One of the issues that we see come up from time to time is when people need or want to install a flat plate collector flat on a flat or very low pitch roof. While this is easier to install it brings with it it’s own set of problems.
Most flat plate collectors on the market today have some gasket or seal around the glass. This gasket or seal has on top of it a cap rail or a portion of the extrusion. This build up of material on top of the collector (gasket and top rail) creates a lip that will hold a puddle of water. Pretty much every collector on the market has a sealing system that isn’t designed to keep water out when it is fully submerged in water for a period of time. What this translates into is more than a normal amount of fluid entering the collector box.
Flat plate collectors should have ventilation holes that will enable the collector to breath and exhale any excess moisture that gets into the box as a result of humid conditions. The ventilation holes rarely can accommodate the extra moisture that would end up in the collector as a result of the collector sitting flat on its back in a rainy environment. If too much moisture gets into the collector box then the collector will have a tendency to sweat on the inside as the moisture evaporates and then condenses on the glass. Over time this will leave dirt and contaminants on the glass making the glass dingy and difficult to see.
For those of you that think this spells an advantage for evacuated tubes you would be mistaken. Evacuated tubes that use heat pipes require the collectors to be tilted up at 35 degrees in order to allow the heat to move successfully from the bottom of the tube to the heat exchanger at the top.
The long and the short of it is. Tilt your collectors if you want them to last and not have crud build up on the inside that could hamper future performance. We recommend a minimum of 8 degree tilt.