Small-scale power systems

From the energetic point of view all the above-mentioned fields of application can be called small-scale power systems. For each of the devices mentioned self-contained power sources are needed, not depending on large-scale power systems - stationary power plants and power supply lines. In small-scale power systems each individual consumer needs much lower electrical power values and a shorter operation time than one in large-scale power systems (see Figure 2). 

The main power supplying devices for small-scale power systems are electrochemical power sources - galvanic cells and batteries, both of primary and storage type, as well as some types of fuel cells. 

The main differences in high-temperature fuel-cell stack cost structure relate to the fact that they do not contain high-cost precious metals, on the one hand, and that they demand more complex manufacturing process, on the other. It must be noticed therefore, that, the fuel-cell stack is, in many cases, responsible for less than one third of the total capital cost of a fuel-cell system, and that a large portion of the total cost is caused by fuel pretreatment (reforming, cleaning etc.), plant control, and power conditioning. For small-scale SOFC systems, the cost of the stack is of the order of 40-45% of the total cost. 

If a continuous process is to he used for commercial production, a similar small-scale reactor system should he utilized in this second stage of product development. There are a number of reasons for this recommendation. The earher discussion of the difference between batch reactors and CSTRs lists some of these reasons, if, for example, engineering data are to he obtained for design of a commercial unit, the variable relation ps might be quite different for the different reactors. The Smith-Ewart CSTR model predicts a linear relationship between or N and the surfactant concentration [5]. The same mechanistic model for a batch reactor predicts a 0.6 power relationship between Rp or N and... 

The above discussion suggests that the development of a hydrogen system concept based on distributed small-scale power plants should be easier. In this respect, the most appropriate hydrogen production technologies are based on PV-solar, natural gas reformer or wind-turbine resources, even if the last solution expects some infrastructure network to transport hydrogen from the production point to the user points. 

A serious candidate for transportation application is also the direct methanol fuel cell (DMFC) which has been realized already on a laboratory scale. A catalytic burner is requited to evaporate the methanol/water mixture and to bum the exhaust gas at the anode [43]. Considering the complete energy chain, a PEFC is by 50 % more efficient than a diesel engine which consumes 4 1 per 100 km this is also valid for a natural gas driven engine [37]. Fig. 7-6 presents the processing schematics of both IMFC and DMFC. The DMFC offers a much simpler system than the PEFC. The DMFC is currently at an early development stage. It is perceived to offer improved solutions to the need for a small-scale power supply. A program for the construction of a 30 kW stack has recently started [29]. 

The development of small-scale power for isolated regions of Russia has loii slipped the attention of the public and specialists. Development of the United Power System of Russia, creation of high capacity generating facilities and construction of giant power plants and complexes have been considered top priorities over the past years. 

Heat. Heat is mainly supplied by small-scale combustion systems in households and (to a limited extent) by combined heat and power plants (CHP) (approximately 311 PJ of fuel energy in 2007). It has to be noted... 

Fig. 2. Small-scale and large-scale power systems. 

Project Report to New Energy Development Organization (NEDO), 2006. Jatropha Oil for Small Scale Power Generation System Development Project Indonesia. 

Perhaps the ultimate combined appliances, which are currently under development, will he microturbines or fuel cell power generators used as small-scale co-generation systems. These would supply not only electricity, but space and water heating as well. 

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