The Iowa Stored Energy Plant Agency’s (ISEPA) compressed air energy storage (CAES) project is winding down. The project plan was to take  wind turbine energy put into the grid when the demand was low, use it to power compressors to compress air to 1200 psi, store it 3000 feet under ground (at that pressure) in a strata of limestone, release it and blow it across the blades of  a turbine to generate electricity when the demand is high. 

The geology was important.  The sandstone structure must be in the form of an extremely large upside down tea cup;  have a solid and impermeable caprock, and the sandstone must be porous and permeable.  As it turns out  all of those characteristics existed at the ISEPA site in Dallas Center, Iowa — with one small exception.  The exeption was permeability. The sandstone had a unique form or permeability that could not be discovered without actually drilling and taking samples.  It seems that nature mixed in small shards of clay with the sand. This seriously decreased the permeability.  Simply put, there were enough holes between the sand grains (porosity) but the holes didn’t connect (permeability).  This made it extremely difficult for air to flow through the sandstone. 

Even though the geology didn’t work, the project produced a wealth of information regarding energy storage that will be extremely useful for other power companies contemplating an energy storage project.  That information is found in a Department of Energy sponsored report known as “Lessons from Iowa” authored by ISEPA’s due diligence team: Bob Schulte, myself and Kent Holst.

Recently we produced two YouTube video presentations that explain the stored energy project and the lessons learned.  It’s worth a quick look.  The first video talks about the history of the ISEPA project and the second explores the lessons learned.