String Sizing Info for Optimizers

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March 2017

Application Note - SolarEdge String Sizing, North America

Introduction

There are two primary criteria for string sizing in a SolarEdge system. Maximum (STC) power per string, and minimum and maximum

string lengths. This document explains how these values are determined and provides the string sizing rules for the different inverter

and optimizer combinations. For additional system design information refer to the inverter and optimizer datasheets.

Sizing rules typically depend on the type of inverters and optimizers used:



Inverters: single phase or three phase



Optimizers: general or commercial

Commercial optimizers can be used only with three phase inverters, while general optimizers can be used with both single and three

phase inverters.

General optimizers typically have one PV module per optimizer, and commercial optimizers typically have two modules. However

these are not fixed requirements and as long as the cumulative power and voltage/current of the modules meets the optimizer

specifications as detailed in the datasheet, connecting additional modules per optimizer is permitted (for example connecting

2x120W modules in series to a single P300 general optimizer). Refer to the Connecting Multiple Modules to Power Optimizers

application note for details.

NOTE

In the context of this document, string length refers to the number of optimizers and modules in the string. When designing the

installation make sure to maintain the maximum physical string length as well: The total cable length of the string (including power

optimizers’ cables) should not exceed 1000ft./300m from DC+ to DC- of the inverter (2,300ft./700m when using the SE14.4KUS and

SE33.3KUS inverters).

Maximum String Power

Maximum string power is simply the “Inverter Nominal DC Input Voltage” multiplied by the “Optimizer Maximum Output Current”.

These values can be found on the inverter and optimizer datasheets respectively. Table 1 details the values of available products.

Inverter Model

AC Grid Voltage

[V]

Inverter Nominal DC

Input Voltage [V]

Optimizer Max

Output Current [A]

Maximum String

Power [Wp]

Single phase inverters

SE3000A-US – SE11400A-US

240

350

5,250

Single phase HD-Wave

Inverters SE3000H-US –

SE6000H-US

240

380

5,700

Single phase HD-Wave Inverter

SE7600H-US

240

400

6000

SE9KUS, SE14.4KUS

120/208

400

6000 (or 6500 in

some cases

)

18 (P800)

7200

SE10KUS, SE20KUS, SE33.3KUS

277/480

850

12750 (or 15000 in

some cases

)

18 (P800)

15300

Table 1: Maximum string power

For SE14.4KUS only, when used with P600/P700/P730, it is allowed to install up to 6500W per string when 3 strings are connected

to the inverter and when the maximum power difference between the strings is up to 1000W.

For SE33.3KUS only, when used with P600/P700/P730, it is allowed to install up to 15000W per string when 3 strings are connected

to the inverter and when the maximum power difference between the strings is up to 2000W.

Summary of content (2 pages)

PAGE 1
March 2017 Application Note - SolarEdge String Sizing, North America Introduction There are two primary criteria for string sizing in a SolarEdge system. Maximum (STC) power per string, and minimum and maximum string lengths. This document explains how these values are determined and provides the string sizing rules for the different inverter and optimizer combinations. For additional system design information refer to the inverter and optimizer datasheets.
PAGE 2
Minimum and Maximum String Length The minimum number of optimizers per string depends on the “Maximum Output Voltage” of the optimizer and on the “Nominal DC Input Voltage” of the inverter: the optimizers connected in series in the string must be able to achieve the inverter’s nominal voltage. There is a buffer added to ensure the operability of the string also in some shading or fault conditions.