Solar Powered Charging Station: Mid-Term Presentation Design Team: Ben Hemp Jahmai Turner Rob Wolf, PE Sponsors: Conn Center for Renewable Energy Dr. James Graham, PhD Dr. Chris Foreman, PhD Revision A, 10/3/11

Background The design, fabrication, assembly and integration / testing of a solar powered charging station 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 2

Solar Data for Louisville, KY Source: PVWatts 3

Electric Vehicle Specifications NoGas Vintage Scooter 50 MPH Top Speed 50 Mile Range 72 VDC, 40 Ah Lithium-Ion Batteries with BMS Regenerative Braking 340 lb. capacity Built-in Charger 110V Charging with 1-8 hr. max charge time regenerative braking Front and rear hydraulic disk brakes Hydraulic shocks front and rear 4

Charging Requirements Fundementals AH = Power / Battery Voltage Power = Vehicle Efficiency * Range Scooter – 72 VDC, 40 Ah Batteries Power = AH * Battery Voltage = 40 Ah * 72 VDC = 2.88 kW Efficiency = Power / Range = 2.88 kW / 50 miles = 57.6 W / mile 5

Charging Requirements (Cont.) Assume Driven 20 Miles Per Day: Power = Efficiency * Range = (57.6 W/mile) * (20 miles) = 1152 W AH Required to Charge = Power / Battery Voltage = (1152 W) / (72 V) = 16 Ah Assume 8 Hour Charging / Day Requires 2Ah to Batteries 6

Charging Requirements (Cont.) Requirements Based on Solar Study DC Rating: 500W AC to DC Derate Factor: 77% AC Rating: 385W Solar Hours / Day: 2.96 (December) & 4.71 (Average for Year) December Output 500W System = 385W * 2.96 Hours = 1140 Wh / Day Yearly Average Output 500W System = 385W * 4.71 Hours = 1813 Wh / Day 7

Charging Station Components Solar Panels Inverter Battery Bank Charging Station Remote Monitoring and Control Data Logging 8

Solar Panel Technologies Solar Panels (SP’s) convert photons (light) into DC current. This technology is called photovoltaic (PV). Maximum efficiencies for most commercial SP’s is around ~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 high efficiency SP. Common output powers for large SP’s are W per panel. SP’s may be combined in series to increase voltage, or parallel to increase current.

Solar Panel Technologies Mono-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 $/watt Thin-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.

Solar Panel Technologies Temp CTemp FKyocera VoltageKyocera CurrentKyocera PowerSharp VoltageSharp CurrentSharp Power w *Values determined using V oc and I sc temperature coefficients from manufacturers

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 would power building and charging station would be powered by building) Need instrumentation to compare power into building versus power supplied to charging station 12

Distributed Inverters / Microinverters 13

Centralized Inverters 14

Comparison of Inverter Technologies Microinverters Lower DC Voltages (30-50V) Modular & Expandable Lower Initial Cost Compensates for Shading Connectorized Cables Remote SCADA Interface Centralized Inverters DC Voltages Up to 600 V Not Easily Expanded Higher Initial Cost Lowest Output Panel is Weakest Link of System Standard Wiring Methods Typically Requires More Integration for SCADA 15

What to Do with Excess Power Grid-tied More efficient use of power Requires two branch circuits No Additional Space Required Off-grid Using Batteries Limited by Battery capacity Only requires DC to DC battery charger Batteries Need Conditioned Room, which will require building wiring 16

Questions? 17