The energy rate aka power of sunlight is measured and known to be about 1kW/m^2. In a square area of one meter by one meter, how many people can live? One human consumes about 100W of power for a 2000 Cal diet per day. So if human is caged like a chicken farm, Sun can grow max 10 humans per square meter. How big is the earth normal to sunlight direction? Earth radius is known to be about 64000kM. Simple math of an area of circle is 3.14 * 6400kM * 64000kM = 3.14 x 6.4 x 10 ^6 m x 6.4 x 10^6 m ~ 129 x 10^12 m^2 = 1.29 x 10^14 m^2. Considering non-ideal cases, let us suppose a yield of one human per square meter with 10% efficiency. One million is 10^6, one billion is 10^9, one trillion is 10^12. In a simple calculation, 100 trillion humans can live on earth sustainably. Currently there are less than 100 billion people living on earth. Gee, a thousand times more people still can live with the energy received from generous Sunlight. With 1 dollar for 10kWh rate, 1.29 x 10^14 m^2 x 1kW/m^2 x 1 dollar / 10kWh= 1.29 x 10^15 dollars/h = 1.29 x 10^15 dollars/3600s ~ 358 x 10^9 dollars/s = 358 billion dollars per second. So we seem to receive 358 billion dollars every second from Sun. Everyone on earth should earn 3 dollars per second. The minimum wage should be 10 thousand dollars per hour. Then why are we not rich? Where does all the money go?
Is it really free?
You don’t know until you have to pay for it.
Is it not enough?
If everyone uses a thousand times more energy than needed, it is not enough. We need to find an alternative energy source. One example is well known fossil fuel that captured previously given sunlight and stored in the form of oil, gas and coal, etc. Another is from energy-matter conversion using E=mc^2, the energy captured in the form of matter in the very early stage of our Universe. The fossil fuel is current major energy supplier with a limited inventory. Energy-matter conversion has seen a limited success in the laboratory so far with a promising result to come later. Energy-matter conversion is what the Sun is doing to give us free energy.