What is it about?
One of the major barriers to increasing the solar energy share is its intermittency. Solar energy’s large variability in different timescales is driven by natural solar astronomical cycles and weather. Ground-based measurements are important for evaluating variability at high temporal resolutions, but they are the only representative of small areas close to the measurement sites. Satellite observations come as an alternative to analysis over large areas. However, they have coarse temporal and spatial resolutions. Here, we first evaluated the variability in different time steps, using one-year of 1-min resolution ground-based irradiance measured at three sites located in different Brazilian climate regimes. The results showed that more humid months have the largest variability. By contrast, the driest locations presented more variability on short timescales, probably due to the presence of a large number of clouds, even in very dry conditions. We also compared observations of solar irradiance variability at the surface with satellite cloud variability, with 30-min resolution. For the same timescale, the results were promising, with a Pearson correlation of up to 0.93, depending on the site. However, when the frequency of the solar irradiance measurements increased, the correlation decreased. A solution may be to analyze a larger pixel area around the sites. Another option would be the use of downscaling methods. This topic, however, will be the subject of the future study. The most important result achieved in this study was the development of a simple methodology for evaluating the surface solar irradiance variability using cloud cover obtained from visible satellite imagery.
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Why is it important?
The results can be of concern to Brazilian energy planning since the cloud cover variability in the Brazilian Northeastern region is the most prominent region for concentrated solar power generation.
Perspectives
This study was a first step towards increasing understanding of solar irradiance variabilities induced by clouds in some Brazilian climate zones. However, it is important to continue advancing the investigation in other climate zones. An example of one important area which needs to be studied is the Midwest region of Brazil. In this area, a lot of burning of biomass events take place every year during the May to September dry season and release high loads of aerosols into the atmosphere, affecting the cloud cover determination by satellite. The Brazilian Northern region is another important area which needs to be investigated due to the presence of the Amazon rainforest and its very hot and humid tropical climate. The methodology can be useful for other regions, but it is important to investigate the relationship between cloud cover data provided by satellite images and solar irradiance at the surface. Cloud detection performance can be affected by different field of views each satellite provides depending on the region of interest. Future research might lead to the development of tools and services which could provide data on the intermittency of solar energy based on the cloud cover data acquired by geostationary satellites. Such a tool might contribute to identifying the best places for installing solar power technologies and would be of great importance to energy planning in Brazil, and allow for a larger share of solar energy on the electricity grid.
Dr Fernando Ramos Martins
Universidade Federal de Sao Paulo
Read the Original
This page is a summary of: Analysis of intra-day solar irradiance variability in different Brazilian climate zones, Solar Energy, June 2018, Elsevier,
DOI: 10.1016/j.solener.2018.04.005.
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