Bilal Babar

• Boström, Tobias; Babar, Bilal; Hansen, Jonas Berg & Good, Clara (2021). The pure PV-EV energy system – A conceptual study of a nationwide energy system based solely on photovoltaics and electric vehicles. Smart Energy. 1. doi: 10.1016/j.segy.2021.100001. Full text in Research Archive Show summary

  The objective of this conceptual study is to reveal the substantial potential and synergy of solar energy and electric vehicles (EVs) working together. This potential is demonstrated by studying the feasibility of a nationwide energy system solely reliant on solar energy and EVs. Photovoltaic (PV) solar energy is already an important energy source globally, but due to its intermittency it requires energy storage to balance between times of high and low production. At the same time, a global drive is underway in the transport sector: the change from internal combustion engines to EVs. Cars are in fact stationary 95% of the time, and when the vehicle is connected to the grid, the EV battery can regulate the intermittent PV source using vehicle-to-grid (V2G) technology. This paper presents a conceptual study of a pure PV-EV based energy system, with Spain as a case study. Provided that Spain’s entire fleet of 29.4 million road going vehicles is switched to EVs, the study shows that 3.45 billion m² of PV (73 m² per capita) could give Spain a completely self-reliant energy system. The theoretical study is based on a combination of measured values, simulations, and assumptions. The conclusion of the analysis is undoubtedly extraordinary, namely that an entire country like Spain can power its complete energy system solely on PV, using EVs as the only energy storage resource.

• Babar, Bilal; Luppino, Luigi Tommaso; Boström, Tobias & Anfinsen, Stian Normann (2020). Random forest regression for improved mapping of solar irradiance at high latitudes. Solar Energy. ISSN 0038-092X. 198, p. 81–92. doi: 10.1016/j.solener.2020.01.034. Full text in Research Archive
• Babar, Bilal; Graversen, Rune & Boström, Tobias (2019). Solar radiation estimation at high latitudes: Assessment of the CMSAF databases, ASR and ERA5. Solar Energy. ISSN 0038-092X. 182, p. 397–411. doi: 10.1016/j.solener.2019.02.058. Full text in Research Archive Show summary

  There is a growing demand for the estimation of solar energy potential at high latitude locations. This study compares four datasets; Cloud, Albedo, Radiation dataset Edition 2 (CLARA), Surface Solar Radiation dataset – Heliosat Edition 2 (SARAH), ECMWF Reanalysis 5 (ERA5) and Arctic System Reanalysis v2 (ASR) on high latitude locations. Global horizontal irradiance (GHI) from these datasets is compared with in-situ ground-measurements over multiple locations in Norway. The first two datasets are mainly based on satellite estimation of solar radiation, while the latter two are based on a combination of a weather-prediction model, satellite data, and other observations. The datasets are evaluated against quality-controlled in-situ measurements of solar radiation from pyranometers. Overall, CLARA, SARAH, and ERA5 show moderate errors, while those of ASR are considerably larger. Monthly averages of global horizontal irradiance have mean absolute deviation (MAD) of 5.6 Wm−2, 5.0 Wm−2, 6.8 Wm−2, and 16.1 Wm−2 for CLARA, SARAH, ERA5, and ASR, respectively. Seasonal error analysis of these datasets reveals that CLARA and SARAH have low errors in all seasons. The datasets are classified into clear-sky, intermediate-cloudiness, and overcast categories, by using two thresholds of cloudiness based on the ratio of radiation at ground to its corresponding clear-sky value (clear-sky index). The categories obtained from satellite and reanalysis data are then compared against estimates based on corresponding in-situ observations; this analysis shows that both CLARA and SARAH perform better than ERA5 and ASR for these categories. SARAH and CLARA perform similarly in all types of conditions, but a gradual increase in errors for an increase of cloudiness is observed for ERA5 and ASR. Yearly energy analysis shows that CLARA performs better than other datasets for locations above latitude 65°N, and SARAH performs better in locations below 65°N. A further analysis is performed to assess the cloud sensing abilities of ERA5. On a shorter time scale, there are errors due to inaccurate representation of clouds, however on longer time scales i.e. months and years, these errors are considerably reduced. ERA5 is observed to overestimate TCWC (the total cloud water content defined as the mass of water and ice in a cloud) in clear-sky and intermediate-cloudy categories, while in overcast category it is underestimated. Generally, an overestimation of solar radiation is observed in reanalysis and an underestimation is observed in satellite methods.

• Babar, Bilal; Graversen, Rune & Boström, Tobias (2018). Evaluating CM-SAF solar radiation CLARA-A1 and CLARA-A2 datasets in Scandinavia. Solar Energy. ISSN 0038-092X. 170, p. 76–85. doi: 10.1016/j.solener.2018.05.009. Full text in Research Archive Show summary

  Estimating/retrieving solar radiation through satellite-based remote sensing provides larger spatial coverage compared to other methods. Accurate estimates of incoming solar radiation is important when planning new solar energy installations. In addition, these estimates are also used in climate studies. Geostationary satellites are ideal for estimating solar radiation but cannot be used for high latitudes because of an unfavourable viewing angle; however, polar-orbiting satellites provide an alternative. CLoud, Albedo RAdiation edition 2 (CLARA-A2) is the latest retrieval product of cloud properties, surface albedo and surface solar radiation by Satellite Application Facility on Climate Monitoring (CM-SAF) based on Advance Very High Resolution Radiometer (AVHRR) observations from polar orbiting satellites. This data set covers the whole earth and provides daily and monthly averages. In this study, we have evaluated the CLARA-A2 data set and the previous version CLARA-A1 to in-situ high-quality observations from specific locations in Scandinavia, with a focus on solar radiation at high latitudes. The results show that both datasets perform within the target accuracies of CM-SAF, although the new data points, which were previously not available in CLARA-A1 due to snow-cover and cloud differentiation, have high deviations. Nevertheless, yearly average energy estimates are more accurate in CLARA-A2 because of these new points. For Swedish locations, mean absolute deviation (MAD) of 8.1 W m⁻² and 8.7 W m⁻² for CLARA-A1 and A2 respectively were calculated for updated values. Similarly, for Norwegian locations MAD of 8 W m⁻² and 8.9 W m⁻² were calculated for CLARA-A1 and A2. Overall, for all locations MAD lies at 8.1 W m⁻² and 8.8 W m⁻² for CLARA-A1 and A2, respectively. CLARA A2 has more temporal data points than CLARA A1, however, the MAD of the new data points that were not available in CLARA-A1 are 15.2 W m⁻² and 17.7 W m⁻² for Swedish and Norwegian sites, respectively.

• Boström, Tobias; Solbakken, Kine & Babar, Bilal (2016). Correlation of wind and solar power in high-latitude arctic areas in Northern Norway and Svalbard. Renewable Energy and Environmental Sustainability. ISSN 2493-9439. 1, p. 42–42. doi: 10.1051/rees/2016027. Full text in Research Archive
• Babar, Bilal & Boström, Tobias (2016). Estimating solar irradiation in the Arctic. Renewable Energy and Environmental Sustainability. ISSN 2493-9439. 1. doi: 10.1051/rees/2016048. Full text in Research Archive Show summary

  Solar radiation data plays an important role in pre-feasibility studies of solar electricity and/or thermal system installations. Measured solar radiation data is scarcely available due to the high cost of installing and maintaining high quality solar radiation sensors (pyranometers). Indirect measured radiation data received from geostationary satellites is unreliable at latitudes above 60 degrees due to the resulting flat viewing angle. In this paper, an empirical method to estimate solar radiation based on minimum climatological data is proposed. Eight sites in Norway are investigated, all of which lie above 60 N. The estimations by the model are compared to the ground measured values and a correlation coefficient of 0.88 was found while over all percentage error was −1.1%. The proposed models is 0.2% efficient on diurnal and 10.8% better in annual estimations than previous models.

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• Babar, Bilal & Boström, Tobias (2016). Uncertainties in ECMWF solar radiation data at high latitude Prospects of using Era interim above 60N. Full text in Research Archive

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