Question 4: Power Needed for Decarbonizing the Transport Sector

The goal of this question is to quantify the additional electric power needed in the US to replace:

(a) All gasoline-powered cars and light trucks with battery electric vehicles (EVs).

(b) All diesel-powered heavy trucks with hydrogen-powered fuel-cell vehicles.

(a) Assume gasoline engines are 30% efficient in converting fuel energy into mechanical energy, and that 90% of this baseline mechanical energy must be supplied by electric motors powering the replacement EVs. For the EVs, assume "round trip efficiency" for battery charging of 90%, with the resulting battery power output delivered to 95%-efficient direct current (DC) motors, for which no inverter is needed. "Round trip efficiency" is the percentage of electricity used to charge the battery that can be retrieved later as useful energy output. Calculate the total amount of new electric power generation (in TWh) needed to replace the gasoline vehicle fleet completely with EVs.

(b) Assume diesel engines are 40% efficient in converting fuel energy into mechanical energy. The conversion efficiency for the proposed replacement (i.e., fuel cells) is 25% when using electricity to electrolyze water to produce hydrogen gas (\(H_2\)), then compressing the \(H_2\) for storage in fuel tanks of trucks, and finally using \(H_2\)-powered fuel cells to generate electricity. Assume that DC electric motors on heavy trucks also operate at 95% efficiency. Using the same approach as in part (a), calculate the total amount of new electric power generation (in TWh) needed to replace the diesel truck fleet with \(H_2\) fuel cell-powered trucks.

Given Data:
- US gasoline sales, \(G = 140\) billion gallons (national total)
- US diesel fuel sales for on-road engines, \(D = 40\) billion gallons
- Gasoline density, \(\rho_s = 740 \, \text{g/L}\)
- Diesel fuel density, \(\rho_d = 840 \, \text{g/L}\)
- Both fuels have about the same lower heating value, \(\text{LHV} = 44 \, \text{kJ/g}\)
- Baseline electric power generation in the US was about 4000 TWh

Note: An additional 20 billion gallons of diesel fuel were consumed by off-road engines such as railroad locomotives, construction and farm equipment, ferries, and fishing boats, etc. We will exclude off-road engines and their associated fuel use/power needs from this analysis.

To calculate the total amount of new electric power generation required to replace gasoline-powered cars and light trucks with battery electric vehicles (EVs), we need to consider several factors.

For gasoline engines, assuming an efficiency of 30%, only 30% of the fuel energy is converted into mechanical energy. Out of this baseline mechanical energy, 90% needs to be supplied by electric motors in EVs. Therefore, the effective energy conversion efficiency from fuel to electric power is 30% * 90% = 27%.

Assuming a round trip efficiency for battery charging of 90%, and DC motors with 95% efficiency, the overall efficiency from fuel to useful electric power for EVs is 27% * 90% * 95% = 23.29%.

To calculate the electric power needed, we can divide the total energy consumption of gasoline vehicles by the overall efficiency:

Electric power = Gasoline sales (in gallons) * fuel energy density * overall efficiency

= 140 billion gallons * 740 g/L * 44 kJ/g * 23.29%

≈ 1.678 × 10[tex]^14[/tex] kJ

Converting this energy to terawatt-hours (TWh):

Electric power (TWh) = 1.678 × 10[tex]^14[/tex]kJ / (3.6 × 10[tex]^6[/tex] kJ/TWh)

≈ 46.61 TWh

Therefore, approximately 46.61 TWh of additional electric power generation would be needed to replace the gasoline vehicle fleet completely with EVs.

For diesel-powered heavy trucks, assuming an efficiency of 40% in converting fuel energy to mechanical energy, the effective energy conversion efficiency for H2 fuel cell-powered trucks would be 40% * 25% * 95% = 9.5%.

Following the same calculation as in part (a), using diesel fuel sales for on-road engines (40 billion gallons) and the appropriate energy density, we can estimate the electric power needed to replace the diesel truck fleet with H2 fuel cell-powered trucks.

Electric power (TWh) = Diesel fuel sales (in gallons) * fuel energy density * overall efficiency

= 40 billion gallons * 840 g/L * 44 kJ/g * 9.5%

≈ 1.343 × 10[tex]^13[/tex] kJ

Converting this energy to terawatt-hours (TWh):

Electric power (TWh) = 1.343 × 10[tex]^13[/tex] kJ / (3.6 × 10[tex]^6[/tex] kJ/TWh)

≈ 3.73 TWh

Therefore, approximately 3.73 TWh of additional electric power generation would be needed to replace the diesel truck fleet with H2 fuel cell-powered trucks.

learn more about Electric Vehicle Transition.

brainly.com/question/31459769

#SPJ11