# New Developments and Progress in Absorption Chillers for Solar Cooling Applications
## 1 Introduction
The other recent large-scale installations were in 2017 in India (528 kW cooling capacity using 1575 m\({}^{2}\) evacuated tube collectors), Nicaragua (1023 kW cooling capacity using 4450 m\({}^{2}\) flat plate collectors), and Singapore (880 kW cooling capacity using 2472 m\({}^{2}\) flat plate collectors) [3]. Only a few solar thermal cooling systems have been installed worldwide, although there have been significant technical and economic improvements in solar collector technologies. The main obstacles to the more extensive deployment of these systems are their lack of economic competitiveness, low energy efficiency, large footprint, and operational limitations. This is mostly due to the high capital investment required, the need for compactness, and the limited working range of absorption chillers compared to the grid electricity-driven compression chiller, as well as high parasitic energy consumption and an inefficient backup system. Therefore, absorption chillers with unique technical features can be adopted to address these technical and economic obstacles and implement cost-effective and reliable solar thermal space cooling systems. Solar absorption cooling systems based on classical absorption chiller technologies have been reviewed elsewhere [5; 6; 7; 8; 9; 10] and related aspects have also been discussed [11]. These review papers focused on theoretical studies [5; 6] and experimental investigations [8] into solar heat-driven cooling systems (including absorption, adsorption, and ejector cooling systems). Moreover, [PERSON] and [PERSON] [7] reviewed and discussed the technical and economic performances of various types of solar cooling technologies (including absorption chiller-based systems) using location specific data (for central Spain and the Netherlands). Besides, the type of solar collector technologies used in these cooling systems, their integration, and the system's operation performance have been described and discussed in, for example, [PERSON] et al. [10]. However, these reviews have overlooked the current status of commercially available absorption chiller technologies, and developments in laboratory and pre-industrial absorption chiller prototypes focused on solar cooling applications. Thus, there is a gap in the literature on these aspects and new advances in absorption chiller technologies. Accordingly, the present article presents and discusses recent developments in absorption chiller technologies that are useful for the efficient and cost-effective use of solar resources for space cooling applications. These newly developed absorption chillers have key unique features compared to traditional market-available absorption chillers, namely, a small-capacity air-cooled unit; a compact water/LiBr chiller; a high-efficiency compact reversible absorption chiller for cooling and heating applications; a large temperature glide of the driving heat; efficient use of backup fossil fuel resources, and others. This article is structured as follows. Section 2 describes the layout of a typical solar absorption cooling system and its components as well as the challenges of classical absorption chillers. Section 3 discusses recently developed commercial absorption chillers with the new features. Section 4 discusses advances made in laboratory and pre-industrial absorption chiller prototypes using ammonia-based working fluids and a water/LiBr mixture with a new set of features. Section 5 considers research trends and opportunities to further improve the capacity of these absorption chiller technologies to exploit solar energy. The paper concludes with a summary of the key findings in Section 6.