Time capsule and SolarCity Gateway

This is going to get a bit complicated. I see no inherent reason for the solarcity gateway to interact with the express.

I tried to track down actual setup info for the SolarCity Gateway..

There was only very general info I could find.. but there is something very similar.. can you check if they are using the same device.

https://www.solaredge.com/sites/default/files/se-zigbee-home-gateway-installatio n-guide.pdf

The other bit of this is we need to know exactly how the Time Capsule and the express are configured.

Best way is to give us screenshots from the airport utility.. just the summary will normally do for a start. I need the overall picture.. and click on the TC.. and include its summary.. then click on the express while it is working and give just the summary.

Great start.

Your setup looks completely standard.

So I suspect anything that is going on is fairly complicated. eg the gateway is using a port vital to the express, and we are going to need details for us to figure that out.

Do you have the guest wireless turned on?

Rather than break a leg trying to make incompatible devices work with each other, let me recommend the easy way out.

Buy a standard upnp router. Apple decided they did not need to comply with Microsoft standards.. this made every other gadget in the world have issues when plugged into apple router.

You don't need expensive unit.. as a trial something like the TP-Link C5 or C7 is great. I use Asus models which are a lot more expensive but also a lot more functionality.

Simply put the C5 etc into the network as your main router. Plug the TC into that and put it in bridge mode.. plug the solarcity gateway into the C5.. there is a very good chance spending $50-100 will solve the problem without any fuss.

The rest of the network will continue to work exactly as it did.