Small-scale electricity generator sets – commonly known as gensets – are among the most technologically and commercially mature options for distributed energy generation. Gensets are manufactured on a large scale worldwide, and they are used often to provide primary or backup power in off-grid and underelectrified areas. Generator sets have relatively low capital costs but high running costs due to the need to purchase fuel and provide regular maintenance. If routine maintenance tasks are not carried out regularly, the genset may break down before its time. This is a common fate of community-run gensets in rural areas.
For generator sets with a capacity of less than 3 kW, gasoline and diesel are popular fuels. Genset engines may also use other fuels, such as propane, kerosene, biogas, biofuels or fossil/biofuel mixtures. Biofuels, generally in liquid form, and biogas are fuels obtained from biomass such as crops, grains, seeds, tubers, animal fats, agro/forestry residue and wastes, wood and effluent. Examples of biofuels include alcohols such as (bio) ethanol and (bio) methanol; vegetable oils and fats; and biodiesel (BD).
All types of generating sets that use gasoline as a fuel, irrespective of the size of the generator, can utilize gasoline/ethanol (gasohol) blends containing up to 25% ethanol. However, many generating sets are warranted only for use of a 10% ethanol blend (E10). All types of generating sets that use diesel as a fuel can use biodiesel in any blend proportion with diesel. However, in many countries, suppliers’ warranties and recognized standards permit the use of 20% biodiesel (B20) only. The table below provides two examples of biofuels that, if available locally at an affordable cost, can be used to run small diesel generators for ICTs and other applications.
Alternative Genset Fuels
Restaurant Oil Wastes
Ordinary vegetable oils can be used to power diesel engines in cars, trucks and generator sets. Restaurant waste oils can be used as fuel after filtering and treatment in a waste oil conversion system, or in a diesel engine that has been modified to treat the oil before injection. With some knowledge about which oils are most appropriate and how to operate and maintain the diesel engine to avoid corrosion and other problems, used cooking grease discarded by restaurants can become a cheap source of genset fuel. See the Energy Resources section for more information about liquid biofuels and links to related web sites.
|Biogas, although typically used for heating and cooking, can also be used to fuel a genset to produce electricity. Biodigesters convert animal or human waste and water into methane through anaerobic digestion, a biological process that occurs naturally in the absence of air. The process produces a gas that is typically 55% to 75% pure methane. This gas can be used for a variety of energy applications. Where there are simultaneous needs for improved sanitation, gas for heating and cooking, and electricity for ICTs, a biogas digester may be a feasible option. Although not often used to power ICTs in remote areas, some 3.4 million biogas digesters are in daily use in India, and smaller countries such as Nepal are installing around 26,000 digesters each year.
The main components of a small-scale generator set are the internal combustion engine and the generator. Some models also come with a built-in inverter to output AC electricity.
Operation & Maintenance
Small portable gensets typically require maintenance every 200 to 400 running hours. Maintenance tasks include draining and changing the engine oil, changing the filter, and disposing of the used oil and filter. Maintenance may be performed in-house or by external service companies, such as the genset manufacturer or distributor.
If maintenance tasks such as changing the engine oil are not carried out on a regular basis, genset components can deteriorate, resulting in reduced efficiency and shortened equipment life. In Winrock’s experience, generator set maintenance is at risk of being neglected in schools and other non-commercial facilities, where there is little personal incentive for teachers and other volunteers to ensure long-term care of the equipment. Entrepreneurs whose livelihoods depend on keeping the gensets running smoothly are more likely to make sure that proper maintenance is done.
The main environmental drawbacks of genset use are air pollution, noise, and emission of greenhouse gases. It is also common to have leaks or spills of engine oil and fuel around the generator during the process of maintenance and refilling the tank. This can introduce pollutants to nearby waterbeds and rivers.
Noise can be an important environmental factor for local communities to take into account when considering the use of a generator set. The noise level for a 3 kW diesel generator can be 70 or 80 dB, about as loud as freeway traffic or an alarm clock. Generator noise has caused problems in rural schools when the generator is located near a classroom.
The type of fuel used can lessen air pollution to some degree. Compared to diesel, biodiesel reduces emissions of carbon monoxide and particulate matter as well as total unburned hydrocarbons. Since the sulfur content of biodiesel is very low, it does not contribute to the sulfur dioxide emissions that are often a major concern with the use of regular diesel. A joint study by the U.S. Department of Energy and Department of Agriculture estimated that biodiesel reduces life cycle carbon dioxide by 78% (Ref).
The initial cost of a small-scale generator system, including additional components and services such as batteries, BOS, installation and engineering, is in the range of $1,000 per kW installed, less for higher capacity systems. However, this does not include the cost of fuel and maintenance, which are likely to be multiples of the initial investment over time if the generator is used as the primary power source.
Fees related to labor and parts depend on local conditions. According to the California Energy Commission, the maintenance costs of gasoline gensets range from US$0.007/kWh to US$0.015/kWh, while maintenance costs of diesel gensets range from US$0.005/kWh to US$0.010/kWh (Ref). One Indian manufacturer of small portable gensets provides maintenance service at a cost of 250 Rupees (US$5.45) for labor plus Rs150 to Rs250 (US$3.27 to US$5.45) for materials. At the latter rates, a generator with output of 1.5 kW, that required maintenance every 200 to 400 running hours, would have an O&M cost ranging from $0.015/kWh to $0.036/kWh.
The price of a diesel-fueled portable generator is normally higher than that of a gasoline-fueled generator. However, diesel generators tend to have lower fuel costs than gasoline generators over time. Fuel costs represent the largest ongoing cost of operating a genset, and fuel prices vary widely from country to country. In late 2003, diesel costs worldwide ranged from less than $0.35/liter (Philippines) to $0.90/liter (Rwanda). Biodiesel is normally more expensive than diesel. The production price difference between the two types of fuel is reduced in some markets as many governments provide various tax incentives for “green” fuels.
Purchasing a genset often appears to be the simplest and least expensive option for powering a small-scale ICT facility. This perception is at least partly due to the relatively low up-front capital costs of gensets compared to other options. However, when the lifetime costs of fuel and maintenance are included in the equation, a genset is not necessarily the least-cost option, particularly for very small loads. In extreme cases, the cost of purchasing and installing the generator set may account for less than 5% of the lifetime costs of the system.
Gensets can be robust and reliable power systems if properly maintained. Gensets are most viable when the funding for up-front investment in the power solution is severely limited, while the high ongoing costs of purchasing fuel and maintaining the equipment over time can be tolerated. As the size of the total load increases, gensets typically become more economical.
The more a genset is used on a regular basis, the more often it will incur the inconvenience and cost of routine maintenance. A generator that runs 10-14 hours a day may need an oil and filter change every 2-3 weeks. These burdens are reduced considerably if the genset is used mainly for backup power on an occasional basis.
Small-scale gensets may have difficulty powering rural ICT facilities without causing damage. Genset power feeds are not always pure, and the frequency and voltage may not be as stable as required by the ICT equipment. In addition, there may be up to a two-minute window between the time a power outage occurs and the time the generator kicks in. This two-minute period may be enough to cause serious damage to computer and network systems. If a battery back-up system is present, the problem may be alleviated since the battery power kicks in between the main power feed going off and the generator feed coming on. The battery bank also serves to "clean up" or stabilize the power feed from the generator.
For generators whose capacity is small in relation to the total load, the nonlinear fashion in which some computers, UPS systems and other ICTs draw power can cause voltage fluctuation and disruptive currents that can damage sensitive computer components. The effects of nonlinear loads can also lead to excess heat in the generator. Over time, these side effects can shorten the lifespan of the ICT devices, the genset or both. There are a number of ways to compensate for the effects of nonlinear loads on a small genset, but they are technically complex and difficult to generalize. One fairly straightforward practice is to oversize the generator in relation to the loads it is serving. This typically requires that the generator have a rating at least 2 to 3 times the rating of the entire load. However, due to wide differences in output impedance for generators, it is not possible to specify an oversizing factor that guarantees a solution to the problem.
Related Web-based Resources
Related Case Studies
Mali - CLIC in Bougoula - Multifunctional Platform
Tanzania - Biogas computer lab