Solar Tractor for UC Merced Fleet Service

University of California, Merced School of Engineering
ElecTrac - Solar Powered Tractor
Josue Lopez , Angel Mendoza,Timothy De la Fuente,Van Duong, Alecsandr Badalov
Mission Statement: To convert UC Merced’s
electric tractor into a self-sustainable vehicle that
fulfills the needs of the campus’s compost program
while providing assistance for additional campus
tasks.
Design Components
Prototype and Model Analysis
Our design focuses in stability, spreading the weight of the various
components evenly. The panels are mounted on the tractor to have
accessible charging where ever the tractor might be, withstanding winds of
up to mph.
Abstract
As the world’s population increases, natural resources decrease, leading to an
increase in pollution and environmental issues. Having an electric tractor on
campus was eco-friendly enough for us, but could still be improved upon;
therefore we decided to make self sustainable via solar power. The solar
powered tractor will be used to transport the campus’s compost with zero
emissions. It can also charge a battery pack, consisting of 4-12V lead acid
deep cycle batteries connected in series, in about three hours. This provides
about three hours of runtime using a 15 hp electric motor, and towing a max
load of 4000 lbs. The tractor is powered by two 290 polycrystalline solar
panels mounted directly onto the tractor for easier charging no matter where
the tractor might be. The compost is loaded onto a trailer that was adapted for
towing mainly compost, having a door that becomes a ramp to load the bins,
but it can be used for other tasks as well. This design fits University of
California, Merced’s sustainability goals to consume no offsite or
nonrenewable energy, to produce no net carbon emissions, and to produce no
landfill waste by 2020. The tractor fulfills the compost program’s needs along
with the campus’s environmental goals.
Intended Purpose
The tractor has been desigedn to transport the campus’s compost in an
eco-friendly manner by not emitting any greenhouse gases into the
atmosphere. The tractor will be towing the compost from the dinning
commons area to the compost area located about 2 miles away. The
setup consist of a reinforced almond trailer, and two solar panels
mounted on the tractor to charge the battery pack that power the motor.
Design
Performance
Runtime
Charge Time
3 mph (70% eff)
1st gear
2nd gear
3rd gear
4000 lbs
2.08
1.67
1.25
4500 lbs
1.86
1.48
1.11
*Assuming 70 % eff. on motor at 5mph
Torque
(F ⋅ r)
=
Gear
GearRatio
(mph ⋅ 5280 ⋅ gear-ratio)
ω[rpm] =
(2 ⋅ 60 ⋅ A ⋅ r)
Torque
1
Power[hp] =
Gear ⋅ ω 5252 ⋅ eff
kW-hr
Runtime[hr] =
Power ⋅ hp conversion
Two- Polycrystalline 290 Watt Panels
P[Volts] = V[Volts]• I[Amps]
Panel Mounting
Solar declinations:
360
δ = 23.25⋅
365⋅ (n − 81)
Alternate angle: β = 90 – L + δ
Panel tilt: θ = 90 – β
Average θ = 37.43 o
*L = latitude of Merced
n = given day of the year
Center of Gravity
Tractor:
Xcg = Σ(MnXn)/Σ(Mn) = 1.84 ” from center
Ycg = Σ(MnYn)/Σ(Mn) = 9.2” from center
Zcg = Σ(MnZn)/Σ(Mn) = 0” base of tractor
* In order for the CG to be in between the trailer and
tractor; the tractor need an additional 450 lbs in the
front when fully loaded.
Estimated Cost
The estimated cost to convert a diesel tractor into a solar tractor can range from about
$6,000-$7,000 depending on the solar panels/components used when converting.
Assuming a diesel tractor consumes 1.6 gallons of diesel/hour, and a gallon cost $4.50,
and the tractor is operated 250 hrs/year it has a cost of $1,800 in fuel/year. The operating
cost/hrs of a solar tractor is about $.0017, times 250 hours is less than half a cent.
Therefore it will take less than 4 years, (4*1800 = $7200) for tractor to pay off the
conversion in fuel savings.
Prototype Cost
P[Watts] = V[Volts]⋅ I[Amps]
P 580
I= =
= 12.1Amps
V 48
Capacity[Amp ⋅ hrs]
Time[hrs] =
Current[Amps]
225[Amp ⋅ hrs]
Time =
= 3.0[hrs]
75[Amps]
Solar Panel + Controller
Accessories (paint, oil, bolts, etc.)
Batteries 12v (4pc)
Allrax Speed Controller
Motor (Mars 15hp)
Beam Support
$ 1325
$ 350
$ 300
$ 650
$ 650
$ 150
*Assuming battery pack is fully drained and peak level 580W
Total
$ 3425
References: [1] “Standard Handbook of Engineering Calculations” [2] “Mechanics of Materials” [3] “Mechanical Vibrations” [4] “Renewable and Efficient Electric Power Systems”
Drag Forces
Assumptions:
Cd = 1.2
𝝆 = 1.169 kg/m3
v = 22.35 m/s
2
2Fd
Cd ρ v A
Cd = 2 → Fd =
ρv A
2
(1.2)(1.169)(22.35)(3.464)
=
= 1214N
2
Frontal Area:
A = (h)(w)*sinθ (neglecting depth)
= (4m)(1m)*sin60 = 3.464m2
Column Buckling
Our supports for the Solar panels consist
of 4 hollow square tubes made of steel.
They are goverened by:
2
−Px
v=
3Lx
6EI
Recommendations for Operation
The tractor has been designed to tow 4000 lbs, due to the 15 hp driving it, this includes
the tractor and trailer. The axle of the trailer is rated for 1500lbs.
Acknowledgements: Angel Mendoza Sr.,Prof. Leal Quiros