Final answer:
The exact number of concentrated solar power plants in the U.S. as of 2007 is not provided; however, CSPs represent a smaller portion of the renewable energy sector compared to photovoltaic power, with significant contributions from California and Arizona.
Step-by-step explanation:
As of 2007, the number of concentrated solar power (CSP) plants in the United States was comparatively small. Solar thermal power plants use concentrating solar collector systems to collect and concentrate sunlight, generating high temperature heat required for electricity generation. An example of such a facility is the Ivanpah solar thermal plant which utilizes 170,000 mirrors and covers 4000 acres of public land near the Mojave Desert. These plants, located especially in sun-saturated deserts, are capable of substantial power production. Although the exact number of CSP plants in 2007 is not stated, the information indicates that solar thermal power is a smaller contributor compared to photovoltaic (PV) power. By 2018, solar thermal power production was mainly located in four states, with the largest share in California and Arizona.