| Energy research in developing countries |
|Volume 7: Nonconventional energy|
Marshal F. Merriam
This paper discusses the use of wind for electricity generation in the developing world. Technical topics include the four steps necessary for the assessment of the wind resource and its conversion to electricity. The output and costs of the wind industry are described (based on experiences in California). The generation of electricity from the wind is discussed with particular concern for the developing world. Special problems in developing countries include financial, technological, managerial, and physical difficulties. The paper concludes with a discussion of problem areas, R&D priorities, and policy recommendations for LDCs.
Because wind speeds fluctuate widely and depend on time and location, equipment should be sited with great care. Potential sites are difficult to identify because the resource is invisible and inconsistent. The four steps needed to assess the wind resource at a given site are
· Preliminary reconnaissance, which includes a review of existing records for localities with mean wind speeds of at least 5.5 m/s, a review of maps of local topography and weather patterns, and consultation of "local lore,"
· Field reconnaissance, in which a small crew with a vehicle and portable anemometers measures the "run of wind," looks for wind-modified vegetation, talks to locals, and makes short-run measurements of average wind speed in promising regions,
· Modeling, in which the most promising localities are modeled, either numerically or physically, and
· Site verification, an expensive but necessary step, in which wind speed is recorded for an extended period (months or years) before the commitment is made to install wind generators.
In addition, other factors (for example, proximity to the local power grid) should be considered. Although there is a strong demand for assessments of wind power, data are often sparse, particularly for developing countries, and this makes the first step critical and often extends it.
Technological Fundamentals and Limits
There are several technological fundamentals and limits that govern the conversion of wind energy:
· Wind power is highly variable in both space and time because power available from the wind is a function of air density and wind velocity cubed.
· A good wind installation would have a power coefficient of about 0.3, which means that, on average, the installation would extract 30% of the energy in the wind it intercepts each year.
· Rated wind speed (RWS) is the wind speed the generator needs to reach its rated electrical output (the usual practice is to choose a machine with an RWS 1.5-2 times the average wind speed at the site).
· Plant capacity factors (ratio of average to capacity output) that are economic are generally between 0.25 and 0.35.
· Availability is the fraction of time that the wind generator is fit for service (because maintenance, repair, and replacement of parts must be expected, no generator can be 100% available).
· Solidity refers to the amount of blade material necessary to intercept a certain area of wind.
· Most machines in use today have a horizontal axis (however, vertical-axis designs promise better cost effectiveness and fewer mechanical-drive problems, but they are less reliable).
· The design of generator rotors must focus on two major requirements -the desire to extract as much energy as possible from the wind and the need to control the revolutions per minute and to stop the machine reliably in high winds.
Output and Costs
There are no statistics for the global industry; however, a study of California's experiences shows the outputs and costs of the wind industry. In California, by the end of 1983, there was 239 MW of wind-generated electricity connected to the grid, and projects to generate another 1 202 MW were contracted to be built. None of the California projects would have been feasible without large tax incentives. The most cost-effective wind generators produce in the range of 0.1-0.5 MW. However, emphasis continues to be placed on the development of larger machines, likely because of the influence of the large aerospace firms on the US government.
There seems to be little prospect of commercial grid-connected equipment that could compete with conventional generators in electricity production. In developing countries, the potential for smaller stand-alone wind generators is much greater than in developed countries. If there is a good wind, a small stand-alone wind generator may be appropriate even if the location is not remote. As a matter of public policy, these generators should be emphasized more than grid-connected applications in the developing world. Unfortunately, although the social importance of smaller, stand-alone units is greater, their commercial attractiveness is less.
Special Problem in Developing Countries
Problems encountered in the use of wind energy in industrialized countries may be exacerbated in the developing world. In order of importance, these problems are financial, technological, managerial, and physical.
The financial difficulties stem from the long payback period for grid-connected generation equipment and from severe competition for scarce capital. Rates of return for many projects in LDCs can be much higher (typically 15-30% annually) than for projects associated with grid-connected generation equipment. Therefore, investors may be risk-averse to investment in new wind technology. The use of foreign exchange for the purchase of stand-alone systems can also be a special problem for LDCs.
Technological problems are caused because there is a lack of the support services and facilities that are readily available in the North. Limited availability of trained personnel to erect, repair, and operate the equipment and a lack of imported spare parts are also important problems.
Most LDCs are weak in managerial resources; therefore, employees are used inefficiently. Managerial problems penalize attempts to harness the wind economically.
The physical problems stem from the lower latitudes and warmer climates of most developing countries. Wind speeds tend to be lower and the air is less dense. As a result, less power can be derived from wind energy.
Suggestions for Further Research
The main problems in the generation of electricity from the wind are unreliable equipment, high costs and short life of the equipment, inadequate profits and high risks for manufacturers, and the inability of government demonstration programs to transfer the technology and experience to the private sector or to government-owned corporations.
R&D priorities in developing countries include
· The contracting of local engineering laboratories to develop improved wind generators,
· The local manufacture of inexpensive electronic controls to improve the operation of wind-powered machines and to help develop national expertise,
· The development of a package that consists of a rugged, reliable wind generator operating in parallel with a diesel- or gasoline-driven generator,
· The development of packaged stand-alone systems with battery storage and small generators that could be used for specific purposes (for example, power for runway lights at unattended airstrips, or power systems for lighting, heating, and alarms at park headquarters or small museums in unelectrified areas), and
· The development of a standard wind-farm package for connection to local grids at suitable sites.
Policy recommendations include the following:
· Large and highly visible demonstration projects should be avoided.
· Wind-farms should not be developed for fuel saving in grids unless the fuel to be saved is oil.
· The first projects should be directed toward finding good wind sites.
· The needs and characteristics of the country should be considered in the wind program.
· The need to conserve foreign exchange and national pride may dictate a program of solely indigenous content (local design and construction of wind generators is possible, but only at a cost).
· Government laboratories and universities can play a useful supporting role, but the major portion of any successful wind program must be undertaken by the private sector.
· The idea that the purpose of electricity generation from the wind is job creation should be resisted.