Solar panels absorb energy from the UV rays of the sun. They will generate electricity on cloudy days as well as sunny days. The solar panels create DC electricity, and the more panels wired together, the more electricity the roof will be able to generate.
The inverter is the brain of the solar installation. It takes the DC electricity from the solar panels and converts it to AC electricity, which is the type of electricity provided by the utility grid. Inverter technology is very efficient and is able to convert almost 100% of the energy passing through. It also makes adjustments based on temperature and sun intensity to maximize the wattage coming off the roof.