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Abstract With impending climate change and ever decreasing supplies of easily extractable fossil fuel, means to produce renewable and sustainable replacement fuels are being sought. Plants or algae appear ideal since they can use sunlight to fix CO2 into usable fuel or fuel feedstocks. However, as the world population approaches the 1010 (10 billion) mark, the use of agricultural land to produce fuel instead of food cannot be justified. Microalgal biofuel production is under intense investigation due to its promise as a sustainable, renewable biofuel that can be produced using non-arable land and brackish or non-potable water. Some species accumulate high levels of TAGs (triacylglycerols) that can be converted to fatty acid esters suitable as replacement diesel fuels. However, there are many technical barriers to the practical application of microalgae for biofuel production and thus a number of significant challenges need to be met before microalgal biodiesel production becomes a practical reality. These include developing cost-effective cultivation strategies, low energy requiring harvesting technologies, and energy efficient and sustainable lipid conversion technologies. The large culture volumes that will be necessary dictate that the necessary nutrients come from wastewaters, such as the effluents from secondary treatment of sewage. Economical and energy sparing harvesting will require the development of novel flocculation or floatation strategies and new methods of oil extraction/catalysis that avoid the extensive use of solvents. Recent advances in these critical areas are reviewed and some of the possible strategies for moving forward are outlined.

Cutting-edge contributions intended to guide major decisions on investment and energy policy is relevant for climate change research. This study develops an innovative approach that combines three physical climate simulations (Geophysical Fluid Dynamics Laboratory model, Goddard Institute of Space Studies model, and the United Kingdom Meteorological Office climate model) with a general equilibrium model of global trade in order to study the real economic impacts of climate change. For the most part, climate change projected up to the year 2060 leads to welfare gains in the range of 0.07–1.4%, and welfare losses between 0.04 and 2.2% in some cases. All three climate simulations, point to welfare gains in China and marginal losses in low- and middle-income countries as a result of climate change. These findings underscore the importance of properly accounting for the direct effect of CO2 on crop growth and farm level adaptation, as ignoring these leads to substantial welfare losses in all examined regions. While a more systematic trade-off analysis is required for making strong generalizations, the broadest conclusion from the applied models is that, as long as CO2 fertilization effects and farm level adaptation are fairly included with the simulations, global agriculture does not appear to be particularly threatened by climate change. For this reason, agricultural policies aimed at mitigating CO2 emissions but problematic to food security, especially in developing countries, should be treated with caution.

Different from conventional compressed air energy storage (CAES) systems, the advanced adiabatic compressed air energy storage (AA-CAES) system can store the compression heat which can be used to reheat air during the electricity generation stage. Thus, AA-CAES system can achieve a higher energy storage efficiency. Similar to the AA-CAES system, a compressed air energy storage in aquifers (CAESA) system, which is integrated with an aquifer thermal energy storage (ATES) could possibly achieve the same objective. In order to investigate the impact of ATES on the performance of CAESA, different injection air temperature schemes are designed and analyzed by using numerical simulations. Key parameters relative to energy recovery efficiencies of the different injection schemes, such as pressure distribution and temperature variation within the aquifers as well as energy flow rate in the injection well, are also investigated in this study. The simulations show that, although different injection schemes have a similar overall energy recovery efficiency (~97%) as well as a thermal energy recovery efficiency (~ 79.2%), the higher injection air temperature has a higher energy storage capability. Our results show the total energy storage for the injection air temperature at 80 ̊C is about 10% greater than the base model scheme at 40 °C. Sensitivity analysis reveal that permeability of the reservoir boundary could have significant impact on the system performance. However, other hydrodynamic and thermodynamic properties, such as the storage reservoir permeability, thermal conductivity, rock grain specific heat and rock grain density, have little impact on storage capability and the energy flow rate. Overall, our study suggests that the combination of ATES and CAESA can help keep the high efficiency of energy storage so as to make CAESA system more efficiency.

Similar to many other countries, all nations in the Greater Mekong Subregion (GMS) have planned or are planning to develop strong national biofuel programs. The overall goal of this paper is to better understand the impacts of global and regional biofuels on agriculture and the rest of the economy, with a specific focus on the GMS. Based on a modified multi-country, multi-sector computable general equilibrium model, this study reveals that global biofuel development will significantly increase agricultural prices and production and change trade in agricultural commodities in the GMS and the rest of the world. While biofuel in the GMS will have little impacts on global prices, it will have significant effects on domestic agricultural production, land use, trade, and food security. The results also show that the extent of impacts from biofuel is highly dependent on international oil prices and the degree of substitution between biofuel and gasoline. The findings of this study have important policy implications for the GMS countries and the rest of the world.

Abstract This paper studies the role of potential investors in financing renewable energy systems—specifically, relating to crowdfunding as a financing mechanism, with the enhancement of internet and social-media tools. The research question in this study is whether crowdfunding with a novel socio-technical product reward program attracts potential customers to a more sustainable milk product with a specific integrated photovoltaic water pumping (PVWP) system. The particular case study we empirically investigated is product reward crowdfunding in dairy milk production in China. The milk production chain was supplied by PVWP system integration, which generated solar energy both for feed production for dairy cows and for the operation of dairy farms. 48 semi-structured in-depth interviews were conducted between the research team and customers in order to perform qualitative analyses of the determinants of customers’ milk purchase behaviors. In addition, 357 online surveys were collected for quantitative analysis. Binary and ordered probit regressions were employed to use survey date to systematically estimate purchase intention and willingness-to-pay for sustainable milk. Customer behaviors, environmental consciousness, and individual socio-demographic factors were investigated as potential explanatory variables. Over 82% of the survey participants showed intentions to purchase the sustainable milk with the PVWP system. In the survey and interview samples, results showed that milk quality, nutrition improvement, emissions reduction, and environmental benefits attributed to the integrated PVWP system were the major factors considered by interviewees who showed intentions to purchase the crowdfunded dairy milk. Regression model results suggested that potential customers with higher income levels, and those of parenting age, and those with young children or planning to have children, had a higher willingness-to-pay than other customers for the crowdfunded sustainable dairy milk. The familiarity with and popularity of online shopping and pre-sale purchases in China made customers more open to and proactive towards pre-pay and crowdfunding mechanisms. This article evaluated key factors which may influence potential customers for crowdfunding, and used a discrete choice model to estimate customers’ willingness-to-pay for reward-based projects. These results could help producers of sustainable milk products to identify potential target groups in China and estimate market demand. This exploratory study could provide a framework with both quantitative and qualitative assessment of crowdfunding for renewable energy systems in a national or international context.

Abstract Due to the groundwater migration in the underground aquifer, the heat transfer between ground heat exchangers and surrounding ground changes from heat conduction to the conjugated conduction–convection mode. To investigate the aquifer effects on the ground temperature distribution surrounding the ground heat exchanger, a realistic model was established and numerically solved, including a ground heat exchanger and alternatively stacked aquifer and aquifuge layers. The results show that a variation in groundwater velocity would result in a significant fluctuation in the aquifer temperature field close to the ground heat exchanger, but has less effect on the aquifer temperature field away from the ground heat exchanger. The difference between the initial temperature and local stable ground temperature, and the time for the aquifer to reach the stable temperature are both negatively correlated with the groundwater velocity, and positively correlated with the distance to ground heat exchanger on the downstream. The thermal influence radii are ranging from 7.4 m to 143.0 m in the aquifer layer under tested groundwater velocities ranged from 3.15 m/a to 315 m/a respectively, while the radii of aquifuge layer are about 8.3–8.4 m. There exists a critical velocity that makes the radius of thermal influence in the aquifer layer the same as that in the aquifuge layer. When the groundwater velocity is greater than the critical velocity, the thermal influence radius shows an increasing trend with the increase of aquifer layer thickness, while it shows a reversed trend for the velocity lower than the critical velocity.

Abstract The methane yield and microbial community resulting from co-digestion of dairy manure and switchgrass at different mixing ratios [4:0, 3:1, 2:2, 1:3, and 0:4 based on total solids (TS) content] were evaluated. The results indicated that switchgrass is an excellent feedstock for biogas production when co-digested with dairy manure. Mono-digestion of a high dose (>4% TS) of switchgrass led to volatile fatty acid accumulation and process failure, whereas co-digestion of switchgrass and dairy manure could increase the buffering capacity and improve the fermentation efficiency. The optimal mixture ratio of dairy manure and switchgrass was 2:2, with a methane yield that was 39% higher than that obtained by digestion of the individual substrates. The added amount of 8% TS at the 2:2 ratio achieved the highest methane yield of 158.6 mL/g VS, which corresponded to a 1.3-fold increase in the volumetric productivity of methane compared to mono-digestion of 4% TS switchgrass. Quantitative polymerase chain reaction and clone library analyses showed significant differences in the bacterial community resulting from the different co-substrate ratios. Planctomycetes (28%), Chloroflexi (24%), and Bacteroidetes (24%) were the dominant phyla in digesters with a co-substrate ratio of 2:2.

Abstract Progressive replacement of petroleum chemicals with biomass derived products is an essential research goal toward sustainability. However, the progress of the development of new generation biorefinery has been affected by many factors, i.e., prices of crude oil, food, and carbon. To quantify the environmental and social impacts of the technologies, this study constructed a sustainability index for calculating two new bio-butanediol production processes with oil palm empty fruit bunches as example feedstock. The performance of organosolv pretreatment using butanediol was compared with the whole slurry conversion process using sulfite pretreated biomass, over the petroleum refinery and first generation biorefinery with food crop feedstock. The organosolv biorefinery process successfully converted the biomass into 77.3 ± 1.63 g/L of bio-butanediol (0.45 g/g yield), which is slightly higher (5.5%) than that of the sulfite-based process. The integration of biorefinery techniques, with oil palm farming shall result in 6.8 kg-CO2 and 0.5 kg-food benefits per kg butanediol produced, yielding a sustainability index of 7.30. The food index for first generation biorefinery is −1.04 kg food per kg butanediol produced. Using empty fruit bunches for butanediol production could save 1.54 kg food crop consumption, which turns the “food vs. fuel competition” into a “food plus fuel nexus”.

Abstract The United Nations Sustainable Development Goals have highlighted the challenges brought about by increasing energy consumption and climate change. Previous studies have concentrated on accounting for urban and rural household energy requirements in China at a macro-scale, which neglects the analysis of individuals and their socio-economic driving factors at the micro-scale. To fill this gap, this study began with an accounting of energy requirements for urban and rural households based on the provincial Multi-Regional Input-Output (MRIO) tables and household survey covering over 25,000 unique samples from 25 provinces in 2012. Multilinear Regression models were employed to estimate the average effect of various demographic and socioeconomic characteristics of samples, and Tree-based models were applied to classify energy requirement groups and identify the key individual characteristics. The results suggest that the energy requirements per capita on average range from 34 to 211 GJ for urban samples and 34 to 149 GJ for rural samples across different provinces, and that the gap between individuals can be over 100 times. Indirect energy requirements representing above 90% of the total is the focus of the study. Changes in lifestyle factors include eating out, drinking and smoking, were all correlated with indirect energy requirements. Furthermore, the one-child family has had a positive effect on indirect energy requirements, while the two or more children family has had a negative effect. In addition, an individual’s mental health plays a role in the level of indirect energy requirements for high-income rural residents, while geographic location plays a key role for urban residents.