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| Fig. 1: Viability of generation schemes based on local cost in Africa. Area represents number of people who have the ability to pay for electricity from that source (triple overlap is 1.5 million). Data from Maher et al. [6] |
Across the world as many as 1.5 billion people lack consistent access to electricity. [1] Many of these people live in remote or rural areas where it is often too difficult or costly to transmit power using standard extensions of the power grid. The lack of access to this vital resource has hampered economic progress and is widely considered to be a major contribution to the continued poverty in these areas. [1] Though there has been extensive penetration of some modern technologies, such as mobile telephones and smartphones, the electricity required to operate these devices remains a serious challenge.
Fortunately, there do exist some solutions to bring electricity to these areas. The more advanced and complete solutions involve the construction of a micro-grid. These systems mimic the structure of a traditional power grid with centralized and continuous generation and allow for relatively high consumption, including home appliances and even industrial usage. They also do require a considerable capital investment in the range of millions of dollars and specialized maintenance. [2]
The other class of solutions relies upon truly distributed generation and are at much smaller scale. These solutions provide only sufficient electricity for a few extremely basic necessities such as LED lighting. They are typically simple and inexpensive methods of electricity generation that require little to no expertise to set up and operate. [3] Both the micro- grid and off-grid solutions can have tremendous impact on economic development and both rely upon a combination of traditional and state-of-the-art technologies.
There exist a vast array of methods of generating electricity completely independently of a grid infrastructure. Here we will review some of the economically favorable and interesting methods for remote and rural areas.
Diesel Generators: The modern diesel generator has proven to be an exceptionally versatile and robust method of providing moderate amounts of electrical generation. From critical backup generators at hospitals and nuclear power plants to diesel-electric locomotives and ships, the high power-to-weight ratio and reliability of diesel generators has made them very popular. [4] The fuel is relatively common and can be stablized, and has high volumetric and weight energy density. [5] There are, however, some serious drawbacks to diesel generators for rural, off-grid electrification. Fuel can be extremely expensive, or completely inaccessible. An estimate of the energy cost for a diesel generator in Africa suggests the cost can be as high as USD $3.00/kWh due to the difficulty to transporting fuel, among other issues. [6] Maintenance is non-trivial, especially where spare parts may be unavailable. Finally, the generators are often noisy, highly polluting and have low overall efficiency.
Micro/pico-hydro: Recent developments have made the age old technology of water power more useful for off- grid, small scale electrical power. These systems range in size from ~100W to ~10kW. The smallest systems rely on simple paddle wheels mated to off the shelf generators, such as modified automobile alternators or pumps driven in reverse. [7] They may require only immersion in a rapidly moving stream, or possibly a simple pipe to build additional water pressure with a controlled descent. The amount of power provided by these generators is sufficient to recharge small battery powered electronic devices such as mobile phones and LED lanterns. Larger micro-hydro plants require a small dam (often constructed of locally available materials) and can provide power for appliances such as refrigerators and desktop computers. Both the small and somewhat larger hydroelectric generation suffer from a critical problem - they rely upon consistent flow of water. Without the buffer afforded by a large dam, these generators can fail during times of drought or dry season. They are otherwise quite environmentally friendly, simple to maintain and do not require fuel. In one example the installation cost per household for a 2.2kW system is USD $81, and the electricity is then provided at the extremely reasonable cost of USD $0.15/kWh. [6]
Solar: An obvious choice to supply electricity to remote and isolated areas is solar photovoltaic power. With the recent reduction in the cost of solar panels, solar electricity has become quite affordable and accessible. [8] Peak solar irradiated power is greater than 1kW/m2, and though cheap solar panels have modest efficiency (~12%), it is still possible to harness considerable energy with this solid state technology. Solar electricity has the clear advantages of not requiring fuel, and simple maintenance. A basic direct current solar system can last over 20 years. An estimate of the cost of solar photovoltaic power based upon typical efficiency, cost and lifespan shows the cost to be USD $0.25/kWh for small installations, though a different measurement found the cost to be USD $1.09/kWh. [7] Of course, solar energy is only available during the day, and even poor weather can render a system nearly useless. This problem can be avoided with energy storage, but this is difficult and costly.
Wind: Though large scale deployment of wind turbines has advanced considerably in the last few decades, wind power has not had a significant impact on rural and remote electrification, especially in poverty stricken areas. [9] The basic technology has existed for considerable time, as small scale wind turbines are in common use to provide power to recreational marine vehicles and some high-end off grid homes. The relative complexity, high-cost and inconsistent generation have thus far restricted the application of wind power in rural electrification. A typical installation for a 10kW wind turbine may cost as much as USD $55,000, which is simply too high for these economically disadvantaged regions. [10]
Thermoelectric: Thermoelectric generation from a temperature difference is not typically considered as a means of providing electricity, except in certain specialized applications such as waste heat recovery and harsh environment wireless sensing. [11,12] Current state of the art thermoelectric generation is limited to small capacity and generally poor thermodynamic efficiency. [13] It does have certain undeniable advantages for the application in consideration here. Even the most remote and undeveloped areas typically still have a heat source used for cooking and providing warmth for survival. Whether this is a wood fire, kerosene stove or other source of heat, there is inevitably a considerable amount of waste heat. This waste heat can be used to generate a small amount of power with off-the-shelf thermoelectric modules. This may be sufficient to charge a mobile device or lamp, but without considerable developments in thermoelectric technology, the scale is likely to remain largely insufficient. In addition, usual materials used for thermoelectric modules such as lead, tellurium and bismuth are toxic.
Usually at low voltage and low power, these systems are safe, and do not require massive capital investment. These generation strategies, among others such as hand crank/human/animal driven generation, are beginning to provide small, but important amounts of electricity in locations such as Africa, southeast Asia and the Indian subcontinent. All of these methods provide enormous economic benefits to the end-users, compared with the lack of access to electricity or cost of battery power alone.
For larger scale power generation and distribution, the basic generation strategies, like those mentioned in the above section, must be scaled up and synchronized. The infrastructure required to do this is referred to as a micro-grid. Micro grids are typically designed to be capable of providing continuous power supporting the same levels of demand as a full scale electrical grid. Unlike off-grid generation, micro-grids can support factories and large appliances like refrigerators. In order to provide these levels of service, micro-grids are much more complex and costly than off grid generation. A typical system may cost in the range of USD $30M. [2]
In order to provide consistent power, a micro-grid must have some level of redundancy, and not rely entirely upon inconsistent generation sources like solar or wind. The basic architecture of a micro-grid is as follows: Generation source(s) (and fuel), load balancing electronics, power conditioning electronics and distribution network. The generation source often is a combination of a renewable source and diesel or gas generator, possibly with a battery bank to better match the load and capacity. The electronics required to autonomously operate micro-grids must be fast responding as there is typically less averaging due to the smaller number of generation sources and loads. [14]
Micro-grids also have the benefit that as the centralized grid expands, it can be relatively simple to merge the two grids, ultimately powering the micro-grid area completely from the main grid. Though micro-grids are a much more complete solution than off-grid generation, they are expensive, require specialized maintenance are are simply not practical in many situations.
In previous mass-electrification efforts, like South Africa, there have been broad and substantial economic gains achieved almost immediately. The technologies discussed above have the potential to create much of the same effect, reducing poverty in some of the most disadvantaged areas of the world. As the cost of manufacturing and physical transportation for technologies like solar and micro-hydro continues to decrease, deployment will increase. Already more and more electricity generation methods are becoming competitive at the level that could be afforded by these relatively poor areas (see Fig. 2). This may allow for greater wealth, and subsequently the ability to pay for more complete electrification. These first steps, whether they be a few watts of local generation to power lights to extend the day, or a micro-grid to run a sawmill and machine shop are absolutely essential to unlocking the human potential in rural and remote, un-electrified areas.
© David Heinz. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] "Energy Strategy Approach Paper," The World Bank Group, October 2009.
[2] K. Bullis, "How Solar-Based Microgrids Could Bring Power to Millions of the World's Poorest," Technology Review, 24 Oct 12.
[3] A. B. Sebitosi, P. Pillay, M. A. Khan, "An Analysis of Off Grid Electrical Systems in Rural Sub-Saharan Africa," Energ. Convers. Manage., 47, 1113 (2006).
[4] P. Arun, R. Banerjee, and S. Bandyopadhyay, "Optimum Sizing of Battery-Integrated Diesel Generator for Remote Electrification Through Design-Space Approach," Energy 33, 1155 (2008).
[5] B. D. Batts and A. Z. Fathoni, "A Literature Review on Fuel Stability Studies with Particular Emphasis on Diesel Oil," Energy Fuels 5, 2 (1991).
[6] S. Szabó et al., "Energy Solutions in Rural Africa: Mapping Electrification Costs of Distributed Solar and Diesel Generation Versus Grid Extension," Environ. Res. Lett. 6, 034002 (2011).
[7] P. Maher, N. P. A. Smith, and A. A. Williams, "Assessment of Pico Hydro as an Option for Off-Grid Electrification in Kenya," Renew. Energ. 28, 1357 (2003).
[8] N. S. Lewis, "Toward Cost-Effective Solar Energy Use," Science 315, 798 (2007).
[9] R.H. Crawford, "Life Cycle Energy and Greenhouse Emissions Analysis of Wind Turbines and the Effect of Size on Energy Yield," Renew. Sustain. Energ. Rev. 13, 2653 (2009).
[10] K. Shevory, "Homespun Electricity, From the Wind," New York Times, 13 Dec 07
[11] L. E. Bell, "Cooling, Heating, Generating Power, and Recovering Waste Heat with Thermoelectric Systems," Science 321, 1457 (2008).
[12] H. Bottner et al., "New High Density Micro Structured Thermogenerators for Stand Alone Sensor Systems," IEEE, 4569484, 3 Jun 07.
[13] J. P. Heremans
[14] F. Katiraei and M.R. Iravani, "Power Management Strategies for a Microgrid With Multiple Distributed Generation Units," IEEE Trans. Power Sys. 21, 1821 (2006).