import matplotlib.pyplot as plt
import numpy as np


def get_data_and_ticks():

    # generate dummy load duration curve
    dur = 2500
    y = np.random.normal(60, 30, dur + 1)
    y[::-1].sort()

    x = range(0, dur + 1)
    perticks = np.linspace(0, 1, 11)
    xticks = perticks * dur
    yticks = np.interp(xticks, range(0, dur + 1), y)

    return x, y, xticks, yticks


x, y, xticks, yticks = get_data_and_ticks()

# create figure object with axe object
fig, ax1 = plt.subplots(figsize=(10, 7))
ax1.plot(x, y)

# create second axis
color = "tab:blue"

ax2 = ax1.secondary_yaxis("right")
ax2.set_yticks(yticks)
ax2.set_yticklabels(labels=[f"{i*10}%" for i in range(11)])
ax2.tick_params(axis="y", color=color, labelcolor=color)

# draw grid lines on the secondaryaxis
# The problem is at this line
ax2.grid(color=color, which="major", linestyle="--")

plt.show()