Whether you fire pellets at lasers or squeeze together hydrogen atoms, nuclear fusion has long held the potential to create a clean, green, and virtually endless power source. But that day may finally be closer after a breakthrough in 2021.
Even so, many scientists warn that pursuing fusion is a distraction from taking more immediate steps to lower greenhouse gas emissions.
Hydrogen from Waste
Hydrogen is the most abundant chemical element in the universe, and it's in every living thing. But it's rare as a gas - less than one part per million in our atmosphere. Scientists are discovering that different organic waste streams can be used to create hydrogen, which is an ideal clean fuel because it doesn't produce greenhouse gases when burned.
Companies such as Amazon and Walmart are replacing diesel-fueled trucks and other equipment with zero-emission fuel-cell vehicles powered by hydrogen produced from solid waste. This approach can also help governments meet their waste reduction and sustainability targets, as well as generate electricity.
Current hydrogen production technologies such as steam reforming of natural gas and petroleum, partial oxidation of heavy hydrocarbons and coal gasification require large amounts of energy. Next-generation thermochemical processes that convert biomass, medical waste and municipal solid waste into hydrogen without incinerating it could address this issue.
Carbon-Negative Concrete
Concrete is one of the most common construction materials on earth, and it's also responsible for a significant amount of carbon emissions. Engineers at Washington State University have developed a variety of concrete that emits less carbon than it creates during its lifetime.
The researchers replaced a third of the cement in their concrete with biochar, a type of charcoal made from agricultural and forestry waste. The biochar helps the concrete bind together and provides strength.
A startup called Carbonaide is taking this technology further. Its product uses a magnesium mineral from seawater and electricity generated through renewable energy sources to power electrochemical reactors that harvest the Mg2+ ions. The company hopes to eventually use the process to produce concrete that absorbs more CO2 than it emits. If successful, it could help decarbonize the building industry.
Vibrational Energy Harvesting
Vibrational energy harvesting uses ambient mechanical vibration to create energy that can be used to power electronic devices. This is an especially attractive powering option for wireless sensor networks where battery replacement or recharging is impractical and continuous operation without maintenance is desirable.
Energy harvesters are generally fabricated using either microelectromechanical systems (MEMS) processes or by conventional mechanical fabrication methods. MEMS technologies typically allow for smaller harvester dimensions, resulting in more efficient harvesters.
Nonlinear electromagnetic vibration energy harvesters generate power from an electric field generated by a change in capacitance. However, this type of energy harvester is not as effective for high-amplitude vibrations such as those that are produced by human movement. In order to deal with this limitation, many harvester designs employ a buffer between the energy harvester supply and the energy user. This allows the energy harvester to trickle charge a rechargeable battery rather than directly power the device.
Geothermal Binary Plants
Geothermal energy hasn't made much of a splash, but new technology could bring it out of its doldrums. Startups like AltaRock are using millimeter waves to heat water without boiling it. Eventually they'll be able to use that water to create steam and electricity.
But the real breakthrough in geothermal comes down to drilling technology that lets us get down 10 km (6 miles) or more and tap into the even hotter "deep shale" EGS source. This kind of innovation makes a 100 percent clean energy future seem more within reach.
And it offers a way for the struggling oil and gas industry to put its skills to work in a more sustainable field. That's why some oil and gas companies are starting to invest in geothermal startups. They're betting the technology will take off.
Ocean Current Energy
The kinetic energy in ocean currents can be used to create electricity. Engineers have designed underwater turbines that, like wind turbines, use rotor blades to convert rotational energy into electricity. However, seawater is more corrosive than air and waves can make it difficult to harvest energy from the ocean.
Experts say wave energy is still years behind solar and wind, but it could be important for countries that don't have the best access to fossil fuels. Japan, for example, has subpar solar potential and doesn't control any nuclear power plants, so it must focus on alternative energies.
Tidal flow is a reliable source of electricity, but it's only available in specific places around the world. Ocean currents, on the other hand, are a massive untapped resource that is very reliable and clean. And, unlike wind and solar, it is never dependent on weather conditions.
Fungi Bioenergy
Fungi are responsible for things like mildew and athlete’s foot, but they can also create pencillin, a vital drug used to treat cancer patients. Fungi live all over the world, storing carbon and rotting wood for plants, acting as decomposers, and helping to regulate the weather.
Unlike plants, they cannot generate their own food through photosynthesis, so they must absorb nutrients from the environment. Fungi can be yeasts, molds, puffballs or the macroscopic filamentous fungi that form fruiting bodies (such as mushrooms).
Scientists are exploring ways to turn fungi into sources of energy. For example, physicist Sudeep Joshi turned a mushroom into a mini energy farm by using 3-D printing and conductive ink to generate electricity from cyanobacteria growing inside it. He hopes to develop the technique further. This could lead to a greener, more sustainable way to create electricity.
Bioenergy is a versatile renewable energy source that can be used to produce transportation fuels, heat, and electricity. It is created through the conversion of living or recently living organic materials like trees, plants, food waste and perennial grasses, waste biomass, or wood pellets.
Biomass can be converted to liquid transportation fuels by fermentation or pyrolysis or into electricity through combustion or direct conversion. It is currently the largest contributor to renewable energy in the transport and heating sectors and also has significant potential for hard-to-electrify applications such as aviation and shipping.
Dry biomass has low energy density, but it can be pressed into pellets or briquettes to increase its energy density, making it more economically viable for transport. It can also be sourced locally to reduce transportation costs and environmental impact. It can even be combined with carbon capture and storage (BECCS) to become a negative emissions technology.
Salinity Gradient Power
The chemical potential difference between two liquids with different concentration of salt – known as salinity gradient power - can be used to create energy. The resulting osmotic power can be harnessed through a membrane-based process to produce electricity.
The main technologies are Pressure Retarded Osmosis (PRO) and Reverse Electrodialysis (RED). Both use semi-permeable membranes that generate osmotic pressure to drive a turbine to create electricity.
These systems can be installed along coastlines to extract osmotic power from natural water flow. There are environmental concerns, however, such as disruption of the natural habitat, changes to water quality, and risks for organisms at intake and release points. The most significant risk is that this technology will accelerate the mixing of fresh and sea water, reducing biodiversity in marine or brackish waters. This is particularly a concern in deltas and fjords.
Thermophotovoltaics
Researchers have long known that solar cells can capture light from the sun with record-setting efficiency, but now scientists have shown that hot objects emit light too. They've created a new photovoltaic device called a thermophotovoltaic cell (TPV) that can capture energy from a hot source at far higher efficiency than previous designs.
TPVs are optimized for temperatures much higher than those used in conventional steam turbines, so they can be used to power natural gas or hydrogen-fueled power plants, as well as other grid-scale energy storage systems. Reaching a TPV efficiency of 40% would allow these systems to store the equivalent of a day's worth of renewable energy and then release it later, creating "dispatchable" renewable energy.
MIT's experimental TPV cell was just one square centimeter, but Henry says the technology to build larger devices already exists. It's just a matter of making them faster and cheaper, so they can be widely deployed to lower fossil fuel use.
Gravity Storage
For over a decade, companies have been developing gravity storage systems that use the universal force to create energy. While they may not be as well known as lithium-ion batteries, they offer a lower cost and strong environmental adaptability.
To store energy, the system pumps water uphill during off-peak electricity usage. When demand for power spikes, the water is released downhill, and the force of gravity powers turbines that produce energy.
Energy Vault, a company that recently listed on the New York Stock Exchange, has been working on a version of this technology for over a decade. They're currently building two large-scale gravity storage projects in the US and China that could prove its utility or futility. Unlike traditional batteries, this type of mechanical storage can be constructed from materials like mining tailings or decommissioned wind turbine blades.
Bio-Electrochemical Systems
The ability to convert microorganisms’ metabolic energy into electrical power allows a unique potential for the treatment and valorization (as electricity or hydrogen) of diverse liquid or gas waste streams. To date, most research efforts have been directed at the most efficient BES: microbial fuel cells (MFCs).
In BESs, an oxidation or reduction reaction is catalyzed on an anode and cathode by an electrochemically active microbial community. The reaction is fed with electron donors such as organic carbon or sulfides and reacted with an electron acceptor like oxygen or nitrate. When the system is connected to a grid, it can be harvested as electric power or used to produce other chemical compounds such as methane or hydrogen (Fig. 1).
BESs have also been applied to various other processes, such as desalination and the recovery of metals. In these applications, anaerobic digestion of lignocellulosic biomass, for example, has been integrated with BES to facilitate bio-methanogenesis and the production of valuable chemicals such as acetic acid, formic acid and hydrogen.
BESs are highly complex systems that rely on the interaction of many different components. The most critical factor is the effective transfer of electrons between electrodes and microorganisms. This is mainly achieved through the formation of a dense and stable biofilm on the electrode surface. Recent developments in the design of porous conductive materials as well as the use of outer membrane cytochromes and other appendages allow for high electron transfer rates, even over long distances.
