Unit Capital Costs Research Articles

Economic evaluation for anoxic biological system integrated with external membrane for pharmaceutical wastewater treatment

The integrated system of biological treatment (anoxic /activated sludge ) and ultrafiltration membrane economic study was investigated. The biological treatment results indicate that the performance of pharmaceutical industrial wastewater treatment using activated sludge with an anoxic zone was enhanced by increasing the ability of the pre-acclimatized activated sludge to degrade organic compounds in the industrial wastewater. The residues compounds from biologically treated water were treated by UF membrane and gave a separation efficiency of 99.4%. The results indicate that using the (anoxic /activated sludge) biological treatment step as a pretreatment step before the membrane can provide high-efficiency removal of the contamination of all drug compounds in the wastewater. An economic evaluation of the system was investigated and the calculations indicate that the unit capital cost of the estimated system per cubic meter was 1.27 $/m3, which was lower than the estimated traditional cost.

Impacts of electric field-magnetic powder coupled membrane bioreactor on phenol wastewater treatment: Performance, synergistic mechanism, antibiotic resistance genes, and eco-environmental benefit evaluation

A novel electric field-magnetic powder coupled membrane bioreactor (EM-MBR) was constructed, which was superior on improvement of phenol treatment performance and sludge characteristics, and mitigation of membrane fouling. EM-MBR enhanced the phenol degradation via the improvement activity of phenol degrading enzymes. The EPS contents and SVI of EM-MBR were significantly reduced by 49.3 % and 58.7 % than that of the conventional MBR, respectively. Moreover, EM-MBR successfully reduced fouling rate by 57.0 %, delaying the membrane resistance. The EPS contents were positively correlated with the SVI and fouling rate, implying that the sludge settleability was strengthened by improving the properties of EPS with the assistance of electromagnetic, thus mitigating the membrane fouling. Microbial co-occurrence network demonstrated that EM-MBR enriched phenol-degrading and EPS-degrading genera correlated to Fe redox cycle. Furthermore, the activation of the antioxidant system in the EM-MBR resulted in the suppression of reactive oxygen species (ROS) generation, consequently impeding the dissemination of antibiotic resistance genes (ARGs). Co-occurrence patterns of MGEs and ARGs revealed that intercellular binding facilitated by ist and Integrase may account for the horizontal transfer of ARGs. The reduction of unit capital costs (15.63 %), running costs (53.00 %), and total average carbon emissions (15.18 %) indicated that EM-MBR was environmentally beneficial.

Grid parity analysis of photovoltaic systems considering feed-in tariff and renewable energy certificate schemes in Hong Kong

The Hong Kong government has actively promoted the development of renewable energy with two local utility companies to achieve its renewable energy target. Accordingly, two crucial initiatives, the feed-in tariff (FiT) and renewable energy certificate (REC) schemes, have been launched to boost the installation of renewable energy systems, particularly photovoltaic (PV) systems. However, the efficiency and effectiveness of these schemes on grid parity achievement have not been investigated from the perspectives of different stakeholders. To fill this research gap, this study adopts the levelized cost of electricity (LCOE) models to evaluate the role of FiT and REC schemes on realising the grid parity from the residential PV installers' and utility companies’ perspectives, respectively. As a supplementary indicator, the levelized profit of electricity (LPOE) is applied to investigate the economic profitability. The superiority of this study is to expand a general LCOE model into context-specific LCOE and LPOE models considering different grid parity judgement standards from the two sectors. Through a comprehensive analysis, it is indicated that for residential PV installers, the achievement of grid parity is affected by the government electricity subsidy scheme, the trend of PV system capital cost as well as which utility companies they subscribe. For utility companies, the REC price is found sufficient to compensate the lifetime expenditures on large-scale PV systems. Sensitivity analysis indicates that unit capital cost and annual solar power generation are the most critical factors to reduce LCOE in order to achieve earlier grid parity years.

Optimal design of offshore wind power farm in high resolution using geographical information system

This study presents a novel optimization-based framework for the design of offshore wind power farms (OWFs). In the framework, the characteristics of the OWF facilities are decided. Then, feasible locations for installing the facilities are identified by utilizing geographical information system (GIS). Finally, a MIFP optimization model is formulated for micro-siting of turbines and offshore substations, cable routes, and grid connection, by minimizing levelized cost of electricity. A case study is performed in Jeju Island, South Korea. The unit capital cost of the resulting optimal OWF design in Jeju Island is estimated as 2.3 MM$/MW, which is at par with existing and planned OWFs. Scenario analyses are performed to examine the effect of the spatiotemporal resolution of the model on the optimized design and cost of the wind farm. Moreover, a stochastic programming formulation is proposed to address the wind uncertainties and the resulting design shows improved or equal economics.

The cash flows in push and pull supply chains under supply disruptions

AbstractIn a supply chain with a supplier and a buyer, this paper studies two typical contracts: a push contract and a pull contract. The supplier suffers from a supply disruption, and the buyer faces uncertain demand. We derive the equilibrium solutions under both contracts. We show that the order quantity and the firms' profits always increase in the supplier's reliability probability. Furthermore, we investigate how the firms' unit capital opportunity costs and the supplier's reliability probability affect the firms' preference of contracts. Finally, we identify the conditions under which the push contract is better than the pull contract for different firms.

New insight for purifying polluted river water using the combination of large-scale rotating biological contactors and integrated constructed wetlands in the cold season

Ecological treatment technologies, applied to deal with polluted river water in the low temperature season, remain limited. In this study, a new insight was put forward for purifying polluted river water using a combination system (CS) of large-scale rotating biological contactors (RBCs) and integrated constructed wetlands in autumn and winter. The treatment performance, average removal contribution (RC), nitrification and denitrification rates, microbial community structure, and ecosystem service value were considered to estimate the combination system. Results revealed that the average removal efficiencies of ammonium (NH4+–N), total nitrogen (TN), total phosphorus (TP), and chemical oxygen demand (COD) reached 93.9%, 20.8%, 36.5%, and 37.1%, respectively. The combination system showed excellent removal efficiency of NH4+–N regardless of the effect of low temperature. The maximum values of nitrification and denitrification rates were 59.57 g N/(m3·d) and 0.78 g N/(m2·d), respectively. Considerable differences in bacterial community diversity, richness and relative abundance of functional microbes were observed in the main treatment units, resulting in different average RC to pollutants. The unit capital cost of CS purifying polluted river water was 260 USD/m3 and the operation and maintenance cost was 0.144 million USD/yr. Meanwhile, the ecosystem service value of the CS was 0.334 million USD in autumn and winter. CS not only possessed excellent pollutant purifying efficiencies, but also achieved high ecological service value in the cold season.

Capital cost estimation for advanced nuclear power plants

The first-of-a-kind (FOAK) nuclear plants built in the last 20 years are 2X over budget and schedule in the US and some European countries. One of the nuclear industry's proposed remedies is the small modular reactor (SMR). SMR designs leverage five factors to be more economically competitive than large reactors: 1) multiple units; 2) increased factory production and learning; 3) reduced construction schedules; 4) plant design simplification and 5) unit timing. There are currently no bottom-up studies that quantitatively account for these factors and compare different near-term light water reactor SMRs with Gen III + large plants. This work presents a nuclear plant cost estimating methodology using a detailed bottom-up approach for over 200 structures, systems, and components. The results compare relative costs for two large pressurized water reactors, one with active safety and one with passive safety, to two SMR designs, one with multiple reactor power modules and one with a single reactor module. Passive safety systems showed noticeable savings at both the large and small-scale reactors. The power uprating of an SMR by 20% resulted in ∼15% savings in the overnight unit capital cost. Overall, if built by an inexperienced vendor and work force, the two SMRs' overnight costs were higher than large reactors, since significant on-site labor still remains while losing economy of scale. However, the single-unit SMR had significantly less total person-hours of onsite labor, and if built by an experienced workforce, it could avoid cost-overrun risks associated with megaprojects.

Scoping Study of the Economics of CO2 Transport and Storage Options for Steel Manufacturing Emissions in Eastern Australia

The main source of CO2 emissions in an integrated steel manufacturing plant comes from the need to use a carbon source, often coal, in the steel making process. Among the pathways for reducing CO2 emissions is the application of carbon capture, transport and storage (CCS) technologies. This study undertakes a scoping-level evaluation of the economic viability of transport and storage location options for CO2 captured from an iron and steel plant located in Port Kembla, NSW, situated on the eastern coast of Australia. Both pipeline and ship transport of CO2 are considered, as well as two injection locations: the Darling Basin in NSW and the Gippsland Basin in the state of Victoria, Australia. The cost of CO2 transport and storage are estimated for four specific transport and storage options in south-east Australia, including the cost of pipelines/shipping, boosters, wells, other facilities, monitoring, energy and on-costs. The cases consider either a single CO2 source (emissions from Port Kembla) to a single pipeline or shipping port, or the contribution by the CO2 source from Port Kembla to a collection of CO2 sources including other CO2 sources in NSW, into a pipeline network. The sensitivity of the results to several economic and design parameters, such as flow rate, and project lifetime, is also assessed. Scoping level cost estimates for transport and storage of the CO2 are lowest for the hub transport case injecting at the Gippsland basin and highest for the case involving shipping with injection in the Gippsland basin. For the single-source cases, transport via pipeline to the Darling basin is a slightly more attractive option in terms of unit costs. Although pipeline transport to both the Darling and Gippsland basins are very close in terms of transport and storage costs (less than 0.2% difference), the cost of transporting to the Darling basin is less sensitive to variations of the cost parameters explored in this study. The lowest transport and storage costs found in this study were for the pipeline hub transport cases, more than 35% lower on average than for the single source cases. Regardless of the sensitivity scenario, the hub transport cases were between two-thirds and half of the cost of the shipping case. This highlights the importance of economies of scale in CO2 transport, achieved by employing larger diameter pipelines. This leads to decreases in both the unit capital costs by allowing larger capacities of transport, as well as in operating expenses by decreasing pressure losses along the pipelines, thus requiring less energy for compression. Although the shipping transport option presented the highest cost of the cases considered, there is still a case to be made for ship transport if the project duration is short. As ship transport is less CAPEX intensive (35% of total cost), this mode of transport becomes competitive with pipeline transport if the project duration is decreased, or if the discount rate is increased. Further, shipping also becomes more competitive for longer transport distances. For example, if the hub transport options would take several years to implement, a case could be made for utilising ship transport for a few years while the hub pipeline is constructed, and then transporting via the hub once it is available.

Estimating capital cost of parabolic trough collector based concentrating solar power plants for financial appraisal: Approaches and a case study for India

An attempt has been made to estimate the unit capital cost of parabolic trough collector (PTC) based concentrating solar power (CSP) plants in India to facilitate their financial appraisal. While reviewing approaches mentioned in the literature, a significant variation is observed in unit capital cost estimates for a 50 MW wet cooled without storage PTC based plant (US $1700 to US $2662 per kW). To internalize the effect of alternate condenser cooling options and thermal energy storage on the unit capital cost, a new approach that is based on inventory of material used and associated costs have been suggested. With the use of this approach, the unit capital cost of a 50 MW wet cooled PTC plant is estimated at US $1734 per kW. Similarly, for the same nominal capacity plant with dry cooling, the unit capital cost is estimated at US $1994 per kW. Moreover, the effects of increased nominal capacity and hours of thermal energy storage on the unit capital cost have also been investigated.

Unit Labour Cost and Unit Capital Cost Indicators in Slovenia and the Other Euro Area Countries

Prices and costs are often the main points of interest in a typical competitiveness analysis. If studying prices cover the inflation and exchange rate perspectives, studying costs usually covers the relationship between labour costs and labour productivity. Strictly focusing on the labour side within the cost analysis does not offer a complete cost-overview of the production process. In this paper we try to complement the toolbox for assessing competitiveness in Slovenia and the rest of the euro area countries by constructing a unit capital cost index (UKC).

Methodology for the design and economic assessment of anaerobic digestion plants to produce energy and biofertilizer from livestock waste

The generation and poor disposal of waste from livestock industries is the major cause of pollution of water sources, soil, and air. Therefore, profitable alternatives are required for their correct disposal and use. Anaerobic digestion plants are a technologically viable solution to overcome this problem. In this study, it is proposed a methodology for the design and economic assessment of projects using anaerobic digestion plants to produce electrical energy, thermal energy, and biofertilizer from livestock waste. The methodology is developed based on the assumption that the process is mainly composed of an anaerobic digester and an electric generator having a Diesel-cycle internal combustion engine. It is programmed in “MS Excel” sheet and assessed using technical and economic data from a three real anaerobic digestion plants. The methodology obtains technical parameters such as energy production efficiency with an average difference of 35% compared to the real plants data. In addition, the unit capital costs are calculated, obtaining a value of €3789/kW with a difference of 21.1%, as well as unit operating costs of €729/kW per year with a difference of 15.2%. The financial viability of the project is assessed by calculating the net present value and obtaining €577,050 with a difference of 17.8% and an internal rate of return with a percentage difference of 3%. The proposed methodology specifies the technical parameters and the basic engineering of an anaerobic digestion plant in a stationary state, where the basic streams and dimensions of primary equipment, such as anaerobic reactors and electric generators, are specified. Moreover, the methodology calculates capital and operating expenses for an anaerobic digestion plant, which may be useful to assess the technical and financial feasibility for a project of this type.

Shale gas production costs: Historical developments and outlook

This paper aims at better understanding the potential future of shale gas in the light of the evolution of its wellhead production costs. Based on the most recent literature, we focus on cost data in the US to identify the structure of shale gas costs, their evolution and drivers. In particular, while the role of technology, which has led to a 25%–30% decline of unit capital costs since 2012 is emphasized, the relevance of considering additional risk factors when analyzing future costs is discussed. Further, we investigate future shale production costs on the long term by simulating contrasted supply and demand scenarios (from the authors, as well as replicated IEA scenarios) with consideration of different cost curves adjusted with the latest EIA cost data. Modelling results show costs ranging from $2.5/MMBtu to $6.0/MMBtu in 2040, with the conclusion that shale production costs are expected to remain relatively moderate until 2040, whereby the role of technological progress is deemed to be crucial. The paper finally assesses the key determining factors explaining the current gap in shale gas production costs between the US and other world regions.

Financing Multiple Heterogeneous Suppliers in Assembly Systems: Buyer Finance vs. Bank Finance

Buyer finance has been practiced by manufacturers/assemblers for years; however, few papers have investigated the efficacy of buyer finance in an assembly system with multiple suppliers. This paper fills the literature gap by comparing buyer finance with bank finance in a supply chain with one assembler and multiple heterogeneous capital-constrained component suppliers. We characterize the equilibrium solutions for different financing schemes (i.e., buyer finance, bank finance, and no finance). We show that in buyer finance the assembler should charge the suppliers the lowest possible interest rate, which may be even below its own unit capital opportunity cost, leading to interest losses in financing suppliers. However, the assembler can benefit more from enhanced inventory backup and lower component purchasing prices resulting from the low buyer-finance interest rate. We further compare the two financing schemes from the perspectives of the assembler, the borrowing and nonborrowing suppliers, and the whole supply chain. Our analysis reveals that the assembler may offer buyer finance even if its own unit capital opportunity cost is higher than the bank risk-free interest rate. We also demonstrate how the suppliers’ initial capitals, production costs, and their heterogeneities affect the assembler’s selection of the optimal financing scheme and identify the conditions under which buyer finance is better than bank finance for different parties in this assembly supply chain. The online appendix is available at https://doi.org/10.1287/msom.2017.0677 .

Desalination Technologies for Developing Countries: A Review

Fresh water is rapidly being exhausted due to natural and anthropogenic activities. The more and more interest is being paid to desalination of seawater and brackish water in order to provide fresh water. The suitability of these desalination technologies is based on several criteria including the level of feed water quality, source of energy, removal efficiency, energy requirement etc. In this paper, we presented a review of different desalination methods, a comparative study between different desalination methods, with emphasis on technologies and economics. The real problem in these technologies is the optimum economic design and evaluation of the combined plants in order to be economically viable for the developing countries. Distillation plants normally have higher energy requirements and unit capital cost than membrane plants and produces huge waste heat. Corrosion, scaling and fouling problems are more serious in thermal processes compare to the membrane processes. On the other hand, membrane processes required pretreatment of the feed water in order to remove particulates so that the membranes last longer. With the continuing advancement to reduce the total energy consumption and lower the cost of water production, membrane processes are becoming the technology of choice for desalination in developing countries.

A novel path toward methanol and olefins production fueled by syngas via a coupling of coke-oven gas reforming with pulverized coke chemical looping combustion

Efficient utilization of a large quantity of coke-oven gas (COG) to produce methanol and further olefins is an important technical path toward coal-to-chemicals. The current COG-to-olefins process (CGTO) suffers from inefficient utilization of hydrogen resource in the COG, limited olefins productivity, lower energy efficiency, and ultimately uncompetitive in product cost. Its major technical issues are the insufficient carbon supply and energy intensification. This study provided a novel technical path toward olefins production fueled by syngas from efficient coupling of COG reforming with pulverized coke chemical looping combustion (PCCLC). The CO2 generated by the PCCLC was used as carbon source to effectively adjust hydrogen-to-carbon ratio of syngas to 2.0, ideally adapting to methanol production first and further olefins. The coupling and integration in material streams and energy utilization were considered in the new process. Modelling and integration results supported the competitiveness of this novel process, revealing that its hydrogen efficiency and exergy efficiency can be increased to 43% and 60%, comparing to only 29% and 52% in the CGTO. The olefins capacity was also increased from 0.6Mt/y in the CGTO to 0.9Mt/y by an additional consumption of economic pulverized coke 0.43Mt/y. Although total capital investment of the new process was 21% higher than the CGTO, the unit capital investment and product cost were 19% and 6% lower because of its larger olefins capacity.

Use of Markov Models in Assessing Spare Transformer Requirements for Distribution Stations

This paper describes a probabilistic method based on Markov models for assessing the number of spare transformers, regular units and mobile units, required for a group of distribution transformers. The proposed method uses two criteria in determining the required number of spare transformers. The first criterion assumes that a pre-determined level of the group availability is given and the number of spare units is determined when the calculated group availability exceeds the pre-determined level of the group availability. The second criterion uses a cost/benefit analysis method in calculating the number of the spare units. In the second criterion, the number of spare units (optimal number) is determined when the total cost (spare unit capital costs and unit outage costs) is minimum. The proposed method is also used to evaluate the impacts of multi-transformer stations (stations with transformer redundancy) and station capabilities for use of mobile unit transformers on the number of spare units. Two distribution transformer groups of the Hydro One's distribution system are used to illustrate the proposed method of assessment and to compare the results obtained using the two criteria.

Will second‐generation ethanol be able to compete with first‐generation ethanol? Opportunities for cost reduction

AbstractThe production costs of a lignocellulosic ethanol process, both currently and projected for 2020, were compared to a corn ethanol process, to determine its economic competitiveness. A techno‐economic model was used to estimate the current production costs for a base‐case, 50 ML yr‐1 softwood facility, as well as providing a basis for cost‐reduction test cases assessing different feedstock, scaling, enzyme, and coproduct options. The progress ratio indicated that lignocellulosic ethanol could be competitive with corn ethanol by 2020, based on volumes mandated by 2007 EISA. However, cost reductions must occur across all components of the production process. The ambitious cellulase enzyme cost reductions that have been projected were shown to be challenging as cellulase costs still need to be significantly lower than those of amylase enzymes on a unit‐of‐protein basis. Opportunities for capital cost reduction relative to first‐generation plants were primarily restricted to the pre‐treatment/hydrolysis unit operations, with operational conditions such as the severity of pre‐treatment and hydrolysis residence times, significantly influencing operating costs. Alternative operating strategies, such as maximizing hydrolysis rate with shorter residence times rather than maximizing ethanol yield and using the unhydrolyzed residue for heat and power production, showed some promise. Increasing the size of the facility to 1 BL yr‐1 output substantially reduced the per unit capital costs, but not to a level competitive with an average (150 ML yr‐1) corn ethanol facility. © 2011 Society of Chemical Industry and John Wiley & Sons, Ltd

Unit Labor Costs in the Eurozone: The Competitiveness Debate Again

Current discussions about the need to reduce unit labor costs (especially through a significant reduction in nominal wages) in some countries of the eurozone (in particular, Greece, Ireland, Italy, Portugal, and Spain) to exit the crisis may not be a panacea. First, historically, there is no relationship between the growth of unit labor costs and the growth of output. This is a well-established empirical result, known in the literature as Kaldor’s paradox. Second, construction of unit labor costs using aggregate data (standard practice) is potentially misleading. Unit labor costs calculated with aggregate data are not just a weighted average of the firms’ unit labor costs. Third, aggregate unit labor costs reflect the distribution of income between wages and profits. This has implications for aggregate demand that have been neglected. Of the 12 countries studied, the labor share increased in one (Greece), declined in nine, and remained constant in two. We speculate that this is the result of the nontradable sectors gaining share in the overall economy. Also, we construct a measure of competitiveness called unit capital costs as the ratio of the nominal profit rate to capital productivity. This has increased in all 12 countries. We conclude that a large reduction in nominal wages will not solve the problem that some countries of the eurozone face. If this is done, firms should also acknowledge that unit capital costs have increased significantly and thus also share the adjustment cost. Barring solutions such as an exit from the euro, the solution is to allow fiscal policy to play a larger role in the eurozone, and to make efforts to upgrade the export basket to improve competitiveness with more advanced countries. This is a long-term solution that will not be painless, but one that does not require a reduction in nominal wages.

The economic viability of nuclear power in a fossil-fuel-rich country: Australia

This paper assesses the economic viability of investment in nuclear power generation in Australia in the future and, in addition, domestic factors which may influence government policy towards such investments. It argues that the structure of the grid in Eastern Australia and the nature of the existing generator mix would require nuclear technology that has similar attributes to current combined cycle gas technology; i.e. modular construction of (relatively) small generating units, load following capability, low unit capital cost, and a general acceptance by the Australian public. The current generation of nuclear plants possesses none of these attributes. Therefore this paper concludes that it is only technology with similar characteristics to some Generation IV nuclear technology concepts that has the potential to be part of Australia's energy mix after 2030.

The CCS paradox: The much higher CO2 avoidance costs of existing versus new fossil fuel power plants

Abstract CO2 avoidance cost economics are an essential tool for analysis of the potential for future CO2 capture and storage (CCS) utilization. The CO2 avoidance cost is the CO2 tax at which the product cost is the same for either a fossil fuel plant without CO2 mitigation (but paying the CO2 tax) or the same fossil fuel plant that includes the added capital and efficiency losses of adding CCS (but avoiding most of the CO2 tax). The CO2 tax must be higher than this CO2 avoidance cost to justify the higher risks, capital, and lower efficiency of utilizing CCS. Understanding which issues impact CO2 avoidance costs the most is fundamental to economically encouraging the massive CO2 reductions enabled with CCS. SFA Pacific recently completed two similar economic analyses of coal-based power plant CO2 mitigation costs. Both analyses included the options of converting to lower CO2 emissions with natural gas (with and without CCS) and continued coal use with and without CCS. One analysis was for an existing coal-based power plant baseline as part of a Massachusetts Institute of Technology (MIT) Workshop and Report entitled Retrofitting of Coal-Fired Power Plants for CO2 Emissions Reductions . The second analysis was for a new coal-based power plant baseline as part of an analysis of CO2 mitigation options by the U.S. Business Roundtable entitled The Balancing Act: Climate Change, Energy Security and the U.S. Economy . However, the resulting CO2 avoidance costs for these two analyses were very different. Specifically, the CO2 avoidance cost was about twice as high for the existing coal power plant than for the new coal power plant baseline. There are basic technical and economic reasons for this big difference in CO2 avoidance costs. They are best explained by simply showing the costs and performance of each baseline without and then with CCS in simple, transparent, and consistent one-page models. This enables easy, insightful side-by-side direct comparisons. Since first developing a cost and performance economic screening model of CCS for our GHGT-4 paper in 1998 , SFA Pacific has continued to improve the model which focuses on objectivity by stressing transparency and consistency with easy to compare cases. SFA Pacific has clearly shown identical inputs for key items such as fuel costs, non-fuel operating costs, unit capital costs, contingencies, site location factors, cost indexes, and especially capital charges. This makes it easy to see that power costs for the existing coal power plant baseline can be very low when the power plant is old and most of the existing capital is already paid-off. This GHGT-10 paper presents the most updated SFA Pacific analysis of CCS retrofit for existing coal power plant CO2 mitigation. The paper focuses on showing and explaining why the CO2 avoidance costs can be much higher for the existing plants versus new fossil fuel power plants. CO2 taxes which are high enough to discourage new coal power plants with high CO2 emissions would likely have little or no impact on existing coal power plants. Until the over 1,200 GW of existing old coal power plants begin reducing their high CO2 emissions, there can be little net reduction in worldwide CO2 growth. Converting or replacing this large capacity of existing coal power plants is essential to obtaining large CO2 reductions .