Pump as turbine applied to micro energy storage and smart water grids: A case study

The need of energy storage in micro scale is recently emerging and becoming more relevant in the rising era of decentralised renewable energy production. This paper provides a technical overview of the design and the outcomes of a first-of-its-kind Pumped Hydro Energy Storage (PHES) micro facility. The described micro-PHES is integrated in a smart grid and it is designed to store energy produced by the connected renewable energy sources. Interestingly, this micro-PHES runs with a single centrifugal pump for both pumping and generating phases. Variable speed regulation allows the pump to constantly operate at the maximum hydraulic efficiency in order to deal with load variations. In the same way, the pump running in reverse, namely Pump as Turbine (PaT), runs at the most suitable speed and it keeps high efficiency (near to 0.71%) over a range of 40–120% of the nominal load design. The pump/PaT is selected according to the presented methodology and it is experimentally characterized in the current case study. The PHES implementation is defined in relation with the smart grid consumption and renewable energy production and it reaches a total round-trip yield up to 42%. In addition, this paper defines the techno-economic parameters for a micro-PHES cost-effective solution and provides an important dataset for micro-PHES feasibility breakdown. The use of a storm-water basin as reservoir produces an expense cut greater than 28% of the total direct cost. This constitutes a valid economic advantage to be integrated in future smart water grid's designs. Also, the system with the described features can reach a Levelised Cost of Energy (LCOE) of 0.58–1.06 €/kWh in micro-PHES.SCOPUS: ar.j