Solar Powered Charging Station MidTerm Presentation Design Team

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, Ph. D Dr. Chris Foreman, Ph. D Revision F, 10/23/11

Agenda • • Project Objectives Scooter Specifications Scooter Charging Requirements Trade Studies and Research System Diagram Major Components Project Status 2

Project Objectives • Design, fabricate, assemble and test a solar powered charging station for a plug-in electric vehicle (EV) • The electric vehicle to be used with the charging station will be a pluggable electric motor scooter • Tasks • Optimize requirements • Budgets • Facilities • Performance • • Size and specify solar panels Component research and evaluation Component selection Data collection and evaluation for the EV and charging station 3

Scooter Specifications • Manufactured by No. Gas LLC in Nashville, TN • 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 4

Scooter Charging Requirements • Batteries: 72 VDC, 40 Amp-hour batteries • Electrical Power = 2. 9 k. W • So, the charging station should be able to supply approximately 3. 0 k. Wh to charge the batteries in one day IF the batteries are fully discharged (3. 0 k. Wh/day) • The worst case day is the shortest day of the year, when the sun is at its lowest angle • Lowest efficiency due to solar angle, since the tilt of the solar panels will be fixed • A solar study is required to determine the range of available energy 5

Solar Panels • The Conn Center for Renewable Energy will furnish two solar panels from their preferred vendor for this project • However, we are tasked to design a fully-capable system, and to implement a more limited capability this semester • In order to understand the expandability of the system, the design must accommodate the maximum requirement • 3. 0 k. Wh per day to charge the batteries if the bank is fully discharged • Worst case solar day • The solar panels become the driving requirement for the system design • So, we must discuss them before proceeding further into the presentation… 6

Solar Panel Overview • Photo. Voltaic (PV) Solar Panels convert photons into electrical power (DC voltage * current) • The maximum efficiency for most commercial solar panels is about 20% • To create equivalent power, a lower efficiency solar panel requires more surface area than a higher efficiency panel • Efficiency is typically expressed in Watts/m 2 • There are three major types of PV technology: • Mono-crystalline, poly-crystalline, and thin-films 7

Solar Panel Types Mono-crystalline • Most efficient technology • Most expensive $/watt Poly-crystalline • Mid-grade efficiency • Less expensive than mono-crystalline per equivalent $/watt Thin-Film • Least efficient technology • Price in $/watt varies • Available in thin flexible mats, artificial shingles, and other form factors 8

Conn Center Solar Panels Alternative Energies (Danville, KY) • Received two 230 W poly-crystalline panels from the Conn Center • Alternative Energies fabricates the panels 230 W Panel Specifications • Each panel has 60 cells • Vmax (1000 W/m 2, 25°C, AM 1. 5) = 29. 7 VDC • Imax (1000 W/m 2, 25°C, AM 1. 5) = 7. 5 A • ~18% efficient • Size = 39. 375” (~3. 25’) x 65. 5” (~5. 5’) • ~ 2. 0 yards 2 or 1. 9 m 2 9

Solar Array DC Rating • Each Conn Center panel to be provided is “DC Rated” at 230 Watts • DC Rating means that AT THE EQUATOR, under normal incidence of sunlight, on the brightest part of the day, the selected panel will output 230 Watts • When you move the panels to Zip Code 40208, performance degrades rapidly • Lower angle of incidence of the sun • Many other variables • In order to understand how many solar panels are required to produce 3. 0 k. Wh, a solar study is required…. 10

Solar Study Results • Used the NREL PVWATTS Grid Data Calculator for the solar study • http: //www. nrel. gov/rredc/pvwatts/grid. html • Uses hourly typical meteorological year weather data, and • Allows users to create estimated performance data for any location in the United States • Provides a PV performance model to estimate annual energy production • Using the PVWATTS calculator, the following data was entered: • Zip code = 40208 • DC Rating = 1. 5 k. W, AC to DC Derate Factor = 0. 77 • Solar Array Type = Fixed Tilt • The results calculated are shown on the following slide…. 11

PVWATTS Results Worst Case Month 12

Discussion of Solar Study Results • The following observation can be obtained from the previous slide, and the input data to the PVWATTS calculator • For 1, 500 Watts of DC Rated power, 6. 5 solar panels of the type provided by the Conn Center would be required • For the worst case month (December), we would obtain 106 k. Wh for the ENTIRE MONTH • This equates to ~3. 5 k. Wh/day • So, a system that meets the charging requirement on the worst month would require 7 panels • We are being provided with 2 panels • We need to design a system that will work with 2 panels, but can be expanded to 7 panels • Derating to a 2 panel design, we should be able to obtain about 1. 0 k. Wh/day 13

Inverter Definitions Distributed vs. Centralized • Distributed: Each solar panel is connected to its own inverter • Centralized: Multiple solar panels are connected to one inverter Off-grid vs. Grid-tied • Off-grid: Batteries are required for energy storage as a secondary power source • Grid-tied: Inverters are required to be tied to electrical grid as a secondary power source 14

Inverter Tradeoffs Microinverters • Operate at lower DC voltages (16 -50 VDC) • Capable of working with low quantities of solar panels • Modular & expandable • Lower initial cost • Compensates for shading (panels operate independently) • Plug-and-Play cables • Available remote interface • Does not support batteries Centralized Inverters • Operate at higher DC voltages (~150+ VDC) • Must be procured at max power required • Not easily expanded • Higher initial cost • Lowest output panel can be weakest link of system (series wiring) • Standard wiring methods • Typically requires more integration for SCADA 15

Study Conclusions • Use distributed inverters • Allows expansion to the full system by adding inverters as the system is expanded • Grid tie the inverters • Addresses the anti-islanding requirement • Eliminate battery bank • Required in project description • Not feasible at this time, since commercial inverters don’t support it 16

Block Diagram 17

Charging Station Components • • • Solar Panels Inverter Building Connection Power Converter Charging Station Instrumentation 18

System Requirements • Solar panels are customer furnished • The inverter architecture has been previously derived from research and trade studies • The following slides describe the remaining design decisions for the major components of the system 19

Solar Panels 20

Conn Center Solar Panels Alternative Energies (Danville, KY) • Received two 230 W poly-crystalline panels from the Conn Center • Alternative Energies fabricates the panels 230 W Panel Specifications • Each panel has 60 cells • Vmax (1000 W/m 2, 25°C, AM 1. 5) = 29. 7 VDC • Imax (1000 W/m 2, 25°C, AM 1. 5) = 7. 5 A • ~18% efficient • Size = 39. 375” (~3. 25’) x 65. 5” (~5. 5’) • ~ 2. 0 yards 2 or 1. 9 m 2 21

Inverters 22

Distributed Inverters 23

Enphase Features One inverter panel Easy expandability Improves shading performance Pre-fabricated cables 15 year warranty No single point system failure Low voltage DC connections (22 -40 VDC) Includes optional gateway / monitoring and analysis software • Complies with UL 1741/IEEE 1547 • • 24

Energy Storage 25

What to Do with Excess Power? Grid-tied Off-grid Using Batteries • More efficient use of power (ie – only limited by building energy consumption) • Requires a branch circuit • No additional space required • Unused solar energy flows into building for use • Limited by Battery capacity • Only requires battery charger for regulation • Batteries need conditioned room, which will require additional building penetration for wiring • Requires more maintenance 26

Grid-tied System Safety Requirements UL-1741 and IEEE-1547 Anti-Islanding standards • Grid-tied system must comply with these two standards • Anti-islanding: Inverter may not recognize loss of grid power if load circuits operate at same frequency as grid (~60 Hz) causing it to not shut off • Standards ensure inverter detects loss of power grid to prevent creating a live output (safety hazard to line workers) when grid power is lost 27

Power Converter 28

Power Converter • 240 x 480 – 120/240 V Transformer • 2000 VA 29

Charging Station 30

Charging Station • Provides 120 VAC Interface to Scooter • NEMA 5 -15 R receptacle with weatherproof casing • No. Gas scooter features a three-prong charging cable 31

Instrumentation 32

Power Monitoring • Solar energy generated is compared to the energy drawn from the power grid for charging station • Used to indicate whether the system is generating enough energy for charging station • Energy flowing from power grid means not enough solar energy generation • Smart meters with embedded web interface allow user to connect from web browser at computer 33

Current Status • Solar panels have been received • Scooter has been purchased • Eaton is donating transformer, disconnects, and power monitoring equipment • Grid circuit has been ordered from Physical Plant 34

Next Steps • • • Purchase all needed remaining equipment Design solar panel mounting structure and equipment layout Determine how all equipment will be connected Work with electricians during installation Test final product 35

Questions? 36