• Energy Research
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All-electric ships are now a standard offering for energy/propulsion systems in boats. In this context, integrating fuel cells (FCs) as power sources in hybrid energy systems can be an interesting solution because of their high efficiency and low emission. The energy management strategy for different power sources has a great influence on the fuel consumption, dynamic performance and service life of these power sources. This paper presents a hybrid FC/battery power system for a low power boat. The hybrid system consists of the association of a proton exchange membrane fuel cell (PEMFC) and battery bank. The mathematical models for the components of the hybrid system are presented. These models are implemented in Matlab/Simulink environment. Simulations allow analyzing the dynamic performance and power allocation according to a typical driving cycle. In this system, an efficient energy management system (EMS) based on operation states is proposed. This EMS strategy determines the operating point of each component of the system in order to maximize the system efficiency. Simulation results validate the adequacy of the hybrid power system and the proposed EMS for real ship driving cycles.

Abstract This paper reports meta-regressions of substitution elasticities between greenhouse gas (GHG) polluting and nonpolluting inputs in agricultural production, which is the main feedstock source for biofuel in the U.S. We treat energy, fertilizer, and manure collectively as the “polluting input” and labor, land, and capital as nonpolluting inputs. We estimate meta-regressions for samples of Morishima substitution elasticities for labor, land, and capital vs. the polluting input. Much of the heterogeneity of Morishima elasticities can be explained by type of primal or dual function, functional form, type and observational level of data, input categories, number of outputs, type of output, time period, and country categories. Each estimated long-run elasticity for the reference case, which is most relevant for assessing GHG emissions through life-cycle analysis, is greater than 1.0 and significantly different from zero. Most predicted long-run elasticities remain significantly different from zero at the data means. These findings imply that life-cycle analysis based on fixed proportion production functions could provide grossly inaccurate measures of GHG of biofuel.

In recent years, the literature in the field of general equilibrium modeling has increased. For long-term energy projections, general equilibrium models are more adequate than standard econometrics in evaluating alternative economic policies in a theoretically consistent framework. The well-known structure and economic mechanism of those models makes it easier to analyze structural changes of prices and quantities demanded or supplied for a given data set of an economy, national income accounts figures, and trade balance effects. The dynamic formulation of these models via investment decisions and capital formation also enables an intertemporal interpretation of structural adjustment and growth processes.

This paper examines the contribution of SEA in six international electricity sector planning case studies. All cases showed some "best practice" evidence such as participation, alternatives consideration and impact assessment; however, considerable variability was found in the types of alternatives considered and the approach to impact assessment and monitoring depending on the timing of SEA application in the PPP process. Regarding substantive contributions, SEA was identified by stakeholders as improving communication during planning and informing lower-level decision making, but fared less well in influencing the nature of the PPP at hand; only two cases clearly incorporated SEA recommendations into the final PPP. Overall, results show considerable potential for SEA to support PPP assessment and decision making in the electricity sector, but also a considerable need for improvements in understanding of the importance of the timing of SEA in the PPP process and how to integrate the results of SEA into PPP development.

This thesis consists of four papers studying economic aspects of natural resource and environmental management in Namibia. Paper [I] analyses changes in Namibian energy use patterns between 1980 and 1998. The study finds that, unlike their counterparts in many other developing countries where energy use has been studied, Namibian energy users appear to have been quite flexible in changing to energy-saving technologies and to technologies using different energy sources altogether. One explanation for this difference may be that Namibia has had relatively high energy prices and has had high taxes on oil-based fuels, which may have made Namibian energy users more interested in potential energy savings. Paper [I] has been published in the South African Journal of Economics (link: http://www.saje.co.za/saje/default.asp) (Stage, J. (2002). Structural shifts in Namibian energy use: An input-output approach) Paper [II] studies variables affecting property pricing in the township areas of Windhoek, Namibias capital city. Plots close to a garbage dump sell at substantial discounts, while plots close to a recreation area sell at premium prices. These results suggest that environmental quality may be more important for households in township areas than has previously been believed. Neglecting issues of environmental quality in town planning for township areas may thus be a serious omission. Paper [II] has been published in Environment and Development Economics (link: http://journals.cambridge.org/bin/bladerunner?REQUNIQ=1062057331&REQSESS=6438487&118200REQEVENT=&REQINT1=148368&REQAUTH=0) (Humavindu, M. N. and Stage, J. (2003). Hedonic pricing in Windhoek townships) Paper [III] uses Namibian farm price data to study the impact of groundwater access on farm profitability. Potentially, groundwater can function both as an extra source of water in areas with low rainfall and as a buffer source of water in areas where rainfall is higher but variable. If groundwater mainly functions as a buffer source of water in high-rainfall areas, it could be replaced by various means of water storage fairly easily. Providing extra water by other means in low-rainfall areas, on the other hand, is likely to be prohibitively expensive. The study does not provide clear-cut results, suggesting that on precautionary principles one should assume that groundwater will be difficult to replace with other water sources. Paper [III] has been published in Development Southern Africa (link: http://search.epnet.com/direct.asp?jid=B8E&db=buh) (Stage, J. and Williams, R. (2003). Implicit water pricing in Namibian farmland markets) Paper [IV] studies optimal allocation between commercial and recreational fishing for one of Namibias fish species, the kob. The biological dynamics of the kob are modelled using an age-class model with age-specific mortalities, in order to capture the fact that the two fisheries target different age classes. The length of the planning horizon is crucial for the results: If a short planning horizon is used, the results indicate that a large share of the catches should be allocated to commercial fishing. With a longer planning horizon, however, the higher profitability of recreational angling leads to the conclusion that it would be preferable to limit commercial fishing in order to permit kob stocks to recover and improve angling success. Paper [IV] will appear in Natural Resource Modeling (link: http://rmmc.eas.asu.edu/nrm/nrm.html) (Stage, J. (2004): Optimal harvesting in an age-class model with age-specific mortalities)

The aim of this paper is to investigate the causal relationship between electricity consumption and GDP growth for the kingdom of Bahrain during the period 1980–2008. By performing an error-correction model, our results reveal that electricity consumption and GDP are cointegrated. The granger causality tests indicate bi-directional relationship between electricity consumption and GDP growth in the long-run while results of the short-run reveal unidirectional causality relationship between the two variables.

We analyze the effects of climate conditions and crop insurance on farm-level land allocation decisions among corn, soybeans, winter wheat, and hay in 10 Midwest states. Based on ARMS data, we estimate farmers' land allocation equations that control for market conditions, climate and soil variables, and insurance. A multivariate sample selection model is used for estimation. We find that: 1) beneficial heat has positive effects on corn and soybean acreage but negative effects on winter wheat acreage, 2) excessive heat has negative effects on corn and winter wheat acreage but have positive effects on soybean acreage, 3) an increase in precipitation by 1% increases corn acreage by 0.6% but decrease soybean and winter wheat acreage by 1.0% and 1.6%, 4) soybean acreage is more sensitive to summer drought, and 5) crop insurance alters farmers land allocation.

This paper estimates a US frontier residential aggregate energy demand function using panel data for 48 ‘states’ over the period 1995 to 2007 using stochastic frontier analysis (SFA). Utilizing an econometric energy demand model, the (in)efficiency of each state is modeled and it is argued that this represents a measure of the inefficient use of residential energy in each state (i.e. ‘waste energy’). This underlying efficiency for the US is therefore observed for each state as well as the relative efficiency across the states. Moreover, the analysis suggests that energy intensity is not necessarily a good indicator of energy efficiency, whereas by controlling for a range of economic and other factors, the measure of energy efficiency obtained via this approach is. This is a novel approach to model residential energy demand and efficiency and it is arguably particularly relevant given current US energy policy discussions related to energy efficiency.