Can evacuated tube solar collectors perform well in cloudy winter?

Operating Efficiency in Cloudy Conditions

Evacuated tube solar collectors have a higher operating efficiency in cloudy conditions compared to flat plate collectors. This is due to their ability to absorb infrared radiation from clouds, which is typically lost in flat plate collectors. However, the overall efficiency is still reduced by 30-40% in cloudy conditions compared to ideal conditions with direct sunlight.

Collector Angles and Orientation

To maximize the performance of evacuated tube solar collectors in cloudy winter conditions, collectors should be installed at an optimal angle to capture the available sunlight. A general rule of thumb is to tilt the collectors at an angle equal to the latitude of the location. For example, if the latitude is 40°, the collector angle should be around 40°. Additionally, collectors should be oriented towards the south to maximize the amount of direct sunlight received.

Supplementing with Additional Heat Sources

To maintain consistent water temperatures in cloudy winter conditions, evacuated tube solar collectors can be supplemented with additional heat sources such as back-up heaters or heat pumps. This can help maintain the desired water temperature, even on extremely cloudy days. Consider installing a 2-3 kW back-up heater to supplement the solar collector’s output, especially during periods of prolonged cloud cover.