Does ground wire need to be same gauge as power conductors?

In the high voltage DC lines from the array to the inverter, does the ground wire need to be same gauge as power conductors?
I'm making a substantial upgrade to my solar installation (adding a bunch more panels). The array is about 200-250' from the inverter and the wires are run underground in 1" ID black plastic conduit. There's three conductors, a positive, neg and ground. All are insulated 4 AWG wires. When i install the new array, i'm probably going to have to run a new, larger conduit... unless... if i pull the 4awg wire out and replace them with larger positive and negative wires, and a small-ish ground, then i may be able to get enough current through the existing conduit.
I'm making a substantial upgrade to my solar installation (adding a bunch more panels). The array is about 200-250' from the inverter and the wires are run underground in 1" ID black plastic conduit. There's three conductors, a positive, neg and ground. All are insulated 4 AWG wires. When i install the new array, i'm probably going to have to run a new, larger conduit... unless... if i pull the 4awg wire out and replace them with larger positive and negative wires, and a small-ish ground, then i may be able to get enough current through the existing conduit.
Comments
Edit, Attached pdf file nec table 250.122 would indicate tha tthe ground size is determined by the rating or setting of the overcurrent device. The second pdf shows the ground size for given wire gauge nmd 90, which contradicts the NEC table from 12 gauge 20A rating using 14 gauge ground, go figure. The electrical code is always evolving, so there's that to consider.
Sometimes using a charge controller which allows a higher input say 600 VDC is cheaper than running large gauge conductors a second time, simply increase the series panel count and use the existing home run. Naturally without knowing what it is you currently have in terms of panels and controller, it's impossible to make an informed comment.
Second system 1890W 3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.
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More detail on our install. We're already have 2 strings of 13 panels in series (about 400v) from the array to the inverter, so there's not a lot of gain to be had by going higher voltage, but there is some. It's direct grid-tie, no batteries or charge controller.
So it looks like the equipment ground conductor could maybe be sized smaller than the power conductors, but maybe only by one awg step. So if i upgrade to 2awg power conductors, i'd still need the ground to be 4awg.
http://www.calculator.net/voltage-drop-calculator.html?material=aluminum&wiresize=0.8152&voltage=400&phase=dc&noofconductor=1&distance=250&distanceunit=feet&eres=20&x=80&y=21
Second system 1890W 3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.
5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.