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What will happen to the extra power that the grid-tie inverter is producing if the demand is less than what the load needs?

I have this planned system that I will be implementing soon. The good thing about connecting the solar panel to the grid-tie inverter is that there is already a built-in MPPT in it, eliminating the need for a solar charge controller. However, I am a bit concerned on what will happen to the extra power that the grid-tie inverter is putting to the system if I am disconnected to the grid e.g. black out and I'm using my off-grid inverter to power my house.

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    \$\begingroup\$ it will do whatever it's been programmed to do. If I was designing one and the output voltage rose due to no load, I'd stop MPPT'ing and start constant voltaging. However, you might find ones designed by programmers with a sense of humour who would let the voltage rise and blow up everything downstream. Check the data sheet, then test. \$\endgroup\$ – Neil_UK Aug 24 '19 at 5:34
  • \$\begingroup\$ If you have additional information related to your original question, use the "edit" button to add the information there. Do not create a duplicate question. \$\endgroup\$ – Dave Tweed Aug 24 '19 at 13:20
  • \$\begingroup\$ Sir that's a different question. This question is about injecting extra "unused" power to my micro grid. That question was about using a constant current power supply in a grid tie inverter. I would mark this question as answered because of what Neil_UK said but he didn't post it as an answer. \$\endgroup\$ – thisjt Aug 24 '19 at 15:06
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This is actually a problem, during a blackout the grid tie inverter will still source power, but it probably won't be enough to power the loads (houses) around you and will send current back out to the line and cause problems:

First and foremost is the technical reason. The electronics that control a solar system constantly adjust voltage and current to keep the panels operating efficiently as the sunlight changes. To do this, the system produces quantities of power that aren’t dependent on how much your house is actually using in a given moment. In a grid-connected system, any excess power is put back onto the grid for others to use, and your utility credits you on your bill for that power.

Solar power output varies directly with sunlight levels. So, even if you disregard the need for efficiency, connecting this variable resource directly to your home’s electrical system would cause your lights to blink, damage your refrigerator, and wreak havoc on your computers and television.

The second reason that solar shuts down during a blackout is safety.

During a power outage, the power utility sends out repair crews to find and fix the points of failure. Linemen and women will be jeopardized if there is a local power generator (like a solar array) leaking power onto the grid lines. Therefore, utility rules mandate that in the event of a power outage, solar arrays must automatically shut down. Solar systems have detectors that sense whether power is coming across the grid, and whenever grid power is down, they automatically shut down too, to protect utility workers.

Source: https://thirdsunsolar.com/residential/does-solar-work-in-a-blackout/

For this reason most (but not all) grid tie inverters don't source power when the grid goes down. There are some that can detect grid faults and disconect the building power from the grid during a blackout.

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  • \$\begingroup\$ Thank you for this answer. However, during a blackout a breaker will be used to disconnect my whole house from the power grid, thereby preventing power from going back up to the power lines. And about the variable solar power output thing, that's why I will power my house with an off-grid inverter powered by my batteries that will trick my grid-tie inverter that power is on, thereby allowing the grid-tie inverter to inject power to my house to charge my battery and my loads. \$\endgroup\$ – thisjt Aug 24 '19 at 6:25
  • \$\begingroup\$ My question though is, where will the extra power go if I produce more power than what both my house and the battery charger will use? \$\endgroup\$ – thisjt Aug 24 '19 at 6:42
  • \$\begingroup\$ "during a blackout the grid tie inverter will still source power" -- No, it won't. They're specifically designed and certified NOT to do that. If grid power disappears, then a grid-tie inverter simply shuts down. \$\endgroup\$ – Dave Tweed Aug 24 '19 at 13:17
  • \$\begingroup\$ If you connect it to an off grid inverter it will as shown in the diagram, still source power \$\endgroup\$ – Voltage Spike Aug 24 '19 at 14:37
  • \$\begingroup\$ Dave Tweed is correct. However, as what Voltage Spike has pointed out, the grid tie will be tricked by the off-grid inverter that there is power running in my house, activating it and sending extra power to my house. My question is that what will happen to the extra unused power that the grid-tie is putting out? \$\endgroup\$ – thisjt Aug 24 '19 at 15:13

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