Solar Expansion Tanks

Stagnation: A properly designed solar heating system must be able to stagnate (overheat) and do it often. A system that is not able to handle stagnation will result in quick failure. In fact, stagnation is the "off switch" in a solar system and most controllers will force stagnation at 120 C (250 F) or less to avoid damage to pumps and seals. Stagnation often occurs when the amount of solar energy exceeds the demand energy plus the energy stored in the storage tank. This can happen during holidays or when a pump fails such as a power outage.

When a system goes into stagnation, the pump shuts down so that the hot liquid only remains in the solar collector’s manifold. The collectors may quickly reach a temperature of 210 C (410 F). This temperature is above the boiling point of any glycol mixture and causes the glycol to boil and turn to steam. The steam has a much greater volume than the liquid and increases the pressure of the closed loop system. An expansion tank must be able to accommodate the steam volume by accommodating this increased volume inside it's tank. If designed properly for the number of collectors a solar heating system should be able to stagnate for days with out any damage. In fact, proper certified solar collectors such as SunRain TZ58 1800 30R our our Thermax Extreme Flat Plate Collectors must pass a 30 day test of 100% stagnation to ensure the collectors can with stand the heat before they are approved.

Note: using proper solar glycol is very important. Most glycol can not withstand the extreme temperature of stagnation and quickly break down. Solar glycol is completely vaporizable meaning no liquid remains in the collector header under stagnation & it is rated for temperature exceeding 450 F.

This is probably the most important part of designing a solar heating system and has many variables. However, we take the guess work out of sizing by proving complete DIY Solar Pool Heating Kits with the tank size already factored into the design. You can be assured that when purchasing any of our solar heating system you will be supplied with a safe and reliable expansion tank capable of allowing your system to safely stagnate. For those that want more information on sizing of expansion tanks click on this link.