This is a alternate power method of nickel plating. There are a number of excellent guides to nickel plate, this instructable is meant as a supplement.
Step 1: Materials
1 Mason Jar
Something Nickel (guitar string was chosen)
Step 2: Electrolyte
Fill the mason jar with the vinegar and add some salt. A small amount of salt will do.
Step 3: Prep the Source Material
In this case guitar string was used.
Wind it up to keep it together.
Step 4: Prep the Wire
Get your USB wire cut off the one end (the one that doesn't plug into the solar panel).
Strip the Red and Black wires.
Step 5: Create the Nickel Bath
Get the source material and some alligator clips (if handy)
Clip the material to the negative side and put it in the electrolyte.
Put the positive cable in but don't let it touch the negative (which would lead to a short).
Connect the USB cable to the solar panel and with enough light supplied to the panel, you should begin to see the material bubble in the electrolyte.
Let the process continue until you end up with a light green color.
Step 6: Begin Plating
Once you have your nickel bath connect a small amount of your nickel material to the positive side.
Dip in the thing you want to plate (in this case it was a whammy bar) and clip it to the negative end.
If it is too long to all fit in the bath, you can flip it after the one side finishes.