Assessing the effectiveness of low-enthalpy geothermal energy for greenhouse temperature regulation towards enhancing desert agriculture – Nature

Report on the Effectiveness of Low-Enthalpy Geothermal Energy for Sustainable Desert Agriculture

Executive Summary

This report details an investigation into the viability of Earth-Air Heat Exchanger (EAHE) low-enthalpy geothermal systems for greenhouse climate control in arid regions, specifically addressing the challenge of limited meteorological data. By integrating ERA5-Land data with a subsurface soil temperature model, this study presents a robust methodology for designing and predicting the performance of sustainable agricultural infrastructure in data-scarce environments like Bahariya Oasis, Egypt. The findings confirm the significant thermal stability of subsurface soil, establishing it as a consistent energy source in alignment with SDG 7 (Affordable and Clean Energy). Initial simulations demonstrated effective winter heating, and subsequent system optimization via increased airflow successfully maintained greenhouse temperatures within near-optimal ranges year-round. This validates the EAHE system’s dual heating and cooling capability, offering a pathway to enhance food security and promote sustainable agriculture (SDG 2: Zero Hunger) while conserving water resources (SDG 6: Clean Water and Sanitation) and taking climate action (SDG 13: Climate Action).

1.0 Introduction: Addressing Sustainable Development Goals in Arid Agriculture

Greenhouse cultivation presents a significant opportunity to advance sustainable agriculture, a key target of SDG 2 (Zero Hunger). By providing a controlled environment, it enhances crop quality, increases yields, and enables year-round production. A critical contribution to SDG 6 (Clean Water and Sanitation) is the drastic reduction in water wastage through controlled irrigation compared to open-field farming. However, in arid regions, maintaining optimal greenhouse climates requires substantial energy, often from non-renewable sources, which conflicts with SDG 7 (Affordable and Clean Energy) and SDG 13 (Climate Action). Conventional cooling methods, like evaporative cooling, are heavily water-intensive, further straining scarce resources and undermining the goals of SDG 6.

Low-enthalpy geothermal energy, particularly through Earth-Air Heat Exchanger (EAHE) systems, emerges as a sustainable alternative. This technology leverages the stable temperature of the sub-soil to provide heating and cooling without intensive water or fossil fuel consumption. This study addresses a critical barrier to its implementation: the lack of meteorological and subsurface temperature data in remote arid zones. By developing a methodology that uses satellite-derived ERA5-Land data, this research aims to unlock the potential of geothermal energy, fostering resilient infrastructure (SDG 9: Industry, Innovation, and Infrastructure) and promoting sustainable production patterns (SDG 12: Responsible Consumption and Production).

1.1 Scope and Objectives

This report aims to bridge critical knowledge gaps by establishing an integrated methodology for designing EAHE systems in data-limited arid regions. The primary objectives are:

1. To collect and integrate ERA5-Land surface data with a sub-soil temperature profile model to overcome local data scarcity.
2. To model the thermal performance of an EAHE system, providing a clean energy solution (SDG 7) for climate control.
3. To simulate the coupled operation of a greenhouse and EAHE system to assess its potential for year-round heating and cooling, thereby supporting climate adaptation and food security (SDG 13 and SDG 2).

2.0 Methodology

The investigation was conducted using a multi-model approach driven by publicly available satellite reanalysis data, ensuring the methodology is replicable in other data-scarce regions to promote sustainable innovation (SDG 9).

2.1 Study Area

The Bahariya Oasis, Egypt, was selected as a representative hot desert climate (BWh) within the Western Sahara. Its arid conditions and constrained water resources make it an ideal location to test sustainable solutions that align with SDG 6 and SDG 15 (Life on Land) by enabling agriculture without further stressing the ecosystem.

2.2 Data and Models

• Meteorological Data: Hourly data for 2024 (ambient air temperature, land surface temperature, wind speed, solar radiation) were sourced from the ERA5-Land global reanalysis dataset. This approach democratizes access to critical climate information for sustainable development.
• Greenhouse Model: An energy balance model was applied across the greenhouse’s five constituent elements (cover, indoor air, and three soil layers). The model was previously validated with an Average Absolute Deviation (AAD) of ±1.13°C.
• EAHE Model: The low-enthalpy geothermal system was modeled using the Number of Transfer Units (NTU)-effectiveness method. The system consisted of PVC pipes (0.016 m diameter, 50 m length) with an initial air speed of 2 m/s. This model was previously validated with a prediction accuracy of 2.4%.
• Soil Temperature Model: A heat conduction model for a semi-infinite solid was used to predict the subsurface temperature profile, a critical parameter for designing an effective geothermal system. This model uses ERA5-Land surface temperature data as its primary input.

2.3 Analysis Procedure

Simulations were performed for the following cases to assess the system’s contribution to climate-resilient agriculture (SDG 13):

1. Greenhouse without temperature regulation.
2. Greenhouse with temperature regulation using an EAHE system (10 pipes at 2 m/s air velocity).
3. Greenhouse with an optimized EAHE system (10 pipes at 4 m/s air velocity).

Performance was analyzed on hourly, daily average, and diurnal scales for the year’s coldest and warmest days.

3.0 Results and Discussion

3.1 Climate and Subsurface Temperature Profile

The ERA5-Land data confirmed the extreme climate of Bahariya Oasis, with summer temperatures exceeding 30°C and winter temperatures dropping below 5°C, making year-round cultivation without climate control impossible. This underscores the need for technological interventions to achieve SDG 2 (Zero Hunger) in such environments.

The soil temperature model, driven by ERA5-Land data, revealed that at a depth of 3-5 meters, the soil maintains a remarkably stable temperature with minimal fluctuation (±2°C) year-round. This finding establishes the subsurface as a reliable, natural thermal battery, providing a consistent source for clean heating and cooling in line with SDG 7. An installation depth of 4 meters was selected for the EAHE system.

3.2 Greenhouse Thermal Performance

• Without Temperature Control: The uncontrolled greenhouse experienced intolerable temperature extremes, exceeding 60°C in summer and falling below 10°C in winter, rendering it unsuitable for crop production.
• With EAHE Integration (Case 2): Integrating a 10-pipe EAHE system at 2 m/s air velocity provided effective heating, maintaining winter temperatures near 20°C. However, summer temperatures reached approximately 40°C, indicating a need for enhanced cooling capacity.
• With Optimized EAHE (Case 3): By increasing the air velocity to 4 m/s, the system’s cooling performance improved significantly. Summer temperatures were successfully reduced to approximately 35°C, while winter temperatures remained above 20°C. This demonstrates the system’s ability to maintain a near-ideal thermal environment for year-round cultivation.

3.3 Contribution to Sustainable Development

The optimized EAHE system provides a stable thermal environment highly conducive to continuous crop cultivation, directly supporting SDG 2 (Zero Hunger) by enabling consistent agricultural production and enhancing food security in arid lands. By providing a reliable, non-water-intensive cooling and heating solution, the system is a powerful tool for SDG 6 (Clean Water and Sanitation) and SDG 13 (Climate Action). The daily average greenhouse temperature was maintained between 20–32°C, creating a resilient agricultural system that can adapt to extreme external weather variations.

Analysis of diurnal cycles revealed that the EAHE system is not required continuously, suggesting that an on-off control mechanism could further reduce energy consumption. This optimization enhances the system’s alignment with SDG 7 (Affordable and Clean Energy) and SDG 12 (Responsible Consumption and Production) by minimizing energy inputs.

4.0 Conclusion

This study successfully demonstrated that an EAHE low-enthalpy geothermal system, designed using globally available ERA5-Land data, is an effective solution for greenhouse climate control in arid, data-scarce regions. The research validates the subsurface soil as a stable, year-round thermal reservoir for both heating and cooling.

By optimizing airflow, the EAHE system successfully maintained near-optimal temperatures, proving its dual-function capability in extreme climates. This technology provides a robust, data-driven methodology for implementing sustainable, climate-controlled agriculture. It offers a tangible pathway to advance multiple Sustainable Development Goals, including:

• SDG 2 (Zero Hunger): By enabling year-round, reliable crop production.
• SDG 6 (Clean Water and Sanitation): By offering a cooling alternative that does not consume water.
• SDG 7 (Affordable and Clean Energy): By utilizing renewable geothermal energy with minimal operational power needs.
• SDG 9 (Industry, Innovation, and Infrastructure): By providing an innovative and resilient infrastructure solution for agriculture.
• SDG 13 (Climate Action): By reducing emissions from conventional energy sources and enhancing agricultural adaptation to climate change.

5.0 Recommendations for Future Work

To further advance the implementation of this sustainable technology, the following areas of research are recommended:

1. Conduct a detailed economic analysis covering capital, operational, and maintenance costs to assess financial viability and scalability.
2. Investigate the system’s performance with the inclusion of crops to understand the complete thermal dynamics during a full growth cycle.
3. Explore the integration of passive cooling strategies, such as shading, to further enhance system efficiency and reduce energy loads during peak summer conditions.

Analysis of Sustainable Development Goals (SDGs) in the Article

1. Which SDGs are addressed or connected to the issues highlighted in the article?

The article on using Earth-Air Heat Exchanger (EAHE) systems for greenhouse climate control in arid regions connects to several Sustainable Development Goals (SDGs). The analysis identifies the following relevant SDGs:

• SDG 2: Zero Hunger: The core focus of the article is on enhancing agricultural productivity in challenging environments. By enabling year-round crop cultivation in arid regions like the Bahariya Oasis, the technology directly supports sustainable agriculture and food production, which are central to ending hunger.
• SDG 6: Clean Water and Sanitation: The article explicitly addresses the issue of water scarcity in arid regions. It highlights that conventional greenhouse cooling methods like evaporative cooling are “heavily reliant on water,” consuming vast quantities. The proposed EAHE system is presented as a “non-water-intensive sustainable alternative,” thus promoting water-use efficiency.
• SDG 7: Affordable and Clean Energy: The study promotes the use of low-enthalpy geothermal energy, a renewable and clean energy source, to replace energy-intensive conventional heating and cooling systems in greenhouses. It also suggests methods for optimizing fan operation to enhance energy efficiency, contributing to sustainable energy use.
• SDG 9: Industry, Innovation, and Infrastructure: The research represents an advancement in scientific and technological innovation. It develops a “robust, data-driven methodology” for designing and implementing sustainable infrastructure (climate-controlled greenhouses) in data-scarce regions, upgrading the technological capabilities of the agricultural sector.
• SDG 13: Climate Action: The article addresses the need for agriculture to adapt to extreme climate conditions (“pronounced hot summer,” “winter, temperatures frequently drop below 5°C”). The EAHE system strengthens the resilience and adaptive capacity of agricultural practices to climate-related hazards, making food production more stable in vulnerable arid zones.
• SDG 15: Life on Land: By developing technologies that make “desert farming” more “sustainable and economically viable,” the research contributes to combating desertification. It promotes the productive use of arid lands, which helps in restoring land and preventing its degradation.

2. What specific targets under those SDGs can be identified based on the article’s content?

Based on the article’s discussion of sustainable agriculture, resource efficiency, and technological innovation, the following specific SDG targets can be identified:

1. Target 2.4: By 2030, ensure sustainable food production systems and implement resilient agricultural practices that increase productivity and production, that help maintain ecosystems, that strengthen capacity for adaptation to climate change, extreme weather, drought, flooding and other disasters and that progressively improve land and soil quality.
   • Explanation: The article’s entire premise is to create a resilient agricultural practice (greenhouse cultivation) in an extreme climate (arid desert) using a sustainable system (EAHE). The study validates that this system allows for “continuous, year-round crop cultivation,” directly contributing to increased productivity and resilience against extreme temperature fluctuations.
2. Target 6.4: By 2030, substantially increase water-use efficiency across all sectors and ensure sustainable withdrawals and supply of freshwater to address water scarcity.
   • Explanation: The article identifies high water consumption from evaporative cooling as a major challenge in arid regions, stating it can be “up to four times the amount of irrigation water.” The EAHE system is proposed as a solution to “minimize water consumption,” thereby directly addressing the need for increased water-use efficiency in the agricultural sector.
3. Target 7.2: By 2030, increase substantially the share of renewable energy in the global energy mix.
   • Explanation: The study’s focus is on harnessing “low-enthalpy geothermal energy,” which is a renewable energy source. By demonstrating its effectiveness for greenhouse climate control, the research promotes its adoption in agriculture, contributing to an increased share of renewables.
4. Target 9.5: Enhance scientific research, upgrade the technological capabilities of industrial sectors in all countries, in particular developing countries, including, by 2030, encouraging innovation.
   • Explanation: The research develops and validates an “integrated methodology” that combines ERA5-Land data with modeling to design EAHE systems in “data-scarce arid regions.” This represents a direct effort to enhance scientific research and upgrade the technological capabilities of the agricultural sector in a developing country context (Egypt).
5. Target 13.1: Strengthen resilience and adaptive capacity to climate-related hazards and natural disasters in all countries.
   • Explanation: The technology is designed to function in “extreme climates” with high summer and low winter temperatures. By successfully regulating greenhouse temperatures, the EAHE system enhances the adaptive capacity of agriculture to these climate-related hazards, ensuring stable production despite external weather volatility.

3. Are there any indicators mentioned or implied in the article that can be used to measure progress towards the identified targets?

Yes, the article mentions or implies several quantitative and qualitative indicators that can be used to measure progress towards the identified targets:

• Indicator for Target 2.4 (Sustainable Food Production):
  • Maintenance of Optimal Greenhouse Temperature Range: The article explicitly states the success criterion is maintaining temperatures “below 35°C in summer, above 20°C in winter.” This temperature range is a direct, measurable indicator of the system’s ability to create a resilient and productive growing environment.
• Indicator for Target 6.4 (Water-Use Efficiency):
  • Reduction in Water Used for Cooling: The article contrasts the EAHE system, a “non-water-intensive” method, with evaporative cooling. Progress can be measured by the volume of water saved by adopting EAHE technology instead of traditional water-based cooling systems in greenhouses in arid regions.
• Indicator for Target 7.2 (Renewable Energy Share):
  • Adoption Rate of Geothermal Systems in Agriculture: The study provides a methodology for implementing EAHE systems. An indicator of progress would be the number or percentage of new or retrofitted greenhouses in arid regions that adopt this low-enthalpy geothermal technology for climate control.
• Indicator for Target 9.5 (Innovation):
  • Use of Data-Driven Methodologies in System Design: The article’s use of ERA5-Land data to overcome the lack of local meteorological stations is a key innovation. The adoption of this “robust, data-driven methodology” for designing agricultural systems in other data-scarce regions would be a measure of technological upgrading.
• Indicator for Target 13.1 (Climate Adaptation):
  • Degree of Temperature Regulation: The effectiveness of the system is quantified by its ability to moderate extreme temperatures. For example, without control, summer temperatures exceed 60°C, while the EAHE system keeps them near 35°C. This temperature differential is a clear indicator of enhanced adaptive capacity.

4. Table of SDGs, Targets, and Indicators

Source: nature.com