### Solar-Thermal Atmospheric Water Generator: Exploiting Radiative Cooling and Solar Heating This atmospheric water generator (AWG) system uses a combination of **radiative cooling** at night and **solar heating** during the day to create distilled water through condensation. The system is simple, passive, and primarily driven by solar energy with water as both the working fluid and the thermal battery. Here's how it works: --- ### **System Components and Process Overview** 1. **Radiative Cooling at Night**: - At night, a radiative cooling panel (like a solar pool heater) is exposed to the clear sky, facing the zenith. - The water inside the system radiates heat to space, cooling down significantly due to the radiative heat loss (using the infrared transmission window in the atmosphere). - This cools down the water in a **cold water tank**, which serves as a heat sink during the day. 2. **Solar Heating During the Day**: - During the day, the system uses a **solar thermal collector** (e.g., a solar pool heater) that is mounted on a **single-axis tracker** (south-facing) to maximize solar gain. - The water is heated up by the collector, raising the temperature of rain or waste water. - As the water heats up, it becomes humid and expands, forming warm, moist air. This air is circulated through a condenser coil submerged in the **cold water tank** from the night before. 3. **Condensation**: - The cold water in the tank causes the warm, moist air to cool rapidly, condensing the moisture into liquid water. The condensed water is then collected as distilled water. - This system relies on the **temperature differential** between the heated water from the solar thermal collector and the cooled water stored in the cold water tank from radiative cooling at night. 4. **Water as Heat Battery**: - Water is the working fluid and also serves as a heat battery, storing thermal energy during both radiative cooling at night and solar heating during the day. - The system can circulate water between the thermal collector, the storage tank, and the condenser as needed to maintain the temperature differential that drives condensation. --- ### **Calculation of Daily Heat Energy Potential** Let’s assume: - **Radiative cooling at night** removes 192.5 W/m² (from previous calculation). - **Solar insolation during the day** is 5 kWh/m²/day. #### 1. **Nighttime Radiative Cooling Energy** The cooling panel (same as in the earlier example) radiates heat away at 192.5 W/m². Over 10 hours of nighttime cooling: \[ E_{\text{night}} = 192.5 \, \text{W/m²} \times 10 \, \text{hours} \times 3600 \, \text{seconds/hour} \] \[ E_{\text{night}} = 6.93 \times 10^5 \, \text{J/m²} \, \text{(6570 BTU/m²)} \] #### 2. **Daytime Solar Heating Energy** Solar insolation delivers 5 kWh/m²/day, which is: \[ E_{\text{day}} = 5 \, \text{kWh/m²/day} \times 3600000 \, \text{J/kWh} \] \[ E_{\text{day}} = 1.8 \times 10^7 \, \text{J/m²} \] The **net energy** available per square meter of the system, combining both daytime solar heating and nighttime radiative cooling: \[ E_{\text{total}} = 1.8 \times 10^7 \, \text{J/m²} + 6.93 \times 10^5 \, \text{J/m²} \approx 1.87 \times 10^7 \, \text{J/m²/day} \] --- ### **Estimating Water Production** The water production depends on how much of this energy can be used to condense moisture. To estimate the amount of water that can be condensed, we use the **latent heat of vaporization** of water, which is the amount of energy required to condense 1 kg of water vapor: \[ L_{\text{v}} = 2260 \, \text{kJ/kg} = 2.26 \times 10^6 \, \text{J/kg} \] Now, divide the total energy by the latent heat to find the amount of water that can be condensed: \[ m_{\text{water}} = \frac{E_{\text{total}}}{L_{\text{v}}} = \frac{1.87 \times 10^7 \, \text{J/m²/day}}{2.26 \times 10^6 \, \text{J/kg}} \] \[ m_{\text{water}} \approx 8.3 \, \text{kg/m²/day} \] Since 1 kg of water is roughly 1 liter, the system could potentially produce **8.3 liters of water per square meter of panel area per day** under ideal conditions. --- ### **System Summary and Potential Benefits** - The **radiative cooling** at night lowers the temperature of the cold water tank, increasing the temperature differential between the solar-heated water and the cold tank during the day. This larger temperature differential enhances condensation efficiency. - During the day, **solar thermal heating** increases the temperature of the water, generating warm, moist air that passes through a condenser coil cooled by the radiatively cooled water. - The system could potentially produce **8.3 liters of water per square meter** of solar collector area per day in a dry, sunny climate with clear skies. --- ### **Final Thoughts on Energy Dissipation** This system uses **water** as a thermal battery and relies on **radiative heat transfer** to increase efficiency, ultimately helping to dissipate solar energy more effectively than a standard solar water heater. It aligns with the **entropic theory of life** in that it efficiently transfers solar energy into useful processes like distillation and heat transfer, contributing to a more **energy-dissipative** system on Earth.