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If on-grid solar system is connected in parallel with grid, solar system give power to the grid when local (at house) consume power less than generated power from solar system.

The question is:

When solar system (or any AC source) tied to grid, that means it share the total load connected to that grid, how power of solar system output can be controlled?

Example: if total load connected to the grid is 100 kW, and power of solar system is just 2 kW, how could make solar system give only 2 kW (to not exceed its capacity)?

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closed as too broad by Robherc KV5ROB, Trevor_G, pjc50, brhans, DoxyLover Apr 28 '17 at 1:45

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • \$\begingroup\$ If you buy a grid-connection certified inverter, it will handle this, and several other, legal qualification(s) for you, it's already "built-in." -- If, however, you're wanting to build your own grid-tied inverter, then you're going to have to first do some research into all of the qualifications for it to be legally connected to the grid (frequency/voltage cut-in/out, phase synchronization, anti-islanding, etc). \$\endgroup\$ – Robherc KV5ROB Apr 27 '17 at 19:54
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    \$\begingroup\$ It's kind of like 10 guys pushing a bus. The 10guys being the electric company. If you come along and push with one hand, you add a little bit of force but all you can add is all you can give. It wont take more than that. If however the bus is on a hill and all the other guys leave, you had better have a way to get out of the way quick when the bus backs up. \$\endgroup\$ – Trevor_G Apr 27 '17 at 20:00
  • \$\begingroup\$ i asked to make a report in university i read articles and book and not understood this point, so i ask her about your example, how projection idea on voltages and currents ? i need details \$\endgroup\$ – Computer_guy11 Apr 27 '17 at 20:11
  • \$\begingroup\$ Here's a starting point...it may not make sense to you at first, but if you study induction motor and induction generator well, it will help you think in the right way to understand your own question better. \$\endgroup\$ – Robherc KV5ROB Apr 27 '17 at 20:54
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If you have a solar system with a grid-tied inverter, the inverter is part of the grid and is pushing onto the grid as hard as necessary to send away the power it has made -- and no harder. In other words it is just another generator on that grid - like the stinky coal plant and Oroville Dam and Kursk Unit 3 and that offshore wind farm. Unlike those loads, your grid-tie inverter won't "back off" or try to load-follow, it will just push until its power is delivered.

If it can deliver power to your house, that's nice. From the inverter's perspective, it's part of the grid and your house is just another load served by that grid.

Your grid-tie solar array runs full-boat if it runs at all. How does it match up to the grid? By making small adjustments to output voltage. Too low and no current will flow. Too high and too much current will try to flow. The inverter seeks the voltage where the right amount of current flows.

If local grid demand is high, voltage will be sagging - and the inverter reduces its voltage to match. If load is light and voltage is running high, the inverter will raise voltage as necessary to push exactly what it has to give.

The inverter is also watching for line voltage gone out of bounds. If voltage spikes much too high, it means the other generators are not backing off (or more likely, the grid is broken) and the grid-tie inverter shuts down. Also, if voltage goes too low (severe brownout) the inverter will also shut down, partly to prevent "islanding".

Solar panels notwithstanding, other large generators are designed to react dynamically to varying loads on the grid. If voltage rises high, those generators will "back off" and generate less power. These work as a counterpoint to solar and wind, which generate at max capacity no mattter what. Hydro is particularly good at this, it can even "back-pump", intentionally allowing the grid to push the generator and cause it to pump water up back into the reservoir to be used later. A solar inverter can't be pushed, because it's basically an array of diodes.

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    \$\begingroup\$ @RobhercKV5ROB After a false start I made an effort to address what you suggested. It was in my original edit, just lost in clutter. \$\endgroup\$ – Harper Apr 27 '17 at 21:26
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    \$\begingroup\$ Thank you very much, i understand what you wrote, the solar controller reduce or increase its output voltage to maintain its power but i think this increase or reduce in voltage must be in millivolts \$\endgroup\$ – Computer_guy11 Apr 27 '17 at 22:46
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    \$\begingroup\$ @Computer_guy11 indeed it is. But this sort of matching/syncing is more passive/automatic than you might think. We've been doing it for 100 years. Longer in the DC world, trolley systems have had more than one substation since like 1885. \$\endgroup\$ – Harper Apr 27 '17 at 23:30

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