Grid-Tie Inverter Theory and Operation Confusion - Solar Panel Talk

I understand the principles of a Grid-Tie Inverter (GTI), but there's a few key items that aren't clear I was hoping to tap into the knowledge base on the forums. This is a GTI with no batteries, no charge controller. Just PV Arrays and GTI

A GTI is (first question) a dumb device. It's doesn't know anything about "load". Its job is to take whatever is connected to its input and drive as much power out as possible. If it can provide more power than the house needs, that raises the impedance of the home panel above that of the grid, and power flows out to the grid. When the Inverter produces less power, it lowers the impedance of the house panel and power flows from the grid to the home. I think this is correct.

Now for the more specifics.

A GTI has 1 or many PV inputs. People say your DC to AC ratio should be 1 to 1.5. This means to oversize your panels based on your inverter specs. This is the confusing part, since most inverters have two limits. The first limit is the total output power (i.e. 5Kw, 7Kw, or 10Kw inverters for example). That means the inverter, regardless of how much DC power gets shoved into it, will max out at its absolute limit. This is called "clipping".

Now back to the inputs. Each GTI has limits as to what can be connected to it in terms of input. There is a Voltage and Amperage range for inputs. Let's say the inverter has 2 inputs rated at 360v @15amps each. Now, if I overdrive a singular input with more panels, that means I'm either exceeding the inputs Voltage or Amperage rating based on the PV array configuration. From what I understand, the GTI doesn't "Clip" the input lines, only the output lines. So if you provide 360V @100amps on the PV input, the inverter will try to convert every ounce of that and most likely will burn something out in the process. The Inverters don't "clip" inputs, thus, why its so critical to size PV arrays correctly.??

a 10Kw GTI has two inputs rated at 360v @15amps for a total of ~5Kw per input for a max output of 10Kw. However, if someone tried to only connect one PV input with 360v@30amps, although the ouput is identical, the inverter will blow up because the the single input exceeded the amp limit of that input? davidcheok

Yes, all good stuff, but, you missed the core question. In your graph, you are increasing VOLTAGE to increase your DC to AC ratio and by that definition your AMPs are staying uniform for your WATTS calculation across all voltages.

The question is the direct opposite of this. What if VOLTAGE remains constant and only AMPS is adjusted? If your inverter input is rated for 360v @15 amps and you size your array for 360v @1,000 amps (insane number but that's the point). Will the inverter, on that single input, try to max its output power, exceed the rating on that input and go poof.

In equation form:

GTI Input #1 = PV array 360v@15amps = ~5Kw (Contacts on input are rated for 360v@15amps)
GTI Input #2 = PV array 360v@15amps = ~5Kw (Contacts on input are rated for 360v@15amps)
GTI Input #3 = unused
Total GTI rated ouput = 10Kw

Now, change the PV array:

GTI input #1 = PV array 360v@30amps = 10Kw (Contacts on input are rated for 360v@15amps)
GTI input #2 = unused
GTI input #3 = unused
Total GTI rated oputput = 10Kw or is the total just 5Kw because the inverter is self limiting how much it pulls to 15amps although the PV array has 30amps available?

In both scenarios, the total output of the PV arrays are equal to the Inverter max output. As you can see, however, the second configuration OVERLOADED the amps on a single string. The question continues

Will the inverter try to convert all 30amps on the single line to max its output of 10Kw, or, will the inverter "pull" up to 15amps on that line and the remaining 15amps available is wasted, since the inverter will only "pull" up to 15amps on that line the output is limited to 5Kw even tho there is 10Kw available from the PV array?

Can the inverter self-limit how many amps it pulls, or, does it just do VoltsxAmps=Wattage until Wattage equals max output and it doesn't care, per se, what the voltage or amps are on the line, it will just try to convert it. If either the Volts or Amps exceed the input limit, the inverter goes POOF because its just doing VOLTSxAMPS until that combination equals 10Kw? Its up to the person to "limit" the PV array accordingly for BOTH VOLTs and AMPs not to exceed the input limits of the GTI for each input?

The inverter can reach it's max output in either scenrio, but, will the inverter reach its max output in the second configuration? Will the inverter go POOF on the second configuration?