Final Report: Improving Efficiency of Building-integrated Photovoltaic Panels Using Phase Change MaterialsEPA Grant Number: SU836127
Title: Improving Efficiency of Building-integrated Photovoltaic Panels Using Phase Change Materials
Investigators: Boetcher, Sandra
Institution: Embry - Riddle Aeronautical University
EPA Project Officer: Page, Angela
Project Period: September 1, 2015 through August 31, 2016
Project Amount: $15,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2015) RFA Text | Recipients Lists
Research Category: P3 Awards , Pollution Prevention/Sustainable Development , Sustainability , P3 Challenge Area - Built Environment
The objective of the EPA P3 Phase I (SU83612701) project is to improve the efficiency of building-integrated photovoltaics (BIPV) by regulating the temperature of the photovoltaic (PV) cells with a solid-to-liquid phase-change material (PCM). Lowering the temperature of PV panels can increase their efficiency significantly. The advantage of using PCMs to regulate the temperature of PV panels is that PCMs undergo phase transformation by absorbing or releasing large amounts of energy, called latent heat, at constant temperature. When the PV panel is heating up, the PCM keeps the panel at constant temperature. The constant temperature the panel is kept at is lower than a panel without thermal regulation, maintaining a higher efficiency in the thermally regulated PV panel.
Another advantage to using PCM to thermally regulate BIPVs is that the material will allow for the storage of the waste heat from the PV panels. This waste heat can be used for other applications such as space heating, radiant floor heating, and/or domestic hot-water heating. A model demonstrating the use of the waste heat for radiant floor heating will be presented at the 2016 EPA P3 Expo in Washington, DC.
PV panels may be actively or passively cooled. Active cooling requires putting energy into the system to pump a fluid over either the front or the back surface of the PV panel. Passive cooling usually relies on natural convection heat transfer due to the circulation of air (buoyancy) in the open space behind the PV panel. Thermal regulation using PCM is also a passive cooling method. PCM does not actually lower the temperature of the panel. i PCM keeps the temperature of the panel constant, giving the physical sensation of cooling. When the mechanism for cooling also captures and stores heat for later usage, the system is then called a photovoltaic/thermal (PVT) hybrid collector.
One of the goals of the Phase I project is to evaluate the effectiveness of using encapsulated phase-change material in a water bath to thermally regulate BIPV panels. The reason for using encapsulated PCM is twofold. First, PCM that is not encapsulated is difficult to contain due to material compatibility issues. The solvents in PCMs are not compatible with many common seal materials; however, PCM is compatible with various metals and high-density polyethylene (HDPE). The materials compatibility often makes it difficult to seal bulk PCM. If the PCM is already encapsulated with a compatible material, in this case HDPE, then that makes it easier and safer to implement in BIPV-PCM applications. Second, PCM inherently has a very low thermal conductivity. The water bath surrounding the encapsulated PCM helps to more effectively transfer the heat from the BIPV panel to the PCM. Another goal is to determine the effectiveness in using fins to reduce the PV panel temperature. Fins are a common method to increase the heat transfer from one object to another. The addition of fins to the BIPV panel in will help thermally regulate the PV temperature.
A sampling of preliminary results is presented in this project report/Phase II proposal. In the results, the main metric in evaluating whether or not the PCM was effective is the temperature of the PV panel. According to preliminary experimental data, the bulk PCM keeps the PV panel below 50 degrees C for the longest time. It is important to note that the bulk is difficult to package due to the materials incompatibility problem and the encapsulated PCM may be more conducive to real-life packaging. These results present preliminary findings and more experiments are currently underway.
Preliminary results from the numerical simulation study show that the longer the fin, the better performance. An interesting result is that at the longest fin length, which corresponds to the fin being connected to the bottom of the PCM container, the PCM melt time goes up, but the PV panel temperature is low. This suggests that the connected fin is best utilizing the PCM volume. Long melt times and low temperatures are the desirable outcome of using PCM to cool a PV panel.
The methods and techniques investigated are technically effective and economically feasible in the long term. Preliminary results show that cooling BIPV panels with PCM is effective. Not only will PCM cool the panels, but it will store the waste heat for reuse later. Economically, the long-term cost benefit will outweigh the initial cost. The research will help solve environmental problems by making PV panels more efficient and reusing waste heat from PV panels for other applications such as radiant floor heating, attic space heating, and hot water pre-heating.
The project successfully blends the elements of people, prosperity, and planet by developing a system that both makes PV panels more efficient, but also makes use of the waste heat generated by the PV panels.
The project will benefit people by sustaining and improving human health. BIPV-PCM systems produce no emissions and the construction materials are environmentally friendly. The project serves as a vehicle for outreach and education to the local community. Several previous ERAU EPA P3 projects have been featured in community news sources such as the Daytona Beach News Journal. In addition, Embry-Riddle Aeronautical University has been selected to compete in the 2017 Solar Decathlon. The house will serve as a testbed for the technology developed in Phase II, increasing the outreach audience to an international scale.
The BIPV-PCM system will also promote prosperity. It is expected that upfront costs of the BIPV-PCM system will be larger than that for a regular BIPV device. However, due to the increased efficiency of the PV cells and the heat recovery and usage, the overall lifetime cost of the BIPV-PCM system will be less than that of a BIPV. A major outcome of many EPA P3 projects, including one at ERAU, is the founding of a start-up company, AquaSolve Ventures, LLC. The potential is high for a BIPV-PCM commercial system to be developed from the award of an EPA P3 Phase II grant.
Finally, the project will benefit the planet. BIPV-PCM systems are expected to last 20 years or more. They require no fuel, produce zero emissions, and no waste products are made. The materials, particularly the PCM, are environmentally friendly and non-toxic.