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I've got a solar panel system with a Growatt inverter. The system has a monitoring platform. To connect the inverter to the internet to let it communicate with the monitoring portal, you need a "data logging stick". This stick is an apart (optional an relatively cheap) device you plug into the USB port on the inverter. The stick comes in multiple types, like Wifi, LAN, and GPRS. I've got a Wifi stick.

My question:

The stick sends data to the server every 5 minutes. But I came to the conclusion that the system is capable of two-way communication. In the app you have options to change settings of the inverter. When you do this, a command is sent to the inverter. This works regardless of wether your phone is in the same wifi network or just has internet through another way. In addition, it seems that the support can remotely operate/update/read the inverter. How can this work while the end-user (me) never had to change any router configuration or the like. And what about security?

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    you should be asking the manufacturer
    – jsotola
    Jan 25 at 23:11

1 Answer 1

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2 way comms with a device on a home (NAT'd) networks is not hard, you just need to remember 2 things.

  1. TCP/IP (and UDP, but a little harder) is a 2 way pipe, information can flow in both directions once the connection is established.
  2. Having a device inside the network connect out to a known location on the internet is not hard (It's basically what all your devices do already).

So what most likely happens the Inverter is making a outbound connection via the USB stick which is connected to your WiFi network, to the companies servers out on the internet (95% likely hosted on AWS...).

The device sends it telemetry over this connection to the company, and the company can send commands back to the device.

The device is probably not using HTTP but more likely a protocol like MQTT which makes 2 way communication simpler (it is possible with HTTP using long poll or WebSockets, but MQTT adds other things that make life easier).

None of this requires any changes to your router, and if you don't trust the company, you should never have connected the hardware to your WiFi network...

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  • So, as long as there's a long running connection open between inverter and server, they can send commands from server to inverter. But if there's no connection open (anymore) but still internet access, is the server still able to establish a new connection to the inverter on its own initiative? In other words, could the (datastick on) the inverter be seen as some kind of mini webserver?
    – user2190492
    Jan 29 at 21:55
  • There is always an outbound connection, the device will set it up as soon as it's started and will recreate if it gets dropped. That is how it gets past the NAT/firewall in a domestic internet connection
    – hardillb
    Jan 29 at 22:23

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