Dr. Jeffery Lee Johnson's #SolarMOOC slide set on the electrical installation of a typical pv system

1. Email: jeff.johnson@todo-solar.com-mx Tele: (+52) 871 722 9522 www.todo-solar.com.mx
Electrical Installation of a PV System
Making the Right Connections…
Dr. Jeffery Lee Johnson
CTO Todo-Solar
Coahuila, Mexico

2. 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

3. 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

4. INTRODUCTION, BACKGROUND AND
ASSUMPTIONS ABOUT THE SYSTEM

5. 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

6. Electrical diagram: Generic System
General Schematic
One-line diagram

7. Sample SMA Wiring Diagram with
external DC Disconnect
Combiner Box

8. Sample SMA Wiring Diagram with
integrated DC Disconnect
Combiner Box

9. Sample System
3 strings of 10 panels
250W Siliken
SMA sunny Boy SB7000US

10. THE DC SIDE OF THINGS

11. Always use components rate for UL 1703 and
IEC standards

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

13. Characteristics of Panels in Series
String is a series of panels with predetermined current and voltage output
V = V1 + V2 + …Vn = ∑ Vi
I = I1 = I2 = …In

14. 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 !

15. 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

16. 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

17. 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

18. 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

19. 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

20. MEETING IN THE MIDDLE
CONNECTING DC TO THE INVERTER

21. 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

22. 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

23. THE AC SIDE OF THINGS

24. 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)

25. The AC connection
AC Disconnect
Main Panel
connection
AC Outputs

26. 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

27. 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 switch
Shut off all DC inputs to inverter
Connect Neutral and Physical Ground
Connect L1 to Phase 1 using breaker
Connect L2 to Phase 2 using breaker
or use two pole breakers
** Phase numbering is for convenience

28. 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

29. SYSTEM MONITORING

30. 30
Monitoreo de Bluetooth para Internet o iPhone, iPad

31. (Solar Energy made available to Everyone)
http://www.todo-solar.com.mx
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Twitter: @TodoSolar