Variables and style rules

Bold variables need to be discussed.

variable	description	comment
tz or timezone	timezone	jforbess: shrug
latitude	latitude
longitude	longitude
dni	direct normal irradiance
dni_et	direct normal irradiance at top of atmosphere (extraterrestrial)	uvchik: Is 'et' obvious? Or better something like 'extra' oder 'extrat'? wholmgren: maybe extra is better. jforbess: agree extra is better
dhi	diffuse horizontal irradiance
ghi	global horizontal irradiance
aoi	angle of incidence
aoi_projection	cos(aoi)
airmass	airmass
airmass_relative	relative airmass
airmass_absolute	absolute airmass
poa_ground_diffuse	in plane ground reflected irradiation
poa_direct	direct/beam irradiation in plane
poa_diffuse	total diffuse irradiation in plane. sum of ground and sky diffuse.
poa_global	global irradiation in plane. sum of diffuse and beam projection.
poa_sky_diffuse	diffuse irradiation in plane from scattered light in the atmosphere (without ground reflected irradiation)
surface_tilt	tilt angle of the surface
surface_azimuth	azimuth angle of the surface
solar_zenith	zenith angle of the sun
solar_azimuth	azimuth angle of the sun
temp_cell	temperature of the cell in Kelvin	likewise, temp_module, temp_air. jforbess: Does it have to be Kelvin? The data will never be recorded in Kelvin.
voltage_mpp	module voltage at the maximum power point	likewise: current, power. jforbess: I prefer the latter. Also, here I actually prefer v_mp, i_mp and p_mp, if that's still a possibility, but I understand if it's too far outside guidelines.