اندازه باتری برای سریال پلاگین در وسایل نقلیه هیبریدی الکتریکی: یک تجزیه و تحلیل اقتصادی مبتنی بر مدل برای آلمان

The battery size of a Plug-in Hybrid Electric Vehicle (PHEV) is decisive for the electrical range of the vehicle and crucial for the cost-effectiveness of this particular vehicle concept. Based on the energy consumption of a conventional reference car and a PHEV, we introduce a comprehensive total cost of ownership model for the average car user in Germany for both vehicle types. The model takes into account the purchase price, fixed annual costs and variable operating costs. The amortization time of a PHEV also depends on the recharging strategy (once a day, once a night, after each trip), the battery size, and the battery costs. We find that PHEVs with a 4 kWh battery and at current lithium-ion battery prices reach the break-even point after about 6 years (5 years when using the lower night-time electricity tariffs). With higher battery capacities the amortization time becomes significantly longer. Even for the small battery size and assuming the EU-15 electricity mix, a PHEV is found to emit only around 60% of the CO2 emissions of a comparable conventional car. Thus, with the PHEV concept a cost-effective introduction of electric mobility and reduction of greenhouse gas emissions per vehicle can be reached.

Anthropogenic CO2 emissions contribute to climate change and may cause substantial societal costs in the future (Stern, 2006) if significant and rapid CO2 mitigation is not achieved. Anthropogenic CO2 emissions originate mainly from the combustion of fossil fuels. Due to their very intensive use of fossil fuels the power generation and transportation sectors play a major role in the CO2 abatement strategies in Europe in general and in the largest European economy, Germany, in particular. These sectors contributed 40.8% and 17.7%, respectively, to overall anthropogenic CO2 emissions in Germany in 2008 (UBA, 2010). Therefore, the European Commission and the German government have adopted several CO2 reduction policies in various energy-related fields. For example, the transport sector will be regulated via emissions performance standards for new passenger cars. Between 2012 and 2015, the average CO2 fleet emissions of a certain percentage of an automaker's annual new passenger car sales must not exceed 130 g CO2/km, with gradually stiffened interim targets. By 2020, the target value for the fleet emissions is 95 g CO2/km. The regulation also defines ‘super-credits’ for cars with emissions below 50 g CO2/km, allowing them to be counted as 3.5 cars in 2012. These ‘super-credits’ will be gradually phased-out until 2016, but until then might act as a significant incentive for car manufacturers to accelerate the diffusion of PHEVs (EU, 2009), as their tailpipe CO2 emissions are reduced to zero in electric driving mode. Beyond that, the German government has set the further-reaching goal to get one million electric vehicles on Germany's roads by 2020 (Bundesregierung, 2009), because electric mobility can offer manifold benefits (Sovacool and Hirsh, 2009), such as the reduction of CO2 emissions by means of reducing oil-based fuel consumption in the transport sector and by increasing electricity generation from volatile renewable energy sources, using electric vehicles as active storage systems in the grid—the so-called vehicle-to-grid (V2G) concept (Kempton and Tomic, 2005a and Kempton and Tomic, 2005b). With this in mind PHEVs offer the possibility to reap the benefits of electric mobility by simultaneously overcoming its major barriers on the consumer side, because they enable motorists to drive in electric mode during parts of their trips, without having the limitations concerning the driving range of full-electric cars. However, a transition to electric car mobility strongly depends on consumer acceptance, which in turn is heavily affected by the cost-effectiveness, the driving range and the recharging conditions for these new types of cars, especially when they are compared to conventional vehicles with an internal combustion engine (ICE) (Dena, 2010 and Achtnicht et al., 2008). Since the PHEVs' electric drivetrain is an additional cost factor it is necessary to have a closer look at the total cost of ownership (TCO) over the vehicles' lifetimes, which primarily consists of operating cost, maintenance cost and purchase price, to assess their economic effectiveness. The purchase price of PHEVs in turn is mainly influenced by the battery cost and thus by the car's battery size, which differs largely among the recently announced PHEVs, depending on the manufacturer. For instance, while the Toyota Prius will be endowed with a 5.2 kWh battery and is designed as a parallel hybrid concept, the Chevrolet Volt and Volvo Recharge will be equipped with much larger 16 kWh batteries and a serial hybrid concept, although all these PHEVs will on average have the same engine power of 100 kW. Moreover, not only the purchase price is affected by the electrification of the drivetrain, due to, e.g. the downsizing of the ICE and the additional need for an electric engine and power electronics, but also the operating and maintenance costs are reduced. This is caused by a general decrease in fuel consumption, considerably lower fuel costs when driving pure electrically, and possibly lower motor vehicle taxes compared to conventional ICE vehicles, if the vehicle's taxable base also accounts for CO2 emissions and not solely for engine displacement, as is currently the case in Germany (BMF, 2009). The disparity in these three cost segments between PHEVs and conventional ICE vehicles expectedly results in a cost advantage of the PHEV when the battery costs are ignored in the calculation. This value can be contrasted with different battery sizes and battery price scenarios to calculate the most favorable battery size regarding cost-effectiveness. In this paper we investigate the economic consequences of different battery sizes of an average PHEV in Germany and undertake a sensitivity analysis with respect to key parameters. The second aim of the paper is the calculation of the annual CO2 emissions of the two different power trains under various energy mix scenarios, because aside from economic factors environmental considerations are a main decision criterion in vehicle choice in Germany (Dena, 2010). The remainder of this paper is organized as follows: the methodological approach is outlined in more detail in Section 2. In Section 3 the energy consumption of the gasoline engine, the electric drivetrain and the range extender (RE) are calculated and compared. Section 4 assesses the total cost of ownership. For this purpose, we estimate the development of the gasoline and electricity prices, calculate the mobility costs for an average driver, derive the cost differences regarding initial and annual costs up to 2020, and conduct a sensitivity analysis to assess the impact of changes in the technical and economic assumptions. In Section 5, the CO2 emissions of the vehicles are estimated for different fuel mix and vehicle charging scenarios. Section 6 summarizes and concludes.

6. Summary and conclusions Based on our assumptions about the daily and annual driving patterns, the development of energy prices until 2020, the vehicle size and horse power, the vehicle taxes, the differences in the maintenance and initial costs, and the efficiency of the electric components, we find that there is substantial potential to reduce the total cost of ownership of a PHEV in comparison to a standard and even to an optimized ICE vehicle within the next few years. Based on our model results, especially cars with smaller batteries (e.g. 4 kWh) are found to be cost-effective within less than 5 years. Larger batteries reduce the CO2 emissions if they are charged with green electricity, but have significantly higher initial costs. In the standard scenario, for example, a 12 kWh battery system would become economical after a usage period of 8–9 years. To be competitive compared to conventional ICE cars, however, the break-even has to be reached at least within the average first-hand ownership time of the new car of about 7.5 years (DAT, 2009 and DAT, 2010). Concerning the recharging strategies we showed that the presented alternatives did not differ significantly. The over-night recharging strategy is the most economical way but needs an infrastructure and a billing system that is capable of supplying time-variant tariffs. In Germany, the installation of such a grid and metering infrastructure has only just begun and will take years to be completed. Such intelligent grid infrastructure offers the potential to use the battery in vehicle-to-grid systems in the future, which would support larger batteries, since ancillary grid services are partly paid for just being available and partly per kWh generated. In our very simplified average calculation we also illustrated that the CO2 impact of PHEVs is positive and that even small batteries offer some potential to reduce the CO2 emissions compared to the reference car. With an increasing battery size it is necessary to use clean electricity to further improve the CO2 balance. Nevertheless, the results show that PHEVs with small batteries are close to cost-competitiveness and hence offer a chance to start the transition to full-electric mobility even in the presence of high battery prices. Thus, if the intention of the government is the acceleration of the diffusion of PHEVs, then their incentives should be designed to increase the adoption rate of PHEVs with a small electricity capacity. Looking at our results, a first step might be, for example, a state-wide consumer information program, aimed at increasing the awareness about the long-term benefits of PHEVs due to their lower fuel costs. Another measure could be to force the car manufacturers to label the gasoline and electricity consumption of their vehicles in a clear and easily understandable way, like the European energy label for domestic cooling appliances (EU, 1994). How these results might change when (1) the deterioration of the battery is taken into account or (2) our analysis is widened to account for different driver categories with different driving profiles regarding trip length or annual mileage and/or the inner-city/rural/highway trip ratio and (3) different vehicle classes, leading to a change in size, weight, driving resistance, fuel consumption, etc., is needed to be determined in future research. Besides this analysis of the costs and benefits of electric vehicles in general and especially of PHEVs, further research is needed to gain better insight into vehicle consumer preferences, since consumers normally do not assess the cost savings from energy-efficient technologies objectively. Only when the barriers that lead to consumer rejection of these new vehicle technologies are eliminated a major diffusion of electric vehicles can take place. Finally, it should be pointed out that the research done in this paper is highly dependent on the assumptions made, concerning the price developments in the next couple of years of gasoline, electricity, power electronics, electric engines and batteries in the next couple of years. Since this research was completed end of 2009, some of the assumptions made turned out to be different in reality, while others stayed unchanged. For example, as already mentioned earlier, a mass production of PHEVs and electric vehicles still does not exist, so that there is a persistent lack of resilient market data on purchase price differences between PHEVs and conventional ICE vehicles in general, and the influence of single components, such as power electronics and batteries, on it in particular, so that the data from the literature on which our calculations are based are still valid. The same holds true for the stability of driving patterns of the average German car user. However, gasoline and electricity prices did not follow the paths we assumed in our conservative approach (see footnote 3) and rather increased faster over the last 1.5 years. But since gasoline prices escalated faster than electricity prices, this development should favor PHEVs compared to conventional ICE vehicles, making them more cost-effective and letting them break-even more quickly.