Engineering Concept of Energy Storage Systems Based on New Type of Silicon Photovoltaic Module and Lithium Ion Batteries

Abstract

In recent years, a great importance has been given to hybrid systems of energy generators and energy storages. This article presents the results of our research aimed at checking the possibility of connecting a photovoltaic (PV) module and a lithium-ion battery (LIB), using a simplified control module towards a cheap and efficient system. The photovoltaic modules based on crystalline silicon solar cells, tempered glass as the front layer and ethylene-vinyl acetate (EVA) copolymer as encapsulation material are the most popular type in the industry. The disadvantage of such module type is the high weight of about 15 kg/m2. The weight of PV module used in the presented energy storage system is twice as small. This new type of PV module is based on treated poly(methyl methacrylate) (PMMA) as back sheet; high transparent foil as front sheet. Changing glass layer to PMMA requires additional modification of the lamination process parameters and EVA polymer type. For this reason, an EVA polymer with reduced crosslinking temperature was used in most cases; the voltage obtained from solar panels is significantly different from the one required by battery system. Hence, voltage converters (step-up or step-down) are needed. The use of a voltage stabilizing converter (which is a kind of electrical buffer) between the solar cell and lithium-ion battery can in some cases replace the battery overcharge protection system. However, an indispensable element is the system protecting the battery from excessive discharge. The voltage converter permits direct connection between the electricity storage and power supply, which current-voltage parameters do not match. The converter’s task is to change the value of current and voltage in a way that meets the requirements of the powered receiver, minimizing power losses, increasing the whole system efficiency. Photovoltaic parameters of the energy storage systems were examined in laboratory and real conditions.