Photovoltaic, and specifically solar module, technology represents a rapidly growing market and a significant source of renewable energy. Solar modules provide an effective means of converting ubiquitous solar radiation into much-needed electricity. Temperature monitoring of photovoltaic modules is an important safety measure as well as an ongoing technical challenge. By monitoring the temperature distribution across photovoltaic modules, it is possible to detect the formation of hotspots. Fiber optic sensors are recognized as a promising solution for continuous temperature monitoring, since real-time thermography involves high costs and generates large volumes of data that require processing. In this paper, two types of temperature sensors are utilized to detect hotspot formation in photovoltaic modules: the first based on fiber Bragg gratings (FBG) and the second based on distributed temperature sensing (DTS) using the Brillouin light backscattering phenomenon. Theoretical and experimental studies were conducted to determine their detection limits. We investigated the influence of optical fiber jacketing on DTS performance and demonstrated that a loose-tube cable structure can reduce fiber strain by 35% and decrease the relative error of temperature measurement by 40%. The relationship between hotspot temperature and size, as well as the thermal detection capabilities of fiber optic sensors, was also analyzed. The results show that hotspot formation can be detected with a DTS system when the hotspot temperature is at least 35 °C above ambient and its size is at least 15 cm × 9 cm. In contrast, an FBG sensor can detect a hotspot as small as 1 cm × 1 cm.