1. 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 F, 10/23/11 1

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

3. 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

4. Scooter Specifications Manufactured by NoGas 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

5. Scooter Charging Requirements Batteries: 72 VDC, 40 Amp-hour batteries Electrical Power = 2.9 kW So, the charging station should be able to supply approximately 3.0 kWh to charge the batteries in one day IF the batteries are fully discharged (3.0 kWh/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

6. 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 kWh 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

7. Solar Panel Overview PhotoVoltaic (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

8. 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

9. Conn Center Solar Panels Alternative Energies (Danville, KY) Received two 230W poly-crystalline panels from the Conn Center Alternative Energies fabricates the panels 230 W Panel Specifications Each panel has 60 cells V max (1000W/m 2, 25°C, AM 1.5) = 29.7 VDC I max (1000W/m 2, 25°C, AM 1.5) = 7.5A ~18% efficient Size = 39.375” (~3.25’) x 65.5” (~5.5’) ~ 2.0 yards 2 or 1.9 m 2 9

10. 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 kW, a solar study is required…. 10

11. 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 kW, AC to DC Derate Factor = 0.77 Solar Array Type = Fixed Tilt The results calculated are shown on the following slide…. 11

12. PVWATTS Results 12 Worst Case Month

13. 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 kWh for the ENTIRE MONTH This equates to ~3.5 kWh/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 kWh/day 13

14. 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

15. Inverter Tradeoffs Microinverters Operate at lower DC voltages (16-50VDC) 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

16. 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

17. Block Diagram 17

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

19. 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

20. Solar Panels 20

21. Conn Center Solar Panels Alternative Energies (Danville, KY) Received two 230W poly-crystalline panels from the Conn Center Alternative Energies fabricates the panels 230 W Panel Specifications Each panel has 60 cells V max (1000W/m 2, 25°C, AM 1.5) = 29.7 VDC I max (1000W/m 2, 25°C, AM 1.5) = 7.5A ~18% efficient Size = 39.375” (~3.25’) x 65.5” (~5.5’) ~ 2.0 yards 2 or 1.9 m 2 21

22. Inverters 22

23. Distributed Inverters 23

24. Enphase Features One inverter per 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 UL1741/IEEE1547 24

25. Energy Storage 25

26. 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 Unused solar energy flows into building for use 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 Requires more maintenance 26

27. 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

28. Power Converter 28

29. Power Converter 240x480 – 120/240 V Transformer 2000 VA 29

30. Charging Station 30

31. Charging Station Provides 120 VAC Interface to Scooter NEMA 5-15R receptacle with weatherproof casing NoGas scooter features a three-prong charging cable 31

32. Instrumentation 32

33. 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

34. 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

35. 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

36. Questions? 36