Grid-tie switchover & voltage remote monitoring using a Pi?

[coolamasta]

Hi, this might be a long-shot but I have seen a few vids on YouTube where people have been using a Raspberry Pi or Arduino to monitor voltage/ampage from a small solar set up which then has an upper and lower voltage threshold set to trigger a relay, so putting that into laymen's terms, solar panels are connected to a relay and then split into A) charge controller and B) grid-tie inverter so the idea is the solar defaults to charge controller and charges the batteries and then once a certain set voltage is hit it flicks the relay over to the grid-tie inverter and then when voltage drops to a lower set level then it flicks back over to the charge controller.

I expect there are devices out there that are standalone that can do that so any suggestions on any would be great although im doing this on a budget as its a project but I would like to do it using a Raspberry Pi as I have a couple lying about and I know you can buy voltage/ampage modules to monitor power but was hoping there might be some help with how I set it all up on the Pi?

Also if its all being done on a Pi then I was thinking about remote voltage monitoring so like a simple web page I could view displaying voltages/ampage but that's only if its possible!

Many Thanks for any help, much appreciated

[SunEagle]

It depends on the grid tie inverter you plan on using.

Most legal grid tie inverters that are set up with a hybrid charger for batteries will do that by using their own control system that is probably more sophisticated then the Raspberry Pi.

Now if you want to first charge your batteries and then power a load not connected to the grid I am sure you can come up with the voltage settings and control logic to make it happen. But I wouldn't use the Pi with a grid tie inverter.

[inetdog]

Any scheme that uses relays to switch the way the panels are wired can get expensive very fast. The reason is that grid tie inverters (other than the illegal plug-and-pray imports) require a fairly high string voltage (~200V or more) and relays that can interrupt DC circuits under load at that voltage are not cheap. It is difficult to stop a DC arc when opening the relay contacts and this causes relay damage or even fires.
If you have one load break rated master relay for the grid tie input and one load break rated master relay for the CC input you could essentially shut the system down momentarily while cheaper relays reconfigure the panels, then close the master relays again.
But each time you do this the GTI would be out of operation for at least five minutes as it restarted and re-qualified the grid voltage.