⚡ electrical engineering

Performance Investigation of a Solar-Driven Air Gap Membrane Distillation System Coupled with PEM Electrolysis

This study validates a solar-powered hybrid system integrating Air Gap Membrane Distillation and PEM electrolysis, demonstrating its capability to simultaneously produce freshwater and green hydrogen while identifying key operational parameters that optimize performance for sustainable decentralized resource generation.

Original authors: Mokhless Boukhriss, Slah Farhani

Published 2026-07-02

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Mokhless Boukhriss, Slah Farhani

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine a world where the sun doesn't just warm your skin but also fills your water bottle and fuels your car. That is the dream behind this research paper. The authors, Mokhless Boukhriss and Slah Farhani, have built a "two-in-one" machine that uses sunlight to solve two big problems at once: thirst (lack of fresh water) and energy hunger (the need for clean fuel).

Here is how their invention works, broken down into simple concepts and everyday analogies.

The Big Idea: A Solar Power Plant with Two Outputs

Think of this system as a solar-powered factory with two assembly lines running side-by-side:

The Water Line: It turns salty or dirty water into pure drinking water.
The Fuel Line: It turns that same pure water into "green hydrogen," a clean fuel that can power vehicles or machinery.

The magic is that the water produced by the first line is the exact same water needed to run the second line.

How the Machine Works (The Step-by-Step)

1. The Solar Heater (The Sun's Kettle)
First, the system uses a solar thermal collector. Imagine a giant black pan sitting in the sun that gets very hot. Instead of cooking food, this pan heats up salty water.

Analogy: Think of it like a pot of soup boiling on a stove, but the stove is the sun.

2. The Magic Filter (The Air Gap Membrane)
This hot salty water flows into a special chamber called an Air Gap Membrane Distillation (AGMD) unit.

The Membrane: This is a thin, waterproof fabric (made of PTFE, similar to a high-tech raincoat) that has tiny holes. It lets water vapor (steam) pass through but blocks salt and dirt.
The Air Gap: Here is the clever part. Between the hot salty water and the cold side where the water collects, there is a tiny, empty space filled with air.
Analogy: Imagine a hot shower in a bathroom. The steam rises and hits the cold mirror, turning back into water droplets. In this machine, the "mirror" is separated from the "shower" by a thin layer of air. This air gap acts like a thermal blanket, keeping the heat from escaping too quickly and making the process very efficient.

3. The Split (Water vs. Fuel)
The machine produces pure, distilled water. It then splits this water into two buckets:

Bucket A: Goes straight to people to drink.
Bucket B: Goes to a machine called a PEM Electrolyzer.

4. The Fuel Maker (The PEM Electrolyzer)
This machine uses electricity from solar panels (PV) to take the pure water from Bucket B and "zap" it.

Analogy: Think of water as a Lego castle made of Hydrogen and Oxygen blocks. The electrolyzer uses electricity to knock the castle apart. The Oxygen is released into the air, and the Hydrogen blocks are collected and stored as a gas. This Hydrogen is "Green Hydrogen" because it was made using only sun power.

What the Researchers Found (The Results)

The team built a real-life model of this system and also created a computer simulation to test how it behaves. Here is what they discovered:

Heat is the Engine: The hotter the salty water gets, the faster the system works. When they heated the water to about 83°C (181°F), the machine produced water very quickly (about 12 kg of water vapor per square meter of membrane per hour).
The Air Gap Matters: The size of that empty air space is critical. If the gap is too wide, the system gets sluggish. If it's just right, the heat stays where it needs to be.
The Membrane Holes: The more "holes" (porosity) the membrane has, the more water vapor can pass through. However, if there are too many holes, the membrane might get weak or leaky, so a balance is needed.
Salinity Doesn't Stop It: Even when using very salty water (like from the Red Sea), the machine still worked well. The water coming out was so pure that it had almost no salt left in it (less than 20 µS conductivity).
The Double Output: Under bright, sunny conditions, the system could produce:
- 4 to 5 liters of fresh water per hour (enough for a family to drink).
- 0.15 to 0.20 cubic meters of hydrogen per hour (enough to fuel a small vehicle or store energy).

Why This Matters

The paper concludes that this system is a promising "proof of concept." It shows that in sunny, dry places where water is scarce, you don't have to choose between getting water or getting energy. You can use the sun to do both simultaneously.

The researchers suggest that for this to work all day long (even when the sun goes down), we would need to add batteries (to store electricity) or thermal storage (to keep the water hot), but the core technology of linking the water maker and the fuel maker works as they predicted.

In short: They built a solar-powered machine that boils salty water, catches the steam to make drinking water, and uses the leftover pure water to make clean fuel, all without using any fossil fuels.

Technical Summary: Performance Investigation of a Solar-Driven Air Gap Membrane Distillation System Coupled with PEM Electrolysis

1. Problem Statement

The study addresses two critical global challenges: freshwater scarcity, particularly in arid and semi-arid regions, and the urgent need for clean energy transition to mitigate climate change. While desalination technologies like Reverse Osmosis (RO) and Multi-Stage Flash (MSF) exist, they are often energy-intensive and reliant on fossil fuels. Simultaneously, the production of "green hydrogen" via electrolysis requires high-purity water, creating a dependency on existing freshwater supplies. The paper identifies a gap in research regarding tightly integrated systems that can simultaneously generate freshwater and hydrogen using renewable energy, specifically combining membrane distillation with electrolysis.

2. Methodology

The research employs a hybrid experimental and numerical approach to investigate a system coupling a Solar Thermal Collector, an Air Gap Membrane Distillation (AGMD) unit, and a Proton Exchange Membrane (PEM) electrolyzer.

System Configuration:
- Solar Thermal Collector: Heats saline or brackish feedwater.
- AGMD Unit: Utilizes a flat-sheet hydrophobic PTFE membrane (Area: 12 m², Thickness: 0.14 mm, Porosity: 0.78) with an air gap (0.22 mm). The system separates water vapor from the heated feed, which condenses on a cold surface to produce high-purity distillate.
- PEM Electrolyzer: Powered by Photovoltaic (PV) electricity, it splits a portion of the produced distillate into hydrogen and oxygen. The electrolyzer has a rated power of 400 W and operates at 8 V.
Experimental Setup: Experiments were conducted under varying conditions, including feedwater temperatures (38–83 °C), different flow rates, and solar irradiation levels.
Numerical Modeling: A semi-empirical model was developed using MATLAB/Simulink. The AGMD module was divided into longitudinal elements to simulate mass and energy balances. Key assumptions included steady-state equilibrium, constant pressure in the air gap, and heat transfer via conduction and diffusion. The model calculated vapor flux ( $J_v$ ) based on vapor pressure gradients and Faraday's law for hydrogen production.
Sensitivity Analysis: The study evaluated the impact of feedwater temperature, membrane porosity, air-gap thickness, salinity, and solar irradiation on system performance.

3. Key Contributions

Integrated System Design: The paper proposes and validates a proof-of-concept for a hybrid system that co-produces freshwater and green hydrogen, utilizing solar thermal energy for desalination and solar PV for electrolysis.
Model Validation: A robust mathematical model was developed and validated against experimental data, showing a strong correspondence with deviations below 5% for vapor flux predictions.
Parameter Sensitivity: The study provides a detailed analysis of how specific operational parameters influence the efficiency of the AGMD-PEM coupling, offering insights for system optimization.

4. Key Results

Performance Metrics: Under peak solar irradiation, the system achieved freshwater production rates of 4–5 liters per hour and hydrogen generation rates of 0.15–0.20 Nm³ per hour.
Temperature Dependence: Water vapor flux increased exponentially with feedwater temperature. The maximum flux reached approximately 12 kg m⁻² h⁻¹ at 83 °C.
Water Quality: The system demonstrated high desalination efficiency, with the produced distillate maintaining a conductivity consistently below 20 µS, indicating nearly complete salt rejection.
Membrane Characteristics:
- Porosity: Higher membrane porosity resulted in a nearly linear increase in vapor flux, though the study notes the need to balance this with mechanical stability.
- Air Gap: Vapor flux decreased as the air-gap width increased, with the system showing high sensitivity to small variations in gap width.
- Length: Increasing membrane length led to a decrease in vapor flux due to reduced temperature differences across the membrane over the flow path.
Salinity Impact: Using saline feedwater (5.6 wt%) resulted in slightly lower vapor flux compared to deionized water due to reduced vapor pressure, but did not significantly compromise distillate quality.
Solar Irradiation: Both freshwater and hydrogen production rates were directly proportional to solar irradiation intensity, with peak production occurring between 1 p.m. and 2 p.m.

5. Significance and Claims

The paper claims that the integrated AGMD–PEM system offers a sustainable solution for decentralized water and energy generation in regions with abundant solar resources but limited water availability. By utilizing solar thermal energy for the energy-intensive phase of desalination and PV energy for electrolysis, the system optimizes renewable energy utilization.

The authors position this work as a step toward addressing global resource limitations while mitigating environmental impact. They state that the system demonstrates substantial promise for simultaneous water and energy production, aligning with Sustainable Development Goals (SDGs) 6 (Clean Water), 7 (Clean Energy), and 13 (Climate Action). The study concludes that while the current setup is a proof-of-concept, future work should focus on prolonged operation, techno-economic analysis, and the integration of thermal energy storage to ensure stability during periods of low solar radiation.