Final answer:
Unused electricity from home solar panels is typically redirected back to the utility grid, Arizona and Nevada are likely locations for solar thermal power plants in the U.S., and high installation costs are a major obstacle to widespread solar panel use on residential buildings.
Step-by-step explanation:
Unused electricity generated by solar panels on a home is typically b) Redirected back to the utility grid, where it can be used elsewhere or credited to the homeowner's account. This is because the majority of solar installations are grid-tied and most households do not use battery storage due to the additional cost and maintenance. It is possible to store excess electricity in a home battery system, but this often doubles the cost of the system and the batteries require replacement before they pay for themselves in electricity bill savings.
You would most likely find a solar thermal power plant in locations with high solar irradiance, such as deserts, which makes a) Arizona and d) Nevada ideal locations in the United States. These plants require substantial land and are commonly placed in areas with high sunshine and low water availability, leveraging the intense sunlight to generate electricity efficiently.
The major problem impeding the widespread use of solar panels on residential buildings is the a) High installation costs. The high upfront costs combined with the intermittency of solar generation make solar panel deployment more challenging. Batteries can resolve intermittency issues but add significant costs and require regular maintenance and replacement over time.