Its sounds ideal: a domestic energy plant that generates heat and electricity works almost without emissions and also exclusively utilises the sun and bioalcohol as renewable energy. Researchers from the Fraunhofer Institute for Solar Energy systems ISE are working on such a plant. The heart of the system comprises a fuel cell combined with a newly developed reformer that generates the hydrogen required for the fuel cell from bioethanol.

The reformer and the high-temperature polymer electrolyte membrane fuel cell (HT-PEM) are integrated within a stratified hot water storage tank. The waste heat from the fuel cell-reformer system is completely stored in the storage tank. With a thermal output of 6 kW, the system is designed for single- and double family houses that are well insulated to the KfW-60 standard in accordance with the applicable German Energy Saving Ordinance. The fuel cell has an electrical output of 1.2 kW. The electricity can be used in the building or correspondingly fed into the electricity grid in accordance with the German Renewable Energy Sources Act.

A new kind of ethanol reforming catalyst works in the reformer. It catalyses ethanol and water to form a reformate gas whose volume consists of 50 % hydrogen, 25 % methane and carbon dioxide. A decisive aspect is the tiny proportion of carbon monoxide (CO), which is less than 1 %. Because the fuel cell’s special high-temperature membrane can tolerate up to 5 % CO, this makes it possible to dispense with carbon monoxide purification. It considerably simplifies the overall system, reduces costs and facilitates the integration of the reformer-fuel cell system within the storage tank. A bioethanol- and gas-fuelled porous burner was developed for operating the reformer.

The search goes on

The fuel cell used in the tests was a one-off example that is not commercially available. The researchers are still searching – so far without any success – for a suitable commercial HT-PEM fuel cell with which there has been sufficient long-term experience. This would enable the system’s integration in the stratified storage tank to be further developed and a prototype could then be constructed.

Considerable market potential

Increasing heating costs are facilitating the introduction of innovative and high quality technologies. In Germany, around 400,000 boilers are installed each year. Around 5 % of the customers would like a comprehensive domestic energy supply based on renewable energy. That corresponds to an annual potential of approximately 20,000 boilers. The buyers in this market segment are often prepared to accept higher costs than in a mass market. For them, ecological aspects play a greater role when making purchasing decisions. One of the project partners working with the Freiburger researchers, SOLVIS GmbH & Co. KG, already predominantly serves this market niche. The consortium is hoping to corner 25% of the market, i.e. 5,000 units. The medium-sized consortium can develop this production level in just a few years.

For the complete system including the fuel cell, reformer, solar circuit, heating circuit pump group and exhaust gas system, the project partners are looking to introduce the system to the market at a selling price of 25,000 euros. Whether this will be achievable or not depends on the availability of the fuel cell.

Further information

Further information on the project, which is funded by the German Federal Ministry of Economics and Technology, is available as a PDF file (in German, 165 KB).

About ethanol

Ethanol is commonly known as potable alcohol. It is generally produced as bioethanol by fermenting cereals, sugar beet or sugar cane. There are still no commercially available domestic heating systems that can be fuelled with bioethanol. In Germany, it is principally used as a fuel by blending it with conventional petrol at concentrations of 5 or 10 per cent (E5, E10). In Brazil it is also used as a main component in fuels (E85).

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