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GTZ has acquired most of its practical experience with three PV technology options for rural electricity supply:
- Central-station village power-supply systems
- Battery-charging stations
- Solar home systems (SHS).
Of the three, the central-station approach is most similar to the conventional option of seeing up isolated grids fed by diesel-powered generators to serve large villages. Thus, it also competes economically with diesel-based systems.
Battery-charging stations, by contrast, are decentralized facilities, many of whose customers must haul their automotive batteries considerable distances to be recharged. Transporting the batteries is inconvenient, time-consuming and expensive, and each time they are recharged they provide only a limited amount of electric power for lighting and to run home entertainment equipment.
The advantage that solar-powered battery-charging stations have over grid-fed or diesel-based facilities Is that they can be installed closer to users. In many cases, the batteries need only be transported a few hundred yards. Moreover, with battery-charging stations the users do not have to buy an expensive solar panel, as they do with SHS. Indeed, the only investment that is required is the outlay to purchase a 12-volt battery, which even the poorest rural dwellers can nearly always afford.
The most decentralized approach is that involving solar home systems. SHS provide only a basic electricity supply for lighting and the operation of cassette players, etc. Thus, the small PV systems hardly ever provide all of the services supplied by a conventional power supply system. Accordingly, they do not compete economically with the classic electrification options, but rather with lighting oil, kerosene, candles, dry-cell batteries and car batteries used in non-automotive applications.
In its projects, GTZ has acquired experience with all three of the options discussed above, and we are therefore in a position to assess their relative advantages and drawbacks.
The technical feasibility of central-station village power-supply systems has been clearly demonstrated. Three systems of this type have been installed in GTZ projects in Senegal and the Philippines, and for some time now they have been providing continuous, trouble-free service to the users. But their economic feasibility is doubtful. Central-station village systems do not today constitute a viable alternative to diesel-based isolated grids, and not even a dramatic decline in the price of solar cells would alter this.
It will not be economically feasible to utilize photovoltaic technology and storage bakeries to provide an uninterrupted supply of electric power over a 220-volt alternating current network unless there is a relatively large, continuous demand for that power. And if most of the demand occurs during certain peak periods when lamps and home entertainment equipment such as radios or cassette tape players are operated, this criterion will not be met. If electric power is needed primarily at night, when the output of a PV generator falls to zero, the system will have to include expensive electricity storage facilities (batteries), and in such cases it will usually be cheaper to obtain electricity from diesel generators.
However, if the cost of the panels comes down substantially, solar power stations whose output is fed directly and without intermediate storage into the networks of large demand centres to save fuel and stabilize voltages (in branch networks) could be an attractive option for developing countries at some point in the future.
PV battery-charging stations are small "photovoltaic filling stations" that operate independently of power grids and are designed to serve persons who use 12-volt DC equipment. The users take their own bakeries to the station, and they usually pay around 1.50 US$ per charge.
Diesel generators should only be used as a power source for battery-charging stations if the capacity of the generator will be utilized to a high degree, so as to maximize the efficiency and the service life of the unit. It is common for the diesel generators that are used in battery- charging stations to be used in other applications as well (e. 9. to operate the equipment in a workshop or supply the power to run a boat), and, as a result, they are only available part of the time for charging batteries. In sparsely populated areas the minimum prerequisites for economically feasible operation of a diesel-powered charging station are rarely met, since in such cases systems are needed for small output ranges (below 1 kW). However, diesel generator outputs usually start at around 2 kW. Moreover, diesel-powered units are frequently unsuitable for use at very remote sites because it is difficult to purchase even the small quantities of diesel fuel that are required for their operation on a regular basis and thus to provide a reliable, continuous charging service.
It Is in such cases that the advantages of photovoltaic charging stations quickly become apparent: With just a small number of panels, a technically optimal supply of electric power is ensured even if demand levels are low. If demand increases, the capacity of the station can be expanded very easily by simply adding more panels. The system can also be installed in the immediate vicinity of the users, thus reducing their transport costs.
The target group for battery-charging stations is that part of the population which cannot afford to make major investments to obtain a supply of electricity and also has absolutely no access to credit. The purchase of an SHS is a virtual impossibility for this segment of the rural population, but the livelihood of their being able to buy a suitable battery is high.
It is best for PV charging stations to be operated by utility companies or electricity cooperatives. The reasons for this are as follows:
- The ownership situation is clearly defined (the PV generator and the regulator belong to the financially responsible institution, while the users own the battery and the load equipment).- Trained personnel will be available to ensure that necessary repair and maintenance work (charging station and batteries) are performed.
- The running costs incurred by the target group are very low.
- Because of the modular nature of the system, its capacity can easily be expanded or reduced in response to changing demand levels.
And if such installations are run by cooperatives and they succeed in keeping the administrative costs down by having their own members carry out all operational and management tasks, then a system of this type is an extremely attractive option for supplying the poorest segments of the population with electricity.
The time has now come to formulate a coherent policy for the dissemination of solar home systems. GTZ has gained extensive experience with various approaches to the diffusion of this technology, ranging from distribution by private enterprises to government-run promotion programs.
Before proceeding, however, let us first take closer look at the technical components of an SHS. Since certain of the system components have not yet been perfected, it is essential to establish quality standards and require that all future projects adhere to these norms. Minimum technical standards have already been introduced for the charge regulator and the ballast. It should also be determined whether the inability of past programs to set in motion large-scale, self-sustaining dissemination processes has been due to technical problems; this is a distinct possibility.
SHS are small-scale photovoltaic systems that are designed primarily for use in private households. They produce 12-volt direct current, and given their modest output (20 to 100 Wp) they are mainly used to operate transistorized lamps ( =fluorescent lamps equipped with electronic ballasts) and home entertainment equipment such as radios and television sets. The basic system components are a PV panel, a charge regulator, a battery and one or more lamps. *)
Especially when selecting electronic ballasts and charge regulators, it is essential to choose robust, long-lasting devices that have been specifically designed for SHS applications. In other words, "improvised" or "home-made" equipment should not be used under any circumstances. The utilization of a good charge regulator can prolong the life of the battery considerably, and this in turn has an enormous impact on the economic viability of an SHS.
In the meantime, minimum standards have been established for the charge regulator and the electronic ballast on the basis of data generated by GTZ's field projects. Among other things, they are intended to help eliminate the technical problems that are still being encountered with these components. (For example, operating problems are still being reported due to difficulties with the load disconnecting relay in the charge regulators, and these problems must be solved.) Moreover, local manufacturers must be held to the same technical standards as equipment suppliers in industrial countries: When it comes to selecting charge regulators for use in SHS, quality must not be sacrificed for the sake of "local content".
Certain components are still not suitable for local production. Thus, for example, it would not be advisable at present for developing countries to set up their own production facilities for solar cells and panels since the equipment that is used in the requisite manufacturing processes is very expensive and the processes themselves are still changing quite rapidly. The electronic devices (regulators and ballasts), on the other hand, are suitable for local production. Here the principal aim must be to significantly improve the quality of locally manufactured products, which so far has fallen considerably short of what is needed. It must be made easier for the relevant firms in developing countries to purchase electronic components; their production facilities must be upgraded through the acquisition of new machines and tools; and the qualifications of their employees, especially those responsible for after-sales service and maintenance work, must be improved. Systematic support for specific aspects of product development can also help to improve the quality of locally produced electronic components. If technical problems are to be eliminated, it will also be imperative to establish binding technical standards and monitor compliance with them. In its role as a Technical Cooperation organization, GTZ can help developing countries to address the existing constraints in all of these areas by providing information and assigning short-term experts to advise relevant government agencies and upgrade the capabilities of local electronics firms.
It might also be possible to substantially improve the quality of locally produced equipment if final assembly of the devices in question were the only part of the production process that took place in developing countries, i. e. if design, product development, specification and component procurement were handled by manufacturers in an industrialized country. With this type of arrangement, the units - charge regulators, for example - would be shipped to the developing country in the form of ready-to-assemble kits in lots of, say, 100, 500 or 1,000 and then assembled, tested and delivered to the firms responsible for puffing together the complete SHS by qualified local manufacturers.
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