What Happens When Too Much Shade Hits Solar Hot Water Collectors?

Reduced Energy Harvest

When solar hot water collectors are shaded, the energy they collect is greatly reduced. Even partial shading can lead to a significant decrease in efficiency, as the collectors are designed to work best in direct sunlight. For example, if a collector is 50% shaded, its efficiency can drop by as much as 30%. To mitigate this issue, it’s essential to ensure that the collectors are mounted to allow for maximum sunlight exposure throughout the day.

Shading Impact on System Performance

The impact of shading on system performance can be quantified using the “Shading Coefficient” (SC). The SC is a measure of how much the system’s performance is affected by shading. A higher SC indicates a greater impact on performance. For example, if the SC is 0.8, the system’s output will be 80% of its expected value. System designers can use the SC to estimate the potential impact of shading on the system’s performance and design accordingly.

Optimizing Collector Placement

To optimize collector placement and minimize the impact of shading, it’s essential to follow these guidelines:

• Install collectors at a high angle (30-40°) to maximize exposure to sunlight throughout the day.
• Ensure collectors are mounted at least 10 feet above nearby obstacles to prevent shading.
• Install collectors on a south-facing roof or wall, ideally with a slight overhang to prevent shading from nearby structures.
• Consider installing a tracking system to move the collectors to follow the sun’s movement, but this can add significant complexity and cost to the system.