Abstract: A system and an associated method for determining parking space vacancy using solar irradiance is disclosed. Whether a parking space is occupied by a vehicle or is currently vacant can be determined by taking frequent irradiance readings at one or more parking space sensors and comparing the irradiance readings to baseline irradiance readings and covered control irradiance readings taken at a separate central hub. When the solar irradiance readings at the parking space sufficiently approach the covered control irradiance reading—and thus sufficiently differ from the baseline solar irradiance reading at the hub—a determination can be made that the parking space is occupied by a vehicle and is therefore not vacant. In a preferred embodiment, the system is capable of largely powering itself by connecting the solar cell to a storage battery in each parking space sensor and/or coupling the uncovered hub solar cell to a storage battery in the hub.