Ice storage for unitary, direct-expansion air conditioners is a promising load-shifting technology that has the potential to also improve cooling efficiency. This technology typically makes and stores enough ice at cooler nighttime temperatures to satisfy the entire daytime cooling load. As such, it is well suited for shifting air-conditioning loads—which often dominate utility summer peaks—to off-peak times. In field tests, ice storage units successfully shifted 95 percent of the air-conditioning load they were addressing. After a decade of development, ice storage appears to have made large improvements in cost and reliability—but it’s still expensive. However, at an installed cost of $2,100 per kilowatt, it has the potential to compete with several utility-scale storage technologies, including flow and sodium sulfur batteries. It remains to be seen if manufacturers can achieve the savings and reliability levels they are claiming for the latest generation of equipment.