The fuel cell for home

Jun 02, 2014
Production of the cell stacks at the Fraunhofer IKTS. Credit: Fraunhofer IKTS

It converts chemical energy directly into electrical energy. Still, there hadn't been a market breakthrough for the fuel cell. The systems were too complex. Now, Fraunhofer and Vaillant have developed a simple device for home use.

One always speaks of a fuel cell system," says Dr. Matthias Jahn from the Fraunhofer Institute for Ceramic Technologies and Systems IKTS in Dresden. A single cell doesn't produce enough voltage to obtain a sufficient electrical power. In a fuel cell stack, several cells are connected one to the other. Each of them is about the size of a CD. We call the groups 'stacks'," says Jahn. Fuel cells convert directly into . They are many times more efficient than are combustion engines, such as the car engine. These require an intermediate step. First, they convert chemical into thermal energy (heat) and mechanical energy (force). With this force, they drive a generator, which only then generates the electric power. In the process, a large portion of the originally available energy is lost.

Real-life test in private households

Together with the heater manufacturer Vaillant, the IKTS has developed a compact, safe and sturdy fuel cell system that generates electricity and heat in private households from natural gas. The researchers were particularly responsible for the construction of the prototype, the design of the overall system, the design of the ceramic components and the development of the reformer and the afterburner. The devices are currently being tested in private households in the Callux practice test (www.callux.net).

They are as compact as classical gas heaters that only produce heat. Moreover, they can comfortably be mounted on the wall and easily be maintained. With an output of one kilowatt, they cover the average current consumption for a four-person household. The Federal Ministry of Transport and digital infrastructure BMVI is promoting Callux. Currently, in the European demonstration project ene.field (www.enefield.eu), about 150 further units are being installed in several European countries. In addition, Vaillant started the production of a small-scale series in early 2014. Parallel to the practical test, the two partners are already working on new models. "Now, it's all about decreasing production costs and increasing the lifetime of the equipment," says Jahn.

The principle of the fuel cell has been known for over 175 years. So far, however, there has not been a market breakthrough. The main reason was the invention of the electric generator. It knocked the more complex fuel cell out of the running. Only in the 1960s was the technology put into practice by NASA in some Apollo moon missions. In the late 1990s, there were other projects in the automotive industry, which have so far not been able to prevail. The reasons are that the fuel cell is too complex, too expensive, and too unreliable. "In our project with Vaillant, we have made great strides to bring the technology close to the market. Vaillant is already producing a small-scale series, which is sold in funded projects to customers," says Jahn. "For the market breakthrough, the costs still have to be decreased significantly."

The miniature power station for home use is based on a solid fuel cell (SOFC). SOFCs operate at a much higher temperature in comparison to competing approaches, such as the proton exchange membrane fuel cell (PEMFC), which is used in cars, for example. While PEMFCs only reach 80 degrees, SOFCs can reach up to 850 degrees. "This allows the SOFCs to be built much more simply and cheaply," says Jahn.

The electrolyte of an SOFC only transfers oxygen ions, not electrons. Otherwise, there would be a short circuit. "Ceramic is particularly well suited as a material for the electrolyte. It has the desired conductivity and can also endure high temperatures," says Jahn. As a result, even without the use of precious metals, all reactions proceed smoothly, which is necessary for the direct conversion of into electrical energy: If the heater is connected to the gas network, a reformer initially converts the natural gas into a hydrogen-rich gas. This then reacts in the stack with the oxygen of the air in a noiseless "cold combustion", producing power and heat.

Explore further: Using proton-exchange-membrane fuel cells to recover high-purity helium

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Eikka
5 / 5 (2) Jun 02, 2014
The systems were too complex.


No they weren't. They were too expensive.

And the SOFCs so far also have problems in cycling and limited operating hours. They don't like to power up and down because that causes thermal stresses in the stack, so the catalyst wears out too soon.

With an output of one kilowatt, they cover the average current consumption for a four-person household.


Average in what country, in what time? Americans consume three times as much electricity as Brits, for example, because the Brits (and Germans) use more gas powered appliances in the first place.

In reality, a tea kettle draws more than 1 kW so a 1 kW fuel cell on its own is totally inadequate for household power.
HTK
5 / 5 (1) Jun 02, 2014
Imagine, all houses being off the grid.

No more meters and bills or dependency.
Sonhouse
5 / 5 (1) Jun 02, 2014
Those cells look to be based on alumina substrates which I know for a fact cannot take much thermal cycling, we use alumina substrates and putting them through an anneal cycle sometimes makes them explode into pieces if they cool down too fast. If they are alumina substrates they are pretty expensive per substrate and it looks like they have 20 or more to bring the voltage up to a reasonable level. A friend has a machine shop, professional, and they do fuel cell work but those substrates are graphite but I know nothing about how long they last or thermal cycle capabilities.
KenC
5 / 5 (1) Jun 02, 2014
@ HTK - This does not take anyone off the grid at all. In fact, they will be *more* dependent on the grid.

First, users are reliant on the 'natural gas grid' to provide the chemical energy to convert to electrical energy.

Second, as pointed out by Eikka, the fuel cell provides an average output. So the user is totally dependent on the electrical grid to absorb excess power during low demand times, and then they are totally dependent on the electrical grid for power when they require anything above the level of a tea kettle. They will need to pay for that grid infrastructure, even if their net usage is zero.

Overall, this might be a good thing, but it doesn't take anyone off the grid at all, or free them from energy bills. If they want to store energy with batteries and inverters, that will be very expensive, and replacing the batteries after a few years has environmental impacts as well.

How is this system different from the Bloom Energy system from a few years back?
zaq
5 / 5 (1) Jun 02, 2014
Burnerjack
5 / 5 (1) Jun 08, 2014
Seems like a direct copy of the Bloom Box. How is this different?
Burnerjack
5 / 5 (1) Jun 08, 2014
Imagine, all houses being off the grid.

No more meters and bills or dependency.

As long as you have your own Nat Gas well, you're right. Otherwise, your electric and heating bills are consolidated. Now, if this could run off of homegrown methane, that would make off grid a reality for many more.