Transcript Solar Powered Charging Station: Progress Report

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
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Agenda
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Project Objectives
Scooter Specifications
Scooter Charging Requirements
Trade Studies and Research
System Diagram
Major Components
Project Status
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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
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Size and specify solar panels
Component research and evaluation
Component selection
Data collection and evaluation for the EV and charging station
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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
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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
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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…
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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/m2
• There are three major types of PV technology:
• Mono-crystalline, poly-crystalline, and thin-films
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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
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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
• Vmax (1000W/m2, 25°C, AM 1.5) = 29.7 VDC
• Imax (1000W/m2, 25°C, AM 1.5) = 7.5A
• ~18% efficient
• Size = 39.375” (~3.25’) x 65.5” (~5.5’)
• ~ 2.0 yards2 or 1.9 m2
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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 kWh, a solar study is required….
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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….
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PVWATTS Results
Worst Case
Month
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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
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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
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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
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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
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Block Diagram
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Charging Station Components
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Solar Panels
Inverter
Building Connection
Power Converter
Charging Station
Instrumentation
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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
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Solar Panels
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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
• Vmax (1000W/m2, 25°C, AM 1.5) = 29.7 VDC
• Imax (1000W/m2, 25°C, AM 1.5) = 7.5A
• ~18% efficient
• Size = 39.375” (~3.25’) x 65.5” (~5.5’)
• ~ 2.0 yards2 or 1.9 m2
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Inverters
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Distributed Inverters
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Enphase Features
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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
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Energy Storage
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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
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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
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Power Converter
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Power Converter
• 240x480 – 120/240 V Transformer
• 2000 VA
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Charging Station
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Charging Station
• Provides 120 VAC Interface to Scooter
• NEMA 5-15R receptacle with weatherproof casing
• NoGas scooter features a three-prong charging cable
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Instrumentation
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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
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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
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Next Steps
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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
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Questions?
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