Can flat plate collectors compete with evacuated tubes in snowy climates?

Evacuated Tubes vs Flat Plate Collectors: Key Differences

Evacuated tubes are generally more efficient in cold climates due to their ability to collect heat even when the collector surface is covered in snow. A study by the National Renewable Energy Laboratory found that evacuated tubes can maintain a 50% efficiency rate in temperatures as low as -20°C (-4°F), whereas flat plate collectors typically drop to around 20% efficiency in similar conditions. This is because the glass tube and vacuum insulation in evacuated collectors reduce heat loss and allow for better heat collection.

Snow Loading Considerations

When designing a solar hot water system for a snowy climate, it’s essential to consider the snow loading impact on flat plate collectors. A general rule of thumb is to assume a snow load of 20-30 pounds per square foot (97-145 kilograms per square meter). To accommodate this, flat plate collectors may require additional structural support, increasing installation costs. Evacuated tubes, on the other hand, are often designed with snow loading in mind and can be mounted at a slight angle to allow snow to slide off easily.

System Design Strategies

To make flat plate collectors more competitive in snowy climates, designers can employ strategies such as increasing the collector surface area, using a larger storage tank, or incorporating a backup heat source (like a propane heater). For example, a system designed for a small home in a cold climate might use a 10’ x 20’ (3m x 6m) flat plate collector array, resulting in a higher upfront cost but potentially lower operating costs over the long term.