L’empreinte coloniale sur les structures militaires

After projecting the peak coincident demand that is expected at a new project site, it may still be possible to reduce project cost by either reducing the generation or distribution capacity required to meet this peak demand or permitting increased consumer load with the same generating and distribution capacity. This is achieved through demand-side management, i.e., managing electrical demand on the system in order to achieve more efficient use of the investment. For example, original plans might call for a 2 kW grain mill to work during the early evening hours when domestic needs require 8 kW. This would require a genset with a capacity of at least 10 kW. Demand-side management would attempt to restrict milling to hours where it does not coincide with lighting, thereby reducing the required maximum generating capacity to only 8 kW. Box 3 presents other examples of demand-side management.

Box 3. Demand-side management in Nepal.

In the villages around Aserdi in central Nepal, an isolated system supplied by a 1.0 kV line and small transformers serves three types of loads: residential lighting mostly in the evening, hulling of rice and milling of grain generally during the day, and water pumping located at the end of the distribution system. If the pump were to adversely affect the quality of electricity (causing brownouts) by imposing too much demand through the existing distribution line, the demand could be managed by operating the pump during late evening hours when excess line capacity is available. Furthermore, the water system would not be adversely affected by this scheduling because water is stored in a reservoir supplying a gravity-fed water-distribution system.

Another effort at demand management was to implement a capacity-based tariff for the small domestic consumers in the area.^* This is less costly to administer, because no meter, meter reading, or billing is required. But another reason was to encourage off-peak uses of electricity—encouraging 25-W and 50-W consumers to run radios during the daytime to save on battery purchases or encouraging 250-W consumers to use off-peak electricity to assist in cooking.

This latter approach to demand management requires that appropriate electrical end-use equipment be readily available. For example, to encourage the displacement of increasingly difficult-to-find

fuelwood with electricity without the peaks usually associated with electric cooking, various designs for low-wattage heat storage cookers have been developed and were promoted. These were designed to be plugged in most of the day when excess capacity is available in the home, storing heat that can later be used for cooking or heating when needed. In the Aserdi region, the 250-W limit was specifically set with this use in mind; it permitted the simultaneous use of the cooker and one light.

* With a capacity- or demand-based tariff, the consumer pays for using up to a pre-selected level of power (e.g., 25, 50, or 250 watts) but can use this power for whatever period of time. Rather than paying a tariff based on the actual energy (kWh) consumed that is measured by an energy meter that periodically must be read and billed by the utility, the consumer pays a fixed monthly tariff. To ensure that the household consumption does not exceed its pre-selected level of power, any of several forms of current limiter is used to restrict demand.

V. Mapping and system layout

After it has been established that potential consumers appear willing and able to cover the costs that will be incurred according to an agreed-upon tariff schedule, that an acceptable electricity supply is available, and that a well-founded and sustainable organizational mechanism exists to undertake such a project, planning can proceed. This chapter will begin by briefly reviewing steps required in preparing a map of the area to be electrified, a map that will assist with the planning and design process and provide a framework within which to collect the necessary data. This chapter will then review factors affecting the placement of the powerhouse and the physical layout of the mini-grid on the map that has been prepared.

Mapping

The mapping effort should begin with a sketch of the community, starting with the general features found in the village and ending with the placement of specific homes, shops, schools, and other potential village loads.

The map can begin with a sketch that includes the placement of the larger features, including a rough layout of the roads, trails, paths, and streams going through the community. Other landmarks such as village wells, market areas, meeting halls, schools, paddy land, and large trees can then be added. And finally, individual homes should be included.

It will be useful to draw this map somewhat to scale, because distances later will be used to calculate conductor size, pole locations, etc. Although the use of a long surveying tape (30 to 100 m) should give more accurate results, a good first cut should be achieved by simply pacing distances between all the village landmarks and individuals homes. Modern technology such as global positioning system (GPS) receivers can also be used but this requires that another set of skills be developed. Furthermore, the accuracy over small distance such as are found within a community may be less than can be obtained by simply pacing distances.

If distances are to be paced, all individuals involved in gathering data to prepare the map should first calibrate their standard pace. They should decide what feels like their "standard" pace over the actual type of terrain they will be crossing. They should each walk a fixed number of standard paces (e.g., 20) and measure the distance with a tape. From this, they can each estimate the average length of a single pace (e.g., 0.65 m). By doing this several times in different places, they should also be able to get an idea of the accuracy of their pacing. As the village survey proceeds, it would be a good idea to occasionally use a tape to verify the length of these average paces. From this, they can get a feeling for the variation in this average length from place to place and day to day.

Once paces have been calibrated, measurement should start from a specific landmark. Although the finished map should be the same independent of where pacing begins, it would be preferable to start at the location of the proposed powerhouse (see the following section for guidelines in placing the powerhouse).

Then pacing can proceed along what might be the eventual alignment of the distribution system.

Once all measurements have been made on the first sketched map, the map can be redrawn closer to scale.

This map should be adequate for design purposes. Alternatively, once a map has been redrawn based on paces and the initial distribution system laid out, another iteration can be made using a surveyor's tape, but distances can be rounded to the nearest meter. Greater accuracy is not necessary.