Polypropylene atmospheric solar storage tanks have the longest lifespan, at about 50 years. Polypropylene is a rigid plastic that is rotationally molded. Tanks are constructed of Polypropylene but would need to be insulated on site. Polypropylene tanks have a temperature rating of 200 degrees F, but are not recommended for use with temperatures below freezing. Caution: When looking for plastic tanks for your solar water storage needs you need to avoid the more common Polyethylene tanks. The polyethylene tanks can only handle temperatures of around 120 degrees and would not be suitable for solar applications. With polypropylene tanks you need to concern yourself about shipping costs since the large tanks generally only come from a few facilities in the country. These tanks are middle of the road price wise for atmospheric storage tanks.