The market for air-cooled condensers (ACCs) for power generation applications has increased during the past decade due to growing water use restrictions on power plants. While ACCs are very good at reducing power plant water withdraw, this benefit is associated with a drawback caused by the steam condenser’s operating temperature being dependent on the ambient air temperature.[1] On very hot days, the condenser temperature can rise above its design condition, increasing the backpressure experienced by the low-pressure (LP) turbine and limiting its power output. Because of this, net unit heat rate would increase, resulting in an increase in fuel consumption in order to meet demand. This problem is exasperated if the ACCs have not been adequately sized to maintain performance on the hottest days in order to reduce their size and associated capital costs. One approach to supplement the performance of an ACC is to utilize a phase change material (PCM), which can be frozen at night and melted during the day, with the melting process removing heat from the condensate. The proposed PCM-based supplemental cooling system is presented in Figure 1. This system can either be used in series with an existing ACC or be sized to entirely replace it. In this concept, heat is transferred into the PCM through a pipe connecting the PCM-filled trays. At night, this same pipe is used to transfer heat out of the PCM and into the air through fins at the top of the system. The selection of a suitable PCM is critical to the success of the proposed enhanced ACC system, as it must meet several key criteria. First, the PCM must melt and freeze at a temperature between the nighttime temperature and the target condensate temperature. A melt/freeze temperature around 30 °C is a reasonable value, since it meets the cooling requirements for plants in regions where nighttime temperatures fall to around 20 °C. PCM cost is also critical as the expected quantity required for a full-scale system is considerable. The PCM should also have a high energy storage density, be non-hazardous and non-flammable, and maintain its performance during thousands of freezing and melting cycles. There are two major classifications of PCMs, organic PCMs, such as paraffin waxes and fatty acids; and inorganic PCMs, which are primarily hydrated salts.[2–۴] Organic PCMs offer the benefits of high energy storage capacity, little degradation after many operating cycles and minimal corrosiveness. Inorganic PCMs are typically an order of magnitude less expensive than organics, offer high energy storage capacities, and are non-flammable.[5] Some known issues with inorganic PCMs are that they can degrade over time, they tend to be highly corrosive, and they typically require additives to prevent supercooling. However, since PCM cost is a first consideration for this proposed system, inorganic PCMs are considered to be the first choice.