## 1 Introduction  
The greatest primary energy production in the European Union (\(EU\)) in 2022 will come from fossil fuels, at around 69.65%, followed by renewable energy production, which also includes hydroelectric power plants, at around 21.34% [1]. These statistics on primary energy use run counter to the decarbonisation strategies put in place by the \(EU\) for 2030, which can be summarised by the targets set out in the Winter Package [2]: (i) a reduction in greenhouse gas emissions (40%), (ii) increasing the share of renewable energy in the final energy mix (32%), and (iii) increasing energy efficiency (32.5%). Existing renewable energy generation technologies must be improved [3] and new renewable energy technologies must be developed in order to achieve these goals. Hydropower has become a vitally important element in the transformation of the global energy system [4]. In 2021, the World Bank [5] identified hydropower as a key source of fossil fuel substitution. In accordance with their installed capacity, hydropower plants can be classified as large-scale, medium-scale, and small installed capacity hydropower projects [6, 7]. Small hydropower can be used in conditions where large-scale and medium-scale hydropower cannot be deployed, enabling the use of sustainable resources that would otherwise be unusable. Small installed capacity hydropower projects are classified into small, mini, micro, and pico hydropower plants [6, 7]. This classification depends on the country [8]. A hydropower plant with an installed capacity of up to 10 (MW) is considered as small; up to 2 (MW), mini; up to 100 (kW), micro; and from a few hundred watts up to 5 (kW), pico [6, 9]. According to [8], the global installed capacity of small hydropowerplants of less than 10 (MW) was estimated in 2022 at approximately 79.0 (GW), with an estimated potential of 221.7 (GW). Statistics show that there are more than 20,000 small hydropower turbines installed in Europe, in addition to ongoing projects [8]. A small hydropower plant is a renewable energy source which a beneficial impact on electricity grids, as it can provide continuous production for a predictable period of time. In the _EU_, small hydropower (\(SHP\)) plants have the potential to contribute to decarbonisation strategies [10], but the development of efficient and adoptable hydropower technologies needs to be improved. Small hydropower plants can be categorised into different types based on the water head. These include low-head (\(LH\)) hydropower, which refers to heads below 5 (m); very-low-head (\(VLH\)) turbines, with heads below 2.5 (m); and ultra-low-head (\(ULH\)) turbines, with heads below 1.5 (m) [11; 12]. A considerable number of potential hydropower locations where traditional turbines are not cost effective or environmentally viable reflect very-low-head or ultra-low head conditions. A project co-funded by the European Union, called the RESTOR Hydro project [13], estimated that more than 350,000 micro-mini hydro sites may have existed in Europe at one time or another. One of the main outputs of this project was a map showing 65,000 data points or potential micro-mini hydropower plants [13]. The Archimedes screw can certainly be considered one of the most successful innovations in the field of small hydropower plants introduced in the last two decades, as it offers significant advantages over classical axial turbines [14]. These advantages are both technical and environmental. From a technical point of view, head, flow rate, and efficiency are parameters that can be used to compare the Archimedes screw with other hydraulic turbines. Table 1 shows the operating range of hydro turbines, from the point of view of the flow rate and head [15]. According to Table 1, for low-head and very-low-head, besides the Archimedes screw, only the Kaplan turbine [16] can operate in these types of installations. In ultra-low-head installations, the Archimedes screw is the only hydro turbine that can operate under these conditions.