Long-Term Energy and Environmental Strategies
Yasumasa Fujii and Ryo-ichi Komiyama
Abstract This chapter investigates long-term energy and environmental strategies, employing a regionally disaggregated Dynamic New Earth 21 model (called DNE21) which allows us to derive a normative future image of energy systems through the comprehensive incorporation of forecasted future technologies. This integrated energy system model, explicitly considering the availability of advanced nuclear technologies such as nuclear fuel cycle and fast breeder reactors which can improve the usage efficiency of natural uranium resources, employs computational tools to evaluate the optimal global energy mix compatible with low atmospheric CO2 concentrations. Simulation results in the model indicate that massive CO2 mitigation targets can be achieved with the large-scale deployment of innovative technology, highlighting roles for nuclear, renewables, efficient use of fossil fuel, and carbon capture and storage (CCS). The results support the simultaneous pursuit of multiple technologies, rather than focusing merely on realistic technological options based on current perceptions. However, the validity about the expected role of nuclear energy for the future should be critically evaluated in the new technical and political contexts that exist after the Fukushima nuclear accident.
Keywords Energy model • Global energy mix • Nuclear fuel cycle
Innovative technologies are expected to play a key role in long-term transitions of the global energy system. This is particularly the case for the realization of climate change mitigation targets that stabilize atmospheric CO2 concentrations at levels that avoid a greater than 2 °C increase in average global temperatures above preindustrial levels. We have been investigating long-term energy and environmental strategies compatible with low atmospheric CO2 concentrations, employing a regionally disaggregated Dynamic New Earth 21 model (called DNE21). The energy model used here employs computational tools to conduct quantitative analyses on future global energy systems, but the outputs of the energy models should not be like the illusions in a fortune-teller's mystical crystal ball. Its major concern is, therefore, not to forecast a likely future image of the global energy system by extending secular trends in the systems, but rather to derive a normative future image of the systems through the comprehensive incorporation of forecasted future parameters and scenarios published in related academic literature and governmental reports.
Regionally Disaggregated DNE21
DNE21 is an integrated assessment model that provides a framework for evaluating the optimal energy mix to stabilize low atmospheric CO2 concentrations. The recent version of the DNE21 model  has featured a more detailed representation of regional treatments, including nuclear and renewable energy. The model seeks the optimal solution that minimizes the total system cost, in multiple time stages for the years from 2000 to 2100 at 10-year intervals in multiple regions, under various kinds of constraints, such as amount of resource, energy supply and demand balance, and CO2 emissions. The model is formulated as a linear optimization model, in which the number of the variables is more than one million. Figure 5.1 shows the division framework of world regions and assumed transportation routes. In the DNE21 model, the world is divided into 54 regions. In the model, large countries such as the United States, Russia, China, and India are further divided into several sub-regions. Furthermore, in order to reflect the geographical distribution of the site of regional energy demand and energy resource production, each region consists of “city nodes” shown as round markers in Fig. 5.1 and “production nodes” shown as square markers, the total number of which amounts to 82 points. The city node mainly shows representative points of intensive energy demand, and the production node exhibits additional representative points for fossil fuel production to consider the contribution of resource development in remote districts. The model takes detailed account of intra-regional and inter-regional transportation of fuel, electricity, and CO2
between these points.
Fig. 5.1 Regional disaggregation by node and transportation routes
DNE21 involves various components that model energy production, conversion and transport, primary energy resources, secondary energy carriers, final energy demand sector, power generation technology, energy conversion process, and CO2 capture (3 types) and storage. End-use electricity demand is assumed with a specific daily electricity load curve divided into six time intervals. Major modules considered in the model are as follows:
1. Primary energy resources: conventional fossil fuels (coal, oil, natural gas), unconventional fossil fuels (heavy crude oil and oil sand, oil shale, shale gas, other unconventional gas), biomass (energy crops, forestry biomass, residue logs, black liquor, waste paper, sawmill residue, crop residue at harvest, sugar cane residue, bagasse, household waste, human feces, animal dung), nuclear power, hydro power, geothermal power, solar power, and wind power;
2. Secondary energy carriers: hydrogen, methane, methanol, dimethyl ether (DME), oil products, carbon monoxide, electricity;
3. Final energy demand sector: solid fuel demand, liquid fuel demand, gaseous fuel demand, electricity (daily load curves with seasonal variations) demand;
4. Power generation technology: coal-fired, oil-fired, natural gas (Methane)-fired, integrated gasification combined cycle (IGCC) with CO2 capture, nuclear, hydro, geothermal, solar, wind, biomass direct-fired, biomass integrated gasifier/gas turbine (BIG/GT), steam injected gas turbine (STIG), municipal waste-fired generation, hydrogen-fueled, methanol-fired;
5. Energy conversion process: partial oxidation (coal, oil), natural gas reformation, biomass thermal liquefaction, biomass gasification, shift reaction, methanol synthesis, methane synthesis, dimethyl ether (DME) synthesis, diesel fuel synthesis, water electrolysis, biomass methane fermentation, biomass ethanol fermentation, hydrogen liquefaction, liquid hydrogen re-gasification, natural gas liquefaction, liquefied natural gas re-gasification, carbon dioxide liquefaction, liquefied carbon dioxide re-gasification;
6. CO2 capture (3 types) and storage: chemical absorption, physical adsorption, membrane separation, enhanced oil recovery operation, depleted natural gas well injection, aquifer injection, ocean storage, enhanced coal bed methane operation.