In response to the COVID-19 outbreak, the Spanish government declared a State of Alarm that lasted from the 14 th of March 2020 to the 21 st of June 2020. The main measure put in place was a lockdown that suspended most of the activities and the movements in the entire country. The present work investigates the effects of this anti COVID-19 measure on the national electrical energy sector. The lockdown is found to have caused an average decrease in electricity demand of 11%, followed by a more severe drop in electricity prices of 0.09 €/MWh per each GWh of missed daily demand. These led to an average turnover reduction of 6.1 million € per day for the electricity sector. The losses are found to be unevenly distributed across the different power technologies of the energy mix. In particular, the performance of photovoltaics, the fastest growing technology in the country, is investigated in-depth. During the lockdown, for the first time, photovoltaics provided more than 9% of the national electricity, more than double than the previous annual maximum. However, despite the expectations related to the improved air quality, the average capacity factor of photovoltaic systems is found to be lower than in the previous years. The reasons behind this are investigated through the analysis of the behaviors of the environmental factors affecting this technology's performance.

This study presents indoor and field validation results for two versions of the "DUSST" optical soiling sensor, intended to be a low-cost and low-maintenance device for measuring photovoltaic soiling losses. Indoor testing covers irradiance calibration and temperature dependencies, which are necessary to achieve high accuracy, low uncertainty field measurements. Field testing includes an array of different environments including Saudi Arabia, California, Utah, and Colorado. DUSST versions include a configuration with a 530-nm light emitting diode (LED) (discussed in previous work) and a unit with seven white LEDs and a polycarbonate collimating optic.The new design increases light intensity fivefold and demonstrates a single linear calibration coefficient is effective to measure soiling losses as high as 75%. Field data from Utah and California demonstrate that daily soiling loss measurements and soiling rate calculations closely match both reference cell and full-size module measurements of soiling losses and soiling rates. Corrective methods employed on the Utah DUSST sensor suggest that it is possible to achieve measurement errors as low as ±0.1% at two standard deviations. Field data from both Colorado and Saudi Arabia demonstrate that LED lens soiling can occur and that further design optimizations are needed. The lesson learned from all the field deployment locations suggests directions for future design improvements.

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