Currently the world is struggling to keep carbon emissions from rapid growth. But to achieve long-term goals that we have set to stabilize the climate, we must do much more than to gain some renewable energy. Hold the planet from warming 2 degrees above pre-industrial levels means a serious cleaning from the carbon we use energy. And this means that we not only should be completely independent of carbon in the production of electricity, but also to begin to use these clean electrons to provide our needs in heating and transport.
If we talk about cars and buses, this process has already begun. But there’s one weight-sensitive mode of transportation where the battery will not help us: air travel. The relatively low energy density of batteries means that you will need plenty of these to power the plane. For this reason, many people have decided that we need biofuels for clean air travel. However, there are companies that plan to develop electric passenger planes.
Who is right? To find out, an international team of engineers assessed whether electric aircraft batteries to take off and become commercially viable.
Electric airplanes: what’s the problem?
The researchers approached a number of associated problems. First, if the batteries reach an energy density sufficient to be used for air travel. Secondly, whether they will be economical. In addition, was considered and the question of whether the aircraft batteries to help us achieve our goals of emissions.
Most of these problems more complicated than they seem. For example, the planes do not only exacerbate the warming due to carbon emissions; traces of them also create high-altitude clouds have an insulating effect. In addition, the degree to which the batteries can help us to get rid of the emissions, directly related to the amount of renewable energy available for charging.
The scale of the problem, however, is easy to understand. The best lithium-ion batteries currently have an energy density of 250 watt-hours per kilogram. It is assumed that for the working plane on the batteries we need at least three, and maybe eight times more density (2000 W-h/kg). The battery capacity increases by 3% per year. That is, doubling in about 25 years. This progress has sped up a bit lately, but even if we assume a more rapid progress, we will have to wait until mid-century before the batteries will become like we want from them.
However, it is unclear how the chemistry will lead us to such batteries. There are design lithium-air and lithium-sulfur batteries with high energy density, but they can discharge quickly enough to fuel the intense take-off.
In General, the authors decided to simulate the battery on the 800 W-h/kg, which is considered the minimum necessary for airliner-sized 727. However, as an optimistic forecast also considered the 1200 W-h/kg option. First battery means that the weight, which rises the battery is almost two times more than in the case of fuel. However, this combined with the fact that electric motors are more efficient than combustion engines. In addition, the batteries can also power the onboard systems, simplifying the design of the aircraft.
Cut it’s carbon emissions?
Assuming that these electric planes will be able to build, whether they will reduce emissions, really? Currently – no. Given the average level of emissions associated with food, for example, the U.S. power grid, the emissions associated with electric powered aircraft (including transmission losses) will be about 20% higher than the emissions produced by a modern, efficient jet engine. This does not mean that they will be useless from the point of view of climate, no. Once additional effects of warming are taken into account, electrocapillary come forward by about 30%.
Still, future considerations quickly complicate. It is expected that the price of renewable energy will continue to decline, which will make renewable energy a larger part of the energy system and reduce emissions. The study authors estimate that the vast majority of charging will occur during the daytime when there is sunlight. Assuming that future production of solar energy will lead to a discount on electricity usage during the day, it can help the economy of electric aircraft; currently they are economically viable only when the price of fuel around $ 100 per barrel.
How all this will affect the flight depends on the capacity of future batteries. The authors, an effective range of 1,100 kilometers will allow electric planes to cover 15% of the total number the world of the air (and corresponding fuel) and almost half of the total number of flights. This will increase total electricity demand by one percent worldwide, although will affect most of the industrialized countries. The increase in the range of up to 2200 kilometers would provide 80% of global flights only electric aircraft.
Thus, in General, technology is on the verge of commercial viability and may limit the warming caused by air traffic. However, it is extremely important that both of these situations will improve, because renewable energy captures a large share of the generating market. Unfortunately, the only thing holding back the development of all this technology, because the batteries just don’t have the necessary capacity.
It may take 30 more years before we see the aircraft, devoid of the roar of jet engines.
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