With increasing energy costs, using small dry kilns for drying lumber for small-volume value-added wood products has become more of an option when compared with conventional drying. Small solar kilns are one such option, and a number of solar kiln designs exist and are in use. However, questions remain about the design and operation of solar kilns, particularly during the colder months. The main objective of the present study was to evaluate a new solar kiln built using structural insulated panels (SIPs) and its operation in southwestern New Mexico. The study consisted of two solar kiln audits done during winter months for two consecutive years. In the first year, 1-in. ponderosa pine (Pinus ponderosa) random length lumber was kiln-dried from an average of 122% down to 7.7% final moisture content (MC) in 14 days. Drying time for ponderosa pine was consistent between this solar dryer and a dehumidification kiln of comparable size. In the second year, 1-in. pinyon pine (Pinus edulis) single-length lumber was dried from an average of 32.6% to 5.5% final MC in 56 days, a considerably slower drying process that could be at least partially explained by pinyon pine's wood anatomy and also by poor weather conditions and cooler temperatures. In addition, even with the SIP kiln designed to keep the heat gained during the day in the kiln at night, the solar kiln operated considerably worse during the winter months of year 2 when compared with a small dehumidification dry kiln. Recommendations for improving the kiln performance included installing two additional deck fans and setting the plenum space to the correct width to both improve and provide more uniform airflow. After implementing the suggested recommendations, further tests would be needed for drying pinyon pine. Additional runs would evaluate the capability of the solar SIP kiln to dry pinyon pine as well as it did for drying ponderosa pine. These runs would provide information on whether the anatomy of pinyon pine, the kiln structure, weather, or some combination caused the slow drying of pinyou pine in year 2.