lecture 10

Advanced Power Systems

ECE 09.402.02 and ECE 09.504.02Lecture 10: PV System Designs

2 April 2007

Dr Peter Mark Jansson PP PE

Project Help• This page offers many tools specifically for small wind

• http://www.renewwisconsin.org/wind/windtoolbox.html

Technology Aid

• Sun Path Diagrams• Solar PathFinderTM

• SunChart

• Allows location of obstructions in the solar view and enables estimation of how much reduction in annual solar gain that such shading provides

PathFinder and Assistant

www.solarpathfinder.com

Sun Path diagram

Maximize your Solar Window

CURRENT-VOLTAGE (I-V) CURVE

Standard Test Conditions – (STC) 25°C (77°F) cell temperature and 1000 W/m² insolation

Important Points: Maximum Power Point ( Vmp , Imp ) Open Circuit Voltage ( Voc ) Short Circuit Current ( Isc )

Voc

VOLTAGE TERMINOLOGY

Nominal Voltage → 12 V (A PV panel that is sized to charge a 12V battery, but reads

higher than 12V)

Maximum Power Voltage (Vmax/Vmp)→17V-18V

under STC (A 12V module will read 17V 18V under MPPT conditions)

Open Circuit Voltage (Voc) → 20V-22V (This is seen in the early morning, late evening, and while testing the module)

EFFECTS OF TEMPERATUREFahrenheit To Celsius Conversion:

___˚C = (5/9)( ___˚F - 32) OR ___˚F = (9/5)( ___˚C) +32

0

0.5

1

1.5

2

2.5

5 10 15 20Volts

Am

ps

25° C30° C40° C50° C60° C70° C 80° C

3

25

Example: 25˚C = (5/9) (77˚F - 32)

BP 3160

• Rated Power : 160 W

• Nominal Voltage: 24V

• V at Pmax = 35.1

• I at Pmax = 4.55

• Min Warranty: 152 W

• NOTE: I-V Curves

Other I-V Curves

SunPower

WATTAGE COMPARISON

BP Solar Monocrystalline

Uni-Solar Amorphous

BP Solar Polycrystalline

Source: http://www.bp.com/solar

Source: http://www.bp.com/solar

Source: http://www.uni-solar.com

SunPower Back Contact

220 Watts ____________________________________________________________

61.4 in x 31.4 in

___________________________________________________________________

33.1 lbs.

175 Watts ____________________________________

62.8 in x 31.1 in

___________________________________________________

34 lbs.

160 Watts_____________________________________

62.8 in x 31.1 in

_______________________________________________

33.1 lbs.

64 Watts _________________________________________________ _

53.8 in x

29.2 in ______________________________________________________

20.2 lbs.

Source:www.sunpowercorp.com/

JUNCTION BOXES

From modules to arrays

• Method:• First Determine Customer Needs (reduce)• Determine Solar Resource (SP, model, calcs)• Select PV Modules or • Select DC-AC Inverter

• Look for Maximum Power Tracking Window• Max DC voltage & Current

• Assure Module Strings Voc and Isc meet inverter specifications

SERIES CONNECTIONS

Loads/sources wired in series:• Voltages are additive• Current is equal

(through all parts of the circuit)• One interconnection wire is used

between two components (Negative connects with positive)

• Combined modules make a “series-string”

• Leave the series string from a terminal not used in series connection

PARALLEL CONNECTIONSLoads/sources are wired in parallel:

• Voltage remains the same

• Currents are additive• Two interconnection wires are used

between two components (positive to positive and negative to negative)

• Leave from any parallel terminal to the next system component

MODULES WIRED IN SERIES – and PARALLEL

Note: In reality, this system would require series fusing for only 2 series strings and under can go

without fusing by NEC

MODULES WIRED FOR HIGH VOLTAGE

____V

____A

17V x 8 = 136

4

Use the Same Modules

• Significant reductions in output can be observed when using dissimilar modules

• It can be done but you must be very careful in your analysis and design to see if it is worth it

DISSIMILAR MODULES IN SERIES

DISSIMILAR MODULES IN PARALLEL

See Mesa Environmental Solar Audits

• Spreadsheet Customer Monthly Consumption

• Determine potential Shade Free Sites

• ID source for local Solar Resource Info• Model (PVWATTS, PV FCHART, NJCEP)• Weather Service Data• Actual measurements from region

Remember

• PV modules stack like batteries• In series Voltage adds,

• constant current through each module

• In parallel Current adds, • voltage of series strings must be constant

• Build Series strings first, then see how many strings you can connect to inverter

Match Modules With Inverter

• Find Optimal Fit of Series Strings• TO BE IN MAX POWER TRACKING WINDOW

• Assure module #s do not exceed Voc

• Find Optimal # of Strings in Parallel• TO MEET MODULE POWER RATING• CURRENT TO BE LESS THAN MAX Isc

• Are Modules and Inverter a good match?• Overall Hardware Utilization efficiency

Putting it all Together

• Customer Needs (energy usage reduce)

• PV System Design Requirements• Solar Resource Assessment• Potential Sites on Customer Property

• PV Module – Inverter Selection

• Wiring Diagram

• System Economic Analysis

Wiring the System

Utility Interactive PV

Utility Interactive with Battery

Key Concepts of Chapter 9

• Photovoltaic system types

• Resistive loads for I-V curves

• Maximum Power Point Trackers

• Interfacing with Utility - Inverters

• NJ Incentives

• Grid Connected System Sizing

• Stand-Alone System Design

PV system types

• Grid Interactive – and BIPV• Stand Alone

• Pumping

• Cathodic Protection

• Battery Back-Up Stand Alone• Medical / Refrigeration

• Communications

• Rural Electrification

• Lighting

Grid Interactive

Grid-interactive roof mounted

Building Integrated PV

Stand-Alone – First House

Remote

Maximum Power Trackers

NJ Incentives

• NJ Clean Energy Program• 40% rebate for grid connected systems up to

10kW• Smaller rebates for increments above 10kW

• Net Metering to 2 MW

• Solar Renewable Energy Certificates• NJ RPS requires • Currently trading about $250/MWh

Economic / Market Impacts

• Systems would have 25-30 year payback

• With NJCEP reduces to 14 year

• With SREC could be less than 10 year

• Let’s see an example…

Grid Connected System Sizing

See Sample PV System Wiring Diagram

Stand-Alone PV System Designs

Grounding

All equipment should be grounded

All Stainless and copper components – UL & outdoor rated

Bonded to an Earth ground

Specifying Inverter

1. Watts output AC – total connected watts of PV• STC Rating

2. DC voltage window – array voltage• 100-600 Volts DC typical (based on modules, Grid-tied

systems have a high voltage window)

3. Output voltage• 120V / 240V (residential)

• 120V/ 240V/ 208V/ 480V (3-phase for commercial)

4. Frequency – 60hz (U.S.) or 50 hz (Europe)

VOLTAGE INPUT FOR BATTERYLESS GRID-TIED INVERTERS

1. Series string voltage needs to fit the inverter’s input window

2. Voltage in a series string varies with temperature

3. If PV array voltage is lower than inverter’s window no energy production

4. If PV voltage exceeds inverter’s window could damage unit or void warranty

AVAILABLE GRID-TIED INVERTERS

SMASource: www.sma-america.com XANTREX

Source: www.xantrex.com

FRONIUS Source: www.fronius.com

PV POWERED Source: www.pvpowered.com

POWER ONESource: www.power-one.com

SOLECTRIASource: www.solren.com

KACOSource: www.kacosolar.com

AVAILABLE GRID-TIED (WITH BATTERIES) INVERTERS

Source: www.outbackpower.com

Grid-Tied with Batteries

OUTBACKSource: www.sma-america.com

SMA

XANTREX

Source: www.xantrex.com Source: www.beaconpower.com

BEACON

Inverter/Module Sizing Tools

• SMA• http://www.sma-america.com/#

• Fronius• http://www3.fronius.com/worldwide/usa.solarel

ectronics/support/tool.html

INVERTER SPECIFICATION EXAMPLE

Specifications for the Xantrex GT3

Maximum AC Power Output 3000 Watts

AC Output Voltage (Nominal) 240 VAC

AC Output frequency (Nominal) 60 Hz

DC Input Voltage Range 195-600 VDC

 CEC Efficiency 94%

Source: www.xantrex.com/

EFFICIENCY vs. kWhOUTPUT OF INVERTER

Only looking at efficiency can be misleading, other things to consider:

1. MPPT effectiveness (Start up ability during intermittent clouds)

2. KWh output in high temperature

3. Product reliability

4. DC Voltage Window & Start-Up point

How NOT to fuse…

Assure the Hot Leg is Fused

A safe installation has only its hot or (+) conductor fused and its grounding conductor continuously bonded from appliance frames and metal boxes to ground.

How much will PV System Make?

• PVWatts Tool• http://rredc.nrel.gov/solar/codes_algs/PVWATTS/

New homework

• HW #8– due next Monday 9 Apr

• now posted on web

• 9.1, 9.2, 9.4, 9.5, 9.6

Lab Assignment 1

• Specify an 8 kw System for Atlantic City

• Where roof is south facing of 1200 SF

• And plot monthly output

• (According to PVWatts)