I tried to change file /usr/share/kde4/apps/plasma/layout-templates/org.kde.plasma-desktop.defaultPanel/contents/layout.js
var panel = new Panel
panel.location = 'left'
panel.length = 45
panel.height = 1080
The problem is height code does not work.
I guess height is limited to 1/2 of vertical screen or something.
It is not problem in top and bottom panels cuz lenght and height are inverted.