7 Wacky Sources of Alternative Energy

The argument for human-induced climate change can be boiled down to some pretty simple math. The fossil fuels we've consumed since the Industrial Revolution took tens of millions of years to create through biological and geological processes. We've been releasing those hydrocarbons as carbon dioxide at an ever-increasing rate for less than 200 years. For man-made CO2 emissions not to have overwhelmed the planet's natural carbon cycles, we would need to have consumed less than 0.002% of all fossil fuels ever created. Since we've consumed an estimated 135 billion barrels of oil since the days of John D. Rockefeller, that means there would need to be 6,750,000 billion (that's not a typo) barrels of oil on the planet -- a number that far exceeds realistic estimates. Oops.

With that in mind, dozens of nations have pledged to dramatically reduce their CO2 emissions this century to restore some balance. While wind and solar power steal all of the headlines, they're not the only sources of alternative or renewable energy available to us. Take a look at these seven wacky power sources that are displacing traditional energy sources today -- or may in the near future.

1. Bacteria that eat natural gas

The use of microbes to produce fuels and chemicals has enormous potential, although the "biomanufacturing" industry has yet to produce many commercial success stories aside from corn ethanol and a handful of lesser-known chemicals. Genetically engineering yeast to produce jet fuel hasn't panned out, while the Holy Grail of algae biofuel is still decades away at best. But engineered-biology conglomerate Intrexon (NYSE: XON) thinks we're doing it all wrong.

Intrexon is starting with a microbe that naturally lives on methane. It hopes to engineer the bacteria to convert methane -- found in the cheap and abundant natural gas that can be extracted from American shale formations -- into cost-effective transportation fuels. The fuel of choice, butanol, is compatible with existing infrastructure and car engines and is more energy-dense than ethanol. There are quite a few engineering obstacles to overcome, but it may one day be possible to fill up your tank with fuel created from bacteria that munched on natural gas.

2. Tidal power

A rising tide lifts all boats, but it could also power coastal towns and cities. Tidal power projects haven't quite taken off in the United States, but South Korea and France own tidal power plants with power output capacities of 254 MW and 240 MW, respectively -- on par with smaller fossil-fuel facilities. Although America's ocean tides aren't the most economical for this energy source, the country happens to have more deep and navigable rivers than all other nations combined. And as it turns out, rivers have plenty of untapped tidal power potential.

Verdant Power, a tidal power systems manufacturer, has been working with the city of New York to test tidal power generation on the East River for over 10 years. How does it work? Think of the system like a farm of wind turbines that are submerged underwater. Water rushes past the turbine, which spins, generates electricity, and transmits that power to the surface. The company was the first to obtain a commercial license for tidal power in the United States and has since expanded to the United Kingdom and Ireland. If the East River project proves successful after additional environmental monitoring, it could kick-start a tidal power industry capable of supplying 15% of America's electricity needs.

3. Biomethane

The main component of natural gas is methane, which can be burned to produce electricity or heat, compressed into liquid transportation fuels, or (perhaps someday) fed to microbes that convert it into useful fuels and chemicals. In addition to being found in fossil fuels, methane is produced in large amounts from biological processes that break down organic wastes. Cows are the most notorious organic source of methane: According to the EPA, "enteric fermentation" (read: cow burps) accounted for 25% of all U.S. methane emissions in 2015, while manure stockpiles contributed another 10%. However, the decomposing waste in landfills provides an abundant source of biomethane that's easier to industrialize.

Waste Management and Clean Energy Fuels (NASDAQ: CLNE) have developed technology to efficiently capture biomethane from landfills and convert it into transportation fuels. In fact, renewable natural gas-based fuels have recently been among Clean Energy Fuels' biggest revenue-drivers. The company's Redeem brand sold close to 59 million gasoline gallon equivalents in 2016, representing 18% of its total fuel sales, and it has grown 190% since 2014.

The EPA even recognizes biomethane as an official pathway for producing renewable fuels, which provides access to valuable subsidies. It should be enough to ensure these fuels stick around and grow for the foreseeable future.

4. Black liquor

At some point in your life you've probably been encouraged not to waste paper so that you can save trees, but there's not a whole lot of data to support that simple solution. That's because the pulp and paper industry is one of the most sustainable on the planet. Not only have most companies committed to source their trees from sustainable farms, but an astounding 56% of the energy used by the industry is produced within pulp and paper mills. They accomplish that feat with one truly wacky alternative energy source: black liquor.

No, it's not a drink, but rather a byproduct of the pulping process that contains a mixture of chemicals distilled out of wood pulp. Companies such as Domtar (NYSE: UFS) use it to generate up to 76% of their energy needs each year, while others are actually net generators of electricity. You may not have heard of black liquor before, but that may soon change. Many of the boilers used to burn the smelly liquid are nearing the end of their life and need to be replaced, which has scientists looking for additional uses aside from steam generation. Potential applications include low-cost chemicals and fuels that could further displace fossil fuels in the near future.

5. Buildings

We usually think of buildings -- houses, warehouses, and skyscrapers -- as energy consumers. But we could soon be using them to produce energy, too. That could turn electricity and natural gas utilities on their head.

For instance, an apartment complex in Hamburg, Germany, decided to get creative with the 2,100-square-foot surface area of its exterior. The building's outside-facing walls are laced with transparent panels filled with algae that grow using sunlight and industrial carbon dioxide pumped through the panels. A collection system harvests the algae for biomass, dries them into pellets, and burns them to generate biogas for electricity and heat for the building. Some have questioned the economics of such a system, but others think the technology could become an important source of energy -- and spread across an entire city.

6. Mud batteries

If someone asked you to name something with no use or value, then the first thing to spring to your mind just might be dirt. Yet bacteria in the soil interact with each other and their surroundings in complex ways, one of which is transferring electrons back and forth. That means the ground beneath your feet may in fact be a giant battery.

Researchers have experimented with "mud batteries" and microbial fuel cells for years. Essentially, by sticking rods into the ground, it's possible to use muddy ecosystems as a giant power source. While they're not the most efficient source of energy, the microbes central to the process can generate electricity by breaking down toxic industrial pollutants and even uranium waste before it has a chance to contaminate drinking water. If nothing else, such a system could make bioremediation projects more cost-effective by providing a revenue stream from energy production.

7. Ocean thermal gradients

Decades ago, the U.S. Department of Energy (DOE) thought that ocean thermal gradients could become an important source of renewable energy. Congress agreed, as evidenced by the passing of the the Ocean Thermal Energy Act of 1980. It hasn't quite turned out that way, but research is slowly picking up in the area once again.

How would this power source work? Large floating barges would take advantage of temperature differences between warm surface water and cold water hundreds of feet below with something called a "heat engine." Essentially, by pumping water through large pipes, it's possible to create a current, spin a turbine, and generate electricity with little human input.

The state of Hawaii launched a small 100 kW facility in 2015, with hopes it will prove a success and be the first of many such projects. Meanwhile, Lockheed Martin is working with the DOE to design a 10-MW prototype that could eventually pave the way for 100 MW or larger power plants. The power plants could also be configured to sanitize water, produce industrial chemicals, or even help to feed fish by bringing nutrient-rich water closer to the surface. It could prove to be an important alternative energy source sooner than you think.

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Maxx Chatsko has no position in any stocks mentioned. The Motley Fool owns shares of and recommends Clean Energy Fuels. The Motley Fool owns shares of Waste Management. The Motley Fool has a disclosure policy.