sunrun design training key concepts - aee...

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


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


PV Basics

PV Basics – Solar Modules


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


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!

– Installer Handbook


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


• RECORD LOW TEMP-


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…

http://www.solarabcs.org/


• Objective: to avoid exceeding inverter and other equipment maximum voltage rating.



• 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)



• A brief review of the max string sizing equation



• 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


• A brief review of the max string sizing equation



• 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


• 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)



• 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…


• 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


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


• 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


• 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


Questions?

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