Quick Answer
Evacuated tube collectors typically require an average of 2-4 peak sun hours (PSH) of direct sunlight per day in winter to maintain water temperatures above 40°C (104°F).
Winter Performance Characteristics
Evacuated tube collectors are designed to operate efficiently in low sunlight conditions, making them suitable for winter use. They can absorb heat from diffuse radiation, which is more prevalent during overcast days. However, the collector’s efficiency drops significantly below 2 PSH, and temperatures may not reach the desired level.
Design Considerations for Winter Performance
To ensure optimal performance during winter, consider the following design aspects: tilt angle (30-60°) and orientation (south-facing in the Northern Hemisphere). A larger collector array can also help maintain water temperatures, but this increases the upfront cost. Additionally, consider a larger water tank to store heat gained during peak sunlight hours for later use.
Collector Size and Capacity
A typical evacuated tube collector has a capacity of 2-4 kW. For a family of four, a 3-4 kW collector array can provide 20-30 liters of hot water per minute at 40°C (104°F). In winter, the collector may need to operate for longer periods to achieve the same amount of hot water, so a larger collector array or more efficient design is essential to meet hot water demands.
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