Solar Powered Charging Station:Mid-Term Presentation

Design Team:Ben HempJahmai TurnerRob Wolf, PE

Sponsors:Conn Center for Renewable Energy

Dr. James Graham, PhDDr. Chris Foreman, PhD

Revision D, 10/17/11

Agenda• Background Information• System Requirements• Scooter Specification & Charging Requirements• Block Diagram• System Components• Questions

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Background Information• Design, fabricate, assemble and test of solar powered charging

station for a plug-in electric scooter• Our Tasks:• Size and Specify Panels Supplied By the Conn Center• Research Various Technologies (panel, inverters, etc.)• Work with Sponsors to Select Final Design Criteria

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System Requirements

1) Solar Array: Converts solar energy into electrical energy• Perform solar study to determine what size array and panel

technology will be required to charge the scooter in a normal workday in Louisville, KY

2) Inverter: Converts DC power into AC power• Determine inverter type (Centralized or Distributed)

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System Requirements (cont.)

3) Battery BankOriginally required to:• Store energy when scooter is charged or not plugged in• Charge scooter when panels are unable to provide enough

energy

4) Grid-Tied SystemAlternate means of energy storage:• Scooter charged or not plugged in: Building consumes energy• Cloudy Day: Building assists in charging

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System Requirements (cont.)

5) Charging Station• Provides 120 VAC, 60 Hz interface to scooter

6) Instrumentation • Verify how much energy is generated by charging station and

how much is consumed by scooter• Determines net load flow between charging station,

scooter, and building

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Electric Vehicle Specification• The test vehicle for the charging

station will be a NOGAS Vintage pluggable electric motor scooter: • 50 MPH top speed/50 mile range• 72 VDC, 40 AH Lithium batteries

with Battery Management System (BMS)

• Regenerative braking• Built-in charger• 340 lb carrying capacity• 120 VAC charging with 1 to 8 hr.

max charge time• Front and rear hydraulic disk

brakes• Hydraulic shocks front and rear

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Charging Requirements

• Scooter• 72 VDC, 40 Ah Batteries

Power = 2.9 kW

• Charging station should be able to supply approximately 3 kW-h

• 375W-h over 8 hours

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Charging Requirements (Cont.)

• Requirements Based on Solar Study (6 Panels)• DC Rating: 1500W• AC to DC De-rate Factor: 77%• AC Rating: 1200W• Average Solar Hours / Day: 2.96 (December) & 4.71

(Average for Year)• December 22, 1980: 3449 W

• 1004 W from Noon to 1:00

FROM: http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/US/code/pvwattsv1.cgi

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Charging Requirements (Cont.)

• Requirements Based on Solar Study (2 Panels)• DC Rating: 500W• AC to DC De-rate Factor: 77%• AC Rating: 385W• Average Solar Hours / Day: 2.96 (December) & 4.71

(Average for Year)• December 22, 1980: 1150 W

• 335 W from Noon to 1:00

FROM: http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/US/code/pvwattsv1.cgi

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Block Diagram

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Charging Station Components• Solar Panels• Inverter• Building Connection• Power Converter• Charging Station• Instrumentation

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Solar Panel Technologies

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Solar Panel Technologies• Solar Panels (SP’s) convert photons (light) into DC current. • Maximum efficiencies for most commercial SP’s is ~20%.• Three major types of PV technology: mono-crystalline, poly-

crystalline, and thin-films. These are listed in order from most to least efficient.

• To create equivalent power, a lower efficiency SP needs more surface area than a higher efficiency SP.

• Common output powers for large SP’s are 50-300W per panel. • SP’s may be combined in series to increase voltage, or parallel

to increase current.

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Solar Panel TechnologiesMono-crystalline• Most efficient style (least surface area needed)• Best performance during low light and shading• Usually most expensive $/watt

Poly-crystalline• Mid-grade efficiency• Tend to be less expensive than

mono-crystalline for $/wattThin-Film• Least efficient style• May be the least expensive, or similar to others

for $/watt.• Styles capable of roll-up panel mats and

artificial shingles.

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Solar Panel Technologies

Alternative Energies (Danville, KY)• Received (2) 230 W poly-crystalline panels via Conn Center.• Panels built in-house at Alternative Energies.

230W Panel Specifications• 60 cells (Enphase compatible)• Vmax (1000W/m2, 25°C, AM 1.5) = 29.7VDC

• Imax (1000W/m2, 25°C, AM 1.5) = 7.5A• ~18% efficient• 39.375” (~3.25’) x 65.5” (~5.5’)

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Inverters

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Inverters• Centralized versus Distributed• Grid-tied versus Off-grid• Off-grid means batteries required• Grid-tied: Requirements for net-metering

• This project would be tied in W.S. Speed Hall building infrastructure (i.e. – solar panels will power building and charging station will power building)

• Need instrumentation to compare power into building versus power supplied to charging station

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Distributed Inverters / Microinverters

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Centralized Inverters

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Comparison of Inverter TechnologiesMicroinverters

• Operate at lower DC Voltages (16-50V)

• Modular & Expandable• Lower Initial Cost• Compensates for Shading

• Plug-and-Play Cables• Available Remote Interface

Centralized Inverters• Operate at Higher DC Voltages

(150+ V)• Not Easily Expanded• Higher Initial Cost• Lowest Output Panel is

Weakest Link of System• Standard Wiring Methods• Typically Requires More

Integration for SCADA

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Energy Storage

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What to Do with Excess Power?

Grid-tied

• More efficient use of power (ie – only limited by building energy consumption)• Requires a branch circuit• No additional space

required

Off-grid Using Batteries

• Limited by Battery capacity• Only requires battery

charger for regulation• Batteries need

conditioned room, which will require additional building penetration for wiring• Maintenance Headache 23

Grid-tied System• Must comply with UL-1741 and IEEE-1547 Anti-Islanding

standards• Loss of grid causes inverter to de-energize• This is a safety standard

• Cost ~$1000 to run a 120 VAC circuit to charging station• How do we connect a 120 VAC circuit to our 240VAC inverters?

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Power Converter

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Power Converter• 120 – 240V transformer• 1500 VA• Cost ~$300

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Charging Station

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Charging Station• Provides 120 VAC Interface to Scooter• Either NEMA 5-15R receptacle or NEMA 5-15P cord-connected

plug on a reel.

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Instrumentation

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Instrumentation• Smart meters with embedded web interface to allow user to

connect from web browser at computer• Monitor power flow to scooter and power flow from inverters• Indicates whether panels are providing adequate energy or if

energy is being provided from building

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Current Status• System has been designed and waiting for sponsor approval• Ready to order components and build

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Next Steps• Select Final Location for Charging Station• Order Materials• Build Station• Test Final Product

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Questions?

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