DOI: 10.5061/dryad.zcrjdfn9m
title: Girasol, a sky imaging and global solar irradiance dataset

description: The energy available in Micro Grid (MG) that is powered by solar energy is
 tightly related to the weather conditions in the moment of generation.
 Very short-term forecast of solar irradiance provides the MG with the
 capability of automatically controlling the dispatch of energy. We propose
 to achieve this using a data acquisition systems (DAQ) that simultaneously
 records sky imaging and Global Solar Irradiance (GSI) measurements, with
 the objective of extracting features from clouds and use them to forecast
 the power produced by a Photovoltaic (PV) system. The DAQ system is
 nicknamed as the Girasol Machine (Girasol means Sunflower in
 Spanish). The sky imaging system consists of a longwave infrared (IR)
 camera and a visible (VI) light camera with a fisheye lens attached to it.
 The cameras are installed inside a weatherproof enclosure that it is
 mounted on an outdoor tracker. The tracker updates its pan an tilt every
 second using a solar position algorithm to maintain the Sun in the center
 of the IR and VI images. A pyranometer is situated on a horizontal support
 next to the DAQ system to measure GSI. The dataset, composed of IR images,
 VI images, GSI measurements, and the Sun's positions, has been tagged
 with timestamps.
description: We built a system composed of VI and IR solar radiation cameras,
 a tracking system, anda pyranometer, to collect the data. A weatherproof
 enclosure contains the two USB cameras,and it is mounted on top of two
 servomotors. The cameras are connected to a motherboard thatruns a solar
 tracking algorithm. This motherboard is placed inside of a different
 weatherproofenclosure together with a router, a servomotor control unit, a
 data storage system, plus theirrespective power supplies. The enclosure’s
 degree of protection is IP66. This is an internationalstandard utilized
 for electronic equipment that provides protection against dust and
 water. The tracking system and DAQ software is
 currently operative. The software was programmed in Python 2. The system
 is placed on the top roof area of the Mechanical Engineer-ing building at
 UNM central campus (35.0821,−106.6259). The DAQ sessions can be
 visuallymonitored through a webpage. All devices were interconnected via a
 LAN network built by DHCP server.
description: The repository has available recordings of the solar cycle from
 244 days of 3 years. The total amount of data is 110Gb. The sampling
 interval of the cameras is 15 seconds and the observation period is when
 the Sun's elevation angles is higher than 15°. There are
 approximately 1,200 to 2,400 captures per day from each camera depending
 on the day of the year. VI images are 16
 bits with resolution 450 x 450, intensity channel only. Approx. 240KB per
 frame. Between 200 MB to 400 MB per day depending on the amount of images
 in the directory. Images are saved in .png compress-less format in the
 directory   */visible. The image are named by the UNIX time in seconds. 
    IR images are 16 bits with resolution 60 x 80.
 Approx. 8KB per frame. 20MB per day roughly constant. Images are saved in
 .png compress-less format in the directory */infrared. The image are named
 by the UNIX time in seconds. The pyranometer is
 sampled from 4 to 6 times per seconds. The measures are saved in the
 directory */pyranometer in .csv files named with their date (yyyy_mm_dd),
 approx. 4,500KB to 7,500KB per file. The files contain unix time in the
 first column and GSI in W/m<sup>2</sup> in the second
 column.  The Sun position files are generated out of
 the time recorded in the pyranometer files. The positions are saved in the
 directory */sun_position in .csv files named with their date (yyyy_mm_dd),
 approx. 6,500KB to 11,500KB per file. The files contain the unix time in
 the first column, elevation angle in the second column, and azimuth angle
 in the third column, all of them computed with full precision unix
 time. The weather station sample interval is 10
 minutes. Linear interpolation was applied to match the sampling interval
 of the pyranomter. The weather station files are saved in the directory
 */weather_station in .csv files named with their date (yyyy_mm_dd), approx
 14.3MB top 25.4MB per file. The files are organized by columns which
 contain from left to right: unix time, temperature in °C, dew point in °C,
 atmospheric pressure in mmHg, wind direction in radians, wind velocity in
 mile/s and relative humidity in %.