Sunrun Design Training Key Concepts Danny Hytowitz Field Technical Trainer Field Operations Sunrun Tuesday, January 19, 2016 San Diego, CA
Sunrun Design TrainingKey Concepts
Danny HytowitzField Technical Trainer
Field OperationsSunrun
Tuesday, January 19, 2016San Diego, CA
Intro – Sunrun Design
• Department Objectives:
‒ Create and maintain industry leading design requirements which help ensure high performing PV systems
‒ Share best practices with partners as they evolve
‒ Good designs lead to well built systems
Sunrun Design TrainingKey Concepts
Objectives
Session Objectives
• Understand Sunrun specific design requirements
• Agenda:
‒ PV basics
‒ Design requirements
• String sizing
• Overcurrent protection
• Point of connection
• Shading
• Array identification
‒ Project requirements
‒ Plan sets
Sunrun Design TrainingKey Concepts
PV Basics
PV Basics – Solar Modules
PV Basics – Solar Modules
PV Basics – Solar Modules
PV Basics – Solar Modules
PV Basics – Solar Modules
PV Basics – Solar Modules
PV Basics – Solar Modules
PV Basics – Solar Modules
PV Basics – Solar Modules
PV Basics – Solar Modules
PV Basics – Solar Modules
PV Basics – Solar Modules
Sunrun Design TrainingKey Concepts
Wiring Methods
Series Connections
• “Strings” of PV modules are electrically connected in series. This means that
the positive end of one module is connected to the negative end of the next,
so on and so forth.
• In series, the voltage increases (sums) but the current stays
constant.
• V = Voc1 + Voc2 + … + Vocx, I = Isc
Parallel Connections
• Sets of strings of PV modules are electrically connected in parallel. This
means that the positive ends of the strings are connected together and the
negative ends also connected together.
• In parallel, the current increases (sums), but the voltage stays
constant.
• V = Vstring, I = Isc1 + Isc2 + … + Iscx
Sunrun Design TrainingKey Concepts
Inverter Array Matching
Inverter-Array Matching
• Objective: to avoid power clipping at peak production times
• Sunrun allows AC watts up to 110% of the inverters nominal output.
• Max AC Power ≤ 1.10 x Inverter nominal AC Power
• How do I get DC to AC watts? Aka DC to AC derate(quick review)
• Max AC Power = (total # modules x PTC rating x inverter efficiency)
Inverter-Array Matching
Max AC Power ≤ 1.10 x Inverter nominal AC Power
Max AC Power = (total # modules x PTC rating x inverter efficiency)
Example:
(1) SMA Sunnyboy 6000 (95.5% efficient CEC)
(28) Yingli 250 (226.2 CEC or PTC rating)
1.10 x 6000 = 6,600 W
Max AC Power = (28 x 226.2 W x .955) = 6,048 W
6,048 W ≤ 6,600 W
This system works!
Page 23 – Installer Handbook
Sunrun Design TrainingKey Concepts
Module String Sizing
String Sizing – Max # of Modules
• Objective: to avoid exceeding inverter and other equipment maximum voltage rating.
Vmax = {Voc - ((25°C - record low temp°C) * Tvoc)} * # of modules in series
Vmax < Inverter max DC voltage
• Note: Tvoc must be converted to V/°C (Voc * Coeff Voc)
• Note: Temperature selection could either be “record low” for the site or ASHRAE “extreme minimum” per NEC 690.7 (2011)
• ASHRAE temperatures can be found on Solar ABC’s website
String Sizing – Max # of Modules
• RECORD LOW TEMP-
• ASHRAE temperatures can be found on Solar ABC’s website
To navigate to this:
A. Web search for (google) “solar abcs ashrae”
or
B. go to www.solarabcs.org
1. Select “Publications”
2. Select “Expedited Permit Process Report”
3. Select “Map of Solar Reference points”
• Select “Interactive Solar Reference Map”
• Enter install site City and State
• Pick the appropriate nearest reference site…
String Sizing – Max # of Modules
• Objective: to avoid exceeding inverter and other equipment maximum voltage rating.
Vmax = {Voc - ((25°C - record low temp°C) * Tvoc)} * # of modules in series
Vmax < Inverter max DC voltage
• Note: Tvoc must be converted to V/°C (Voc * Coeff Voc)
• Note: Temperature selection could either be “record low” for the site or ASHRAE “extreme minimum” per NEC 690.7 (2011)
• ASHRAE temperatures can be found on Solar ABC’s website
String Sizing – Max # of Modules
• Objective: to avoid exceeding inverter and other equipment maximum voltage rating.
Vmax = {Voc - ((25°C - record low temp°C) * Tvoc)} * # of modules in series
Vmax < Inverter max DC voltage
• Note: Tvoc must be converted to V/°C (Voc * Coeff Voc)
• Note: Temperature selection could either be “record low” for the site or ASHRAE “extreme minimum” per NEC 690.7 (2011)
• ASHRAE temperatures can be found on Solar ABC’s website
String Sizing – Max # of Modules
• A brief review of the max string sizing equation
Vmax = {Voc - ((25°C - record low temp°C) * Tvoc)} * # of modules in series
Vmax < Inverter max DC voltage
• 25°C is the STC module temperature
• Record low temp can be found several ways. weather.com select monthly averages then record low
• Extreme minimum ASHRAE numbers found on Solarabcs.org may allow more options
String Sizing – Max # of Modules
• A brief review of the max string sizing equation
Vmax = {Voc - ((25°C - record low temp°C) * Tvoc)} * # of modules in series
Vmax < Inverter max DC voltage
• Tvoc is the module Temperature coefficient multiplied by the Voc
• From the REC module data sheet this is -0.27% = -.0027
• REC265PE specifies 38.1 Voc @ STC
• Tvoc = -.0027 x 38.1 = -0.10287
String Sizing – Max # of Modules
• Example:
28 REC 265PEBLK modules wired in 2 series strings of 14modules
1 SMA Sunnyboy 6000 US inverter with
4°C record low in Los Angeles CA
Temp Coefficient Voc –0.27%/C (STC) Voc 38.1
Tvoc = (38.1 x -.0027) = -.10287 V/°C
Vmax = {38.1 - ((25°C - 4°C) * -.10287)} *14 = 563.64 V
563.64 V< 600 V
• 14 modules in series works!
• Page 20 – Installer Handbook
String Sizing – Min # of Modules
• Objective: to avoid reduced output on warm days and after modules have degraded
Vmin = {Vmp - ((25°C - (max average high temp°C + 25°C)) * Tvmp)} * # of
modules in series
Vmin > Inverter min DC MPPT voltage + 20 V
• Tvmp often needs to be based on Tvoc
• Tvmp must be converted to V/°C
• Temperature selection could either be “max average high” for the site or ASHRAE “2% high” per NEC 690.7 (2011)
• ASHRAE temperatures can be found on Solar ABC’s website
String Sizing – Min # of Modules
• Objective: to avoid reduced output on warm days and after modules have degraded
Vmin = {Vmp - ((25°C - (max average high temp°C + 25°C)) * Tvmp)} * # of
modules in series
Vmin > Inverter min DC MPPT voltage + 20 V
• Tvmp often needs to be based on Tvoc
• Tvmp must be converted to V/°C
• Temperature selection could either be “max average high” for the site or ASHRAE “2% high” per NEC 690.7 (2011)
• ASHRAE temperatures can be found on Solar ABC’s website
String Sizing – Min # of Modules
• Objective: to avoid reduced output on warm days and after modules have degraded
Vmin = {Vmp - ((25°C - (max average high temp°C + 25°C)) * Tvmp)} * # of
modules in series
Vmin > Inverter min DC MPPT voltage + 20 V
• Tvmp often needs to be based on Tvoc
• Tvmp must be converted to V/°C
• Temperature selection could either be “max average high” for the site or ASHRAE “2% high” per NEC 690.7 (2011)
• ASHRAE temperatures can be found on Solar ABC’s website
String Sizing – Min # of Modules
• Objective: to avoid reduced output on warm days and after modules have degraded
Vmin = {Vmp - ((25°C - (max average high temp°C + 25°C)) * Tvmp)} * # of
modules in series
Vmin > Inverter min DC MPPT voltage + 20 V
• Tvmp often needs to be based on Tvoc
• Tvmp must be converted to V/°C
• Temperature selection could either be “max average high” for the site or ASHRAE “2% high” per NEC 690.7 (2011)
• ASHRAE temperatures can be found on Solar ABC’s website
String Sizing – Min # of Modules
• Sunrun requires that you add 20 volts to the inverter’s minimum FULL POWER / RATED MPPT voltage! (high efficiency range)
Inverter min DC MPPT voltage + 20 V
• Example SMA 3800TL lists Rated MPPT 175-480v
• Sunrun + 20 considers this as 195-480v
• Why?
• Equipment degradation
• Small safety buffer…
• Helps reduce losses due to “on the edge” Shade, Temp etc…
String Sizing – Min # of Modules
• Example:
(28) Yingli 250 and (1) SMA Sunnyboy 6000
(2) strings of 14 modules in series
Located in Los Angeles CA (26°C)
Tvmp = (30.4 x -.0045) = -.1368 V/°C
Vmin = {30.4 - ((25°C - (26°C + 22°C)) * -.1368)} * 14 = 381.64 V
381.64 V > 250 V + 20 V
• 14 modules in series works!
• Page 22 – Installer Handbook
Stringing Concepts
• All modules in a DC series string must always face the same pitch and
azimuth.
• Strings wired or combined in parallel must have the same quantity of
modules
• If different size strings or different mounting planes are needed to
meet system size, multiple inverters OR advanced inverters with
multiple mixed or MPPT independent tracking string inputs
• Micro-inverters don’t apply to these concepts since they convert DC to
AC at the module level and are then connected in parallel.
Stringing Concepts
• Modules in each string co-planer
• (6) modules @ 270 and
(10) Modules @ 180 connected
to (1) ABB (Power-one-PVI) 3.6
• (14) modules connected to
(1) Power-one-PVI-3.0
Sunrun Design TrainingKey Concepts
Overcurrent Protection
Overcurrent Protection - DC
.
• Max Current definition 690.8 (A)(1)
Max DC current= Isc* # parallel circuits * 1.25
• When sizing DC overcurrent protection the circuits are considered “continuous” per 690.8 (B)(1)(a)
Min DC OCPD = Max DC current * 1.25
Min DC OCPD = Isc* # parallel circuits * 1.25 * 1.25
• OCPD required when combining strings. In practice fuse size should be the maximum series fuse rating allowed by the manufacturer (15 amps for most modules)
Overcurrent Protection - DC
.
• Sunrun’s strong preference is not to combine strings prior to the inverter:
‒ Easier troubleshooting and service
‒ Fuses on the roof are a potential point of failure
‒ Cost is very similar
‒ New inverters with multiple MPPT, even less value in combining strings
Overcurrent Protection - AC
.
• Max Current definition 690.8 (A)(3)
Max AC current= Inverter continuous output current rating
• When sizing AC overcurrent protection the circuits are considered “continuous” per 690.8 (B)(1)(a)
AC OCPD = Max AC current * 1.25
• Round up to nearest available trade size breaker listed in NEC 240.6
15,20,25,30,35,40,45,50,60,70,80,90,100 Amps
Overcurrent Protection - AC
.
• Example: ABB (Powerone) PVI-6000-OUTD-US
Max AC current = 6000 W/240 V= 25 A
25 amps * 1.25 = 31.25 A
Next available trade size = 35 A
• Note that this inverter manufacturer publishes a max breaker size of 35 amps
Overcurrent Protection – Point of Connection
• Standard expectations of 705.12
‒ 705.12(D)(2) Load side connection, sum of the overcurrent projection devices feeding the bus bar or conductor cannot exceed 120% of the bus bar rating
• Example: (1) PVI-6000-OUTD-US connected to 125 amp service panel feed by 100 amp main breaker
125A * 1.20 = 150A
150A – 100A = 50A
35A < 50A
• This configuration works!
• Page 25– Installer Handbook
Overcurrent Protection – Point of Connection
• Reducing the main breaker is an alternative strategy to meet the requirements of 705.12(D)(2)
‒ Perform a load analysis
‒ Example: 200amp buss bar, reduce the main to 175amps, 65 amps available for solar
• Upgrading the service panel is an additional strategy
‒ Upgrade service from 100amps to 200amps
‒ “Solar Ready” panels provide dedicated 60amp backfeed locations
Overcurrent Protection – Point of Connection
• Standard expectations of 705.12
‒ 705.12(A) Supply side connection cannot exceed service rating
• If a Supply side connection is performed, the point of connection must be protected by:
‒ Minimum 60 amp rated disconnect per 230.79(D)
‒ Disconnect must be bladed and fused
‒ Fuses/Breakers must be rated for a minimum of 22kA
• Page 27– Installer Handbook
Sunrun Design TrainingKey Concepts
Questions?