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DESIGNING AND BUILDING A STAND-ALONE PV –
POWERED CHARGING STATION FOR AN ELECTRIC VEHICLE
Himesh Razdan
Ahmad Bamasag
SECOND
SOLAR
Introduction: Objectives and Expectations
To design a solar powered charging system• Independent of the existing residential electric system, as well as
the local electric grid
• Able to operate day or night
• Delivers sufficient power to charge a current electrical vehicle
• Has sufficient storage capacity for two days of autonomy
Components: Known Specifications
• Inverter
-Efficiency: 90%
-Maximum Power Rating: 4.0 kW
• Charge Controller
-Upper output current: 83.3A
• Photovoltaic Modules:
-Power: 330 W each
Another crucial thing to note is that everything except the output of
the inverter is 48V in DC
Steps to Solve for Designing a Solar Power
System
1. Figure out the input power to the inverter when the load is on to
decide how many inverters are needed.
2. Figure out the amperage the charge controller provides to the
inverter to decide how many charge controllers are needed.
3. Calculate how much energy the load consumes in kWh per day.
4. Calculate how many solar panels you will need in certain location.
5. Calculate how many batteries you will need for the system to work
without sunlight for a certain number of days.
Step 1: Daily Load analysis:
• An average EV has a capacity of 30 kWh per 100 miles
• Nissan Leaf, world's all-time best selling highway-capable allelectric car
• A capacity 30 kWh battery and a range of 107 miles on a full
battery charge.
• with plug-in power charger of 3.6 kW that can be fully recharged
from empty in 8 hours from 30amp supply
• Assuming the car is being fully charged every day, the daily
energy requirement for the system is 30 kWh
Step 2: Location and available solar insolation
• residential PV system in Phoenix, AZ
• average peak solar hours for the worst month of the year,
December
• Flat-plate collectors facing south at a fixed tilt angle of latitude +150
(48.270)
• Solar radiation is 5.3 kWh/m2/day, which is equal to 5.3 PSH/day
Step 3: Inverter sizing
• Assuming 90% inverter efficiency with a charging load power of
3.6 kW,
Input power = output power / efficiency
= 3600 W / 0.9 = 4.0 kW
Input Energy for inverter = Output Energy / efficiency
= 30 kWh/0.90= 33.33 kWh/day
SMA Sunny Island inverter, which has a rated power of 4.5 kW and
efficiency of 93%, has been selected.
Step 4: PV Array Size
• The array needs to deliver 33.33 kWh as a daily average to the
inverter, however, accounting for various losses:
-3% wire losses
-85% derate factor
-0.92 PV loss factor
• 8.29kW is the minimum power capacity for the PV system.
• Many PV modules in the market can have nominal max power up
to 330 W.
Step 4: PV Array Size (contd.)
• NT = Total PV capacity / max module power
= 8290 W / 330W⇒ 26 modules are required
• Canadian Solar MAXPOWER CS6U has been chosen as an
appropriate PV module
• Ns= required charging voltage / module rated voltage:
= 48 V / 37.2 V => 2 modules in series
• with a total of 26 modules required, 13 strings of two modules in
series would be perfect arrangement in the project
• The nominal DC power by the array would be 26 modules x
330W = 8580 W
Step 5: Battery Bank Size
• Desired energy storage= 2 days x 33.33 kWh = 66.66 kWh
• Accounting for 80% depth of discharge (DoD) factor:
Minimum energy storage = desired energy storage / DoD
= 66,666 Wh ÷ 80% = 83,332 Wh
• daily battery capacity demand= minimum energy storage / system
voltage= 83,332 Wh/48 V= 1,736 Ah
• Battery bank must have capacity > 1736 Ah with system voltage of
48V
• Two Crown 48V, 860 Ah batteries will be connected in parallel to
match the required capacity.
Step 6: Charge Controller
• An MPPT controller is the solution of choice, as it harvests more
power from the solar array
• I input= ISC x number of modules in parallel x Safety factor:
= 9.45A x 13 x 1.25= 153.5 A
• Output current from charge controller I output= Power to inverter /
System voltage= 4,000 W / 48 V= 83.33 A
• The output current of the charge controller must be > 83.3A
• Two Morningstar TriStar TS-MPPT-45 charge controllers will be
connected in parallel, which will have a maximum output current
of 90A.
Cost Analysis: System Cost
Solar module cost = 26 modules x ($252/module) = $6,552
Battery bank cost = $10,120
Charge controller cost = $760
Inverter cost = $4,230
The total system cost = $21,662
Cost Analysis: Annual Saving
Assuming that installing the system would replace consuming 30
kWh from the utility company and knowing that residential electricity
rates in Arizona average 11.3¢/kWh, one can calculate how much
can be saved:
Annual saving = 365 (days/year) x 30 (kWh/day) x 0.113 ($/kWh) =
$1,237 / year
Cost Analysis: Payback Period
• Payback period = Total cost ($) / Annual saving ($/year)
= $21,662 / $1,237 / year
= 17.5 years
Conclusions
Life span of PV modules is about 25 years. Therefore, installing a
stand-alone PV powered charging station for an electric vehicles is an
economically viable solution.
However, this conclusion is based on assumption that other
expensive system’s components, such as battery bank and inverter,
would not be replaced during the next 17 years. Maintenance cost is
assumed to be negligible. On the other hand, the cost analysis here
does not consider any government subsidies and grants that could
reduce the cost of the system.
References
[1] "2016 Fuel Economy Guide." Accessed October 27, 2016.
http://fueleconomy.gov/feg/pdfs/guides/FEG2016.pdf.
[2] "Arizona - National Renewable Energy Laboratory." Accessed October 27, 2016.
http://rredc.nrel.gov/solar/pubs/redbook/PDFs/AZ.PDF.
[3] “Residential Electricity Rates & Consumption in Arizona” Accessed October 28, 2016.
http://www.electricitylocal.com/states/arizona/