All the energy available to all the plants and animals on earth - including humankind - comes from two sources, our sun and Earth. Let's explore the ways in which we harvest the energy they provide.
There are the forces of organic life on Earth:
Living protozoa, rotifers, nematodes, bacteria, fungi and other microorganisms, break down organic materials, making the nutrients available within the soil. They call this the soil food web. Plant cells combine solar energy, air, and nutrients in the soil to produce plant matter.
Primary consumers eat plants.
Secondary consumers eat primary consumers. Tertiary consumers eat secondary, and so on to final consumers.
While there is variation among groups and overlap among categories, all living things die, and the nutrients which comprise their bodies return to the soil nutrient cycle.
Hydrologic Energy
In the hydrologic cycle, the sun drives evaporation, water vapor condenses and falls as rain, creating rivers and streams, eventually the water evaporates again, repeating the process.
Wind Energy
The sun warms air which rises, and then falls as it cools, creating areas of low and high pressure. Wind is created by the air masses attempting to reach equilibrium, moving from high pressure areas to low. The wind also creates ocean waves, from which we can harvest energy.
Solar energy
Solar radiation can be collected, stored and distributed as heat by anything with mass, as occurs with passive solar designs. Otherwise, we can store the sun’s energy as electricity through the use of photovoltaics, which employ semiconducting materials.
Fossil fuels - Petroleum, coal and natural gas
Plants and animals harvest the energy of the sun over the course of their lives, then die, and over millions of years under the pressure and heat of the earth, turn into liquid, gas or solids which can be burned.
These methods of harvesting the sun’s energy are extremely inefficient because beyond taking literally millions of years to create, they require huge expenditures of resources in order to harvest
and utilize them, and have wildly harmful side effects such as pollution and carbon emissions, which then require energy to be spent to mitigate the damage.
While nothing much would be happening on the earth without our sun, we do have access to the stored energy of the earth itself.
Gravity
The Earth's mass exerts force toward its center. This natural force is highly useful, but only in one direction, and thus its usefulness has limits.
Biofuels
Liquid or gas fuels created from crop plants or organic waste. These include bioethanol, biodiesel, and methane from anaerobic digestion. This category has both high and low greenhouse gas producing options.
Electromagnetic energy
This is a spectrum of wave energy that can be efficient and useful but are often complex and require expending further resources in their use. Microwaves, x-rays, tv, visible light and radio waves all fall in this category.
Fuel cell energy
Derived from chemical reactions, this energy requires a continuous source of fuel and oxygen. It is emission free and can have varying degrees of efficiency. There may come a time when we make better use of this form of energy.
Nuclear energy
This is energy derived from fission, decay or fusion of radioactive material. While it is a low carbon emission energy source, its waste disposal and high-risk materials make this energy source fraught with concerns.