Governments worldwide are increasingly prioritizing the use of renewable energy due to environmental concerns, the finite nature of fossil fuel reserves, and their rising costs. Although various innovative solar thermal systems have been proposed in the literature, most are typically bulky and require a separate thermal energy storage unit. The system proposed here is a solar air heater (SAH) that integrates both the solar thermal collector and the heat storage unit into a single compact structure. Such a combined system is currently unavailable in the commercial market and has limited representation in academic literature.

The proposed SAH unit has dimensions of 150 cm (length), 75 cm (width), and 10 cm (thickness). It features a wavy absorber plate designed to increase the heat transfer surface area by approximately 30%. This absorber plate is coated in black to maximize solar heat absorption and is covered with a transparent glass or plastic sheet that permits solar radiation to enter while minimizing convective and radiative heat losses.

Beneath the absorber plate, a phase change material (PCM), such as paraffin wax, is placed. The PCM, with a melting point around 45 °C, serves as the thermal energy storage medium. For different geographic regions, PCM with melting points in the range of 40 °C to 60 °C can be used, depending on the local solar radiation and ambient temperature conditions.

During daylight hours, solar radiation is absorbed by the black-coated absorber plate. The resulting heat is utilized in two main ways:

1. Active Heating of Air: Ambient air enters the SAH through an inlet, flows along its longitudinal axis, and exits from an outlet at the opposite end. As it passes through, the air is heated by convective heat transfer from the absorber plate. A fan or blower, appropriately sized based on the required flow rate, is installed at the outlet to ensure continuous airflow through the system.
2. Latent Heat Storage: Simultaneously, a portion of the absorbed heat is conducted to the PCM located in direct contact beneath the absorber plate. This heat melts the PCM, thereby storing thermal energy in the form of latent heat.

After sunset or during periods of low solar irradiance, the absorber plate temperature drops below the PCM’s melting point. The PCM then begins to solidify, releasing the stored heat. This released energy helps maintain the absorber at a temperature higher than the ambient air, enabling continued heating of the incoming air during the evening or night.

Benefits of the Proposed System

• Provides clean and sustainable thermal energy for applications such as agricultural drying, space heating, and industrial processes.
• Operates effectively even after sunset due to integrated thermal storage.
• Compact design integrates both the collector and storage system, reducing installation space.
• Can be fabricated using low-cost materials by personnel with low to medium skill levels.
• Well-suited for developing countries, where demand is high for affordable and reliable energy solutions.