Fuel cells

Eugene Leitl (eugene.leitl@lrz.uni-muenchen.de)
Sat, 5 Jun 1999 13:24:10 -0700 (PDT)

Ron Kean writes:

> I don't know specifically about that, but in some other countries,
> especially those formerly communist, it is not uncommon for towns and
> portions of cities to be heated from a central heating plant. In

If you drive through Moscow today you won't fail to notice giant poorly-insulated tubes worming their way through the city -- very much like a drabber version of "Brazil". Apart from substandard, leaky insulation, the central heating installation are often of gargantuan proportions, which results in in enourmous losses (>>50%, all paid by the customers) due to bad suface/volume ratio of the extensive pipe infrastructure.

(On a more anecdotal side, undetected leaks often result in cavities, which on occasion have collapsed and broiled alive pedestrians while they were walking their dogs).

On the other hand, in Germany there is a trend to build small-scale (10..50 home units, or a communal pool) natural-gas driven electricity generators which also utilize thermal power for heating purposes. With compact methane fuel cells yet to profit from economies of scale there is no reason why every home couldn't create it's own heat and electricity.

> All systems which produce electrical power from fuel generate lots of
> waste heat. The thermal efficiency of the best coal-fired power plants

Correction: all Carnot-cycle based machines. Electrochemical energy generation can in principle run at room temperature. Most polymer-electrolyt fuel cells run around ~100 deg C for ensure sufficient reaction kinetics.

> is no more than 45%, and 35% is more common. So in principle it may be
> attractive to use that waste heat for building heat. But there are big
> practical problems with actually doing that. Multi-building heating
> systems are most economical for large buildings heavily concentrated near
> each other, as in the downtown part of a city. But power plants are

In Europe the building density is much higher on the average. This is less desirable for use of photovoltaics, but excellent for shared-infrastructure facilities.

> generally not built in such areas, because the plant, with its
> switchyards and transmission lines and infrastructure for fuel delivery
> and handling takes lots of land, and the land is just too expensive
> there. There are some cities where power plants were built downtown

Natural gas pipes are not particularly bulky. Your arguments are true for coarse-grain installations, but not for fine-grained ones. Additionally, methane burns very cleanly. If planned correctly today, the methane duct infrastructure could be used for a hydrogen economy (if necessary, since methane can be used in fuel cells, whether directly, or via reformers) without modifications.

> (usually by a river) in the early years of the century, but those plants
> are obsolete and not capable of meeting present power demands, and are
> being closed to free up the land for other uses. Also, the waste heat
> from a power plant is at a relatively low temperature, about 100 degrees
> C or less, which makes it difficult to effectively deliver the heat any
> significant distance while maintaining a temperature high enough to be
> useful in building heating. It sometimes makes sense to locate an

Which obviously dictates the use of small-scale facilities. Also, large-surface heating systems like floor heating can utilize heating fluid only slightly above room temperature: utilizing shallow thermal gradients is the elegant thing to do anyway.

> industrial user of heat, such as a paper mill, near a power plant.
> Georgetown University in Washington, DC has an existing central heating
> plant for the campus, and they have been considering piggybacking
> electric power generation into the heating plant system. The plan would
> be to sell the power to the local electric utility.
> Ron Kean