How many kilowatt hours of electricity will the solar panels generate in 20 days?

A house with a south-facing roof has Photovoltaic panels on the roof. The photovoltaic panels have an efficiency of 10.3 % and occupy an area with dimensions 3.35 m by 8.55 m. The average solar radiation incident on the panels is 305 W/m2, averaged over all conditions for a year. How many kilowatt hours of electricity will the solar panels generate in 20 days?

What’s the most efficient way to make electricity from solar power on a large scale?

What’s the most efficient way to make electricity from solar power on a large scale? Is it using Photovoltaic cells, or mirros and a turbine or what? I’d be interested in a web site that compares all the options by efficiency, cost, reliability in cloudy weather, and stuff like that.