## 1 Introduction
The use of photovoltaic solar cells for pumping water has been steadily increasing in the last decade, particularly in developing countries such as China and India, but also in many European and African countries [11; 12; 13]. [PERSON] and [PERSON] [14] reported that there is a growing interest in solar-powered irrigation and conducted a review of historic and current trends that included surveys, interviews and site visits covering many case studies worldwide. GIZ [15] summarized some fundamental opportunities for the use of solar-powered groundwater pumping systems (e.g., low operational costs, low environmental impacts, growth of photovoltaic cell markets, remedying unreliable grid power and connection to the grid) as well as some hurdles (e.g., high initial capital investment, the lack of financing and policies, exposure of equipment to weather extremes and theft). Ref. [16] highlighted that the adoption of solar energy for irrigation is an attractive option, however a technical and economic assessment is required to determine feasibility at specific sites. The results from five case study sites (in Spain, Saudi Arabia, USA, Lebanon and Jordan) indicated that solar-powered irrigation is technically feasible and sustainable in areas with high solar radiation as long as groundwater has sufficient capacity to recover and enough land is available for solar arrays. The economic benefits outweigh the conventional fossil fuel and electricity systems in the long run, although the initial capital costs are high. Feasibility assessments were conducted in previous international research for solar-powered groundwater pumping systems [15; 17]. A reliable water source of acceptable quality is the main pre-requisite for the success of the interventions. Equally to water, the availability of solar radiation and land, groundwater depth and aquifer hydraulic characteristics, water storage infrastructure and required hydraulic lift, required volumes and operating flow rates, suitable topographic and climatic conditions, land use/cover,earthworks required and distance to roads are essential geotechnical aspects to be considered [18; 19; 20; 21]. For the technical and engineering feasibility, a number of procedures and tools were published for the design, configuration and sizing of solar cells, controllers and groundwater pumps [22; 23; 24; 25]. A number of applications and optimization studies for solar-powered pumping systems were reviewed in [26]. [PERSON] [27] provided a number of practical recommendations for small-holder farmers in a developing country based on a case study conducted in Senegal, including benefits from bulk procurement, logistics, transaction costs and interconnectivity to the grid. Dedicated software was also developed [28; 29] as well as procedures for performance analysis and optimization [30; 31; 32]. The technical assessment also includes the manufacturing of the system, its efficiency, longevity and utilization [12; 33], data requirements and monitoring [14; 15]. The socio-economic feasibility of the systems was investigated in the literature through users' perception [15; 34]. [PERSON] and [PERSON] [11] proposed 14 determinants for the sustainability of solar-powered irrigation systems that relate to the social, economic and environmental sustainability. Ref. [11] also proposed strategies to promote the adoption and expansion of the technology, including building awareness, prioritizing areas for deployment, business models, subsidies and policy support. A business model for the management and maintenance of solar-powered groundwater abstraction systems and MUS needs to be put in place [15], ideally run by communities and gender-unbiased, for which policy support, financing and capacity development are often required [13; 14; 35; 36; 37]. The choice of the appropriate business model for MUS depends ultimately on the community and the social set-up.