Surface measurement of total solar and ultraviolet irradiance and ancillary meteorological data at the South-West Indian Ocean Solar network (IOS-net) stations

The observational data described in this article are collected at several locations in the South-West Indian Ocean (SWIO). Platforms equipped with radiometers and a weather transmitter, and located over Comoros, Madagascar, Mauritius, La Réunion and Seychelles islands, are used to measure incident global and diffuse shortwave radiation and incident global UV A + B-band radiation along with air temperature, relative humidity, wind speed and direction, air pressure and rainfall amount with a sampling frequency of 0.1 Hz. The data are stored as 1-min averages and automatically transmitted to the LE2P-ENERGY lab at the University of La Réunion. The dataset is hosted on the website: https://galilee.univ-reunion.fr, and is uploaded to Zenodo repository. Such a dataset will help in providing information related to solar energy forecasting and assessment for solar energy implementation at a regional and national level in the SWIO.


a b s t r a c t
The observational data described in this article are collected at several locations in the South-West Indian Ocean (SWIO). Platforms equipped with radiometers and a weather transmitter, and located over Comoros, Madagascar, Mauritius, La Réunion and Seychelles islands, are used to measure incident global and diffuse shortwave radiation and incident global UV A + B -band radiation along with air temperature, relative humidity, wind speed and direction, air pressure and rainfall amount with a sampling frequency of 0.1 Hz. The data are stored as 1-min averages and automatically transmitted to the LE 2 P-ENERGY lab at the University of La Réunion. The dataset is hosted on the website: https: //galilee.univ-reunion.fr , and is uploaded to Zenodo repository. Such a dataset will help in providing information related to solar energy forecasting and assessment for solar energy implementation at a regional and national level in the SWIO.

Value of the Data
• Accurate knowledge of the quantity and spatiotemporal variability of the solar resource at given locations needs to be addressed to enable integration of high levels of solar power (photovoltaic or PV systems) into the national utility grids. This is especially the case for the South-West Indian Ocean (SWIO) Islands (Comoros, La Réunion, Madagascar, Mauritius and Seychelles) where accurate ground-based Surface Solar Radiation (SSR) measurements with high temporal resolution (~1 min) remain sporadic. Given the objective of these islands to become self-sufficient for their electricity with renewable energies, solar-energy assessment and forecasting are essential for solar energy project policy and planning. • Global horizontal irradiance (GHI) and diffuse horizontal irradiance (DHI) are helpful for translation of the GHI to in-plane irradiance as required by the majority of PV systems. • Single or combined use of the data allows for estimation of PV output power -either indirectly by means of a physical model that converts the measured global horizontal irradiance into electricity, or directly by using the meteorological data (air pressure, temperature, relative humidity, wind, rain) as input variables to machine learning algorithms. Data contained herein also allows for analysis of PV module performance losses due to temperature, relative humidity and UV irradiation under different climatic conditions. • Data contained herein allows for comparison of ground-based measurements of solar irradiance on the SWIO Islands against values derived from satellite observations or simulated with regional climate models.

Data Description
The data are collected at the radiometric stations of the network developed by the LE 2 P-ENERGY lab in the SWIO since the early 2010s ( [1] ). The dataset readily available with this article includes observed meteorological and SSR data from 10 sites on the insular territories covered by the Indian Ocean Commission: Comoros, La Réunion, Madagascar, Mauritius and Seychelles ( Fig. 1 ). The data are gathered since the end of 2019 at all these sites except Bras d'Eau in Mauritius (2015), Plaine Corail in Rodrigues (2017), and La Plaine des Palmistes in La Réunion (2018; see also Table 1 ) using multi-instrumented sensor platforms as displayed in Fig. 2 . The SSR data are presented in terms of global and diffuse shortwave and global UV-A + B irradiances, and are expressed in W/m 2 . The meteorological data include air temperature (in °C), air relative humidity (in %), wind speed (in m/s) and direction (in °), air pressure (in hPa) and rainfall amount (in mm). The data, with sampling frequency of 0.1 Hz, are stored as 1-min Table 1 Location of the 10 IOS-net stations described in the present paper.    CF-convention metadata. Ultimately, the data collected by the LE 2 P-ENERGY lab at all the sites of its network will be made public through this TDS. In addition, the NetCDF dataset has also been uploaded on the international data repository Zenodo: https://zenodo.org . While the dataset on Zenodo is updated on a yearly basis (that is on the 1 st of January of each year), the TDS offers the most up to date version of the dataset and includes data recording up to the day before.

Experimental Design, Materials, and Methods
The data are obtained from 10 sites over the SWIO ( Fig. 1 and Table 1 ). The special locations of the measuring sites on the islands of the SWIO make those sites challenging places for solar energy studies and applications. Each measurement station has roughly the same design including autonomous power supply based on renewable (solar) energy. The dataset was obtained using ( Table 2 ): -a Delta-T Devices SPN1 pyranometer which simultaneously measures GHI and DHI (in W/m 2 ), -a Vaisala WXT530 Series weather transmitter located at a distance of 1.5 m from the pyranometer, which measures air pressure (in hPa), air temperature (in °C), relative humidity (in %), wind speed (in m/s) and direction (in °), and rainfall (in mm), mounted on a structure at ground level (2-m high; Fig. 2 ). Except for Bras d'Eau (Mauritius), Plaine Corail (Rodrigues) and La Plaine des Palmistes (La Réunion), the measurement stations also include a Kipp&Zonen SUV5 UV radiometer which measures the global UV A + B -band irradiance (in W/m 2 ). All sensors are connected to a Campbell Scientific CR10 0 0X datalogger for data collection. Data transmission to the server is ensured via TCP/IP protocol or GPRS network. Data presented herein are raw data. Thus, we highly recommend that all users perform their own quality checks of the data before using them (e.g., [3] ).

Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships, which have, or could be perceived to have, influenced the work reported in this article.