Energy Efficiency Analysis of Combined Heat Pump-PV-Solar Collector-Based Underground Thermal Storage Systems

Abstract

This paper presents a novel renewable energy system that can be used to deliver heating and electrical energy to buildings. The system consists of a thermal storage unit buried underground, PV panels with a cooling system, evacuated tube solar collector, heat pump and buffer tank. The waste heat from PV panels cooling is stored in a high-capacity storage tank installed underground. The solar collector unit is used to preheat the water, to maximize the solar energy transfer to coolant liquid. The underground tank is not insulated, so exchange the heat with the surrounding ground. Therefore, a large amount of heat can be effectively transferred from the tank to the ground. The ground is partially insulated (from the top, and the sides), to reduce the heat losses to surroundings. The idea of the system is to use the heat from the storage unit, to improve the COP of the heat pump and maximize the energy system performance. The heat pump is powered using the electric energy produced by PV panels and then stored in the grid. A mathematical model of the proposed energy system is developed and the system performance is studied for Cracow city in Poland. The Finite Volume code written in MATLAB language is developed to study a transient two-dimensional temperature distribution underground, and to evaluate the heating energy stored.