Solar power is most commonly associated with the photovoltaic arrays found on residential and commercial rooftops, or those used in utility-scale solar farms. However, the general public is unaware that most energy sources used by society depend on the sun in one way or another. This article will describe the role of solar energy in many electricity generation systems that are not considered “solar power” strictly speaking.
Wind turbines and solar photovoltaic arrays are similar because both technologies use a variable energy input that is free, and both operate without producing greenhouse gas emissions. However, a wind turbine actually harnesses solar power indirectly:
In a few words, when you use a wind turbine you are actually extracting solar energy from the air. One could argue that wind turbines are another type of commercial solar power system. The main difference is that solar panels harness sunlight directly, while wind turbines use solar energy that was first converted to heat and then kinetic energy.
Hydroelectricity is another power generation technology that is very dependant on the sun. Consider that hydroelectric power plants use water that flows from higher to lower locations, but that water had to reach high places first, in the form of precipitation.
For precipitation to occur, water has to evaporate from rivers, lakes, oceans and other bodies of water. It then condenses to form clouds in the upper atmosphere. In turn, the evaporation process is caused by solar heating.
In a few words, hydroelectricity is only possible because the sun causes water to evaporate. Otherwise, there would not be a water sources for the rivers used by hydropower facilities.
Hydropower is demanding in terms of site conditions, since you must find a suitable site for a reservoir where the environmental and social impact is minimized – a hydroelectric facility can be very disruptive for surrounding ecosystems and communities.
When we use fossil fuels, we are actually using solar energy from millions of years ago. Consider that fossil fuels have formed from the remains of ancient organisms, mostly plants. When these plants lived, their main source of energy was photosynthesis, where the main input is sunlight. Even if fossil fuels also come from animal remains, consider that plants are at the bottom of the food chain.
Fossil fuels have been the dominant energy source for decades because they hold a large amount of energy per unit of volume, and they can be burnt at any time to drive steam turbines. However, the use of fossil fuels comes with a high price: greenhouse gas emissions that threaten to destabilize global climate by the end of the century.
Biomass power consists on processing organic waste into a usable fuel for heating or electricity generation. In many cases, crops are harvested with the sole purpose of providing a biomass source, and the concept is also viable for farming and food processing operations with abundant organic waste.
Farming operations depend on sunlight for photosynthesis, and at the same time the entire food industry rests on agriculture. Biomass power comes from vegetable or animal waste, or directly from processed crops – applying the same logic used for fossil fuels, one can conclude that biomass power is possible thanks to sunlight.
Waves are caused when the wind transfers it energy to the ocean surface, causing crests and troughs. Although the required technology is still in its early stages, using wave motion to produce electricity is possible. Considering that waves are caused by the wind, and in turn the wind gets its energy from the sun, this would be yet another method of harnessing solar power indirectly.
As implied by its name, tidal power consists on generating electricity with the rise and fall of tides, which exist due to interactions between the gravitational fields of the sun and moon. Although the moon also plays a role in this case, it is another energy source that is possible thanks to the sun.
Geothermal and nuclear power are the only major electricity sources that do not depend on the sun:
However, it is important to note that the sun is essentially a giant fusion reactor, bound together by its own gravity. If humanity manages to deploy nuclear fusion as a commercially viable electricity source, we would be imitating the sun even if the technology does not depend on it.
Astrophysicists have also determined that elements such as iron and carbon are formed in the cores of stars due to nuclear fusion, and when these stars explode as supernovae these elements become the building blocks for planets. All the atoms that compose the Earth were formed by fusion in stars like the sun.