Modeling and Optimization of Solar PV System With Pumped Hydro Energy Storage System

Introduction

Standalone SES with feasible energy storage unit can work as an effective micro-grid system with regards to feasibility, proximity to user end requirements, economics and eco-friendliness for satisfying the solar energy needs of people. Design of micro-grid for the user end requirements is an important consideration when the user’s load situation, reliability/autonomy requirements are of different scales. The optimization in such situations could be a crucial design aspect so as to make the SES reliable and cost-effective. In the available literature (Hoppmann, et al. 2014; Nair & Garimella, 2010; Mahmoud, 2014; Shaahid, & Elhadidy, 2007) Technical and economic assessment of grid independent hybrid photovoltaic-diesel-battery power system for commercial load in desert environments, Renewable and Sustainable Energy Review, 11: 1794-1810 battery storages have been successfully integrated to SES due to their simplicity and high load stability nature. Another popular storage unit often integrated to SES is PHS technology, which is one of the most mature technologies due to long term energy storage (Saini, 2011; George, 2002). Though in some real projects (Manolakos, et al., 2004; Li, et al., 2012; Ma, et al., 2014), the performances of PHS have been optimized for renewable energy power supply, but the optimum solution might sometimes result in a too large upper reservoir capacity to accommodate (Ma, et al., 2014), and therefore such designs may not be always feasible when the user’s load demand is low. Additionally, the feasibility and economic analysis of PHS combined with battery based system has also been studied in literature (Saaty, 1989; Brauers, & Zavadskas, 2006; Karande, & Chakraborty, 2012; Chakraborty, 2011) for some real projects of the world. However, there is a need to optimize sizes of such storage units if these are to be integrated with SES at varied user-load conditions. In the field of sizing under different conflicting criteria of techno-economic costs, reliability, and autonomy for SES, different types of mathematical modelling, optimization methodologies and simulation software have been adopted by various researchers (Sarkar, et al., 2015; Singaravel, et al., 2016; Tzeng, & Huang, 2011; Ma, et al., 2014). SES has also been designed in terms of its optimized sizing for real application projects (Ma, et al., 2014 & Kaldellis, et al., 2013). Different mono-objective and multi-objective optimization functions have been used in the sizing of SES. For example, Genetic Algorithm (GA) gives the flexibility to consider all the aspects of RES design considerations such as technical feasibility, economical feasibility, optimality and reliability. Mathematical equations for major components of the systems are used for sizing and modeling.

The hour-by-hour simulation program has been developed and systems are optimized with respect to their Life Cycle Cost (LCC), COE, and UE using integrated MCDM method. Both mono-objective and double-objective function optimizations have been implemented for each RES. A sensitivity analysis has been performed by considering the effect of percentage UE (from 0% to10%, i.e. reliability between 90% and 100%) on the COE for different storage capacity of PHS, so as to design optimum storage units for the end user requirements. The methodology is finally applied on an academic block of an educational institute at Silchar, India having low load factor user-load condition, and based on the results various conclusions are drawn at the end.

The PHS system with PV power generation can store large amount of energy for long period and working principle is also very simple. Bulk storage, reliability, and maintenance free storage are the reasons why PHS is preferred to battery bank. Although batteries are less costly, they require more maintenance and need to be replaced after 3-4 years of use. Moreover, depth of discharge and state of charge of the battery bank need to be correctly maintained at the set level in case of battery, which need not to be rigorously followed for PHS, hence the latter has higher reliability. Moreover, the number of autonomy days can also be higher in case of PHS. However, as the construction cost of PHS is high, hence it is to be used in case of bulk storage requirements, for e.g. remote village electrification, micro-grid, etc.

Figure 1.

The stand-alone PV-PHS based SES