Establishment of Traceability of Photovoltaic Devices in Thailand

As Thailand is located in tropical zone near the equator, solar energy is the primary renewable energy source in the country. The Thai government has been actively promoting the use of renewable energy to reduce dependence on fossil fuels and to address environmental concerns. According to the Alternative Energy Development Plan (AEDP2024), the goal is to support the use of over 41,000 MW of solar energy by 2037. It has been estimated however that for each percentage point of uncertainty between the predicted to actual energy yield by photovoltaics equates to a financial uncertainty worth $410 M. Currently, only photovoltaic systems, such as solar farms, solar floating and solar rooftops, are used for electricity production. Therefore, the demand for solar panels will be dramatically increased in the near future. Traditionally, solar panels were sold based on ‘peak power’ output calculated under standard test conditions (STC). Therefore, all solar panels must undergo testing to confirm their performance at STCs as claimed. This can be done by using a measurement system consisting of a solar simulator, an I-V measuring unit and a reference solar cell. However, all manufacturers or assemblers of solar cells in Thailand must send reference solar cells abroad for calibration, as there is no traceable calibration of solar cell efficiency measurements in the country. Therefore, the National Institute of Metrology Thailand (NIMT) needs to develop standards for calibrating such instruments. Recently, NIMT has developed a facility to measure the efficiency of solar cells by measuring their differential spectral responsivity (DSR). In principle, the spectral responsivity of the reference solar cell under test is simultaneously measured under the bias light against a reference detector, traceable to SI via the cryogenic radiometer at Physikalisch-Technische Bundesanstalt (PTB) in Germany. So far, the developed facility can be used to calibrate reference solar cells of 2 x 2 inches size including world photovoltaic scale (WPVS)-type reference solar cells with the measurement uncertainty of 1.0%. When the spectral responsivity of solar cells is known, then the spectral mismatch correction can be calculated. Additionally, a steady-state solar simulator class AAA with I-V measuring unit has been procured to test the I-V curve of secondary reference solar cells up to 6 x 6 inches to meet the demand for secondary level calibration. In the future, the calibration system will be upgraded to a primary calibration system, and also extended to calibrate reference solar cells of 6 x 6 inches. Moreover, the traceability will be changed to SI via an own cryogenic radiometer at NIMT. Not only in Thailand, NIMT aims to provide the calibration services for all PV manufacturers in southeast Asia country i.e. Vietnam, Malaysia and Indonesia. Therefore an international comparison with other NMIs with already established will be required in order to verify our calibration capabilities.