17 of 20 - Module-Level Rapid Shutdown (MLRSD)

Created by Victor Herrera, Modified on Thu, Jun 9, 2022 at 1:53 PM by Victor Herrera

Note: the large red mushroom switch on the right side of the inverter (if you're looking straight on at it) is the rapid shutdown switch. Pressing this switch disconnects the internal MLRSD PLC signal transmitter from AC power, which will cause the RSD receivers to enter "safety mode" within ten seconds. If the system is set up for backup mode, the red DC switch on the left side of the inverter must also be turned to off in order to initiate RSD mode.

Please give the switch a quarter-turn clockwise to ensure that it is "popped out" and not pushed in, this will ensure the transmitter can get the AC power it needs to turn on. Once Backup has been turned on, this switch will not shut down the receivers, please keep that in mind.

Please first review MLRSD Best Practices and MLRSD Compatibility with Solis Inverters

The Solis Energy Storage Inverter is able to come with an integrated SunSpec-certified rapid shutdown (RSD) transmitter. Alternatively, the inverter can come with an integrated Tigo transmitter instead. The SunSpec transmitter will work with any SunSpec certified rapid shut down device. However, a PVRSS or PVRSE certification is required for the the system to be considered "UL 1741 certified". This inverter series has PVRSS/PVRSE with APS, Zerun, Tigo, and NEP. For a full list of This article will give the rundown on how to install, troubleshoot, and commission the rapid shutdown receivers.

But first, the transmitter.

The RSD transmitter is a small board located at the very back of the inverter's wire box.
This board is difficult to reach - essentially the wire box needs to be completely disassembled
The transmitter communicates with the receivers using PLC signal that is sent over the DC wires
When AC power is on, a signal is sent to the receivers that tells them not to interfere with the modules performance
When the AC power goes off, the transmitter stops sending that signal to the receivers and then the receivers ramp the DC voltage down to "safety voltage" from operating voltage
1. APSmart receiver safety voltage is around 0.67 Vdc per receiver
  1. When measuring the DC voltage of one module connected to one receiver, it should be around 0.67V
2. Zerun safety voltage is around 0.7 Vdc per receiver

Note: Safety voltage is a very useful thing:

It greatly reduces the chances of electrical shock from the PV array
Testing strings is easier because if you divide the Voc of the string by the safety voltage then you can determine exactly how many receivers (and thus - modules) are in that string.
On the flip side, if you know how many modules you have in a string and your safety voltage calculation says that one is missing, you can easily identify the source of an issue in the array.

APSmart RSD Receivers

The receivers come with metal clips designed to slide over a module frame. MC4 connectors are what the receiver uses to connect with the module and with the other receivers. This makes them easy very quick and easy to install. See the two methods below for the most efficient way to set up receivers in series:

The module leads (+) and (-) plug into the short leads of the receiver.

The receiver's long leads connect to each of the receivers on either side.

Here are some basic specs on the receivers:

Operating input voltage range: 8-80 Vdc
Maximum continuous input current: 15A
Maximum input power: 800W
Maximum system voltage: 1000V/1500V

When the AC power is off, the receivers keep the module at safety voltage - meaning it's much more difficult to get a shock from the string leads at the inverter. Also, the safety voltage can tell you if the modules are connected together correctly. Measure the string leads and divide by 0.67 to verify that all of the modules are connected.

Once the inverter is turned on (AC and DC) then the DC voltage of the PV strings should ramp up to normal operating voltage. There are no other commissioning steps required for this RSD system, you're done!