The turbine is a heart of power generation in a hydroelectric power system. A variety of different turbines are available for that purpose. The common types of Hydraulic turbines are; Pelton, cross flow, Francis, Kaplan, and propeller turbine. However, using conventional turbines for low head and flow rate (i.e. micro hydropower) applications are not economically feasible. A low-cost alternative is to use the pump as a turbine. In this paper, existing Peer-reviewed articles from (Scopus, google scholar, umbrella, etc.) that are directly related to pump running as a turbine are collected and reviewed. Theoretical, numerical, and experimental investigations are considered. Performance improvement techniques for PAT are summarized and research gaps in related works are identified.

The case study presents a lifetime cost benefit analysis for RET evacuated tube SWH comparing with EWH for domestic hot water production. The study is important to show the SWH technology is competitive, strengthen local electric use capacity and to stimulate acceptance of the solar technology in Ethiopia. To accomplish the study, conduct thermal performance test of imported RET evacuated tube SWH in order to see the feasibility with current condition of Addis Ababa. And analyze lifetime cost benefit of proposed RET Evacuated tube SWH and compare with commonly used EWH to show technical and economic advantages. In Addis Ababa, home builders and commercial sectors has alternatives of installing SWH and purchase EWH. However, from technical comparison study SWH has an advantage of improve energy security and risk management; reduce the use of electricity; reduce the GHG emissions; improve the quality of life through renewable energy; less payback period over EWH. Similarly, the breakeven analysis confirms that the life cycle save is about 1414.06 ETB and 943.36 ETB per year from electricity bill without considering maintenance and other exploitations, and SWH is profitable less than 6 and 14 years by installing SWH rather than using electrical storage type boiler and instant water heater respectively. In the long run, home builders are both technically and economically beneficial to install SWH.