Abstract. Solar Two is a utility-led project to promote the commercialization of solar power towers by retrofitting the Solar One pilot plant from a waterhteam-based system to a molten salt system. Solar Two is capable of producing 10 MW, net electricity with enough thermal storage capacity to operate the turbine for three hours after sunset. The plant was turned over to its operations and maintenance contractor in February 1998, marking transition from start-up to the test and evaluation phase. Solar Two has collected as much as 230 MWh thermal and generated as much as 72 MWh, gross electricity in one day. The plant has demonstrated dispatchability after dark, during clouds, and during sunshine hours. To date, Solar Two has collected thermal energy at a maximum rate of 39 MW, and generated gross electricity at a maximum rate of 1 1.1 MW,. Important lessons have been learned in the areas of heat trace, valve selection, materials of construction, and steam generator design. Testing has begun in a number of areas relating to receiver performance, storage tank performance, salt chemistry, overnight thermal conditioning, electricity dispatching, performance monitoring and evaluation, availability tracking, and receiver controls.