Solar thermal energy storage (TES) has the potential to significantly increase the operating flexibility of solar power. TES allows solar power plant operators to adjust electricity production to match consumer demand, enabling the sale of electricity during peak demand periods and boosting plant revenues. To date, TES systems have been prohibitively expensive except in certain markets. Two of the most significant capital costs in a TES system are the storage medium (typically molten salt) and the storage tanks. Thermocline storage is a relatively unproven TES method that has the potential to significantly reduce these costs. In a thermocline system, approximately 75% of the required storage medium is replaced with an inert quartzite rock, and only one storage tank is required instead of the two typically needed for high-temperature TES. This report includes preliminary designs and cost estimates for molten salt thermocline systems with capacities ranging from pilot scale to commercial scale. Thermal and system level modeling was conducted to determine the performance of these systems.