Photovoltaic (PV) panels are becoming increasing popular and are proving to be very successful to fulfil the energy demand in the future. However, these PV panels still have some challenges, including the decrease in efficiency with increasing temperature, and non-uniform temperature of the PV panels. It would be worthwhile to assess the cooling impact on the annual electrical PV panel output and to present a new cooling system to overcome these problems. The main aim of this work is to implement an accurate numerical method to predict the annual impact of phase change material (PCM) on the PV panel electric output. In addition, new systems of PV panels incorporated with PCM- metal foam, will be designed to reduce the temperature of the PV panels.
This research includes five contributions. Firstly, a novel one dimensional PV-PCM model has been presented to investigate the annual impact of the PCM on performance of the PV panels with high accuracy and stable solutions based on lumped-distributed parameter model. Secondly, the distributed parameter model, has been developed to include a thermal contact conductance with the explicit and implicit discretization. These models have considered the volume change when the phase change from solid to liquid and vice versa. Thirdly, the lumped-distributed parameter model has been used to investigate the impact of the composite paraffin-PCM on the annual electrical output of the PV panel for Baghdad and Milan. Fourthly, the thermosphysical properties of 29 PCMs have been collected and their impacts with different thicknesses have been investigated. Finally, the impacts of different PCMs with different thicknesses and different aluminium (Al) foam percentages on the annual electrical output of the PV panel have been investigated to find the best PCM, the optimal thickness and the best Al foam percentage for each city.
A novel one-dimensional, lumped-distributed parameter model with time and space discretization for the PV-PCM system has been presented and the time independency investigated. The results indicate that the maximum difference between the one second time step and four second time step is 0.7838oC. The results of the lumped-distributed parameter model have been validated against the literature and the maximum relative error is 6.47 percent.
Secondly, an improvement was implemented by adding the thermal contact conductance in lumped-numerical model. Then, three scenarios were studied to assess the impact on the PV panel efficiency of different technical contacts between the PV panel and aluminium container of the PCM. In the first scenario, the PCM is inside an aluminium box attached to the PV panel with thermal contact adhesive. The second scenario is without thermal contact adhesive. In the third scenario, a 0.5 mm air gap is created between the aluminium box and PV panel. The highest electric efficiency difference found is 3.493 percent between the first with third scenarios.
Thirdly, the lumped-distributed parameter model considers the volume change during phase change from solid to liquid. The results of considering the volume change have been compared with not considering it, and the maximum difference was 4.1 percent.
Next, the explicit and implicit methods for the distributed parameter model, have been implemented using the MATLAB software, and the computer runtimes for these methods have been compared with that solution of the lumped-distributed parameter model. The results indicate that the runtimes required for the implicit method of lumped-distributed parameter model and the distributed parameter model to study a transient 18,000 seconds for the PV-PVM system are 16.813 and 525.045 seconds respectively. The computer runtime for the explicit method for the distributed parameter model to study a one second is 51,391.431 seconds. Therefore, the lumped-distributed parameter model presented in this work is proven to be better able to simulate the PV-PCM module, with faster computer runtime compared with implicit and explicit method for the distributed parameter model.
Finally, this lumped-distributed parameter model for the PV-PCM system has been used to investigate the impact of different PCMs, different thicknesses, and different Al foam percentages on the annual electrical output of PV panels in Baghdad and Milan. The results indicate the maximum enhancements for the annual electrical output of PV panel for Baghdad and Milan are 3.19 and 4.11 percent respectively.
