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Abstract We present the astrometric calibration of the Beijing–Arizona Sky Survey (BASS). The BASS astrometry was tied to the International Celestial Reference Frame via the Gaia Data Release 2 reference catalog. For effects that were stable throughout the BASS observations, including differential chromatic refraction and the low charge transfer efficiency of the CCD, we corrected for these effects at the raw image coordinates. Fourth-order polynomial intermediate longitudinal and latitudinal corrections were used to remove optical distortions. The comparison with the Gaia catalog shows that the systematic errors, depending on color or magnitude, are less than 2 milliarcseconds (mas). The position systematic error is estimated to be about −0.01 ± 0.7 mas in the region between 30° and 60° of decl. and up to −0.07 ± 0.9 mas in the region north of decl. 60°. 

Energy storage is increasingly important for a diversity of applications. Batteries can be used to store solar or wind energy providing power when the Sun is not shining or wind speed is insufficient to meet power demands. For large scale energy storage, solutions that are both economically and environmentally friendly are limited. Flow batteries are a type of battery technology which is not as well-known as the types of batteries used for consumer electronics, but they provide potential opportunities for large scale energy storage. These batteries have electrochemical recharging capabilities without emissions as is the case for other rechargeable battery technologies; however, with flow batteries, the power and energy are decoupled which is more similar to the operation of fuel cells. This decoupling provides the flexibility of independently designing the power output unit and energy storage unit, which can provide cost and time advantages and simplify future upgrades to the battery systems. One major challenge of the existing commercial flow battery technologies is their limited energy density due to the solubility limits of the electroactive species. Improvements to the energy density of flow batteries would reduce their installed footprint, transportation costs, and installation costs and may open up new applications. This review will discuss the background, current progress, and future directions of one unique class of flow batteries that attempt to improve on the energy density of flow batteries by switching to solid electroactive materials, rather than dissolved redox compounds, to provide the electrochemical energy storage.