Short Payback Time Research Articles

A decision support system for waste heat recovery and energy efficiency improvement in data centres

Data centre sector is emerging as one of the largest and fastest growing industrial sectors, accounting for 3% of the global electricity supply and contributing to 4% of total greenhouse gas emissions. A framework for waste heat energy recovery and its accompanying decision support system is presented with the ability to evaluate the waste heat (source) and potential demand (sink) compatibility, perform exergy and temporal availability analysis, and undertake cost-benefits and environmental impact analysis of available heat recovery technologies. This four stages framework is implemented through the case study of a medium-sized commercial data centre to provide evidence of its applicability. The results demonstrated that the framework and decision support system can deliver a streamlined and optimised heat recovery strategy for reducing overall energy requirement in the data centre. About 68% of the inevitable waste heat from IT equipment can be recovered by the recommended solution, allowing the recovered waste heat in the form of warm water to be fed back into the facility for applications such as space heating, achieving about 10% improvement in data centre power usage effectiveness. The solutions given by the decision support system are generally accessible for most data centres as the technologies are readily available and often lead to short payback time and substantial energy savings.

Analysis of the performance of a building solar thermal facade (BSTF) for domestic hot water production

The installation of solar collectors applied or integrated into the building envelope may represent an interesting opportunity to increase the fraction of the building energy demands supplied through solar energy.In particular, building solar thermal facades (BSTFs) could be very useful in high-rise buildings, which do not have sufficient spaces where to install a solar plant.This paper aims to evaluate the energy performances of building solar thermal facades (BSTFs), constructed with two distinct types of solar collectors, flat plate (FPC) and evacuated solar collectors (ETC), through transient simulations, carried out with TRNSYS software, under different climate conditions. Moreover, an economic and LCA analysis on the two types of examined BSTFs were developed.Additionally, this study presents a preliminary investigation on a prototype of ventilated building solar thermal facade (v-BSTF) built in Ragusa.The results of such analysis highlight that BSTFs can represent suitable systems for the DHW production with great environmental and economic conveniences due to the short energy and CO2 payback times.

Biophysical model and techno-economic assessment of carbon sequestration by microalgal ponds in Indian coal based power plants

The present study evaluated the carbon dioxide (CO2) sequestration potential of Thalassiosira pseudonana using the influencing key climatic datasets of an Indian coal based power plant through a biophysical energy balance model developed on MATLAB platform with ODE45s solver. The maximum average areal biomass productivity was predicted to be 111.39 kg ha−1d−1 with maximum growth in February, leading to the CO2 capture of 147.03 kg ha−1d−1. Further, techno-economic analysis was performed utilizing the results of the formulated biophysical model to access the process feasibility using SuperPro designer. Results revealed the technical viability and economic feasibility of the process, with the unit production price of 58.41 $ per ton with a reasonable rate of returns and acceptable short payback time of 2.81 years. A yearly carbon credits of 52 M$ could be earned by the company. Sensitivity analysis showed the process to be highly dependent over the raw material prices and facility operation. The integrated site-specific biophysical model and economic analysis are essential to provide reliable realistic estimates of the algal carbon sequestration technology that could drive the energy policies towards sustainable development.

Polymer Solar Cells-Interfacial Processes Related to Performance Issues.

Harnessing solar energy with solar cells based on organic materials (in particular polymeric solar cells) is an attractive alternative to silicon-based solar cells due to the advantages of lower weight, flexibility, lower manufacturing costs, easier integration with other products, low environmental impact during manufacturing and operations and short energy payback times. However, even with the latest efficiencies reported up to 17%, the reproducibility of these efficiencies is not up to par, with a significant variation in the efficiencies reported across the literature. Since these devices are based on ultrathin multilayer organic films, interfaces play a major role in their operation and performance. This review gives a concise account of the major interfacial issues that are responsible for influencing the device performance, with emphasis on their physical mechanisms. After an introduction to the basic principles of polymeric solar cells, it briefly discusses charge generation and recombination occurring at the donor-acceptor bulk heterojunction interface. It then discusses interfacial morphology for the active layer and how it affects the performance and stability of these devices. Next, the formation of injection and extraction barriers and their role in the device performance is discussed. Finally, it addresses the most common approaches to change these barriers for improving the solar cell efficiency, including the use of interface dipoles. These issues are interrelated to each other and give a clear and concise understanding of the problem of the underperformance due to interfacial phenomena occurring within the device. This review not only discusses some of the implemented approaches that have been adopted in order to address these problems, but also highlights interfacial issues that are yet to be fully understood in organic solar cells.

Retrofit through Add-ons: the ABRACADABRA strategy as an opportunity for the energy renovation of private-owned and public buildings

The EU environmental and energy policies are promoting energy efficiency retrofit actions, in spite of the fact that the renovation rate in the construction sector is very low. The ABRACADABRA project aims to activate a deep renovation market through volumetric additions (add-ons), including one of the most challenging sectors, the social housing. In order to demonstrate how the densification action could be an effective solution to promote energy efficiency interventions and new business models with the scope to shorten the payback time of renovation investments (both at building and urban scale), four different buildings in different urban contexts have been analysed. The simulation made on these case studies is divided in three steps: an architectural feasibility study, an energy saving analysis and a payback time calculation; in this last phase of the study the financial assumptions are fundamental. The real estate values like the sale and the rental rate, as well as the social values were well-thought-out and combined in order to find the best opportunity for profits and the shortest payback time. Moreover, additional issues were taken into account regarding the regulatory aspects and the technical feasibility barriers for this type of approach. Implementing this strategy means to add new units on the rooftop or on the side of an existing building, and this might face obstacles, such as urban regulation restrictions and the consensus among tenants or owners. To overcome these mainly social obstacles, the project promotes new policy recommendations that public authorities could adopt and approve and also counterbalanced measures to help tenants/owners accept and embrace the ABRA strategy.

LCA study of photovoltaic systems based on different technologies

ABSTRACTThis work deals with the application of a Life Cycle Assessment approach for evaluating the environmental and energy impacts ascribed to the production of photovoltaic (PV) cells of first and second generations. PV technologies based on silicon and CuInSe2 (CIS) thin films were taken into account herein. PV systems prepared with amorphous silicon (a-Si) showed a low environmental impact and short energy payback time when compared to those ones obtained using crystalline silicon (c-Si). PV technologies associated with mono-crystal (mono-Si) and polycrystalline silicon (multi-Si) showed large emissions of CO2, nitrogen oxides, non-methane volatile organic compounds, particulates, and SO2 into air per square meter of PV panel processed. In addition, these technologies displayed a significant fossil fuel demand, biological oxygen demand, and global warming potential, which make them eco-unfriendly. Ribbon silicon (ribbon-Si) and CIS thin films showed intermediate impact scores, but further improvements in their production chain are needed before these devices are commercially used. The technologies examined herein were categorized in first- and second-generation technologies in order to compare their environmental impact and conversion efficiency. Much attention was also paid to the development of third-generation PV cells with improved conversion efficiencies and lower environmental impacts.

An investigation of marine waste heat recovery system based on organic Rankine cycle under various engine operating conditions

Energy-saving, stricter regulations on pollution prevention, increasing energy efficiency and reducing operational costs have become common and primary issues for maritime industry, recently. One of the methods to improve these requirements onboard is to use a waste heat recovery system based on organic Rankine cycle. In this article, organic Rankine cycle–based waste heat recovery system for a chemical/oil tanker is investigated at different engine operating conditions by thermodynamic, environmental and economic analyses. The jacket cooling water, scavenge air, exhaust gas and combination of these three sources are used as the waste heat sources. R245fa is selected as the working fluid. The performance parameters of four different organic Rankine cycle–based waste heat recovery systems integrated with the main engine of the tanker are calculated and presented. The results show that by using the organic Rankine cycle–based waste heat recovery system onboard, it is possible to increase the overall thermal efficiency of the ship’s power plant by more than 6% and the combined organic Rankine cycle–based waste heat recovery system can meet all navigation electricity demand when the engine is operated at 82% maximum continuous rating or higher engine loads. In comparison with other organic Rankine cycle–based waste heat recovery systems, the combined organic Rankine cycle–based waste heat recovery system has the highest capital cost, but it has the shortest payback time. Furthermore, this system can reduce the ship emissions by about 6.9%.

Framework Development to Identify the Impact of Green Building Attributes on Rental Value of Commercial Properties in Malaysia

Green office buildings offer maximum comfort using less energy to provide a conducive atmosphere for working which invariably encourage production. It provides adequate return on investment over a long period of time having a shorter payback time compared to non-green buildings. Researchers tried to establish the benefit and cost of maintenance of green building based on different parameters. However, this research reviewed different approaches on the issue of green building cost and benefits including building performance as it relates to supply and demand of green building, green building market value, cash flow and market competition. The inspiration for the development of such methodology arose from the need for measuring the impact of green building attributes on rental value of commercial properties in Malaysia. The paper discusses how the impact of green building attributes on rental value can be measured within the context of commercial properties in Malaysia. It further argues that critical assessment need to carried out to determine the attributes which significantly affect the rental value of commercial green buildings.

Land use change and the carbon debt for sugarcane ethanol production in Brazil

Farming sugarcane, as a renewable source of ethanol for use as a fuel, is a common practice in Brazilian agriculture. Despite being renewable, whether ethanol use actually reduces greenhouse gas (GHG) emissions depends on how the sugarcane is produced. Studies have shown that land use changes due to sugarcane farming are responsible for a substantial amount of the carbon emitted into the atmosphere, and may be equivalent to, or even greater than, the great “villains” of global warming–the fossil fuels. In the context of climate change, are there alternative land use changes that could create a lower overall carbon debt for ethanol and sugarcane production? In attempting to answer this question, this study aimed to: (i) map carbon stocks in the Brazilian biomes; (ii) quantify the carbon loss under different scenarios of land use changes for sugarcane-ethanol production; (iii) calculate the payback time for land conversion to sugarcane; and (iv) quantify the current areas of cultivated and degraded pasture by biome. The results show that the carbon debt from the deforestation of Brazilian biomes for ethanol production is equivalent to 608 Mg CO2 ha−1 for the Amazon, 142 Mg CO2 ha−1 for the Cerrado and 212 Mg CO2 ha−1 for the Atlantic Forest with respective payback times of 62, 15 and 22 years. However, carbon emitted from the conversion of existing pasture land to sugarcane production rather than forest would be much smaller, with a shorter payback time. We conclude that pasturelands, especially those already degraded, would be the most suitable areas for land conversion to sugarcane production for ethanol. Pasture recovery would increase carbon stocks, reduce GHG emissions and reduce the negative direct and indirect land use changes associated with sugarcane expansion in Brazil.

Life-cycle impacts of shower water waste heat recovery: case study of an installation at a university sport facility in the UK.

Recovering heat from waste water discharged from showers to preheat the incoming cold water has been promoted as a cost-effective, energy-efficient, and low-carbon design option which has been included in the UK's Standard Assessment Procedure (SAP) for demonstrating compliance with the Building Regulation for dwellings. Incentivized by its carbon cost-effectiveness, waste water heat exchangers (WWHX) have been selected and incorporated in a newly constructed Sports Pavilion at the University of Brighton in the UK. This £2-m sports development serving several football fields was completed in August 2015 providing eight water- and energy-efficient shower rooms for students, staff, and external organizations. Six of the shower rooms are located on the ground floor and two on the first floor, each fitted with five or six thermostatically controlled shower units. Inline type of WWHX were installed, each consisted of a copper pipe section wound by an external coil of smaller copper pipe through which the cold water would be warmed before entering the shower mixers. Using the installation at Sport Pavilion as the case study, this research aims to evaluate the environmental and financial sustainability of a vertical waste heat recovery device, over a life cycle of 50years, with comparison to the normal use of a PVC-u pipe. A heat transfer mathematical model representing the system has been developed to inform the development of the methodology for measuring the in-situ thermal performance of individual and multiple use of showers in each changing room. Adopting a system thinking modeling technique, a quasi-dynamic simulation computer model was established enabling the prediction of annual energy consumptions under different shower usage profiles. Data based on the process map and inventory of a functional unit of WWHX were applied to a proprietary assessment software to establish the relevant outputs for the life-cycle environmental impact assessment. Life-cycle cost models were developed and industry price book data were applied. The results indicated that the seasonal thermal effectiveness was over 50% enabling significant energy savings through heat recovery that led to short carbon payback time of less than 2years to compensate for the additional greenhouse gas emissions associated with the WWHX. However, the life-cycle cost of the WWHX is much higher than using the PVC pipe, even with significant heat recovered under heavy usage, highlighting the need to adopt more economic configurations, such as combining waste water through fewer units, in order to maximize the return on investment and improve the financial viability.

Optimising energy use in an existing commercial building: a case study of Australia\u2019s Reef HQ Aquarium

Reef HQ Aquarium is a major tourism attraction in tropical North Queensland, Australia. In 8 years, a 50% reduction in grid electricity was achieved through targeted infrastructure investment, whilst growing the business. Initially, grid energy consumption was 2438 MWh per annum, with 490-kW peak demand and energy intensity of 1625 MJ m−2 year−1 used on typical equipment such as HVAC (heating, ventilation and air conditioning), machinery, lighting and catering equipment. Savings of 13% were achieved in the first year by increasing indoor air temperature set-points by 1.5 °C with no significant costs or impacts on occupant thermal comfort or worker productivity. Peak demand was decreased by 46% by upgrading the computerised building management system (BMS), HVAC, machinery and lighting; and by installing a 206-kW photovoltaic (PV) solar power system. This case study illustrates that (a) significant energy use reductions are possible at low cost; (b) capital investment in energy-efficient infrastructure can have short payback times and high direct and indirect benefits, particularly where equipment is ending its life. This study is unique as it examines how a commercial building with integrated chilled water thermal energy storage (TES) and a 3.2-ML chilled seawater aquarium system can be controlled by a BMS to optimise solar power to manage peak energy demand and also increase the utilisation of generated PV power in the absence of electrical battery storage. An interesting building is used to demonstrate efficiency methods with elements such as HVAC and lighting which usually consume over half commercial buildings’ energy use.

Capturing CO2 from Biogas Plants

As a renewable energy, biogas produced from anaerobic digestion and landfill is playing a more and more important role in the energy market. Capturing CO2 from biogas can result in a negative CO2 emission. Depending on how biogas is utilized, there are different routes to capture CO2. A biogas plant that uses raw biogas to produce power and heat can be retrofitted by integrating CO2 capture. In order to identify the best option, three retrofits were compared from both technical and economic perspectives, including SYS-I, which captures CO2 from raw gas and produces biomethane instead of electricity and heat, SYS-II, which captures CO2 using MEA-based chemical absorption after the combustion of raw gas, and SYS-III, which captures CO2 by using oxy-fuel combustion of the raw gas. In general, SYS-I can achieve the highest profit and shortest payback time, mainly due to the high price of biomethane. SYSII and SYS-III are clearly influenced by carbon credit. In order to have positive profits for the retrofits of SYS-II and SYS-III, carbon credit needs to exceed 750SEK (or 100USD)/ton CO2 and 113 SEK (or 15USD)/ton CO2 respectively.

Obtaining prebiotic carbohydrates and beta-ecdysone from Brazilian ginseng by subcritical water extraction

Abstract Subcritical water extraction (SWE) is one of the most promising modern extraction techniques for isolation of bioactive compounds from plant materials. Fructooligosaccharides (FOS) and beta-ecdysone were obtained from Brazilian ginseng roots (BGR) and aerial parts (BGA) by SWE aiming to use the entire plant in a biorefinery approach. The BGR extracts showed a FOS content of up to 8.8 g/100 g of extract and a beta-ecdysone content of up to 0.7 g/100 g of extract. BGA extracts showed a beta-ecdysone content of 0.3 g/100 g of extract. An economic evaluation showed that the manufacturing of BGR for beta-ecdysone production had a good profitability with a short payback time of 1.43 years, while BGA could be used as fuel to supply the energetic requirements of the process and then, enable the utilization of the entire plant. Industrial relevance This study reports the subcritical water extraction (SWE) of fructooligosaccharides (FOS) and beta-ecdysone from Brazilian ginseng roots (BGR) and aerial parts (BGA) aiming the use of the entire plant material in a biorefinery approach. SWE is a promising innovative technology to recover bioactive compounds from plant materials due to the easy manipulation of the dielectric constant of water. The economic evaluation of the process showed the great profitability of SWE to obtain bioactive compounds from Brazilian ginseng. These results demonstrated that SWE is a green, fast and economic process for extracting bioactive compounds from plant materials and can be successfully applied on industrial scale.

Performance of rainwater harvesting systems under scenarios of non-potable water demand and roof area typologies using a stochastic approach

Urban water systems throughout the world are under recurring and increasing water scarcity, given demand growth, aging infrastructure, variability and uncertainty imposed by climate change. Rainwater harvesting systems (RWHS) represent a promising alternative to increase flexibility and robustness of water supply systems. Given the importance of the tank size in establishing a reliable RWHS, we propose an implicit stochastic approach to assess performance and aid designers. The main objective of this study is to simulate common non-potable water demand and roof area typologies and verify how the demand and roof area affect the efficiency of the RWHS. To highlight the usefulness of the model to aid in the definition of tank sizes, we have also performed an economic assessment. Results are specific to the study region’s climate and might vary under different climate. However, we have chosen a rather unfavourable climate, with poor rainfall distribution along the year. Under such conditions, results are likely closer to lower bound benefits. This indicates potential water savings benefits of a RWHS even for unfavourable scenarios. The RWHS indicated to be more efficient at meeting demands with smaller Demand-Roof Area ratios. Furthermore, it was possible to determine the efficiency of the RWHS under various scenarios, identifying the minimum and maximum likely benefits. Several scenarios were compared directly allowing for the establishment of a general maximum tank size per unit roof area in a given region of interest, beyond which no significant benefits are likely. The economic assessment indicates positive net present values for investing in RWHS, especially for large rooftop areas and small Demand-Roof Area ratios. Under such conditions, investing in a RWHS has very low risk and will most likely have short payback times.

The Energy Audit Activity Focused on the Lighting Systems in Historical Buildings

The energy audit for a building is a procedure designed mainly to obtain adequate knowledge of the energy consumption profile, identify, and quantify opportunities for energy savings by a cost-benefit analysis and report, clearly and comprehensively, about the obtained results. If the audit is referred to a building with a significant historical and artistic value, a compatibility evaluation of the energy saving interventions with the architectural features should also be developed. In this paper, analysing the case study of a historical building used as public offices in Pisa (Italy), the authors describe how it is possible to conduct an energy audit activity (especially dedicated to the lighting system) and they show how, for this type of buildings, it is possible to obtain significant energy savings with a refurbishment of the lighting system. A total number of seven interventions on indoor and outdoor lighting sub-systems were analysed in the paper. They are characterised by absolute compatibility with the historical and artistic value of the building and they show short payback times, variable between 4 and 34 months, allowing a reduction of the electrical energy consumption for the artificial indoor and outdoor lighting variable from 1.1 MWh/year to 39.0 MWh/year. The followed methodology and the evaluation results described in the paper, although based on a case study, can be extended to numerous historical buildings used as public offices, a recurring situation in the centres of Italian historical cities.

Ultrafast decoherence dynamics govern photocarrier generation efficiencies in polymer solar cells.

All-organic-based photovoltaic solar cells have attracted considerable attention because of their low-cost processing and short energy payback time. In such systems the primary dissociation of an optical excitation into a pair of photocarriers has been recently shown to be extremely rapid and efficient, but the physical reason for this remains unclear. Here, two-dimensional photocurrent excitation spectroscopy, a novel non-linear optical spectroscopy, is used to probe the ultrafast coherent decay of photoexcitations into charge-producing states in a polymer:fullerene based solar cell. The two-dimensional photocurrent spectra are interpreted by introducing a theoretical model for the description of the coupling of the electronic states of the system to an external environment and to the applied laser fields. The experimental data show no cross-peaks in the twodimensional photocurrent spectra, as predicted by the model for coherence times between the exciton and the photocurrent producing states of 20 fs or less.

Contrasting responses in the growth and energy utilization properties of sympatric Populus and Salix to different altitudes: implications for sexual dimorphism in Salicaceae.

An interesting ecological and evolutionary puzzle arises from the observations of male-biased sex ratios in genus Populus, whereas in the taxonomically related Salix, females are generally more dominant. In the present study, we combined results from a field investigation into the sex ratios of the Salicaceous species along an altitudinal gradient on Gongga Mountain, and a pot experiment by monitoring growth and energy utilization properties to elucidate the mechanisms governing sexual dimorphism. At middle altitudes 2000 and 2300 m, the sex ratios were consistent with a 1:1 equilibrium in sympatric Populus purdomii and Salix magnifica. However, at the lower and higher ends of the altitudinal gradient, skewed sex ratios were observed. For example, the male:female ratios were 1.33 and 2.36 in P. purdomii at 1700 and 2600 m respectively; for S. magnifica the ratio was 0.62 at 2600 m. At 2300 m, the pot-grown seedlings of both species exhibited the highest biomass accumulation and total leaf area, simultaneously with the balanced sex ratios in the field. At 3300 m, the specific leaf area in male P. purdomii was 23.9% higher than that of females, which may be the morphological cause for the observed 19.3% higher nitrogen allocation to Rubisco, and 20.6% lower allocation to cell walls. As such, male P. purdomii showed a 32.9% higher foliar photosynthetic capacity, concomitant with a 12.0% lower construction cost. These properties resulted in higher photosynthetic nitrogen- and energy-use efficiencies, and shorter payback time (24.4 vs 40.1 days), the time span that a leaf must photosynthesize to amortize the carbon investment. Our results thus suggested that male P. purdomii evolved a quicker energy-return strategy. Consequently, these superior energy gain-cost related traits and the higher total leaf area contributed to the higher growth rate and tolerance in stress-prone environments, which might, in part, shed new light on the male-biased sex ratios in Populus. However, no significant sexual difference was observed in S. magnifica for all the above parameters, thereby implying that the female-biased sex ratios in Salix cannot be explained in terms of the energy-use properties studied here.

(Invited) Synthesis and Characterization of Photoactive Porphyrin Electropolymers

The design and development of new polymeric functional material for application in organic optoelectronic devices, like polymer solar cells, is one of the most active areas of research, mainly due to the continuous search for low cost renewable energy sources. Flexibility, solution processability, and short energy payback time, are among the very important characteristics of the organic based materials that make possible their application in large area devices. However, despite the facts that high power conversion efficiencies have been attained with bulk heterojunction structures, and that the potentiality of the organic photovoltaic technology is still huge, to date industrial production and large scale commercialization have not been achieved, a major issue being the transfer of the efficiencies obtained on small area cells to large area modules. Thus, the development of new polymeric materials and devices construction methods are still necessary, in order to find procedures that allow the implementation of this relevant technology. One of the principal difficulties that the use of organic polymers in electronics has to face is the film deposition methodology over the conducting or semiconducting contacts. The most common approaches rely on thermal evaporation and solution-processing methods. However, thermal evaporation requires materials with adequate sublimation capability and thermal stability, properties that are difficult to reach in polymers. Also, solution processes, such as dip - or spin - coating methodologies, require polymeric materials with intrinsic high solubility. On the contrary, electropolymerization of suitable photoelectroactive monomers allows the synthesis and formation of polymeric films in one step, with the possibility to get control over pattern and thickness, two very important aspects in the implantation of industrial processes. In the last years we developed porphyrin polymeric materials, produced by electrochemical methods. These materials exhibited photovoltaic and electrochromic properties. The monomers were planned with the aim to achieve their polymerization through dimerization of the electrochemically generated tryphenyl amine and/or carbazole radical cations, giving rise to tetraphenylbenzidine and/or dicarbazole substructures with hole transport capability. These polymers demonstrate their capacity for the generation of photoinduced charge separated states, with light absorption in a broad region of the visible spectrum, and hold the potentiality for their application in the development of optoelectronic devices.

Technical and economic analysis of integrating low-medium temperature solar energy into power plant

In order to mitigate CO2 emission and improve the efficiency of the utilization of solar thermal energy (STE), solar thermal energy is proposed to be integrated into a power plant. In this paper, seven configurations were studied regarding the integration of STE. A 300MWe subcritical coal-fired plant was selected as the reference, chemical absorption using monoethanolamine solvent was employed for CO2 ​capture, and parabolic trough collectors and evacuated tube collectors were used for STE collection. Both technical analysis and economic evaluation were conducted. Results show that integrating solar energy with post-combustion CO2​ capture can effectively increase power generation and reduce the electrical efficiency penalty caused by CO2 capture. Among the different configurations, Config-2 and Config-6, which use medium temperature STE to replace high pressure feedwater without and with CO2 capture, show the highest net incremental solar efficiency. When building new plants, integrating solar energy can effectively reduce the levelized cost of electricity (LCOE). The lowest LCOE, 99.28USD/MWh, results from Config-6, with a parabolic trough collector price of 185USD/m2. When retrofitting existing power plants, Config-6 also shows the highest net present value (NPV), while Config-2 has the shortest payback time at a carbon tax of 50USD/ton CO2. In addition, both LCOE and NPV/payback time are clearly affected by the relative solar load fraction, the price of solar thermal collectors and the carbon tax. Comparatively, the carbon tax can affect the configurations with CO2 capture more clearly than those without CO2 capture.

Energy balance, greenhouse gas emissions, and profitability of thermobarical pretreatment of cattle waste in anaerobic digestion

In this study modeled full scale application of thermobarical hydrolysis of less degradable feedstock for biomethanation was assessed in terms of energy balance, greenhouse gas emissions, and economy. Data were provided whether the substitution of maize silage as feedstock for biogas production by pretreated cattle wastes is beneficial in full-scale application or not.A model device for thermobarical treatment has been suggested for and theoretically integrated in a biogas plant. The assessment considered the replacement of maize silage as feedstock with liquid and/or solid cattle waste (feces, litter, and feed residues from animal husbandry of high-performance dairy cattle, dry cows, and heifers). The integration of thermobarical pretreatment is beneficial for raw material with high contents of organic dry matter and ligno-cellulose: Solid cattle waste revealed very short payback times, e.g. 9months for energy, 3months for greenhouse gases, and 3years 3months for economic amortization, whereas, in contrast, liquid cattle waste did not perform positive replacement effects in this analysis.