One effective way to reduce energy consumption is to store surplus or waste energy which cannot be used timely. In response to this approach for "carbon peaking and carbon neutrality goals", a novel PCM heat storage unit is combining into a PV/T system to improve heat utilization efficiency. This paper presents the dedicated numerical and experimental investigation of a novel heat storage/exchange unit. This unit comprises of numerous tiny phase change material (PCM) rods which makes smaller heat transfer distances within the PCM block, thus creating larger contact area between the passing water and PCM particles than the traditional PCM-wall-based and PCM-full-filled heat exchangers, leading to the faster melting and freezing of the PCM blocks and increased heat transfer capacity. A numerical model was developed to simulate the temperature distribution, melting/freezing conditions and heat flux across the water flow and PCM blocks, thus enabling the optimization of the geometrical size of the unit and assessment of its thermal performance. A prototype PCM heat exchange/storage unit was constructed and tested in the laboratory to examine the reliability of the numerical mode and validate its accuracy. It was found that simulated and experimental results are in good agreement, with an average discrepancy of around 5.5%. This close agreement provides confidence in our simulation to inform the future design and optimization of appropriate heat exchanger/storage units and assess their performance for solar and other thermal applications. It is shown that the PCM tank used here can store up to 8.6 kWh and provide continuous hot water for 2 hours.