If asked to name a renewable energy source, most people would probably say solar power.
When it comes to small-scale residential projects, solar is the only renewable energy source that can deliver energy at a cheaper overall rate than what utility companies are charging.
But that doesn't mean solar is the only game in town. For large-scale industrial projects, other types of renewable energy often deliver sufficient bang for the buck.
Before covering the different types, however, we first need to understand what makes a certain way of generating power "renewable."
"Renewable" doesn't always mean "clean"
While solar power is both renewable and clean, the two terms aren't synonymous.
An energy source is renewable if it can't be depleted. No matter how much energy you generate from a renewable source, there's always going to be more.
But being inexhaustible isn't the same thing as being clean.
Nuclear power, for example, counts as a renewable energy source since, if we relied on it solely, we'd never have to worry about running out.
But as everyone knows, nuclear energy is anything but clean. Generating it creates radioactive waste—one of the most environmentally unfriendly substances imaginable.
Basically, there are two problems with our current method of burning fossil fuels -- we're polluting the environment and we'll eventually run out.
And, as we'll see, though renewable energy sources solve the second problem, they don't always address the first.
So what are the five most common types of renewable energy in service today?
Solar may be the go-to renewable energy source for homeowners and businesses looking to cut costs, but it isn't the most common.
That distinction belongs to wind, which accounts for a full 10% of all the energy generated by utility-scale projects.
As most folks already know, windpower is generated by gigantic wind turbines. The blades are connected to a driveshaft that turns a generator. When enough wind hits the blades, they start spinning—making the driveshaft rotate as well, which causes the generator to produce power.
That means that—just like solar—wind power is both renewable and clean.
Our second most common type of renewable energy is hydropower, accounting for 6.2% of all the energy generated at US utility-scale projects.
Just lIke wind, hydropower is created by turning a massive driveshaft connected to a generator. But instead of being turned by wind, water does all the work. This usually means building a dam or some other type of structure to divert the natural flow of a river or other body of water over the turbines.
And just like wind and solar, that makes hydropower both renewable and clean.
Solar comes in third, accounting for 3.4% of all the energy generated at US utility-scale projects. You'll find everything you need to know about how solar power is generated in our previous post titled—you guessed it— How Solar Power is Generated.
Though solar is the only type of renewable energy likely to make economic sense for small-scale residential projects, only around 4% of US homes are currently taking advantage of its money-saving potential.
But expect solar to climb higher on the chart as more people become aware of how much money they can save with a simple rooftop system.
Fourth place in the list of US renewable energy sources goes to Biomass, which accounts for 1.3% of all the energy generated at utility-scale projects.
1.3% isn't very much. So a lot of folks probably only have the vaguest idea of how biomass works.
Just like wind & hydro, Biomass energy is created by a giant driveshaft connected to a generator. But this time, instead of air or water doing the work, the shaft is turned by direct combustion—the very same method used by power plants that burn fossil fuels.
Unlike fossil fuels, however, biomass is organic material that comes directly from animals or plants.
Examples include corn stalks, wheat straw, and manure. That makes biomass a renewable form of energy since, with proper stewardship, there's no need to ever run out of any of that stuff.
But, as stated above, renewable doesn't always mean clean.
And, unfortunately, burning Biomass does emit large quantities of ozone-forming gases into the lower atmosphere.
The final place in our list of renewable energy sources goes to geothermal, which accounts for a mere 0.4% of all the energy generated at US utility-scale projects.
Like wind and hydro, geothermal power is created by spinning an enormous driveshaft connected to a power generator. But instead of being turned by air or water, the work is done by steam from underground reservoirs.
And just like wind, hydro, and of course solar, that makes geothermal power both renewable and clean.