scope for phosphorus use reduction, at potentially 6.9 Mt phosphorus, or 32% of 2009 phosphate rock supply. Another 6.1 Mt, or 28% can technologically be recycled from waterways and wastewater, but at a cost substantially above any foreseeable phosphate rock fertilizer price. The model results suggests phosphate rock reserves are sufficient to meet demand into the 22nd century, and can be extended well into the 23rd century with assessed use reduction and recycling measures