Note that the wofati was sited to minimize solar gain in order to test whether enough heat would be in the mass of the berm. I personally would put in some solar collection to heat the core of the berm. Climate batteries are usually designed to bury heat deep in the mass during hot weather so the surface of the mass is still cooling the interior of the structure then the slow migration of the heat reaches the interior of the structure during the cold weather. So far the performance indicates that the interior of the berm is not warm enough to prevent cooling the interior below comfort level because it can only add heat when the temperature of the interior drops below the berm temperature. I would want the core of the berm to be at least 80 degrees by September.