When we think of measuring instruments applied to the generation of electrical energy, we usually think only of electrical quantities such as voltage, current, resistance and power. However, when we deal with renewable energy, such as solar energy (photovoltaic, solar thermal and thermal), we must always think about measuring the source, in this case solar radiation.
Measuring global solar radiation, considering both the direct and diffuse components, on the Earth's surface is of great importance for studying the influence of climatic and atmospheric conditions. The history of these measurements determines the electrical potential that can be generated, thus enabling the installation of generation systems (photovoltaic, solar thermal or thermal) in a given region, ensuring maximum use throughout the year.
In addition to its potential, this instrumentation is of great value in controlling generation efficiency and maintaining the entire system. There is a wide variety of equipment for these measurements that are classified by the WMO (World Meteorological Organization) and also by ISO 9060 (International Standard Organization).
In Brazil, for some specific applications such as qualification in electricity auctions and granting of power generating plants, both EPE (Energy Research Company) and ANEEL (National Electric Energy Agency) have their own resolutions and guidelines on how these measurements should be carried out and what equipment should be used.
Outside of auctions – as in distributed generation, for example – there is no specific national standardization regarding the measurements of these environmental variables, but evaluating generation potentials through local measurements can bring greater security to both installation companies and owners. of the plant, so we can be guided by IEC 61724-1 (International Electrotechnical Commission) of 2017.
It is important to know that although the “types” and classifications of equipment may vary according to the level of generation, their use is always relevant, even in domestic projects, distributed generation, micro/mini-generation and large centralized plants. Below, we show some instruments for measuring solar radiation and their most frequent use.
Pyranometer (GHI/DHI/POA)
Solar radiation meter with primary sensor consisting of a thermopile. Application: Measurement of global radiation (both for the horizontal plane and the inclined plane). When associated with a suitable accessory, such as a “sun tracker” or “shadow ring”, it can also be used to measure diffuse radiation.
Pyrheliometer (DNI)
Spectroradiometers
Meter of spectral bands incident on solar radiation. Application: Qualify solar radiation, specifying the spectral bands.
UV Meter
Ultraviolet radiation (UV) meter, normally UVA, UVB and UVE. Application: Determine the amount of UV radiation.
Pyrgeometer
Atmospheric infrared radiation meter. Application: Determine the amount of longwave (infrared) radiation.
Albedometer
Albedo radiation meter, which has two pyranometers at 180°, normally one pointing towards the earth and the other pointing towards the sky. Application: Determine the amount of longwave (infrared) radiation.
Net-Radiometer
Radiation balance meter, which has two pyranometers and two pyrgeometers at 180°, normally one pyranometer and one pyrgeometer pointing towards the earth and another pyranometer and another pyrgeometer pointing towards the sky. Application: Determine the amount of solar radiation reflected by the surface, including infrared radiation (horizontal plane).
Heliograph and “Sunshine Duration”
Sun tracker
Electromechanical system that follows the trajectory of the Sun, using a set of motors specially designed to attach various sensors, such as pyranometers and pyrheliometers. Application: Associated with the appropriate sensors, it allows measurements of diffuse radiation, direct radiation and also global radiation.
Side shadow ring
Accessory to be used with a pyranometer. Application: Measurement of diffuse radiation when used in conjunction with a pyranometer.
Photo-diode radiometer
Equipment to measure solar radiation in narrower and more specific spectral bands. Application: Efficiency measurement in mono/polycrystalline photovoltaic modules.
Curve tracer
Equipment for plotting or checking the IV curve in photovoltaic module associations. Application: Maintenance of photovoltaic generation systems.
Portable meters
Equipment for various measurement functions, such as global solar radiation, temperature, inclination angle, direction (compass) and electrical quantities. Application: Measurement of thermal and photovoltaic potential for small installations.
References
- WMO Guide to Meteorological Instruments and Methods of Observation, 2008 Edition, Updated 2010
- S. Pless; M. Deru; P. Torcellini; S. Hayter – Procedure for Measuring and Reporting the Performance of Photovoltaic Systems in Buildings, Technical Report NREL/TP-550-38603 October 2005
- FC Treble – EUR 6423 Standard procedures for terrestrial photovoltaic performance measurements, Joint Research Center 1979
- Eko Instruments
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