Email: jeff.johnson@todo-solar.com-mx Tele: (+52) 871 722 9522 www.todo-solar.com.mx

Electrical Installation of a PV SystemMaking the Right Connections…

Dr. Jeffery Lee JohnsonCTO Todo-Solar

Coahuila, Mexico

Agenda

• Resources• Assumptions and Background

• The DC side of things – Choosing and Connecting the Panels in Series– Proper grounding– String combiners

• Meeting in the Middle– DC connection to the Inverter– DC Disconnects, fusing and loading

• The AC side of things– AC Connection to the Inverter– AC Disconnects, fusing and safety– Connecting to the grid

• Summary and questions

Resources

Doc Solstice’s Seasoned Sentiments

Facts about Global PV installations

http://www.pv-tech.org/news/global_pv_installations_reached_27.7gw_in_2011_industry_at_crossroads_says

Global PV installations reached 27.7GW in 2011

That comes to 0.87 KW per second or 3 to 4 panels every second of the year

Global PV Installations to Grow by up to 21 Percent in 2012 Predicts IMS Research

http://www.pvmarketresearch.com/press-release/Global_PV_Installations_to_Grow_by_up_to_21_Percent_in_2012_Predicts_IMS_Research/5

For comparison , the entire grid capacity of the country of Mexico is 53 GW

INTRODUCTION, BACKGROUND AND ASSUMPTIONS ABOUT THE SYSTEM

Key Concepts and Assumptions

• Follow the typical systematic Installation Procedures– Assemble and place racks– Mount and connect panels (DC)– Install combiner box (DC)– Connect DC disconnect (may be integrated) (DC)– Connect DC to inverter (DC)– Mount and configure inverter (AC/DC)– Install AC Disconnect (AC)– Connect inverter to grid via electrical center (AC)– Commission and test (AC/DC– Install or activate Monitoring system

• You have an approved wiring diagram meeting specifications and needs of Locations

– Routing, cable lengths, junction locations, fusing etc a

• You have a complete parts list with prepared components

Electrical diagram: Generic System

General Schematic

One-line diagram

Sample SMA Wiring Diagram with external DC Disconnect

Combiner Box

Sample SMA Wiring Diagram with integrated DC Disconnect

Combiner Box

Sample System

3 strings of 10 panels 250W Siliken

SMA sunny Boy SB7000US

THE DC SIDE OF THINGS

Always use components rate for UL 1703 and IEC standards

Panel Characteristics

Must know VOC, ISC, Vmp Imp Pmp, tolerances under STC and NOTC (preferably)

Characteristics of Panels in Series

String is a series of panels with predetermined current and voltage outputV = V1 + V2 + …Vn = ∑ Vi

I = I1 = I2 = …In

Choosing Panels for Series layout

Issue Voltages for Panels in Series add linearly

Ideally, every series has the same voltage output – but generally not true

When combining series into Parallel Arrays at a combination node (such as a combiner box or Inverter input), the voltage at that node is the weighted average of the series voltages favoring the lowest voltage present

Important to balance your strings by equalizing the string voltages as best as possible !

Balancing String Voltage

Layout your panels in a similar environment of illumination & temperature

Measure and Record VOC for each panel – assign a numbering system

WHY measure VOC? Safer and varies little with changes in illumination

WHEN? Measure during peak hours near solar noon when solar radiation is changing slowly

With knowledge of panel characteristics, group them as best you can so each series will have equal or similar voltage – mix and match high /low performers

Installing panels – measure as you go!

RETURN LINE

Using return line measure VOC as you connect panels

Why? To ensure each connection is secure and voltage sums as you go! Panel interconnect issues are difficult to find after the fact

Make Sure panel connectors and cables are secured to rack

Physical Ground

All panels must have common physical ground and be grounded to racks

Aluminum frames are anodized (resistive)

Most panels provide a ground connection hole

Other technique is to use WEEBs or lugs – electrically connect panel frames to rack and then ground rack

Combiner boxes – adding the current of strings

PV COMBINER BOXES ARE CURRENT ADDERS FOR STRINGS IN PARALLEL

Common buss bar • DC positive inputs• DC Negative inputs• Ground

• Single outputs for Positive, Negative & ground

Each DC positive input (string) is fused before common output

Fuse: 600 VDC with amp rating > 1.45 operating amps

Acts as string switch

Recommendation:Pre-wire the box with negative/ positive cables with mated connectors

DC routing

• Have a DC cable routing plan– DC is on the roof or remote from inverter

• Best solar cables do not need conduit but bundle them nicely using UV resistant cable ties

• For esthetics and some codes, use metal conduit to distribute DC cables

MEETING IN THE MIDDLECONNECTING DC TO THE INVERTER

DC Disconnects

Integrated DC Disconnect Switch(Typically fused inside the inverter)

Stand-alone DC Disconnect Switch

• Fuse: 600 VDC with Amp rating > 1.45 x operating amps for each positive lead

Connecting DC to Inverter

Disconnect all DC power

Follow Inverter manual to connect positive, negative and ground cables*

*Note: some panels are positively grounded … so pay attention

Turn on DC and measure voltage at all outputs and inputs

Turn off DC

THE AC SIDE OF THINGS

Know your Grid

Know which type of grid you are connecting to

Most inverters are reconfigurable by dip switches or programming

Line voltages vary so choose the operating output range that fits your grid conditions

Inverter must be equipped with anti-islanding and must shutdown upon loss of grid power(grid connected systems)

The AC connection

AC Disconnect

Main Panel connection

AC Outputs

AC Disconnect

• Locate AC disconnect near the inverter -- must be accessible

• Fuses or Breakers must be compatible with grid voltage (240 VAC)

• Amp repeating should be 1.45 x the output current under operating conditions

Fused style

Breaker Style

Connecting to the Grid

L1

Phase 2

L2

Phase 1

Typical 240 VAC Connection

Outputs from Inverter are: L1, L2 are positive feed lines Neutral Physical Ground

Shut off AC power at main switchShut off all DC inputs to inverter

Connect Neutral and Physical Ground

Connect L1 to Phase 1 using breakerConnect L2 to Phase 2 using breaker or use two pole breakers

** Phase numbering is for convenience

Commissioning

• Check all connections• Follow manual for startup• Usual procedure is

– For Startup: Turn on AC First then DC– For Shutdown: Turn off DC first then AC

• After shutdown, ALWAYS wait 5 to 10 minutes before opening or working on inverter !!!

• Capacitive load needs to discharge

SYSTEM MONITORING

30

Monitoreo de Bluetooth para Internet o iPhone, iPad

(Solar Energy made available to Everyone)

http://www.todo-solar.com.mx

Twitter: @TodoSolarKidsTwitter: @TodoSolar