#!/bin/env python
# -*- coding: utf-8 -*-
# SPDX-License-Identifier: EUPL-1.2
#
# Copyright (c) 2020-2023 Marc van der Sluys - marc.vandersluys.nl
#
# This file is part of the SolarEnergy Python package, containing a Python module to do simple modelling in
# the field of solar energy. See: https://github.com/MarcvdSluys/SolarEnergy
#
# SolarEnergy has been developed by Marc van der Sluys of the Department of Astrophysics at the Radboud
# University Nijmegen, the Netherlands and the department of Sustainable energy of the HAN University of
# applied sciences in Arnhem, the Netherlands.
#
# This is free software: you can redistribute it and/or modify it under the terms of the
# European Union Public Licence 1.2 (EUPL 1.2).
#
# This software is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
# without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
# See the EU Public Licence for more details.
#
# You should have received a copy of the European Union Public Licence along with this code.
# If not, see <https://www.eupl.eu/1.2/en/>.
"""Functions for solar energy dealing with solar (PV) panels/modules.
"""
# Allow relative imports from __main__() when running this file (PEP 366):
if __name__ == '__main__' and __package__ is None:
__package__ = 'solarenergy'
from dataclasses import dataclass
[docs]
@dataclass
class SolarPanels:
"""Dataclass containing solar-panel parameters."""
# Geographic location of the solar panels:
geo_lon: float = 0.0; """Geographic longitude of the panels (rad; >0 for northern hemisphere)"""
geo_lat: float = 0.0; """Geographic latitude of the panels (rad; >0 for east of Greenwich)"""
tz: str = None; """Time zone where the solar panels sit (e.g. Europe/Berlin)"""
# Orientation of the solar panels:
az: float = 0.0; """'Azimuth' of the panel normal vector (rad; 0=S, π/2=W)"""
incl: float = 0.0; """'Zenith angle' of the panel normal vector (rad; 0=horizontal, π/2=vertical)"""
# Size and capacity of the solar panels:
area: float = 0.0; """Surface area of solar PV panels (m2; typically 1.6m2 per panel)"""
p_max: float = 0.0; """Maximum electrical power of solar PV panels or inverter (kW)"""
# Time dependence of efficiency:
eff0: float = 0.0; """Original efficiency of solar panels + inverter, at installation (0-1; e.g. 0.15 for 15%)"""
deff_dt: float = 0.0; """Linear degradation of efficiency factor over time (yr^-1; -5e-3: degrades to 90% after 20 years)"""
year: float = 2015; """Installation year (e.g. 2015.25 for 2015-04-01)"""
# Other parameters: temperature and angle dependence:
t_coef: float = -0.005; """PV temperature coefficient (/K; typically -0.005)"""
n_refr: float = 1.43; """Refractive index of PV cover (typically 1.43; air: 1.000293)"""
# Inverter model and serial number:
inv_model: str = None; """Model or type of the inverter"""
inv_sn: str = None; """Serial number of the inverter"""
name: str = None; """PV plant name"""
[docs]
def read_solar_panel_specs(cfg_file='.solar_panels.cfg', rel_to_home=True, to_rad=True):
"""Read solar-panel specifications from a configuration file.
Parameters:
cfg_file (str): Configuration file to read specs from (by default relative to home directory).
rel_to_home (bool): File path/name is relative to home directory.
to_rad (bool): Convert angles from degrees to radians (location, orientation).
Returns:
(SolarPanels): Dataclass of type SolarPanels containing the specifications.
"""
sp = SolarPanels()
# Read configuration file:
import configparser
config = configparser.ConfigParser(inline_comment_prefixes=('#')) # Allow inline comments
if rel_to_home:
from pathlib import Path as _Path
config.read(str(_Path.home())+'/'+cfg_file)
else:
config.read(str(cfg_file))
# Use fallback to allow missing sections and keys, and use the default values instead.
# Section Geographic location of the solar panels:
sp.geo_lon = config.getfloat('Location', 'geo_lon', fallback=sp.geo_lon) # Geographic longitude of the panels (rad; >0 for northern hemisphere)
sp.geo_lat = config.getfloat('Location', 'geo_lat', fallback=sp.geo_lat) # Geographic latitude of the panels (rad; >0 for east of Greenwich)
sp.tz = config.get('Location', 'timezone', fallback=sp.tz) # Timezone where the solar panels sit (e.g. Europe/Paris)
# Section Orientation of the solar panels:
sp.az = config.getfloat('Orientation', 'az', fallback=sp.az) # 'Azimuth' of the panel normal vector (rad; 0=S, π/2=W)
sp.incl = config.getfloat('Orientation', 'incl', fallback=sp.incl) # 'Zenith angle' of the panel normal vector (rad; 0=horizontal, π/2=vertical)
# Section Size and capacity of the solar panels:
sp.area = config.getfloat('Capacity', 'area', fallback=sp.area) # Surface area of solar PV panels (m2; typically 1.6m2 per panel)
sp.p_max = config.getfloat('Capacity', 'p_max', fallback=sp.p_max) # Maximum electrical power of solar PV panels or inverter (kW)
# Section Time dependence of efficiency:
sp.eff0 = config.getfloat('TimeDependence', 'eff0', fallback=sp.eff0) # Original efficiency of solar panels + inverter, at installation (0-1; e.g. 0.15 for 15%)
sp.deff_dt = config.getfloat('TimeDependence', 'deff_dt', fallback=sp.deff_dt) # Linear degradation of efficiency factor over time (yr^-1; -5e-3: degrades to 90% after 20 years)
sp.year = config.getfloat('TimeDependence', 'year', fallback=sp.year) # Installation year (e.g. 2015.25 for 2015-04-01)
# Section Other parameters: temperature and angle dependence:
sp.t_coef = config.getfloat('Other', 't_coef', fallback=sp.t_coef) # PV temperature coefficient (/K; typically -0.005)
sp.n_refr = config.getfloat('Other', 'n_refr', fallback=sp.n_refr) # Refractive index of PV cover (typically 1.43; air: 1.000293)
# Section Inverter: model and serial number:
sp.inv_model = config.get('Inverter', 'model', fallback=sp.inv_model) # Inverter model or type
sp.inv_sn = config.get('Inverter', 'sn', fallback=sp.inv_sn) # Inverter serial number
sp.name = config.get('Inverter', 'name', fallback=sp.name) # PV plant name
if to_rad:
from astroconst import d2r
sp.geo_lon *= d2r
sp.geo_lat *= d2r
sp.az *= d2r
sp.incl *= d2r
return sp
[docs]
def pv_cell_temperature(temp_a, glob_insol, v_wind, temp_c_noct=45, eta_c_noct=0.15, t_coef=-0.0045, glob_insol_noct=800, temp_a_noct=20, v_wind_noct=1, tau_alp=0.9):
"""Estimate the PV-cell temperature as a function of ambient temperature, insolation and wind velocity.
Parameters:
temp_a (float): Ambient temperature (°C or K - ensure all temperatures use the same unit).
glob_insol (float): Global projected insolation on PV cell (W/m2).
v_wind (float): Wind velocity (m/s).
temp_c_noct (float): Cell temperature for nominal operating cell temperature (NOCT; °C or K).
eta_c_noct (float): Cell/module efficiency for NOCT (-).
t_coef (float): Temperature coefficient for Pmpp and η_cell (/K).
glob_insol_noct (float): Projected global insolation on the PV module for NOCT (W/m2).
temp_a_noct (float): Ambient temperature for NOCT (°C or K).
v_wind_noct (float): Wind velocity for NOCT (m/s).
tau_alp (float): Tau alpha (τα): the optical transmission-absorption coefficient for the PV module (0-1).
Returns:
(float): PV cell temperature (°C or K).
Note:
- This follows Duffie & Beckman (2013).
- NOCT stands for normal-operation cell temperature and concerns the specifications of the PV module for
realistic conditions. If not available, use STC specs everywhere instead.
- Note that all temperatures should be either in °C or K; they should not be mixed.
"""
# Heat loss to the environment, current vs. NOCT, affected by wind:
u_l_fac = (5.7+3.8*v_wind_noct)/(5.7+3.8*v_wind) # U_L,N / U_L
temp_c = (
temp_a + ( temp_c_noct - temp_a_noct ) * u_l_fac * glob_insol/glob_insol_noct
* ( 1 - eta_c_noct/tau_alp * ( 1 - t_coef * temp_c_noct ) )
) / (
1 + ( temp_c_noct - temp_a_noct ) * u_l_fac * glob_insol/glob_insol_noct * (t_coef * eta_c_noct)/tau_alp
)
return temp_c
[docs]
def pv_efficiency(temp_c, eta_c_stc=0.15, t_coef=-0.0045, temp_c_stc=25):
"""Compute the instantaneous PV effiency for a given cell temperature.
We assume that the efficiency varies linearly with temperature.
Parameters:
temp_c (float): Temperature of the PV cell (°C or K).
eta_c_stc (float): Efficiency of PV (+inverter if desired) for standard test conditions (STC) (0-1).
t_coef (float): Temperature coefficient for P_mpp and η (/K; <0).
temp_c_stc (float): Temperature of the cells under Standard Test Conditions (°C or K, same as temp_c).
Returns:
float: Efficiency of the solar cell.
"""
eta_c = eta_c_stc * (1 + t_coef * (temp_c - temp_c_stc))
return eta_c
# Test code:
if __name__ == '__main__':
# Solar-panel data:
_sp = SolarPanels()