Sgouris Sgouridis

The sower’s way: quantifying the narrowing net-energy pathways to a global energy transition

Planning the appropriate renewable energy (RE) installation rate should balance two partially contradictory objectives: substituting fossil fuels fast enough to stave-off the worst consequences of climate change while maintaining a sufficient net energy flow to support the worlds economy. The upfront energy invested in constructing a RE infrastructure subtracts from the net energy available for societal energy needs, a fact typically neglected in energy projections. Modeling feasible energy transition pathways to provide different net energy levels we find that they are critically dependent on the fossil fuel emissions cap and phase-out profile and on the characteristic energy return on energy invested of the RE technologies. The easiest pathway requires installation of RE plants to accelerate from 0.12 TWp yr-1 in 2013 to peak between 7.3 and 11.6 TWp yr-1 in the late 2030s, for an early or a late fossil-fuel phase-out respectively in order for emissions to stay within the recommended CO2 budget.

Aviation industry's quest for a sustainable fuel: considerations of scale and modal opportunity carbon benefit.

Aviation biofuels require higher processing energy inputs than fuels derived from the same feedstocks used for land-based transport. This article investigates the tradeoffs in the decisions of feedstock and processing by introducing the opportunity carbon benefit metric for the resulting transportation service across modes. We evaluated combinations of feedstocks, processing methods, and transport system use between aviation and surface modes (i.e., pathways) for fuel yields, as well as the process energy and greenhouse gas emissions of several feedstocks to determine their opportunity carbon benefit. In the current conditions, gasification for electricity generation to power electric vehicles would lead to the highest transportation services. Taking into account process energy and the limited number of electric vehicles, diesel and ethanol pathways maintain a lead. Contrary to their relatively high transportation service yields, biomass-to-electricity conversion pathways fail to generate the opportunity carbon benefits of biomass-to-liquid pathways. Biomass-to-liquid pathways vary little, with the jet pathway having a slight disadvantage over the diesel option owing to its higher process energy needs. On the feedstock side, the marginal land feedstocks, such as salicornia and switchgrass, have the advantage over the process energy and cultivation energy inputs, despite their relatively lower per hectare yields.

Defusing the Energy Trap: The Potential of Energy-Denominated Currencies to Facilitate a Sustainable Energy Transition

The universal adoption of fiat currencies and of the fractional reserve banking system coincided with access to and ability to utilize energy-dense fossil fuels leading to unprecedented rates of economic expansion. The depletion of economically recoverable fossil fuels though sets the stage for systemic crises as it is not adequately priced in the current market system. An energy-based system of exchange can be adopted in parallel to or in place of fiat currencies in order to facilitate a sustainable energy transition (SET) and mitigate the impacts of such crises. Energy-backed and energy-referenced currencies are discussed as two possible variants for their ability to realign the economic system to the thermodynamic limits of the physical world. The primary advantage of an energy-referenced currency over the current mechanisms for SET (like feed-in tariffs or carbon taxes) is realized with the decoupling of the monetary and credit functions, especially when debt is tied to future energy availability. While energy-backed (credit) systems can be easier to adopt on a regional scale, the full transition to an energy-reference currency system requires significant reform of the financial and monetary system although it would not radically disrupt the current economic valuations given the high degree of correlation between value and embodied energy.

Investigation of the Impacts of Effective Fuel Cost Increase on the US Air Transportation Network and Fleet

The authors would like to thank the MIT Partnership on AiR Transportation Noise & Emissions Reduction (PARTNER) for access to the Piano-X software package and Brian Yutko for his assistance in its use. This work was supported by the MIT/Masdar Institute of Science and Technology under grant number Mubadala Development Co. Agreement 12/1/06.

Constant elasticity of substitution functions for energy modeling in general equilibrium integrated assessment models: a critical review and recommendations

Applying constant elasticity of substitution (CES) functions in general equilibrium integrated assessment models (GE-IAMs) for the substitution of technical factor inputs (e.g., replacing fossil fuels) fails to match historically observed patterns in energy transition dynamics. This method of substitution is also very sensitive to the structure of CES implementation (nesting) and parameter choice. The resulting methodology-related artifacts are (i) the extension of the status quo technology shares for future energy supply relying on fossil fuels with carbon capture, biomass, and nuclear; (ii) monotonically increasing marginal abatement costs of carbon; and (iii) substitution of energy with non-physical inputs (e.g., knowledge and capital) without conclusive evidence that this is possible to the extent modeled. We demonstrate these issues using simple examples and analyze how they are relevant in the case of four major CES-based GE-IAMs. To address this, we propose alternative formulations either by opting for carefully applied perfect substitution for alternative energy options or by introducing dynamically variable elasticity of substitution as a potential intermediate solution. Nevertheless, complementing the economic analysis with physical modeling accounting for storage and resource availability at a high resolution spatially and temporally would be preferable.

A Net Energy-Based Analysis for a Climate-Constrained Sustainable Energy Transition

The transition from a fossil-based energy economy to one based on renewable energy is driven by the double challenge of climate change and resource depletion. Building a renewable energy infrastructure requires an upfront energy investment that subtracts from the net energy available to society. This investment is determined by the need to transition to renewable energy fast enough to stave off the worst consequences of climate change and, at the same time, maintain a sufficient net energy flow to sustain the worlds economy and population. We show that a feasible transition pathway requires that the rate of investment in renewable energy should accelerate approximately by an order of magnitude if we are to stay within the range of IPCC recommendations.

A Land Suitability Study for the Sustainable Cultivation of the Halophyte Salicornia bigelovii: The Case of Abu Dhabi, UAE

A land suitability study covering an area of 56,655 square kilometers was carried out for the cultivation of a halophytic bioenergy crop, Salicornia bigelovii, in the Emirate of Abu Dhabi using data collected from an extensive soil survey (scale of 1:100,000). Two simple limitation methods (referred to in the paper as the conservative and weighted methods) were used to interpolate soil map unit data for qualitative evaluation of the land. Land suitability was assessed based on a set of criteria developed in accordance with specific plant requirements and two policy scenarios regarding the use of arable land for saline agriculture. Both methods showed similar suitability outcomes, but the weighted method using weighted averages of soil components within a soil map unit produced more realistic results that reflect on the inherent heterogeneous properties of Abu Dhabi soils. Up to 69% of the examined land is found to be moderately suitable for S. bigelovii cultivation but the most suitable areas are located on the coastal zone of Abu Dhabi, and the most limiting factors are predominantly soil salinity and drainage.

Sensitivity of CO2 Emissions to Renewable Energy Penetration for Regions Utilizing Power and Water Cogeneration

Use of renewable energy to produce electricity is generally viewed as a promising means to mitigate CO2 emission. However, the substitution of a significant percentage of electricity generation from fossil fuel fired power plants with renewable energy, such as photovoltaic, concentrated solar power plant, and wind power, might not be as effective in CO2 mitigation in regions utilizing power and water cogeneration. Due to a unique relationship between power cycle efficiency and the ratio of power to water production in the cogeneration system, counterintuitive results might appear as the penetration of renewable energy increases. Our analysis indicates that, without decoupling of the power and water cogeneration or active water conservation, generating electricity with renewable energy alone might be less effective in reducing CO2 emissions than anticipated.

Erratum to: Life cycle assessment of integrated seawater agriculture in the Arabian (Persian) Gulf as a potential food and aviation biofuel resource

Purpose Prospective evaluation of the lifecycle impacts of aviation biofuel production in Abu Dhabi, UAE based on a production system that integrates aquaculture, saltwater agriculture, and mangrove silviculture, termed an Integrated Seawater Energy Agriculture System (ISEAS) in order to investigate its energetic and environmental potential compared to conventional fuels.

Are we on course for a sustainable biofuel-based aviation future?

243 ISSN 1759-7269 10.4155/BFS.12.18