""" Sun path diagram ================ Examples of generating sunpath diagrams. """ #%% # This example shows basic usage of pvlib's solar position calculations with # :py:meth:`pvlib.solarposition.get_solarposition`. The examples shown here # will generate sunpath diagrams that shows solar position over a year. # # Polar plot # ---------- # # Below is an example plot of solar position in # `polar coordinates `_. from pvlib import solarposition import pandas as pd import numpy as np import matplotlib.pyplot as plt tz = 'Asia/Calcutta' lat, lon = 28.6, 77.2 times = pd.date_range('2019-01-01 00:00:00', '2020-01-01', freq='H', tz=tz) solpos = solarposition.get_solarposition(times, lat, lon) # remove nighttime solpos = solpos.loc[solpos['apparent_elevation'] > 0, :] ax = plt.subplot(1, 1, 1, projection='polar') # draw the analemma loops points = ax.scatter(np.radians(solpos.azimuth), solpos.apparent_zenith, s=2, label=None, c=solpos.index.dayofyear, cmap='twilight_shifted_r') # add and format colorbar cbar = ax.figure.colorbar(points) times_ticks = pd.date_range('2019-01-01', '2020-01-01', freq='MS', tz=tz) cbar.set_ticks(ticks=times_ticks.dayofyear, labels=[], minor=False) cbar.set_ticks(ticks=times_ticks.dayofyear+15, labels=times_ticks.strftime('%b'), minor=True) cbar.ax.tick_params(which='minor', width=0) # draw hour labels for hour in np.unique(solpos.index.hour): # choose label position by the smallest radius for each hour subset = solpos.loc[solpos.index.hour == hour, :] r = subset.apparent_zenith pos = solpos.loc[r.idxmin(), :] ax.text(np.radians(pos['azimuth']), pos['apparent_zenith'], str(hour).zfill(2), ha='center', va='bottom') # draw individual days for date in pd.to_datetime(['2019-03-21', '2019-06-21', '2019-12-21']): times = pd.date_range(date, date+pd.Timedelta('24h'), freq='5min', tz=tz) solpos = solarposition.get_solarposition(times, lat, lon) solpos = solpos.loc[solpos['apparent_elevation'] > 0, :] label = date.strftime('%b %d') ax.plot(np.radians(solpos.azimuth), solpos.apparent_zenith, label=label) ax.figure.legend(loc='upper left') # change coordinates to be like a compass ax.set_theta_zero_location('N') ax.set_theta_direction(-1) ax.set_rmax(90) plt.show() #%% # This is a polar plot of hourly solar zenith and azimuth. The figure-8 # patterns are called `analemmas `_ and # show how the sun's path slowly shifts over the course of the year . The # solid colored lines show the single-day sun paths for the winter and summer # solstices as well as the spring equinox. # # The soltice paths mark the boundary of the sky area that the sun traverses # over a year. The diagram shows that there is no point in the # year when is the sun directly overhead (zenith=0) -- note that this location # is north of the Tropic of Cancer. # # Examining the sun path for the summer solstice in particular shows that # the sun rises north of east, crosses into the southern sky around 10 AM for a # few hours before crossing back into the northern sky around 3 PM and setting # north of west. In contrast, the winter solstice sun path remains in the # southern sky the entire day. Moreover, the diagram shows that the winter # solstice is a shorter day than the summer soltice -- in December, the sun # rises after 7 AM and sets before 6 PM, whereas in June the sun is up before # 6 AM and sets after 7 PM. # # Another use of this diagram is to determine what times of year the sun is # blocked by obstacles. For instance, for a mountain range on the western side # of an array that extends 10 degrees above the horizon, the sun is blocked: # # - after about 6:30 PM on the summer solstice # - after about 5:30 PM on the spring equinox # - after about 4:30 PM on the winter solstice #%% # PVSyst Plot # ----------- # # PVSyst users will be more familiar with sunpath diagrams in Cartesian # coordinates: from pvlib import solarposition import pandas as pd import numpy as np import matplotlib.pyplot as plt tz = 'Asia/Calcutta' lat, lon = 28.6, 77.2 times = pd.date_range('2019-01-01 00:00:00', '2020-01-01', freq='H', tz=tz) solpos = solarposition.get_solarposition(times, lat, lon) # remove nighttime solpos = solpos.loc[solpos['apparent_elevation'] > 0, :] fig, ax = plt.subplots() points = ax.scatter(solpos.azimuth, solpos.apparent_elevation, s=2, c=solpos.index.dayofyear, label=None, cmap='twilight_shifted_r') # add and format colorbar cbar = fig.colorbar(points) times_ticks = pd.date_range('2019-01-01', '2020-01-01', freq='MS', tz=tz) cbar.set_ticks(ticks=times_ticks.dayofyear, labels=[], minor=False) cbar.set_ticks(ticks=times_ticks.dayofyear+15, labels=times_ticks.strftime('%b'), minor=True) cbar.ax.tick_params(which='minor', width=0) for hour in np.unique(solpos.index.hour): # choose label position by the largest elevation for each hour subset = solpos.loc[solpos.index.hour == hour, :] height = subset.apparent_elevation pos = solpos.loc[height.idxmax(), :] azimuth_offset = -10 if pos['azimuth'] < 180 else 10 ax.text(pos['azimuth']+azimuth_offset, pos['apparent_elevation'], str(hour).zfill(2), ha='center', va='bottom') for date in pd.to_datetime(['2019-03-21', '2019-06-21', '2019-12-21']): times = pd.date_range(date, date+pd.Timedelta('24h'), freq='5min', tz=tz) solpos = solarposition.get_solarposition(times, lat, lon) solpos = solpos.loc[solpos['apparent_elevation'] > 0, :] label = date.strftime('%d %b') ax.plot(solpos.azimuth, solpos.apparent_elevation, label=label) ax.figure.legend(loc='upper center', bbox_to_anchor=[0.45, 1], ncols=3) ax.set_xlabel('Solar Azimuth (degrees)') ax.set_ylabel('Solar Elevation (degrees)') ax.set_xticks([0, 90, 180, 270, 360]) ax.set_ylim(0, None) plt.show()