How to calculate the annual solar energy output of a photovoltaic system?

First you need to learn what the words mean. Then you need to learn some basic physics. The answer depends on what you are talking about, and it varies wildly.

The sunlight at the top of the atmosphere is roughly 2.6 kilowatts per square yard. The amount of that reaching the ground might be from 0 to 1 kilowatt. That depends on where you are, what latitude, and time of day. It depends on whether your collectors are flat, angled, or motorized. It can be reduced by bird poop or dust on the collector, dust in the air, clouds, trees, anything that casts a shadow. The light that actually reaches the active element in the collector is only partly converted to electrical power, typically 12% or maybe more. So even if everything is perfect, you only get 120 watts out of the 2600 the sun sends. When you realize that, then you might decide to reevaluate your concept of "solar energy". A solar clothes dryer is a rope: a square yard of fabric on a clothesline actually absorbs a rather large fraction of the sunlight falling on it. The only conversion is from heat to water vapor. A solar cooler is a tree. A house built with the long dimension lying east-west uses noticeably less utilities than a house in some other orientation.

If you do a google search for solar power you will eventually realize that the only thing that makes it profitable is the government subsidies.