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Feasibility, emission and fuel requirement analysis of hybrid car versus solar electric car: a comparative study

Hybrid versus solar electric car comparison

International Journal of Environmental Science and Technology volume 14, pages1807–1818(2017)Cite this article

Abstract

The problem regarding environment has been considered as contemporary issue, and to cater this, various technologies have been revolutionized in vehicle transport field. Efforts have been made to make vehicle engine efficient and introducing hybridized vehicles with the aim of reducing emissions and less fuel dependency. In essence of this, trends of solar electric cars in different countries have been reviewed. Feasibility analysis is done by doing fuel cost analysis of two cases, i.e., simple hybrid vehicle and hybrid vehicle equipped with solar module and increased battery energy storage capacity for a specific round trip distance between two cities, i.e., Rawalpindi and Islamabad in comparison with feasibility of third case, i.e., proposed solar electric car model. The solar module selection along with desired number of batteries with charging and discharging time and motor power required to carry five persons weight (70 kg each) is calculated for third case. Moreover, total carbon dioxide emission analysis has been carried out from car material production to its assembly, manufacturing solar module and nickel metal hydride battery for each case. The annual carbon dioxide emitted from fuel in first two cases relative to electric outlet in third case for specific distance has been analyzed. On large scale, emission analyses for hundred cars of each case have been done at 100 km distance. From calculations, it is revealed that overall emissions in third case on large scale and from its material production, assembly, solar module and batteries manufacturing perspective are comparatively less than other cases.

Introduction

Currently the world is facing two major issues regarding environment degradation. One is increased green house gas (GHG) emissions and the other is more reliance on fossil fuels. The later results in high fuel rates thus lead to unsustainable energy and misbalance system economically (Fattori et al. 2014). Regarding the former issue, the future challenge is to limit such emissions as declared by EU (European Union) for 2050 (European Union 2012) in order to restrict a change in climate (IPCC 2014). The energy consumption by transportation sector is about third of the world total energy demands, whereas at the fourth place of total GHG’s emissions (U.S. Energy Information Agency 2013). The current trend of fossil fuel consumption will result in the depletion of these fuels in near future thus leads us to alternative energy resources to meet energy demand for transportation sector.

The road transportation is considered as a paramount source for such emissions and energy consumption. Therefore, it is substantial for introducing energy-efficient transport to curb the emission of CO2 arising from transport sector. According to EU, the energy consumption of road transport is increasing and will tend to increase in the same way in future thus requires increased energy efficiency of road transport in reducing air emissions. The European Commission (EC) aim is to introduce the energy-efficient transport by introducing alternative fuels and efficient engine technologies. In order to achieve their aim, EC has declared the target of using the renewable energy resources of 20% in energy consumption and 10% in road vehicles by 2020. The market is trying to shift toward more energy-efficient vehicles as compared to conventional vehicles due to continuous increase in fuel rates and forthcoming scarcity of fossil fuels. The introduction of hybrid and plug-in hybrid vehicles will lead to lower emissions but not helpful in cut back fuel consumption (Giannouli and Yianoulis 2012).

The electric cars are becoming an important source of reducing CO2 emission and energy-efficient technology as compared to conventional vehicles for a motive power. Due to limited supply of fossil fuels, electric cars can be used as an alternative renewable energy resource (Redpath et al. 2011). As the amount of fuel consumed by engine increases, CO2 emission increases in direct proportion. There has been a development in reduction of those pollutants emission which affect air quality. Although engine efficiency has been increased, there has been less development in reduction of CO2 emissions. The European commission and industry associations of the main motor vehicle manufacturers admitted to cut the CO2 emissions from new vehicles in 1998. According to this understanding, the average 25% CO2 emissions reduction from new vehicles had been done by 2008–2009 to 140 g per km (Soediono 1989). In essence of this, photovoltaic technologies can be utilized in on- and off-road transportation to reduce CO2 emissions in transportation sector. One of the ways is to utilize solar modules by integrating them with hybrid vehicles, thus results in reducing fuel consumption and CO2 emissions. Solar cells cannot provide enough power to energize the motor drive train of hybrid vehicle but can provide power to battery of hybrid vehicles when they are stationary (Giannouli and Yianoulis 2012).

The conventional vehicle efficiency correlates to fuel economy. The increase in US passenger car efficiency relative to average fuel economy and corporate average fuel economy (CAFE) standards is shown in Table 1. From 1978 to 1980, US passenger cars weight decreases and improves acceleration thus makes average fuel economy and efficiency better. During the period of 1980–2004, the passenger car weight increased with advancement in acceleration and powertrain efficiency (Average Fuel Efficiency of U.S. Light Duty Vehicles 2015; Lutsey and Sperling 2005). Further improvement in powertrain efficiency occurred in 2005–2013 at 0.3% per year (Thomas 2014).

Table 1 Historical gain in US conventional vehicle efficiency relative to average fuel economy
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The total production of US conventional vehicles (gasoline, gasoline hybrid and diesel cars) with respect to total passenger cars in particular years is shown in Table 2. In 1980, the gasoline and diesel cars production was 95.7 and 4.3%, respectively. There was an increase and decrease in gasoline and diesel cars manufacturing up to 99.9 and 0.1% in 1990. In 2000, the market shares of diesel cars were constant and gasoline cars decreased by 0.1% relative to 1990. After 2001, a market introduction of 0.1% gasoline hybrid cars and later on increased to 3.8%, while gasoline and diesel cars percentage was 95.5 and 0.7% in 2010. In 2014, the gasoline hybrid cars production were decreased to 2.6% due to the contribution of plug-in hybrid electric vehicles (PHEV’s) and electric type, etc., while gasoline and diesel car production increased to 95.7 and 1.0%, respectively (Environmental Protection Agency 2015).

Table 2 Trends in total number of conventional vehicles in the USA
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The total miles traveled and CO2 emitted by gasoline and diesel fuel by US passenger cars is shown in Table 3. Burning one gallon of gasoline and diesel emits 8887 g and 10,180 g of CO2 (U.S. Environmental Protection Agency 2014). The total amount of fuel required relative to total miles traveled and average fuel economy in 2009 was 4.762 × 1010 gallons (gasoline = 55.8% and diesel = 0.5%). Such fuel usage decreased to 4.404 × 1010 gallons (gasoline = 48.7% and diesel = 0.5%) and 3.979 × 1010 gallons (gasoline = 49.0% and diesel = 0.5%) with improvement in cars fuel economy in 2011 and 2013 subsequently (Davis et al. 2015).

Table 3 US passenger cars, total miles travelled with CO2 emitted by particular fuel usage
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A literature review has been performed about solar panels and batteries key parameters concerned with hybrid and electric vehicles. Such key parameters relevancy to this research is summarized in Table 4.

Table 4 Summary table of point of interest regarding solar cells, batteries and cars in this study
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In this paper, the focus is on the feasibility study of two cases such as simple Toyota Prius car and Prius car equipped with solar module and increased battery energy storage capacity in comparison with PSEC for a selected distance between adjacent cities of Rawalpindi and Islamabad. The route selected has been of 24.6 km, a daily round trip distance between Asghar Mall road, Rawalpindi and NUST University, Islamabad. For specific distance, a fuel cost analysis has been carried out for two cases in relative to electricity required for recharging PSEC from an external source that is supplied by electric supply companies through fuel (gasoline) consumption. Some design modification has been done in roof of a Prius car for PSEC in simulation software and also reduced weight by excluding some components of a Prius car such as engine, Motor Generator (MG1 and MG2) and Power Control Unit (PCU) weight. The motor power required to drag 1690.4 kg including five persons weight with charging and discharging time of batteries has been also calculated. The annual CO2 emissions from fuel utilization perspective by each case in relative to PSEC are also calculated. Total CO2 emission analysis for Prius car material production, its assembly, manufacturing solar module and NiMH batteries has been performed in comparison with PSEC. In last, the annual CO2 produced on a large scale by using hundred cars for each case and PSEC at a selected distance of 100 km has been also investigated.

Trends of hybrid and solar electric cars and their limitations in specified countries with fuel cost analysis

The countries such as Greece, Mexico (Veracruz), Pakistan and Bangladesh were selected for the comparison of their specific cars used in terms of maximum distance range with fuel cost analysis and their limitations.

Greece (Patras)

The Toyota Prius that is a hybrid electric vehicle (HEV) was selected by Giannouli and Yianoulis as a model for performing an experiment by accompanying the solar panel having an area of 1.2 m2 on a roof. The NiMH battery with a capacity of 6.4 MJ and having weight of 39.5 kg was selected. The used battery capacity was 40% of the total battery capacity, i.e., 2.6 MJ. The December and July was taken as the minimum and maximum energy perceived on horizontal surface from sun, i.e., an average daily solar radiation of 6.48 and 26.13 MJ/m2 received in December and July. The daily electrical energy produced by polycrystalline silicon cell with an efficiency of 15.5% in December and July were 1.128 and 4.716 MJ/m2. However, with an efficiency of 22% crystalline silicon cell, the daily electrical energy produced in December and July was 1.668 and 6.732 MJ/m2. Such values represent the limitation of solar cells of not utilizing maximum solar energy even during the sunny months. So Giannouli and Yianoulis have selected the electrical energy of 4.716 MJ/m2 produced in June or July that is sufficient to charge the battery energy storage capacity of 2.6 MJ. This case is selected for short driving range of about 10 km with the recommended additional battery energy storage capacity of 11.6 MJ.

In Greece, the battery storage capacity was increased from 6.4 to 11.6 MJ, thus adding extra battery storage capacity of 5.2 MJ. The peak power of a crystalline and polycrystalline solar cells were 264 and 186 Wp with a module price of 2.14 and 1.74 $/Wp. The PV collector area that was selected for a Toyota Prius was 1.2 m2 with a cost of 565 and 324 $ for crystalline and polycrystalline silicon solar cells. The overall cost in case of using crystalline and polycrystalline silicon solar cell was 1069 and 828 $. By assuming an annual distance of 15,000 km and 1.8 $/L price of a fuel, the annual fuel saved was 100 and 142 L in case of polycrystalline and crystalline silicon solar cells with a driving cycle on battery and fuel of 0.37 MJ/km and 0.045 L/km. The annual cost saved on fuel was 256 and 180 $ for crystalline and polycrystalline silicon solar cells (Giannouli and Yianoulis 2012).

Mexico (Veracruz)

A solar electric vehicle was designed by Veronica et al. for Veracruz, a state of Mexico. The intensive gasoline cars used in Mexico were considered as the major GHG polluter, and in order to cope this, Veronica et al. have designed a solar electric car for that state. Such vehicle had the capability to carry a weight of four persons with total car weight not exceeding 800 kg with a speed of 70 km/h and autonomy of 4 h. A battery having a cell voltage of 3.2 V and 100 Ah capacity was selected (Sánchez et al. 2014).

Sixteen batteries were connected in series in order to produce 52 V and an energy storage capacity of 5.2 kW h in order to run a motor of 10 kW and 48 V. In order to run a motor for at least 4 h autonomy, the required energy capacity needed from battery is 31.2 kW h that can be attained by connecting six battery packs of 5.2 kW h in parallel (Boylested 2010).

The distance of 70 km was selected from Veracruz city of Fortin de las Flores to technological institute of Veracruz by Veronica et al. The conventional vehicle accompanying four cylinders results in a consumption of 1 L petrol per 12 km. Considering the cost of fuel as 10 $/L, this resulted in fuel cost saving of 60 $ when using a solar electric vehicle. (Sánchez et al. 2014).

Pakistan

A solar electric car had been constructed by M. Farooq et al. in Pakistan by keeping in view the scarcity of fossil fuels and environmental pollution. The car accompanied different features such as automatic lights and door movement, where the lights will turn on and off according to light intensity, solar module movement, battery overcharge protection and displaying charging level circuit. The motor was capable in order to carry weight of 150 kg with a protection circuit. A polycrystalline solar module of 200 W and 24 V was selected with a size of 1.16 m2. Two lead acid batteries were used of 12 V and 45 A, respectively, connected in series. The car can cover a distance of 35–40 km on batteries at a speed of 40 km/h, where batteries can be recharged in 3.5 and 1.25 h from solar panel and external outlet through rectifier circuit. The car was designed only for a single person with a total cost of $ 950 approx (Farooq et al. 2014).

Bangladesh

A prototype design for solar electric car was proposed by Sanjana f et al. for Bangladesh. The anticipation is toward using this car as an office car for a roundtrip distance of 40 km selected between Uttara and Matijheel of Dhaka city that is the world most polluted area. Such car was made for two persons. A motor power of 700 W was selected in order to carry 500 kg weight with a speed assumption of 60 km/h. The four lead acid batteries of 12 V and rated capacity of 40 Ah each were connected in series that were recharged through four solar modules of 50 W and 16–17 V each with total area of 1.33 m2, connected in series. A plug-in charging facility was also provisioned in a car. It was calculated that the cost incurred on a solar electric car from operating and electricity consumption during recharging perspective was 2863.47 USD calculated for 20 years. An amount of 16346.16 USD was needed over the same period by a conventional car when fuel was used (Ahmed et al. 2014).

Methodology

The feasibility analysis of three cases, i.e., hybrid car (first case), hybrid car with solar panel and increased battery energy storage capacity (second case) and PSEC (third case) for a selected distance between two cities, i.e., Rawalpindi and Islamabad, has been carried out as shown in flowchart in Fig. 1.

Fig. 1
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Flowchart describing method for feasibility analysis of three cases

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Feasibility of hybrid car for a selected distance from Rawalpindi to Islamabad

The third-generation Toyota Prius car is selected in order to determine the fuel cost saved in Islamabad city with a distance selected of 24.6 km, a round trip from Asghar Mall road Rawalpindi to NUST University H-12 Islamabad city. Such car comprises of 1.8 L gasoline engine with a maximum power of 73 kW at 5200 rpm and a maximum torque of 142 N-m at 4000 rpm. The type of battery used is a nickel metal hydride (NiMH) with an energy storage capacity of 1.3 kWh or 4.68 MJ and a capacity of 6.5 Ah (Ratio et al. 2015). The energy used by the car when driven on a battery is 40% of the total energy storage capacity that is 520 Wh or 1.87 MJ. The control system was designed to control the state of charge (SOC) between 40 and 80%. When battery storage capacity reaches 80%, then further charging was cut off and battery was discharged up to 40% by running electric motor with no fuel consumption. The battery discharges up to 2.6 Ah by providing a power within a range of 15–19 kW to the motor and recharged within 500 s from the 6.4 kW power generated by the generator (Kelly et al. 2002). The total distance a car can travel on an electric or battery mode is 1.6 km under speed limit of 40 km/h (Toyota Prius| The hybrid that started it all 2015) by excluding recharging factor of a battery through regenerative braking system.

Fuel cost analysis with battery energy storage capacity of 4.68 MJ

A car is on an electric mode when driven at a speed of 40 km/h, and considering that it should not exceed that limit will cover a distance of 1.6 km. So when battery discharges up to 40%, a car will convert on a fuel mode and generates electric current through generator to recharge the battery. Such charging duration is of about 500 s or 0.1388 h, and then, a distance travelled by a car on fuel mode in such duration will be 5.5 km. Since the total distance of one day is 24.6 km, so a total distance of 19.8 and 4.8 km will be covered on fuel and electric mode with battery energy storage capacity of 4.68 MJ as shown in Table 5.

Table 5 Distances covered by Prius with a battery energy storage capacity of 4.68 and 9.36 MJ
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The Toyota Prius car consumes 4.6 L /100 km (Fuel Economy 2016). A distance of 19.8 km is covered with a fuel consumption of 0.9108 L. The annual fuel consumption is of 332.4 L. The price of gasoline is 74.79 Rs/L effective from 01 May 2015 (Pakistan State Oil 2015). So the total annual fuel cost is 24863.3 Rs.

Fuel cost analysis with installed solar panel on a car roof with increased battery energy storage capacity of 9.36 MJ

The Toyota Prius car has roof area of 1.2 m2, so by incorporating 13% efficient polycrystalline silicon solar panel with a maximum peak voltage ‘V mp’ and current ‘I mp’ of 23.2 V and 7.33 A (Canadian Solar CS6A-170 (170 W) Solar Panel 2015) and increasing the battery energy storage capacity with the addition of 4.68 MJ thus results in annual fuel consumption up to 278.7 litre with an annual cost of 20,845 Rs. When battery storage capacity is increased up to 9.36 MJ, then initially the car will cover more distance on electric mode as shown in Table 5, and after that, it will cover the distance in same manner as covered with battery storage capacity of 4.68 MJ. The energy consumption pattern from additional battery is assumed to be same as that from existing one. The additional storage capacity will only be used during first drive on electric mode, and after that, it will not provide power until it will be recharged by the roof-mounted PV panel to a specified limit. The charging facility through generator is not given to such supplementary battery and is done by means of a solar panel through additional boost voltage converter with a desired output voltage and current, found through equations shown below.

$$V_{o} = \frac{{V_{\text{in}} }}{{1 - {\text{DC}}}}$$
(1)

(Nelson 1986)

$$I_{\text{in}} = I_{o} \left( {\frac{{V_{o} }}{{V_{\text{in}} }}} \right)$$
(2)

(Nelson 1986) where V o is the output voltage from converter, V in and I in is the input voltage and current from solar panel, I out is the output current obtained from converter, and DC is the duty cycle of converter (Nelson 1986). With a duty cycle of 90%, an output voltage and current of 232 V and 0.733 A can be achieved and thus recharge the battery within 3.5 h, as residing hours in NUST is 8 h. However, such charging hours varies depending on the amount of solar radiation received from solar panel (Green 1982).

The amount of annual fuel cost saving by running a Prius car on an electric mode in both cases, i.e., with and without increased battery storage capacity, is 6027.4 and 10045.8 Rs.

Feasibility of proposed solar electric car (PSEC) for Islamabad

The electric cars are those that consist of electric motors instead of ICE and are driven by battery packs (Poullikkas 2015). Such electric cars are charged either by on-board or off-board method. In former method, charging is done either through supplementary roof-mounted solar panels or by means of an electric outlet during home or at work. In case of off-board, the electric vehicles are charged by electric stations (Tie and Tan 2013). The proposed solar electric car (PSEC) model design will be based on a Toyota Prius hybrid car with some modification done in simulation software as shown in Fig. 2.

Fig. 2
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Proposed solar electric car (PSEC) model

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The polycrystalline silicon solar panel of same specs as discussed in “Fuel cost analysis with installed solar panel on a car roof with increased battery energy storage capacity of 9.36 MJ” section will be installed at the back of PSEC, making an angle of 33.6°, that is, latitude of Islamabad city. This is done in order to attain maximum output from solar panel throughout the year by parking the PSEC in a way that solar panel should face toward south or north depending on the location of that country either it is in northern or southern hemisphere (Green 1982). In this case, the solar panel should face toward south as Islamabad is in northern hemisphere region. PSEC excludes the Prius engine weight that is 6.96% of car mass which becomes 97 kg (Mywikimotors.com 2015), Motor Generator (MG1 and MG2) weight (63.8 kg) based on specific power of 1.6 kW/kg and the Power Control Unit (PCU) weight (13 kg) comprises of inverter related to motor and generator in addition to bi-directional DC to DC converter (Burress et al. 2011). The weight of a Prius car was 1393 kg (Ratio et al. 2015), so total weight of a PSEC becomes 1219.2 kg after excluding different Prius components weight. The total weight of PSEC will become 1340.4 kg after adding weight of solar panel (16 kg (Canadian Solar CS6A-170 (170 W) Solar Panel 2015)), direct current (DC) motor (23 kg) (Servomotors, 2015) and six more NiMH batteries (82.2 kg as described in “CO2 emission analysis during production of third-generation Prius hybrid car, solar panel and batteries and car assembly” section) of same energy storage capacity of 1.3 kWh. The weight of additional boost voltage converter used in PSEC is not considered here.

The motor power required in order to carry five persons weight of 70 kg each is calculated by

$$P = F.v$$
(3)

(Ahmed et al. 2014) where ‘v’ represents cars velocity that is 40 km/h and ‘F’ is the required force to surmount frictional force between tires and road and can be determined by,

$$F = m.g.C_{\text{rr}}$$
(4)

(Ahmed et al. 2014) where ‘m’ is mass of a car plus five persons weight, ‘g’ is acceleration due to gravity, and ‘C rr’ is coefficient of tires rolling resistance (Ahmed et al. 2014) of P195/65 R15 tire size (Ratio et al. 2015). With m = 1690.4 kg, g = 9.8 m/s2 and C rr = 0.0076 (Section and Grade 2005), the force becomes 126 N. Thus, a motor power of 5.04 kW will be needed to drag that much weight. A motor having maximum input dc voltage of 340 V with output power of 5073 W is selected. Such motor has a constant current of 26.7 A peak at stall condition (Servomotors 2015). However, more motor power can be selected depending on nature of road (Ahmed et al. 2014), and in this case, the road between two cities is smooth. It has also been ensured that the battery energy consumption does not exceed the designed limit which is 60%.

Discharging and recharging time of NiMH batteries

The control system will be designed in order to discharge the batteries up to 40% of total energy storage capacity of 9.2 kW h and total rated capacity of 45.5 Ah. The batteries were recharged from solar panel, installed at the back by means of a boost voltage converter in the same way as discussed in “Fuel cost analysis with installed solar panel on a car roof with increased battery energy storage capacity of 9.36 MJ” section or from an external electric source. The boost voltage converter will also be used to step up the voltage of batteries up to motor specified limit of 340 V with a duty cycle of 40.7%.

The batteries will be discharged in 1.1 h when motor is operated at full power. The time required to complete one-way distance of 12.3 km at a speed of 40 km/h is 0.31 h. In 1.1 h, the 5.5 kW h battery energy storage capacity is consumed, so in 0.31 h, the amount of battery energy consumed is 1550 W h. This results in a 28.2% battery energy consumption of total battery energy storage capacity (5.5 kW h). The rated capacity also deceases to 7.7 Ah, and time required to recharge the batteries through solar panel is 10.5 h. The residence time in NUST is 8 h, so 5.87 Ah capacity can be easily recovered. In other words, about 76.23% of the consumed capacity (7.7 Ah) or battery energy storage capacity (1550 W h) can be recharged in 8 h with a traveling hours recovered of 0.24 h. A PSEC can easily reach back to destination from NUST to Asghar Mall road with a battery discharging time left of 0.72 h for the next day. A PSEC can cover a selected distance up to 2.5 times when there is only charging involved from solar module and 1.5 times without being recharged either from solar module or external source. So a PSEC can be further recharged on a third day from an electric outlet up to 1550 Wh in order to cover a distance of 12.3 km from NUST to residence within time interval of 0.31 h or can be fully recharged.

Carbon dioxide emission analysis

The carbon dioxide (CO2) emitted by the third-generation Toyota Prius car is 2.7 metric tons annually or 178 g/1.6 km (Fuel Economy 2016). The annual CO2 produced by the Prius car on fuel mode with battery energy storage capacity of 4.68 and 9.36 MJ is 804 and 674 kg. The net annual reduction of CO2 after installing solar module and adding a battery is 130 kg.

CO2 emission analysis during production of third-generation Prius hybrid car, solar panel and batteries and car assembly

There is energy needed for production of materials and assembly of cars. The mass of the car is based on components with different percentage contribution to total car mass, i.e., body (45%), drivetrain (28%) and chassis (27%). The car is manufactured of different materials, and their composition with required energy for a mid size car is shown in Table 6, where cast iron and cast aluminum are produced from recyclable material, whereas currently 80% of cast aluminum that is used in cars is made from scrap (Cuenca and Gaines 1995) while remaining materials are considered as new. The material composition of a conventional vehicle can be applied for hybrid or electric vehicle except the battery, that is NiMH, will be treated independently (Perdontis 2011). The final energy required for car assembly in a final product form is 3.8 MJ/kg (Cuenca and Gaines 1995).

Table 6 Energy requirements for different material composition of a standard car
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The mass of a third-generation Toyota Prius car is 1393 kg (Ratio et al. 2015). As electricity is produced from different sources such as conventional fuels, hydro, nuclear, wind and solar, so cumulative effect results in combined CO2 emission of 230 g/MJ of energy produced (CO2List.org 2015). The amount of energy required for each material production with carbon dioxide produced with respect to car mass is shown in Fig. 3.

Fig. 3
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Energy required and CO2 produced for different materials with respect to Prius car mass

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In case of glass, the amount of CO2 produced is 0.172 kg per 0.34 kg glass manufactured (CO2list.org 2015), so 37.6 kg of glass is used in car and produces 19 kg of CO2. The amount of energy required for manufacturing NiMH battery and its required materials production are 8.1 MJ/kg and 108 MJ/kg, while less energy of 19.6 MJ/kg is required in manufacturing NiMH battery from recycled materials. The weight of a single battery is 13.7 kg, calculated form maximum battery energy storage capacity of 95 Wh/kg (Sullivan et al. 2010). The amount of CO2 emission from above-mentioned mixed electricity source in manufacturing plus material production of two batteries from new material is 366 kg each. The total amount of energy required for production of 13% efficiency of multi-crystalline silicon module is 4200 MJ/m2, whereas 45% of this energy is needed for manufacturing polycrystalline silicon module (Alsema and de Wild-scholten 2006). The 14 g of CO2 is produced per MJ of energy consumed during production of polycrystalline silicon module (CO2List.org 2015). The total amount of energy required during Prius car assembly, material production (excluding glass), manufacturing solar panel and batteries with total CO2 produced is shown in Table 7.

Table 7 Total energy required and CO2 produce in case of Prius hybrid car and PSEC for specified tasks
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CO2 emission analysis for PSEC

In order to recharge the PSEC up to 1550 W h from an electric outlet at NUST on third day as discussed in “Discharging and recharging time of NiMH batteries” section, an energy of 0.72 MJ is needed, if such electricity is produced from gasoline by electric supply company then 83 g of CO2 produced per MJ of energy consumed (CO2List.org 2015) and results in an emission of 22 kg CO2 annually. The batteries are fully 40% discharged when reached to home and further recharging needed up to 1550 W h thus able the car to travel for 0.31 h for next day or in case of fully recharged up to 5.5 kW h then 19.8 MJ of energy is needed and produces 599.8 kg CO2 annually.

The weight of PSEC becomes 1219.2 kg after excluding weight of engine, MG1 and MG2 and PCU. The amount of energy required and CO2 produced for PSEC with material content as described in “CO2 emission analysis during production of third-generation Prius hybrid car, solar panel and batteries and car assembly” section with respect to its weight is shown in Fig. 4.The total amount of energy required and CO2 produced in material production and assembly for PSEC in addition to solar panel and six NiMH batteries is shown in Table 7. The CO2 emission during manufacturing of specific motor used in PSEC is not considered.

Fig. 4
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Energy required and CO2 produced for different materials with respect to PSEC mass

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Emission analysis of PSEC in comparison with third-generation hybrid Prius car with or without solar panel on its roof on a large scale

Emission analysis has been carried for hundred cars at a selected distance of 100 km for each case as discussed in “First case: third-generation hybrid Prius car excluding solar panel”, “Second case: third-generation hybrid Prius car with solar panel” and “Third case: proposed solar electric car (PSEC)” sections. There is energy of 32 MJ in one litre of petrol (Unit 2004), and the gasoline produces 83 g of CO2 per MJ of energy consumed (CO2List.org 2015).

First case: third-generation hybrid Prius car excluding solar panel

The Prius hybrid car without solar panel is capable of covering a distance of 77.6 km on fuel mode and 22.4 km on electric mode with a speed limit of 40 km/h. Such car can cover a distance of 100 km in 4.6 litre (Fuel Economy 2016) and 2.5 h. So 3.57 L of gasoline consumed in covering a distance of 77.6 km and 114.23 MJ of energy is needed thus results in emitting one time 9.5 kg of CO2 in order to cover 100 km distance.

Second case: third-generation hybrid Prius car with solar panel

The Prius hybrid car with solar panel on its roof and speed limit of 40 km/h will cover a distance of 77 km on fuel mode and a distance of 23 km is covered on electric mode. So similar to first case, a distance of 100 km is covered in same time. The gasoline consumption is of 3.5 litres/77 km thus results in one time emitting a 9.4 kg CO2.

Third case: proposed solar electric car (PSEC)

When a motor runs at its full power at a speed of 40 km/h, then a total distance traveled is 44 km in 1.1 h with a battery energy consumption of 5.5 kW h. In order to cover a distance of 100 km, a PSEC can be recharged from an electric station or any electric outlet. Such recharging is done 2.27 times thus results in total energy consumption of 44.95 MJ and 3.73 kg CO2 emissions. However, charging time varies depending on type of charging station (Gass et al. 2014) to cover a 100 km distance as compared to above two cases, whereas recharging from an electric outlet is a time-consuming method (Wager et al. 2013).

The annual CO2 emission from such hundred cars for first two cases in covering a distance of 100 km is 346.75 metric tons, whereas 136.145 metric ton annual CO2 emitted in third case.

Results and discussion

  1. (1)

    The PSEC can easily cover a 12.3 km distance 2.5 times in a bright sunny day as shown in Table 8 that indicates an energy of 200 W h needed to recharge the batteries at NUST from electric outlet in order to reach home on the third day. So the total batteries watt hours recovered are 1350 W h, and a car can travel for 0.27 h but required more 0.04 h to reach battery energy storage capacity of 1550 W h. See detail in “Discharging and recharging time of NiMH batteries” section to correlate with Table 8.

    Table 8 PSEC battery discharging hours left for selected route on each day
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  2. (2)

    The PSEC is lighter than the Toyota Prius car by 52.6 kg.

  3. (3)

    By mounting the solar panel on the roof of Prius and doubling the battery energy storage capacity thus results in an increase of CO2 emission through their production. There is an emission of more 404.8 kg CO2 as compared to a simple Prius car that can be recovered by reducing annual CO2 emissions from fuel in 3.1 years. There is less emission from PSEC from material production to its assembly and solar module production, whereas more emission during batteries production but the overall CO2 emission compared to first two cases decreases by 2454.35 and 2049.55 kg. In order to cover a daily round trip distance between two cities, the annual emission of PSEC during recharging from any outside source is less as comparative to other cases.

  4. (4)

    A distance of 100 km will be covered in 2.5 h with a speed limit of 40 km/h, whereas recharging time required by additional battery through solar panel is 3.5 h in second case. However, for long journeys with a time requirement more than or equal to 3.5 h, a battery can be recharged, but such recharging time may vary depending on movement of a car. There is more gasoline required by first two cases to cover a distance of 100 km as compared to PSEC if it is recharged from an outside station and if such electricity is produced by electric supply company through gasoline consumption. The total annual CO2 emission from PSEC is less as compared to first two cases for hundred cars for each case. However, the emissions can be further reduced if solar charging stations were made thus only involves emissions during solar module fabrication process.

Conclusion

PSEC is feasible as compared to two cases for a selected distance between two cities at a speed limit of 40 km/h. The fuel cost saved in case of Prius car equipped with solar panel and increased battery energy storage capacity is more as compared to simple Prius car, whereas PSEC consumes less fuel that is used only during charging in the form of electricity from an outside source or at home for a selected distance by electric supply companies. The PSEC weight is less than Toyota Prius car and can also be further reduced by using lightweight materials for manufacturing PSEC. It is concluded that the battery addition in case of a solar panel equipped on a Prius car will only be beneficial for short distance rather than long distances. The only demerit in case of PSEC is the speed limit and time wastage during recharging. The PSEC is economical in case of recharging from electric stations if such recharging electricity is produced through petrol by power supply companies and also helps in controlling CO2 emission, a major green house gas in changing the climate.

Acknowledgement

The author acknowledges the faculty members of US-Pak Centre for Advanced Studies in Energy, National University of Sciences and Technology, for their support and motivation in accomplishing this research.

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Affiliations

  1. U.S.-Pakistan Center for Advanced Studies in Energy (USPCAS-E), National University of Science and Technology (NUST), Sector H-12, Islamabad, 44000, Pakistan

    I. Safdar, A. Raza, A. Z. Khan & E. Ali

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  1. I. Safdar
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  2. A. Raza
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  4. E. Ali
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Correspondence to I. Safdar.

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Research has been carried out at US-Pakistan Center for Advanced Studies in Energy at National University of Sciences and Technology (NUST), Pakistan, from June 2015-Dec 2015.

Editorial responsibility: M. Abbaspour.

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Safdar, I., Raza, A., Khan, A.Z. et al. Feasibility, emission and fuel requirement analysis of hybrid car versus solar electric car: a comparative study. Int. J. Environ. Sci. Technol. 14, 1807–1818 (2017). https://doi.org/10.1007/s13762-017-1332-0

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Keywords

  • Batteries
  • Energy
  • Gasoline-electric vehicle
  • Sun energy