Question

Problem 3: Land footprint of biofuels You are attempting to create transportation fuel in Tempe, AZ on one acre (4,047 m2) of land. You have the option to grow corn, safflower (an oil seed crop that can be dry farmed), or switchgrass. The corn can be used to produce ethanol, the safflower to produce biodiesel and the switchgrass could be used to produce ethanol, diesel or electricity. The yields for the crops and each conversion process is given in the table below Crop Yield Ethanol yieldDiesel yieldElectricity eld Corn Safflower Switchgrass 175 bu/acre 1.2 tons/acre 9 tons/acre 2.8 gals/bu 107 gals/ton 55 gals/ton 2,200 kWh/ton 76 gals/torn (a) Vehicle fuel per acre: How much fuel will you be able to make from each of the five biofuel pathway per acre of production? Please provide your answers in gallons of ethanol, gallons of diesel or kWh where appropriate (b) Vehicle miles per acre: Which of the five biofuel pathway would yield the most vehicle miles per acre of production? Use the table below for the fuel economy of different drivetrains for the 2015-2017 VW Golf Drivetrain Fuel econom Gasoline/Ethanol Diese Electric 20.4 miles/gallon ethanol 38.3 miles/gallon diesel 3.49 miles/kWh (c) Photovoltaic option: A different option is to produce electricity using thin-film photovoltaics with a 12% efficiency. Given the average insolation in Phoenix is 5.38 kWh/m2/day, how many vehicle miles can be produced using photovoltaic electricity in an electric drivetrain? (d) Discussion: Which of the six options is most attractive. Provide two reasons for this choice

Answer 1

(a) basis: 1 acre land for cultivation fully used for same type of plant

ethanol yield from corn=175*2.8 =490 gals

diesel yield from safflower=107*1.2 =128.4 gals

from 1 acre switchgrass,

ethanol obtained=9*76 =684 gals

diesel yield=9*55 =495 gals

electricity yield=9*2200 =19800kWh

(b)vehicles drove via yield from corn=490/20.4=24.02 miles

vehicles drove via yield from safflower=128.4/38.3=3.352miles

vehicles drobe via yield from switchgrass

by ethanol=(684/20.4)=33.53 miles

by diesel=(495/38.8)=12.757 miles

by electricity=(19800/3.49)=5673.352 miles

therefore electricity yield most vehicle miles per acre of production.

(c)average energy by photovoltaics=5.38*.12=0.6456kWh/m2/day

average energy from one acre in one day=0.6456*4047=2612.7432 kWh

distance drove via photovoltaic energy=2612.7432/3.49=748.637 miles

(d) photovoltaic energy is the most attractive one.

Reasons

1. It gives free electricity by converting sunlight into electrical energy.
2. It is having maximum efficiency or lesser losses.