This tutorial explores using TMY data as inputs to different plane of array diffuse irradiance models.
This tutorial requires pvlib > 0.6.0.
Authors:
See the tmy_to_power
tutorial for more detailed explanations for the initial setup
# built-in python modules
import os
import inspect
# scientific python add-ons
import numpy as np
import pandas as pd
# plotting stuff
# first line makes the plots appear in the notebook
%matplotlib inline
import matplotlib.pyplot as plt
# finally, we import the pvlib library
import pvlib
# Find the absolute file path to your pvlib installation
pvlib_abspath = os.path.dirname(os.path.abspath(inspect.getfile(pvlib)))
# absolute path to a data file
datapath = os.path.join(pvlib_abspath, 'data', '703165TY.csv')
# read tmy data with year values coerced to a single year
tmy_data, meta = pvlib.tmy.readtmy3(datapath, coerce_year=2015)
tmy_data.index.name = 'Time'
# TMY data seems to be given as hourly data with time stamp at the end
# shift the index 30 Minutes back for calculation of sun positions
tmy_data = tmy_data.shift(freq='-30Min')['2015']
tmy_data.GHI.plot()
plt.ylabel('Irradiance (W/m**2)')
Text(0,0.5,'Irradiance (W/m**2)')
tmy_data.DHI.plot()
plt.ylabel('Irradiance (W/m**2)')
Text(0,0.5,'Irradiance (W/m**2)')
surface_tilt = 30
surface_azimuth = 180 # pvlib uses 0=North, 90=East, 180=South, 270=West convention
albedo = 0.2
# create pvlib Location object based on meta data
sand_point = pvlib.location.Location(meta['latitude'], meta['longitude'], tz='US/Alaska',
altitude=meta['altitude'], name=meta['Name'].replace('"',''))
print(sand_point)
Location: name: SAND POINT latitude: 55.317 longitude: -160.517 altitude: 7.0 tz: US/Alaska
solpos = pvlib.solarposition.get_solarposition(tmy_data.index, sand_point.latitude, sand_point.longitude)
solpos.plot()
<matplotlib.axes._subplots.AxesSubplot at 0x1189057b8>
# the extraradiation function returns a simple numpy array
# instead of a nice pandas series. We will change this
# in a future version
dni_extra = pvlib.irradiance.get_extra_radiation(tmy_data.index)
dni_extra = pd.Series(dni_extra, index=tmy_data.index)
dni_extra.plot()
plt.ylabel('Extra terrestrial radiation (W/m**2)')
Text(0,0.5,'Extra terrestrial radiation (W/m**2)')
airmass = pvlib.atmosphere.get_relative_airmass(solpos['apparent_zenith'])
airmass.plot()
plt.ylabel('Airmass')
Text(0,0.5,'Airmass')
Make an empty pandas DataFrame for the results.
diffuse_irrad = pd.DataFrame(index=tmy_data.index)
models = ['Perez', 'Hay-Davies', 'Isotropic', 'King', 'Klucher', 'Reindl']
diffuse_irrad['Perez'] = pvlib.irradiance.perez(surface_tilt,
surface_azimuth,
dhi=tmy_data.DHI,
dni=tmy_data.DNI,
dni_extra=dni_extra,
solar_zenith=solpos.apparent_zenith,
solar_azimuth=solpos.azimuth,
airmass=airmass)
diffuse_irrad['Hay-Davies'] = pvlib.irradiance.haydavies(surface_tilt,
surface_azimuth,
dhi=tmy_data.DHI,
dni=tmy_data.DNI,
dni_extra=dni_extra,
solar_zenith=solpos.apparent_zenith,
solar_azimuth=solpos.azimuth)
diffuse_irrad['Isotropic'] = pvlib.irradiance.isotropic(surface_tilt,
dhi=tmy_data.DHI)
diffuse_irrad['King'] = pvlib.irradiance.king(surface_tilt,
dhi=tmy_data.DHI,
ghi=tmy_data.GHI,
solar_zenith=solpos.apparent_zenith)
diffuse_irrad['Klucher'] = pvlib.irradiance.klucher(surface_tilt, surface_azimuth,
dhi=tmy_data.DHI,
ghi=tmy_data.GHI,
solar_zenith=solpos.apparent_zenith,
solar_azimuth=solpos.azimuth)
diffuse_irrad['Reindl'] = pvlib.irradiance.reindl(surface_tilt,
surface_azimuth,
dhi=tmy_data.DHI,
dni=tmy_data.DNI,
ghi=tmy_data.GHI,
dni_extra=dni_extra,
solar_zenith=solpos.apparent_zenith,
solar_azimuth=solpos.azimuth)
Calculate yearly, monthly, daily sums.
yearly = diffuse_irrad.resample('A', how='sum').dropna().squeeze() / 1000.0 # kWh
monthly = diffuse_irrad.resample('M', how='sum', kind='period') / 1000.0
daily = diffuse_irrad.resample('D', how='sum') / 1000.0
/Users/holmgren/miniconda3/envs/pvlibfx36/lib/python3.6/site-packages/ipykernel_launcher.py:1: FutureWarning: how in .resample() is deprecated the new syntax is .resample(...).sum() """Entry point for launching an IPython kernel. /Users/holmgren/miniconda3/envs/pvlibfx36/lib/python3.6/site-packages/ipykernel_launcher.py:2: FutureWarning: how in .resample() is deprecated the new syntax is .resample(...).sum() /Users/holmgren/miniconda3/envs/pvlibfx36/lib/python3.6/site-packages/ipykernel_launcher.py:3: FutureWarning: how in .resample() is deprecated the new syntax is .resample(...).sum() This is separate from the ipykernel package so we can avoid doing imports until
ax = diffuse_irrad.plot(title='In-plane diffuse irradiance', alpha=.75, lw=1)
ax.set_ylim(0, 800)
ylabel = ax.set_ylabel('Diffuse Irradiance [W]')
plt.legend()
<matplotlib.legend.Legend at 0x1191b00b8>
diffuse_irrad.describe()
Perez | Hay-Davies | Isotropic | King | Klucher | Reindl | |
---|---|---|---|---|---|---|
count | 8759.000000 | 8759.000000 | 8759.000000 | 8759.000000 | 8759.000000 | 4578.000000 |
mean | 55.404468 | 52.432929 | 49.100286 | 53.073101 | 53.620056 | 100.715271 |
std | 80.441611 | 75.458356 | 72.136293 | 76.342443 | 78.797163 | 78.428181 |
min | 0.000000 | 0.000000 | 0.000000 | 0.000000 | 0.000000 | 0.000000 |
25% | 0.000000 | 0.000000 | 0.000000 | 0.000000 | 0.000000 | 39.033711 |
50% | 3.732051 | 3.732051 | 3.732051 | 4.009665 | 3.732051 | 87.265688 |
75% | 95.390948 | 91.321869 | 81.172105 | 91.777292 | 90.936414 | 145.523600 |
max | 580.694617 | 533.102519 | 523.420126 | 538.809780 | 544.508380 | 535.970735 |
diffuse_irrad.dropna().plot(kind='density')
<matplotlib.axes._subplots.AxesSubplot at 0x119a0c1d0>
Daily
ax_daily = daily.tz_convert('UTC').plot(title='Daily diffuse irradiation')
ylabel = ax_daily.set_ylabel('Irradiation [kWh]')
Monthly
ax_monthly = monthly.plot(title='Monthly average diffuse irradiation', kind='bar')
ylabel = ax_monthly.set_ylabel('Irradiation [kWh]')
Yearly
yearly.plot(kind='barh')
<matplotlib.axes._subplots.AxesSubplot at 0x1149b9da0>
Compute the mean deviation from measured for each model and display as a function of the model
mean_yearly = yearly.mean()
yearly_mean_deviation = (yearly - mean_yearly) / yearly * 100.0
yearly_mean_deviation.plot(kind='bar')
<matplotlib.axes._subplots.AxesSubplot at 0x114af2710>