Solar hot water systems (SHWS) are often seen as ideal for regions with abundant sunshine and high temperatures. Places like the United Arab Emirates (UAE), with its intense solar radiation and long sunny days, appear to be perfect candidates for widespread solar water heating adoption. However, despite the favourable solar potential, many types of SHWS face a unique set of challenges in such hot climates. Understanding these challenges is key to designing more effective, efficient, and sustainable systems for these regions.
Overheating and System Stress
One of the most significant challenges for solar hot water systems in hot climates is overheating. Since solar thermal systems are designed to absorb solar radiation and convert it into heat, excessive ambient temperatures combined with prolonged sun exposure can push these systems beyond their optimal temperature range. The issues is often experienced in peak summer periods when hot water consumption is reduced. Modern solar thermal collectors can ‘stagnate’
Consequences of Overheating Include:
- Component Degradation: Excessive heat can cause degradation of components such as gaskets, seals, and insulation, leading to leaks or reduced efficiency.
- Pressure Build-Up: Increased temperatures raise the pressure within the system, potentially triggering safety valves or causing pipe damage.
- Reduced Lifespan: Continuous exposure to extreme temperatures can reduce the overall lifespan of the system.
An evacuated tube solar collector installed in Kenya showing signs of damage from overheating
Remedies to Overheating in Solar Hot Water Systems
In regions like the UAE, its important to remedy the issue of overheating. This can be done from a system and component level. Passive or thermosyphon type systems where there is no pump and water is circulated via natural convection are particularly susceptible to damage from overheating as the heating process can not be easily controlled. An active or pumped type solar hot water system is recommended as the heating process is controlled using a temperature controller. This will at least protect the hot water storage tank from over heating, but not the solar collectors! SolarisKit’s flat-packed, prismatic solar collectors have been specifically designed and engineered for use in sunny and hot climates like the UAE and will only heat to a maximum temperature of 90degC making it safer and more reliable.
SolarisKit solar collectors installed at Rixos Hotel in the UAE have been designed to avoid overheating issues in sunny and warm climates
Scaling and Water Quality Issues
In regions like the UAE, water is often desalinated and tends to be hard—rich in calcium and magnesium. When this hard water is heated, it leaves behind scale deposits on the inner surfaces of collectors, pipes, and storage tanks.
Impact of Scaling:
- Reduced Heat Transfer Efficiency: Scale acts as an insulating layer, reducing the efficiency of heat transfer.
- Clogging of Pipes: Scaling can block water flow, increasing maintenance requirements.
- System Failures: Persistent scale build up can lead to complete system failure if not addressed regularly.
Remedies to Scaling and Hard Water Issues
Limiting heating temperature and the choice of system materials is key to tackle this issue. Systems using copper which reach high temperatures should be avoided. Smooth polymer materials are less prone to build-up and scaling making them a good choice, but care must be taken to make sure the system does not reach an unsafe temperature for these materials. The SolarisKit solar collector is made using a high quality engineered thermoplastic material which is smooth and resistant to limescale building up. It provides a new solar hot water solution addressing the issue of scaling.
The SolarisKit solar collector uses a polymer absorber coil which resists limescale build-up
Dust and Environmental Conditions
The UAE experiences frequent dust storms and high particulate matter in the air. These environmental factors significantly affect solar hot water systems.
Issues Caused by Dust:
- Collector Efficiency Loss: Dust accumulation on the collector surfaces reduces solar energy absorption.
- Increased Maintenance Needs: Systems require regular cleaning, which can increase operational costs.
- Corrosion Risk: Dust mixed with moisture can lead to corrosive conditions, especially if materials are not suitably coated or protected.
A flat plate collector solar hot water system installed in the UAE
Mismatch Between Supply and Demand
Another problem is the mismatch between hot water production and usage patterns. In extremely hot regions, the demand for hot water is often lower during the summer, which coincides with peak solar energy availability.
Consequences of Demand Mismatch:
- Energy Wastage: Excess energy generated is not stored or used, reducing overall system efficiency.
- Overheating Risk: Low demand means water stays in collectors longer, increasing the risk of overheating.
- Reduced System Performance: Long stagnation periods can also degrade fluid quality and system materials.
Storage and Heat Loss
While solar radiation is abundant, efficient storage of hot water remains a challenge. Heat losses due to high ambient temperatures, especially at night when the temperature drops, can impact the effectiveness of storage tanks.
Key Storage Challenges:
- Insulation Performance: High ambient temperatures can cause insulation materials to deteriorate faster.
- Night-Time Heat Loss: Even in desert climates, nights can be cool, leading to significant thermal losses if tanks are poorly insulated.
- Tank Placement: Rooftop tanks, common in solar hot water systems, are exposed to the elements and can suffer both thermal and structural wear.
System Design and Adaptation
Many solar hot water systems are designed in temperate or moderately warm regions and are not optimized for the extreme conditions of the Gulf.
Design Limitations Include:
- Non-Optimised Materials: Some materials degrade faster in intense UV and high-heat conditions.
- Lack of Control Mechanisms: Basic systems often lack smart controls to modulate heat absorption or divert excess heat.
- Inefficient Layouts: Poor placement or orientation of panels can lead to sub-optimal performance even in sunny conditions.
Maintenance and User Awareness
Effective performance of SHWS requires regular maintenance and user engagement. Select a partner who is able to offer a Service and Maintenance package with their system.
Maintenance Challenges:
- Lack of Skilled Technicians: There is a shortage of locally available expertise in solar thermal maintenance.
- User Neglect: End-users may not understand the importance of regular flushing, scale removal, or inspection.
- Service Costs: Maintenance services, if outsourced, can be expensive and inconsistent.
Moving Forward: Solutions and Innovations
To overcome these challenges, a combination of technological, design, and policy solutions must be implemented:
- Advanced Materials: Use of UV-resistant, heat-tolerant components.
- Smart Systems: Integration of IoT sensors for real-time monitoring and automation to prevent overheating.
- Hybrid Systems: Combining solar with backup electric or gas systems for reliability.
- Water Treatment: Installation of pre-treatment filters or softeners to reduce scaling.
- Regular Cleaning Protocols: Automated or easy-to-use cleaning systems for collectors.
- Policy Support: Subsidies, awareness campaigns, and training programs to boost adoption.
Conclusion
Solar hot water systems hold great promise for sunny and hot regions like the UAE, but they are not without their challenges. Overheating, scaling, and issues with dust, all contribute to their underutilisation. However, with the right combination of innovation, localised design, and supportive policies, these systems can become a cornerstone of sustainable water heating in the region. By addressing these challenges head-on, the UAE and similar regions can take full advantage of their most abundant natural resource: the sun.
If you are seeking an expert local solar hot water partner, please contact SolarisKit today. We will be happy to support your project!
