4.1 Weak points of gasifier-engine-systems

It became obvious in the late eighties that despite the lively interest in the gasifier technology during the past 10 years no "dissemination" worthwhile mentioning had taken place. The dominant argument to explain this was the claimed "technical immaturity" of the systems. This requires some comments.

It is typical for gasifiers employed in developing countries over the last years that these systems had mainly been developed by research institutions and universities. These plants (all of them prototypes) showed technical shortcomings as soon as they were tested under the rough conditions of "field application". In the end their failure consisted of a sum of mistakes made in details, which only came to light when the favourable conditions of lab application (defined and constant fuel quality, good possibilities for repair and optimization, qualified and motivated operators) were missing: Bad bunker flow of insufficiently prepared fuel, unoptimized container geometry, fast wear of parts subjected to varying temperature, wear of scalings, problems of corrosion, insufficient gas cleaning were wide-spread defects [3].

On the basis of subsequent documentation quite often it can also be reconstructed that grave mistakes have been made in the adaptation between gasifier output and engine size (usually the cylinder volume of the engine was chosen too small, thus preventing the gasifier from reaching the necessary operating temperature). Often there also existed wrong ideas about the application purposes, to which gasifiers might generally be suited or unsuited.

More will be said on the technical aspects later in this paper. First, however, another approach is chosen. The most commonly used argument of the allegedly existing technical "immaturity" of those gasifiers available certainly often holds true for some wellknown cases, but it can no longer be accepted as the sole reason for the hitherto limited dissemination. Technical problems are almost always solvable, once they have been recognized. Meanwhile, knowledge about gasifiers should be sufficient to realize good technical performance. But still the reputation of this technology is not too good.

4.2 The problem of ''acceptance''

If a farmer in a developing country prefers other energy technologies to gasifiers, even though this preference cannot be reasonably explained from a technical point of view, one has to ask for the non-technical reasons. In such cases "acceptance" is always quoted- a mysterious term which circumscribes that the user does not agree to this new technology. In reality technical and non-technical reasons for a lack of acceptance can seldom be clearly separated; the one often stems from the other.

There is one trivial fact which can explain low acceptance of gasifier systems: Nothing is as convenient as an electrical socket. A household connected to the public electrical grid is already something self-understood for inhabitants of towns; for the rural population, too, it symbolizes the modern way of life in a nut-shell. Sockets in the house-this means unlimited access to energy at all times, be it for cooking, washing, ironing, providing light, or watching television.

The typical consumer-and this not only holds true in industrial nations, but in developing countries as well-does not want to take care of any technical service of his energy supply. The public energy supply of industrial nations meets this need to a very high degree: it provides energy at high reliability and acceptable costs. And just that is, what the housewife in a developing country wishes for as well. That is why all decentralized systems, and especially those based on renewable energy, have not much chance to be loved.

But: As attractive as the public electrical grid may be, for many people it will just remain a dream. It is the population of rural areas in the developing world which has to be regarded as the foremost target group for the employment of regenerative energy sources. In general, this target group has no access to the public grid, and no realistic chance ever to gain it: A low population density and a low economic significance of those concerned promise little profit to enterprises selling electricity, should they extend their supply lines to every village. And yet: if you promise people in rural areas a better life, they will, among other things, expect electricity.

Only if access to grid electricity is unrealistic, it will be sensible to ask which energy conversion system the user might prefer as an alternative. The answer can be found in the afore-said: the operating comfort should come as close to the socket as possible. Compared to other alternatives a gasifier will not have the best of chances.

The traditional alternative to the mains is an energy supply by means of local engine-generator-sets. Though an engine-driven generator supplies electricity, it is not the same as being connected to the grid: Fuel has to be bought continuously, and one always lives with the risk of having an engine failure, but not the money for repairs. In brief: one has to take care of it permanently. On top of that, due to bad road conditions and a virtually non-existing infrastructure in the rural areas of developing countries, liquid fuel is very expensive in relation to the low income of the consumers.

Apart from diesel or gasoline engines, there are not many alternatives available. Liquid fuels on biomass basis might present a future option to replace diesel, if the question of rentability could be solved.

With regard to operating comfort, a photovoltaic plant is very attractive, and as far as household illumination and small-scale consumption is concerned, photovoltaics already represent an acceptable solution for those users who are financially well-off. If, however, mechanical or electrical energy is needed for working machinery (water pumps, grain mills, machines for carpentry, and the like) that lie in the power range from 2 kW up, photovoltaics are excluded for reasons of costs.

Small hydro power and biogas plants are other site-specific options for decentralized energy supply.

A gasifier-engine-system using solid fuel, as perfect as it may be, always requires more extensive operating care than an engine run on liquid fuel. But: if not quite love, at least acceptance might arise, if a gasifier offered considerable cost advantage. As the user in developing countries finds himself chronically in a situation of permanent financial difficulties, the term "acceptance" will simply be reduced to his insight in the necessity of saving money.

From this we may derive the kind of demands which have to be put to gasifiers in order to make them acceptable. If we assume that gasifier technology has matured enough to let its operation appear not more difficult than that of other, comparable energy technologies, the potential user will have the following requests:

(1) The operation of a gasifier should have considerable cost advantages when compared to available, competitive technologies (e.g. Iiquid fuel engines).

(2) It should be guaranteed that the plant fulfills the technical requirements of the application it is intended for (or in other words: it has to be clear what a gasifier is suited for, what not).

(3) The effort for preparing the fuel, operating the system and maintaining it should be kept as low as possible.