The story starts with a cloud.
About 4.6 billion years ago, a vast region of interstellar gas and dust, mostly hydrogen, with traces of helium and heavier elements forged in earlier stars, began to collapse under its own gravity. As material fell inward, it compressed and accelerated. Temperatures climbed. In the densest part of the cloud, they eventually reached about 27 million degrees Fahrenheit, the threshold at which atomic nuclei, normally repelling each other, are forced close enough together that a different force takes over.
Nuclear fusion ignited. The sun was born.
It has been running on exactly the same mechanism ever since, and it will keep running on it for roughly five billion more years.
What is actually happening inside it
Most people understand, in a loose way, that the sun produces energy. Fewer people know how.
The sun is not burning in any conventional sense. Burning is a chemical reaction: fuel reacts with oxygen, releases energy, produces ash. The sun has no oxygen. What it does instead is convert mass directly into energy.
In the sun's core, hydrogen atoms are moving so fast and the pressure is so intense that four hydrogen nuclei collide and fuse into a single helium nucleus. A helium nucleus, it turns out, is slightly lighter than the four hydrogen nuclei it was made from. The missing mass does not disappear. It becomes an enormous amount of energy.
The sun converts about four million metric tons of mass into pure energy every second. Four million metric tons is roughly the combined weight of 30,000 fully loaded Boeing 747s. The sun contains enough hydrogen to sustain fusion at its current rate for another five billion years.
The numbers in human terms
The sun's total energy output is approximately 3.8 times ten to the twenty-sixth power joules per second. Put another way: the total amount of solar energy that strikes Earth's surface in a single hour is greater than everything humanity uses in an entire year.
Everything. Every car, plane, and ship. Every factory, server farm, and hospital. Every light left on and every phone charging overnight. All of it, for a full year, is less than what the sun delivers to this planet in about 60 minutes.
Earth intercepts roughly one two-billionth of the sun's total output. The rest radiates outward into space. What reaches us, the one two-billionth, is already more than we can use.
What this means for homeowners
For most of human history, we have used solar energy indirectly. Photosynthesis converts sunlight into plant matter. We ate the plants, burned the wood, and eventually dug up the ancient compressed remains of organisms that had themselves run on photosynthesis. We have always been a solar-powered civilization, just at a remove of millions of years.
The photovoltaic cell, first developed at Bell Labs in 1954, changed the relationship. A photovoltaic cell works by a different principle entirely. When photons of light strike a semiconductor material, they knock electrons loose. Those free electrons, directed through a circuit, become electrical current. A direct conversion of sunlight into usable power.
A solar panel on your roof is not a complicated piece of equipment. It is a semiconductor that converts photons into electrons. What makes it remarkable is what it connects you to.
For many homeowners, electricity rates have nearly doubled in the past 5 years. The sun? It's been creating free, abundant power for nearly 5 billion.
Systems Architect at Daylight. Sunnyside is Daylight’s guide to energy, the grid, and the weather that moves your bill.