Type: Package
Title: Constructing Suns-Voc from Outdoor Time-Series I-V Curves
Version: 0.1.2
Maintainer: Tyler J. Burleyson <tjb152@case.edu>
Description: Suns-Voc (or Isc-Voc) curves can provide the current-voltage (I-V) characteristics of the diode of photovoltaic cells without the effect of series resistance. Here, Suns-Voc curves can be constructed with outdoor time-series I-V curves [1,2,3] of full-size photovoltaic (PV) modules instead of having to be measured in the lab. Time series of four different power loss modes can be calculated based on obtained Isc-Voc curves. This material is based upon work supported by the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy (EERE) under Solar Energy Technologies Office (SETO) Agreement Number DE-EE0008172. Jennifer L. Braid is supported by the U.S. Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy administered by the Oak Ridge Institute for Science and Education (ORISE) for the DOE. ORISE is managed by Oak Ridge Associated Universities (ORAU) under DOE contract number DE-SC0014664. [1] Wang, M. et al, 2018. <doi:10.1109/PVSC.2018.8547772>. [2] Walters et al, 2018 <doi:10.1109/PVSC.2018.8548187>. [3] Guo, S. et al, 2016. <doi:10.1117/12.2236939>.
License: BSD_3_clause + file LICENSE
Encoding: UTF-8
LazyData: true
LazyDataCompression: xz
RoxygenNote: 7.1.1
Depends: R (≥ 3.5.0)
Imports: ddiv, magrittr, stringr, dplyr, purrr, data.table, rlang
Suggests: testthat (≥ 2.1.0), knitr, rmarkdown, ggplot2
VignetteBuilder: knitr
NeedsCompilation: no
Packaged: 2021-04-29 15:48:04 UTC; tylerb
Author: Menghong Wang ORCID iD [aut], Tyler J. Burleyson ORCID iD [aut, cre], Jiqi Liu ORCID iD [aut], Alan J. Curran ORCID iD [aut], Abdulkerim Gok ORCID iD [aut, ctb], Eric J. Schneller ORCID iD [aut], Kristopher O. Davis ORCID iD [aut], Jennifer L. Braid ORCID iD [aut], Roger H. French ORCID iD [aut, cph]
Repository: CRAN
Date/Publication: 2021-04-30 09:30:06 UTC

Create x-by-x Psuedo-IV Curves

Description

This function moves through IV curve data x-by-x, generating psuedo IV curves and binding them together into the output.

Usage

IVXbyX(df, corr_temp = "median", N_c)

Arguments

df

Dataframe containing IV data. Typically, a raw dataframe after filtering by current accuracy based on plot of irradiance vs. temperature. Within this package environment, use read_df_raw to filter the dataset and generate period index.

corr_temp

The temperature for all I-V features to standardize to. Pass the string "median" in order for the function to automatically calculate the median module temperature at 1 sun irradiance and use it, or input a number directly, the temperature unit should be Celsius.

N_c

Number of cells in series; the total number of cells in the system.

Value

Psuedo-IV Curve data with features extracted and evaluation parameters of fitting grouped by time periods of set length.

Examples


df <- read_df_raw(df_wbw,0.02,7)
df_full <- IVXbyX(df, corr_temp = "median", 60)

Convert From Hbase Char String to Dataframe

Description

This function parses the I-V curve string and creates an additional dataframe with current and voltage columns from it.

Usage

char_to_df(str)

Arguments

str

The character string to be converted to a Dataframe.

Value

Dataframe containing IV curve data.

Examples

char_to_df(df_wbw$ivdf[1])

Convert From Dataframe to Hbase Char String

Description

The companion function to this one, char_to_df, parses this string and creates an additional dataframe from it. This function works the other way, converting that dataframe back to a character string.

Usage

df2chr(df)

Arguments

df

The dataframe, typically named "ivdf", to be converted.

Value

Returns a character string representing an IV curve.

Examples

df2chr(char_to_df(df_wbw$ivdf[1]))

1 Year of raw outdoor IV curve data.

Description

This dataframe contains 1 year of anonymous raw outdoor time-series IV curve data.

Usage

df_wbw

Format

Dataframe with 4140 objects in 10 variables:

tmst

A local PosixCT Timestamp

ivdf

IV Dataframe

modt

Module Temperature

poa

Plane of array (POA) irradiance

isc

Extracted Short Circuit Current by ddiv

voc

Extracted Open Current Voltage by ddiv

rs

Extracted Rs (series resistance) by ddiv

pmp

Extracted Maximum Power by ddiv

imp

Extracted Current at Maximum Power Point

vmp

Extracted Voltage at Maximum Power Point

Obtain 1-sun Isc Value

Description

This function is used internally by IVxbyx and others for the calculation of 1-sun Isc values based on Isc and Irradiance measurements.

Usage

isc.1sun(isc, Irrad)

Arguments

isc

Isc values

Irrad

Irradiance values

Value

Returns a calculated Isc value at 1-sun Irradiance.

Examples

isc_1sun <- isc.1sun(df_wbw$isc, df_wbw$poa)

Calculate Median Temperature

Description

This function calculates the median module temperature throughout the data to be used in corrections.

Usage

median_temp(df)

Arguments

df

Dataframe containing timeseries irradiance (column name must be poa) and module temperature (column name must be modt) in unit of Celsius.

Value

Returns an integer value of median reported module temperature of the data.

Examples

T_corr <- median_temp(df_wbw)

Obtain Psuedo IV Curve and other predicted IV features at reference conditions for a given week, used internally in IVxbyx function.

Description

Obtain Psuedo IV Curve and other predicted IV features at reference conditions for a given week, used internally in IVxbyx function.

Usage

p_iv.week(df, temp, N_c, isc_1sun = NULL)

Arguments

df

A dataframe containing timeseries I-V features of one period.

temp

The reference module temperature to correct the Psuedo IV curve to be, unit of the temperature should be Celsius.

N_c

Number of cells in series. Equal to the total number of cells in the system.

isc_1sun

(optional) Input an Isc 1-Sun value manually. Leave NULL to have one generated from the dataframe.

Value

Psuedo-IV Curve data with features extracted and evaluation parameters of fitting grouped for a single, given period.

Examples

df <- read_df_raw(df_wbw,0.02,7)
df_slice <- dplyr::filter(df, df$n_period == 1)
# Check that this has enough data! needs more than 10 rows to be meaningful
nrow(df_slice)
# needs median temperature
temp <- median_temp(df_wbw)
res <- p_iv.week(df_slice, temp = temp, N_c = 60)

Physical Model Power Loss Modes of Single period

Description

This function decouples power loss to different loss modes, specifically current mismatch, recombination, uniform current loss, and Rs loss, from the changes in IV features for a given period, used internally for power_loss_phys_bat function.

Usage

power_loss_phys(init_piv, init_isc1sun, init_prs, degr_row)

Arguments

init_piv

Dataframe containing current andvolatge psuedo-IV curves of initial period, calculated from the the result of p_iv.week function applied to timeseries dataframe of initial period.

init_isc1sun

1 sun isc generated from the p_iv.week output from the initial period dataframe.

init_prs

extracted rs from the psuedo-IV curve of the initial period.

degr_row

one row of output from IVXbyX function.

Value

dataframe containing information about power loss due to various power loss modes for one given period

Examples


df <- read_df_raw(df_wbw,0.02,7)
df_init <- select_init_df(df, days = 21)
init <- p_iv.week(df_init, temp = 30, N_c = 60)
init_piv <- data.frame(V = init$voc_corr, I = init$isc_1sun - init$isc)
init_piv <- dplyr::arrange(init_piv, .data$V)
init_pivf <- ddiv::IVfeature(I = init_piv$I, V = init_piv$V, crtvalb = 0.06)
init_prs <- init_pivf$Rs
init_isc1sun <- init$isc_1sun
df_full <- IVXbyX(df, corr_temp = 30, 60)
power_loss_phys(init_piv,init_isc1sun, init_prs,df_full[1,])

Physical Model Power Loss Modes

Description

This function decouples power loss to different loss modes, specifically current mismatch, recombination, uniform current loss, and Rs loss, from the changes in IV features.

Usage

power_loss_phys_bat(df_iv, init_df, corr_T = 40, N_c, ddiv_param = 0.06)

Arguments

df_iv

Dataframe containing psuedo-IV curves. Generate with IVXbyX.

init_df

Dataframe containing first several weeks of real-world IV data. Generate with select_init_df

corr_T

The temperature from which to create the correction factor. Pass only numeric values.

N_c

Number of cells in series; The total number of cells in the system.

ddiv_param

Parameter passed to ddiv::IVfeature for 'crtvalb'

Value

dataframe containing information about power loss due to various power loss modes

Examples


df <- read_df_raw(df_wbw,0.02,7)
df_init <- select_init_df(df, days = 21)
df_full <- IVXbyX(df, corr_temp = 30, 60)
res <- power_loss_phys_bat(df_full, df_init, corr_T = 30, N_c = 60)

Read in Raw Data from Dataframe

Description

Given an imported datafram of Hbase-Formatted IV curve data, this function reads in the data, filters missing temperature data, and checks for a nonzero maximum power point, in case of power loss. It resets the timestamps based on the minimum timestamp, and filters Isc values for the tracer's accuracy. Finally, a n_period counter is added to the dataframe.

Usage

read_df_raw(df, tracer_accuracy, t_period)

Arguments

df

dataframe; the IV curve data to be filtered

tracer_accuracy

The accuracy of the IV tracer used. See the device's manual to find the exact value at which Isc readings are no longer accurate.

t_period

Data period for the Psuedo-IV curves. Addded as a column to the dataframe based on the timestamp. Use units of days, i.e. daily periods should have t_period 1, weekly periods should have t_period 7, etc.

Value

df_raw, a dataframe containing the raw IV curve data

Examples

df_test <- read_df_raw(df_wbw, 1, 7) # Weekly periods
df_test <- read_df_raw(df_wbw, 1, 1) # Daily periods

Generate Initial Dataframe for power_loss_bat

Description

The power_loss_bat function makes use of a dataframe containing the first several days of psuedo-IV curves. This function creates that dataframe for the user from the raw dataframe containing IV Curve measurement data.

Usage

select_init_df(df_raw, days = 21)

Arguments

df_raw

The raw dataframe containing request input columns the same as the example df_wbw dataset and the column of day, which starts from 1 and column of n_period, which is the index of the period, decided by how many days to be grouped as one period, the column of day and n_period can be generated from the function read_df_raw

days

The number of initial days to subsample. Default: 21

Value

Subset of input dataframe within the first several days decided by the input parameter "days".

Examples

df <- read_df_raw(df_wbw, 1, 7)
df_init <- select_init_df(df, days = 21)

Correct Voc to certain reference conditions, used internally in piv_iv_week function.

Description

This method uses a physical model to correct Voc to certain reference conditions. Since indoor Suns-Voc is conducted at a steady 25C, a correction on the outdoor readings is necessary for meaningful comparison.

Usage

voc.corr(df)

Arguments

df

A dataframe time series data with columns of voc, lnSun and modt, the dataframe is converted from the request input dataframe like df_wbw by the piv_iv_week function before using voc_corr function.

Value

returns a list object of Voc model.

Examples

df <- read_df_raw(df_wbw,0.02,7)
# subset data to first period
df_slice <- dplyr::filter(df, df$n_period == 1)
N_c <- 60 # true of the example data. N_c is the number of cells in series

df_slice <- dplyr::mutate(df_slice, T_K = .data$modt + 273.15,
lnSun = 1.38e-23/1.6e-19 * N_c * .data$T_K * log(.data$isc),
isc2 = .data$isc^2,
T_lnIsc2 = .data$T_K * .data$lnSun * log(.data$isc),
rs = as.numeric(.data$rs),
expVoc = exp(-.data$voc/.data$T_K) / .data$isc,
I0 = (N_c * 1.38e-23 * .data$T_K) / (1.6e-19 * .data$isc))
voc_mod <- voc.corr(df_slice)