I have a problem at one of my on-grid solar system project. There is a problem which lets the solar inverter on, when the grid is off and the diesel generator is on. As you know that, the solar inverter works with the grid signal, and should not operate with diesel generator. Just because the thythronic relay is too expensive, I need to find a cheaper solution for the system. When the diesel generator is on, the relay coil should be on and the contacts should be open, and with this way inverter will be disconnected. I'm not sure about how to design and execute this.


  • \$\begingroup\$ I think I know what you mean, but could you be clearer? It is, of course, entirely possible that everyone who can help understands what you wrote but it wouldn't hurt to improve the question. \$\endgroup\$ – JRE May 22 '15 at 14:13
  • \$\begingroup\$ The problem is, as you know, the solar inverter operates with voltage and frequency signal of the grid. When there is power cut, inverter also must be switched off. Diesel generator switches on in this situation. Just because solar inverter can harm the generator I need to prevent this situation. \$\endgroup\$ – Burak May 22 '15 at 14:34
  • \$\begingroup\$ I hope there is a transfer switch that disconnects your system from the grid when the diesel generator kicks in. If you connect your solar inverter on the grid side of that transfer switch, it won't see the generator power and should shut down. \$\endgroup\$ – jwygralak67 Oct 16 '15 at 17:07

I understand your problem, but as JRE points out in the comments, a bit more structure and explanation to your points would have gone a long way.

There is no guarantees in simple circuits.

A relay running off of the grid to connect grid and inverter to the house & generator, as was my first though, would just keep running off the inverter if the grid dies, accomplishing nothing.

Similar solutions have similar problems.

One thing I assume is that your diesel generator has an internal system, being powered from its own battery & recharge system? There must be some opportunity there to hook up a relay that throws the inverter off the system if your diesel is running.

The normal relay won't be super cheap either, considering you have a reasonable amount of peak power in the house or building using this set-up and you'd need to dimension for worst case, but it wouldn't be particularly expensive and such things can be found second hand. Since the generator runs off a 12V or 24V battery most likely and those coil voltages are very common in relays. Generator on -> Relay on -> Inverter off.

Although, you might want an even cooler system in the long run, where the solar power keeps doing something useful. Anything it does will save you diesel power and since you already paid for the solar panels and will have to keep buying the diesel every time it's used up.


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