Assignee:NASA, USA It is desirable to provide an efficient, inexpensive, commercial small capacity solar refrigerator which can operate for several days in the absence of sunlight. As batteries are often expensive and require regular maintenance, it would further be desirable to provide such a solar refrigerator which does not require batteries. A solar powered vapour compression refrigeration system is practicable with thermal storage and novel control techniques. In one embodiment, the refrigeration system includes a photovoltaic panel, a variable speed compressor, an insulated enclosure, and a thermal reservoir. The photovoltaic (PV) panel converts sunlight into DC (direct current) electrical power. The DC electrical power drives a compressor that circulates refrigerant through a vapour compression refrigeration loop to extract heat from the insulated enclosure. The thermal reservoir is situated inside the insulated enclosure and includes a phase change material. As heat is extracted from the insulated enclosure, the phase change material is frozen, and thereafter is able to act as a heat sink to maintain the temperature of the insulated enclosure in the absence of sunlight. The conversion of solar power into stored thermal energy is optimised by a compressor control method that effectively maximises the compressor's usage of available energy. A capacitor is provided to smooth the power voltage and to provide additional current during compressor start-up. A controller monitors the rate of change of the smoothed power voltage to determine if the compressor is operating below or above the available power maximum, and adjusts the compressor speed accordingly. In this manner, the compressor operation is adjusted to convert substantially all available solar power into stored thermal energy. Patent number: US 6469487 Publication date: October 22, 2002 Inventors: Michael K Ewert, David Bergeron III