13 February 2017 / 0 Comments

 

Supercapacitors and coconuts: A better way to store energy

The key ingredient in powerful devices for storing energy has been charred coconut. Now a company in icy Estonia has figured out how to make a supercapacitor without tropical fruit.

“The problem with coconut shells, naturally, is that the distribution and size of its pores has great variability,” says Taavi Madiberk, chief executive of Skeleton Technologies, a company established in Estonia where, one might expect, the main problem with coconuts would be the small likelihood of finding them, rather than the qualities of its shells. What’s truly surprising, however, is that a company in this northern country is solving the big coconut problem.

This coconut issue is, in fact, a multi-billion euro problem, when you consider the size of the market for supercapacitors, devices for storing energy. By 2024 it’s expected to rise to EUR 6 billion. By and large, all of them have thus far been made of activated carbon generated by charring discarded coconut shells. Until an inorganic — and much more efficient — alternative was developed by Skeleton Technologies. The company last week received a EUR 15 million loan to continue its R&D from the European Investment Bank, backed by the EU budget guarantee of the Investment Plan for Europe.

Why not just keep using coconuts?

When a coconut is charred, it produces carbon that, if thinly spread on a sheet of foil and exposed to electrically charged ions, can store the ions in its pores. Of course, the more densely the carbon is covered by correctly sized pores, the more energy it can store for a given gram of material. Trouble is, depending on the weather and the time of its harvest, a charred coconut will have a varying density of pores. “With coconut, you can’t really tune this density or the size of the pores,” Madiberk says.

“Ultracapacitors are the skeleton of an energy system”

With its proprietary technology for deriving carbon from inorganic carbides, Skeleton Technologies can tune the pores. The result: curved sheets that are one atom thick, one gram of which contains close to 2 000 square meters of uniformly porous area for ions to fit into. The way Skeleton then attaches the carbon to the aluminium foil and stacks or rolls these sheets tightly into cells creates supercapacitors with four times the power density of coconut-based competitors. The name Skeleton, by the way, comes from the fact that under a microscope, the company’s material resembles a human skeleton, Madiberk says. “And more importantly, ultracapacitors are the backbone, the skeleton of an energy system.”

Supercapacitors versus batteries

So what is the difference between a supercapacitor and a battery?

“Let’s take a bottle fitted with a pourer, and a small glass,” Madiberk starts. I recommended piña colada, to stay with the tropical theme, but it turns out he just meant this in the figurative sense. “The difference between a battery and a supercapacitor is like the difference between a bottle fitted with a pourer, and a small glass,” he explains. “It takes forever to pour out of the bottle, or to fill it back up, but it holds more, compared to the glass, which you can empty and fill in an instant.”

So a supercapacitor may not hold as much energy as a battery, but it can release the power in greater, short bursts, and also recharge immediately (in 2-3 seconds). That’s invaluable for a number of applications. One of them is vehicle engines, where acceleration requires a lot of energy in an extremely short time period and braking generates a lot of energy that could be stored in a supercapacitor. Or a crane lifting containers in a port. Lifting the container requires a lot of energy, while lowering it generates energy. This is true for a number of machines that produce kinetic energy, such as excavators.

“Batteries use a chemical reaction to release energy, while supercapacitors use electrostatics. The chemical processes create a greater internal resistance. That lowers the speed of the energy transfer and also slowly eats up the battery, resulting in a lower number of charge-recharge cycles that a battery can take,” Madiberk says. So while batteries can go through a couple of thousand cycles, a supercapacitor can do this a million times. This is what makes a supercapacitor useful for sending it up into space, for example. The European Space Agency uses Skeleton supercapacitors to capture solar energy and uses it to move solar panels and adjust antennae on satellites. It would be a hassle to go up there every now and then to change the battery.

The EIB financing gives the company a significant capital contribution to further invest in R&D, expand production and take the commercialisation step

There are other uses for supercapacitors as well. For example, stabilizing the energy fed onto a grid from a solar power plant. “Solar output of power fluctuates a great deal, which means the voltage and the frequency of power can change. But the transmission needs to be balanced. Even small fluctuations in the quality of the electricity can cause a lot of damage, especially for manufacturing,” Madiberk says.

Based on these various applications, the EIB sees a growing market demand for supercapacitors, with Skeleton Technologies having developed a superior technology and being the only formidable European player in the market.

Due to the specific nature of the company, EIB provided it with a quasi-equity financing, unique to the EU bank. Steady repayment of a classical loan would drain the company’s coffers just when it needs to be investing in research and development. At the same time, an equity investment would dilute the holdings of founders and other key people who bore the risk of financing the early years of development. The EIB quasi-equity financing gives the company a significant capital contribution to further invest in R&D, expand production and continue commercialising its invention, but is remunerated based on the company’s performance, just as an equity investment is.

A European player in a growing market

Skeleton has just finished installing a manufacturing facility in Germany, due to open in March. Its further R&D aims to move from production of energy storage components to providing full solutions — for example, retrofitting fleets of trucks with supercapacitor modules, complete with inverters and software to operate in a more economical and, consequently, also environmentally friendlier fashion, Madiberk says. “We are using the investment to move up the value chain.”

While the battery industry continues to develop their products to be able to charge and recharge faster, and the supercapacitor industry continues its development to be able to hold more power, Madiberk believes the products will remain complementary. “In energy storage there will not be a time when one size fits all application requirements,” he says. He cites the example of hybrid buses, in which capacitors are used for peak power generation and brake power recuperation and batteries are used for maintaining a stable speed in between. “We are not competitors,” he adds.

Sort of like coconuts and lime, really.

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