Model solar insolation on a horizontal surface (W/m2 == J/s/m2) as in http://education.gsfc.nasa.gov/experimental/July61999siteupdate/inv99Project.Site/Pages/solar.insolation.html

Usage

calc_solar_insolation(
  app.solar.time,
  latitude,
  max.insolation = convert_PAR_to_SW(2326),
  format = c("degrees", "radians"),
  attach.units = deprecated()
)

Arguments

app.solar.time: POSIXct vector of date-time values in apparent solar time, e.g., as returned by convert_UTC_to_solartime(..., time.type="apparent solar")
latitude: numeric value or vector indicating the site latitude in decimal degrees (never radians or deg-min-sec, no matter what format is) between -90 (South Pole) and 90 (North Pole).
max.insolation: insolation rate at solar noon, W/m2 == J/s/m2. varies greatly with atmospheric conditions
format: The format of both the input and the output. May be "degrees" or "radians".
attach.units: (deprecated, effectively FALSE in future) logical. Should the returned vector be a unitted object?

Examples

insdf <- data.frame(
  lat=rep(c(0,20,40,60), each=48*4),
  date=rep(as.Date(sprintf('2004-%d-15', rep(c(1,4,7,10), each=48)), tz='UTC'), times=4),
  hour=rep(seq(0,23.5,0.5), times=4*4)
)
insdf <- transform(insdf, datetime=lubridate::with_tz(as.POSIXct(date), 'UTC') +
  as.difftime(hour, units='hours'))
insdf <- transform(insdf, date=as.character(date))
insdf <- transform(insdf, ins=calc_solar_insolation(datetime, lat))
if (FALSE) {
library(ggplot2)
ggplot(insdf, aes(color=date, y=ins, x=hour)) +
  geom_line() + facet_wrap(~lat) +
  ggtitle('solar insolation by latitude (panels) and day of year (colors)')
}