Enlarge / Airbus will be testing hydrogen power on a commercial airliner modified to carry an additional engine. (credit: Airbus )

A complete hydrogen fuel cell powertrain assembly occupied the pride of place in the pavilion of Beyond Aero at the recently concluded Paris Air Show. That a fuel cell system was the Toulouse-based startup’s centerpiece at the biennial aero event is an indication of the steps being taken by a range of companies, from startups to multinational corporations, toward realizing the goal of using hydrogen as fuel in the aviation sector.

“This 85 kilowatt subscale demonstrator was successfully tested a few months ago. Even though in its current form, it serves only ultralight aviation, the successful test of the powertrain is a crucial step in our technical development path for designing and building a business aircraft,” Beyond Aero co-founder Hugo Tarlé told Ars Technica.

Tarlé said that the business aircraft would have a range of 800 nautical miles and will be powered by a 1 MW powertrain. “For generating this power, there won’t be one big megawatt fuel cell. Instead, it will be multiple fuel cells. It will be based on the same technical choices that we made on the subscale demonstrator—i.e. gaseous hydrogen, fuel cell, hybridization of batteries and electric motors."

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In most industrialized countries, solar panels account for only a quarter to a third of the overall cost of building a solar farm. All the other expenses—additional hardware, financing, installation, permitting, etc—make up the bulk of the cost. To make the most of all these other costs, it makes sense to pay a bit more to install efficient panels that convert more of the incoming light into electricity.

Unfortunately, the cutting edge of silicon panels is already at about 25 percent efficiency, and there's no way to push the material past 29 percent. And there's an immense jump in price between those and the sorts of specialized, hyper-efficient photovoltaic hardware we use in space.

Those pricey panels have three layers of photovoltaic materials, each tuned to a different wavelength of light. So to hit something in between on the cost/efficiency scale, it makes sense to develop a two-layer device. This week saw some progress in that regard, with two separate reports of two-layer perovskite/silicon solar cells with efficiencies of well above 30 percent. Right now, they don't last long enough to be useful, but they may point the way toward developing better materials.

Enlarge / Natural gas plants like these may find themselves burning hydrogen over the next 20 years. (credit: Ron and Patty Thomas )

Today, the Biden administration formally announced its planned rules for limiting carbon emissions from the electrical grid. The rules will largely take effect in the 2030s and apply to gas- and coal-fired generating plants. Should the new plan go into effect, the operators of those plants will either need to capture carbon or replace a large fraction of their fuel with hydrogen. The rules will likely hasten coal's disappearance from the US grid and start pushing natural gas turbines to a supplemental source of power.

Whether they go into effect will largely depend on legal maneuvering and the results of future elections. But first, the rules themselves.

Clearing the air

Back in 2007, the US Supreme Court ruled that the Clean Air Act applied to greenhouse gas emissions . This allows the EPA to set state-level standards to limit the release of greenhouse gasses, with the states given some leeway on how they reach those standards. Since then, the court has clarified that these standards must be met on a per-plant basis rather than at the grid level; the EPA can't set rules that assume that the grid has more generation from solar and less from coal plants.

Enlarge / Aerial view/solar panel floating in the dam. (credit: SONGPHOL THESAKIT )

The cost of solar power has dropped dramatically over the past decade, making it the cheapest source of electricity in much of the world. Clearly, that can mean cheaper power. But it also means that we can potentially install panels in places that would otherwise be too expensive and still produce power profitably.

One of the more intriguing options is to place the panels above artificial bodies of water, either floating or suspended on cables. While more expensive than land-based installs, this creates a win-win : the panels limit the evaporation of water, and the water cools the panels, allowing them to operate more efficiently in warm climates.

While the potential of floating solar has been examined in a number of places, a group of researchers has now done a global analysis and find that it's huge. Even if we limit installs to a fraction of the surface of existing reservoirs, floating panels could generate nearly 10,000 TeraWatt-hours per year, while keeping over 100 cubic kilometers of water from evaporating.

Enlarge / An offshore wind farm in the UK. (credit: Dave Hughes )

After years of delays, the federal government has approved what will be the third offshore wind project in the US—and the largest by far. Vineyard Wind, situated off the coast of Massachusetts, will have a generating capacity of 800 Megawatts, dwarfing Block Island Wind's 30 MW and the output from two test turbines installed in Virginia.

Vineyard Wind has been approved a number of times but continued to experience delays during the Trump administration, which was openly hostile to renewable energy. But the Biden administration wrapped up an environmental review shortly before announcing a major push to accelerate offshore wind development.

The final hurdle, passed late Monday , was getting the Bureau of Ocean Energy Management to issue an approval for Vineyard Wind's construction and operating plan. With that complete, the Departments of Commerce and Interior announced what they term the "final federal approval" to install 84 offshore turbines. Vineyard Wind will still have to submit paperwork showing that its construction and operation will be consistent with the approved plan; assuming that the operators can manage that, construction can begin.

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Enlarge / Layers of phosphorene sheets form black carbon. (credit: Wikimedia Commons )

Right now, electric vehicles are limited by the range that their batteries allow. That's because recharging the vehicles, even under ideal situations, can't be done as quickly as refueling an internal combustion vehicle. So far, most of the effort on extending the range has been focused on increasing a battery's capacity. But it could be just as effective to create a battery that can charge much more quickly, making a recharge as fast and simple as filling your tank.

There are no shortage of ideas about how this might be arranged, but a paper published earlier this week in Science suggests an unusual way that it might be accomplished: using a material called black phosphorus, which forms atom-thick sheets with lithium-sized channels in it. On its own, black phosphorus isn't a great material for batteries, but a Chinese-US team has figured out how to manipulate it so it works much better. Even if black phosphorus doesn't end up working out as a battery material, the paper provides some insight into the logic and process of developing batteries.

Paint it black

So, what is black phosphorus? The easiest way to understand it is by comparisons to graphite, a material that's already in use as an electrode for lithium-ion batteries. Graphite is a form of carbon that's just a large collection of graphene sheets layered on top of each other. Graphene, in turn, is a sheet formed by an enormous molecule formed by carbon atoms bonded to each other, with the carbons arranged in a hexagonal pattern. In the same way, black phosphorus is composed of many layered sheets of an atom-thick material called phosphorene.

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Plastics have a lot of properties that have made them fixtures of modern societies. They can be molded into any shape we'd like, they're tough yet flexible, and they come in enough variations that we can tune the chemistry to suit different needs. The problem is that they're tough enough that they don't break down on their own, and incinerating them is relatively inefficient. As a result, they've collected in our environment as both bulk plastics and the seemingly omnipresent microplastic waste.

For natural materials, breaking down isn't an issue, as microbes have evolved ways of digesting them to obtain energy or useful chemicals. But many plastics have only been around for decades, and we're just now seeing organisms that have evolved enzymes to digest them. Figuring they could do one better, researchers in France have engineered an enzyme that can efficiently break down one of the most common forms of plastic. The end result of this reaction is a raw material that can be reused directly to make new plastic bottles.

An unwanted PET

The plastic in question is polyethylene terephthalate, or PET. PET has a variety of uses, including as thin films with very high tensile strength (marketed as mylar). But its most notable use is in plastic drink bottles, which are a major component of environmental plastic waste. First developed in the 1940s, the first living organism that can break down and use the carbon in PET was described in 2016 —found in sediment near a plastic recycling facility, naturally.

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