China Projects - Guanghan
ICSD is currently working together with US and Chinese experts on a model sustainable village in Sichuan, China. The design of Longju Sustainable Village in Guanghan makes maximum use of village resources and relies on renewable energy. The result of this is a healthier environment for residents. Replicating this village on a larger scale will contribute significantly to healthier air and water throughout China.
Guanghan Model Sustainable Village Report
ICSD has been working in wide-ranged projects in the People's Republic of China since the Center's establishment.
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Introduction: Longju village presently has a rice farming based economy with poor sanitation and pollution due to villagers burning rice straw for cooking. In order to improve the villager’s quality of life, ICSD has sought to make maximum use of village resources: the sun and biomass for energy, villager time and energy, and a nearby temple bringing tourists. This village design uses available resources to maximum advantage in order to reduce pollution and boost the economy. This sustainable village will serve as a model not only for villages in Sichuan, but throughout the developing world in agricultural based regions. Passive solar design, solar water heating, and rainwater collection all make use of natural resources. And a solar powered community center provides a community focus with internet, daycare, health clinic and other services.
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Bio-energy cycle: Figure 1 shows a schematic of the bio-energy system for the village. ICSD has recommended a small intensive animal farm as a village business. The animals produce manure sufficient to feed a biogas facility (digester and gas holder in center of figure 1) to provide cooking gas and feed a fuel cell to generate village electricity and hot water. Farm output (meat and eggs) boosts the economy and digester effluent provides fertilizer and nutrient rich water. The fuel cell also produces heat used to warm the digester as well as clean hot water.
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Environmental Benefits of Longju Sustainable Village
Longju Sustainable Village contributes in many ways to a healthy environment. Chief among these are, first, the reduction in energy demands that would otherwise be met by the combustion of coal and, second, the efficient use of village resources (including the "waste" stream) thus avoiding polluting the ground and water of the village and river.
Coal combustion is the main source of power and heating in China, as well as the main source of pollution. Particles in the air (TSP), SOx and NOx contribute to smog, acid rain, respiratory problems, and acid damage to vegetation and buildings.1 The village biogas energy system effectively eliminates the harmful pollutants. Not only that, the net CO2 emission to the atmosphere is zero. Usually, animal manure is left outside to compost aerobically, releasing CO2 directly to the atmosphere (and polluting water run-off). With the anaerobic digester, the same carbon is used to produce methane before burning and release of CO2 to the atmosphere. Since the original source of carbon was CO2 from the air taken up by the crops used to feed the animals, there is no net carbon gain for the atmosphere. Coal remains in the ground.
River and ground water in China is polluted in many places due to the release of industrial, agricultural, and residential waste water directly into the environment. The sustainable village design makes maximum use and re-use of water resources, and the biogas digester and composting toilets prevent untreated water from being released to the environment. Compost from the digester also serves as a natural fertilizer that eliminates non-organic fertilizers from polluting field run-off water.
The contributions of the Sustainable Village toward cleaner air and water can be seen in the different elements of the village design—from that of the homes and community center to the sustainable agriculture system which includes the biogas plant, and including the renewable energy technology.
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The village homes use village generated gas and village generated electric, with water and space heating augmented by solar heating. As discussed below, the village farm is used as an energy source—using animal waste to generate biogas. This in turn supplies homes with cooking gases as well as supplying the energy source for the fuel cell that powers the homes. Lights and appliances are powered by local clean electricity, rather than electricity produced in dirty coal power plants.
The local source of clean gas and electric removes demand on the electric grid and thus on coal-fired power generation. Electric use in the homes is small compared to US homes. Assuming a typical village home will have a small refrigerator, TV, and several fluorescent lights, one can estimate electric use of approximately 3 kWh per day. For a typical power plant conversion efficiency of 30%, it would require 5 kg of coal to produce 3 kWh of electric power. Burning of this coal would in turn produce 14.3 kg CO2 and 0.15 kg SO2.2 Adding the community center, farm, and businesses to the electric budget produces a total village electric use on the order of 500 kWh per day, although initially without appliances like refrigerators the energy use would be much less. Assuming that this 500 kWh load was met entirely with biogas generated electric, the amount of coal displaced yearly would be 315 tons, the amount of CO2 sequestered in the ground would be 900 tons and the amount of SO2 not released to the atmosphere would be 9.1 tons.
Locally distributed biogas will provide cooking gas for villagers. This is estimated at 2 m3/day/home, or roughly 200 m3/day for the village.3 Presently a few villagers might use bottled gas, but most villagers use a factory processed coal/kerosene brick or burn rice straw.4 It is estimated that 200 liters of biogas is enough to boil a family’s daily drinking water supply (approximately 6 liters). This in turn would displace approximately 1 kg of firewood or 0.4 kg of charcoal.5
Table 1 Environmental benefits of village biogas and electric
| Benefit source
|| Net reduction of gas release to atmosphere
| Village electric use (displaces coal)
|| 900 tons/ yr
|| 9 tons/ yr of SO2
| Village cooking gas (displaces coal and rice straw)
|| 50 tons/ yr
|| Cooking gas displaces coal and rice straw: CO, SO2, and smoke particulates.
| Fuel-cell drinking water
|| 5 tons/yr
| Unquantified benefits:
- Cleaner emissions of biogas combustion for cooking (vs. coal brick).
- Reduction in respiratory illness and associated health costs.
- Distributed gas and electric generation gives local control of production and cost and removes influence of gas supply and stability of electric grid.
- Reduction in coal mining impact.
- Improved air quality due to use of electric vehicles.
If the biogas displaced propane, the environmental benefit would not be the reduction of CO2 emissions, but rather replacement of ground-source carbon (propane) with carbon that originated in atmospheric CO2 (biogas). For biogas displacing a coal brick, the benefits also will include the elimination of some of the harmful CO and SO2 and perhaps other pollutants depending on the brick composition. Biogas may have some sulfur content of its own depending on manure and digestion chemistry, but this is scrubbed out.6 Finally, if biogas displaces rice straw combustion the environmental benefits will be even greater, as rice straw generally burns at a low temperature with very unhealthy emissions. Wood smoke emissions (when not properly burned in a woodstove as is the case in the village) include large amounts of particles (primarily hydrocarbon molecules—tars), SOx and NOx and some carcinogenic compounds, and the smoke is irritating to eyes and lungs.
In addition to the fuel cell power and biogas resources, homes will be designed to make use of solar heating in the winter and solar thermal water heating. This improves comfort while reducing energy requirements for space heating and water heating. Homes also will be designed to allow photovoltaic (PV) panel installation on the roofs to allow additional clean power generation.
The sustainable village water is provided in part by rain collection, reducing the load on the city water infrastructure which requires power to operate. In addition, using rainwater conserves water resources that are scarce in many parts of China. Drinking water is produced by the fuel cell, a by-product of the electric generation. The present fuel cell7, rated at 200kW, consumes 58 m3/hr of methane (approximately 100 m3/hr of biogas) which in turn produces 87 l/hr of water. This is sufficient drinking water for a village of 100 homes. However, this assumes that the fuel-cell will run at full-load, which will only be the case if farm size is increased and unneeded electricity sold outside the village or fed to the grid.
Presently, all wastewater from village homes is sent directly to the fields (and from there to the river) without treatment. In the new design, village homes will have indoor plumbing and allowance for treating human waste. Greywater from the homes is sent to the gardens, while composting toilets in the homes serve double duty: they compost the human waste making it useable on the gardens, and they reduce demand for water that would otherwise be needed to flush blackwater to a central wastewater treatment plant. The end result is a healthy and minimal waste stream from the homes that is useful for watering and fertilizing family gardens without releasing contaminated water into the environment.
Table 2 Environmental benefits of water/ wastewater system
| System component
|| Environmental benefit
| Composting of human (and animal) waste
|| Clean water run-off to river, village sanitation and health. No need for water to flush waste to central treatment plant.
| Collection of rainwater
|| Conservation of water resource, reduction in city water treatment and pumping costs.
| Fuel-cell provided drinking water
|| Clean water, no gas required to boil or treatment required of rainwater.
| Greywater use on family gardens
|| No central water treatment required.
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Village homes and other buildings are constructed of compressed earth bricks—manufactured on site. The environmental benefits of these bricks are immense, due mainly to the elimination of firing of the bricks that is done with coal.
The brick making industry in China is dominated by small Town and Village Enterprises (TVEs) with 85% of brick production versus the larger State Owned Enterprises (15%).8 A typical brick kiln occupies about 2 hectares (30 mu or 5 acres) of land (with bricks dried outside prior to firing) and produces about 10 million bricks per year (40,000 bricks per day during the dry/ warm season) and consumes about 1.1 TCE (tons coal equivalent) of coal per 10,000 bricks which is equivalent to 33 GJ of energy and simultaneously releases 27 kg of SO2 (as well as 2300 kg of CO2) into the atmosphere, a main contributor to the acid rain problems in China, something on the order of 30% of total emissions in China. In 1990, Sichuan province had 9000 brick making TVEs and produced 19 billion fired bricks.9 This translates to burning over 2 million tons of coal, and releasing 4.3 million tons of CO2 and 50,000 tons of SO2 into the Sichuan atmosphere, while simultaneously removing 400 square kilometers of land from useful agricultural production.
Compressed earth bricks are produced from materials on site. This frees up the land that would otherwise be used by a brick factory. The materials do not need to be dug from the earth at some remote location, transported to a brick kiln, fired and then transported to the work site. Instead the bricks are taken from the building site, and made without firing. Because heating is not required, and because a small gasoline engine runs the earth brick compression machine (requiring 2 gallons per day, or 14 gallons of gas for 10,000 bricks10), energy required to make a brick is decreased by approximately a factor of 20 as is pollution. Burning the coal required to produce 10,000 bricks produces 27 kg of SO2 and 2300 kg of CO2. Burning the gasoline required to produce 10,000 compressed earth bricks (14 gallons or 40 kg) in an 8-hp Honda 4-stroke gasoline engine will produce less than the CARB standard11 of 4 kg of CO and 0.1 kg of HC + NOx (combined mass of hydrocarbons and nitrogen oxides) while releasing 90 kg CO2. Thus, energy intensity, and pollution and greenhouse gas emissions are reduced resulting in significantly better air quality.
Table 3 Environmental benefits of using compressed earth bricks for village construction
|| Environmental details
| Pollution reduction
|| 200 tons CO2, 3 tons SO2 not released to atmosphere.
| Primary energy use reduction
|| Compressed earth brick production requires only 5% of the energy required to fire clay bricks (1.1 TCE = 10,000 kWh vs. 14 gallons gasoline = 500 kWh)
| Equivalent reclaimed land
|| Construction of 10 villages would take a brick factory out of production for a year and free up 5 acres for farming.
A typical village home of 110 m2 (1200 sf) would require approximately 7000 compressed earth bricks, or 5 days of production from the compressed earth brick machine. Use of earth bricks for the construction of one home would displace approximately (assuming same number of standard fired bricks which are of slightly smaller height and length but require mortar) 1.6 tons of CO2 and 0.02 tons of SO2. Additional reductions in these gases are gained by not needing to transport materials. Construction of the entire village (100 homes, community center, farm and biogas plant) will require roughly 1 million bricks. Using compressed earth bricks will effectively eliminate production of more than 200 tons of CO2 and nearly 3 tons of SO2.
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Farm and biogas facility
The proposed village farm has 11 barns, a large greenhouse, fish ponds, duck and geese ponds, office, storage buildings and the biogas facility. These buildings require lights, tractors for moving loads, power for the anaerobic digester (AD) mixer and pre-mixers and pumps for waste, as well as sprinklers in greenhouses, fans, and storage refrigerators, and other loads. However, these loads can all be met with power supplied by the fuel-cell. The net benefits of the farm and biogas plant are: electric, gas and fertilizer for the village, and a strong economic component for the village.
The waste from the AD is available for fertilizer on the fields. This high quality fertilizer is produced locally, and requires no outside materials or energy to produce. The environmental benefits of this "clean" fertilizer are the reduction in pollution related to the production and transportation of inorganic fertilizers. Farm waste and human waste that is not sent to the AD is composted and likewise available as fertilizer. Crops are chosen not only for money-earning potential, but also for suitability for recycling. All of the waste recycling (especially of animal waste) greatly reduces the load on the environment. Rather than sending animal excrement into a ditch to pollute ground and surface waters, this resource is re-used and harmful bacteria removed in the digestion and composting processes.
Not only is the manure used as fertilizer, but in the process of becoming useful and safe fertilizer the manure is used to produce biogas. This resource effectively displaces natural gas or propane (or worse straw) that would be used for cooking and heating water. While burning of natural gas is much cleaner than coal, producing gas locally displaces the cost of infrastructure and mining operations. If the gas is considered to displace rice straw as a fuel, then the environmental benefit is tremendous.
The biogas is also used to supply the fuel cell. The fuel cell supplies electricity as well as heat and hot water. Running at full capacity, the fuel cell produces 200kW of electric, 260 kW of heat (@ 60C), and 2100 l/day of hot water12. Using this clean energy source not only avoids coal pollution, but also the high environmental cost of coal mining. The source of heat is sufficient for heating the biogas digester and more (e.g. heating water for a laundry facility, distilling water for sale, or other industrial processes). The fuel-cell hot water provides clean drinking water while also displacing the gas that would be needed to boil rainwater or groundwater for drinking.
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Village life and business
The village is designed with the intent of having no gas powered vehicles in the residential area. The community center will have a recharging station to use for charging electric vehicle batteries. The use of electric tractors will reduce the use of fossil fuels and instead use local clean electric power. Internal combustion engine CO2, hydrocarbon, particulates, and noise pollution are all eliminated. While the community center will require more power to supply the HVAC system, computers, lights, and other appliances, the center will also have PV solar electric power.
Instead of burning or wasting the rice straw resource in the village, the village will have a strawboard manufacturing business. This business takes an otherwise wasted resource and rather than burn it (and thereby produce polluting emissions and greenhouse gases), sequesters the carbon into the boards and simultaneously produces a product that can displace building products made with more expensive and less readily available materials.
The Farm Unit Concept
Figure 1 Possible layout of
Longju farm unit
The "Farm Unit" was conceived as a way to provide a source of gas, electric, water, and fertilizer for a village of 100 homes. It is an integral part of the village agricultural and energy system. It provides a means to recycle village waste while cleanly producing energy. The farm unit consists of a concentrated animal operation which feeds manure to a heated anaerobic digester. The gas from this digester is then piped to individual village homes as well as to a fuel cell co-located with the digester. The fuel cell reforms the biogas to hydrogen and then chemically consumes the hydrogen to produce electricity and hot water. The electricity is wired into the village power grid. Fuel-cell waste heat is available for heating the digester and for other heating purposes, while the fuel-cell generated water can be used as a drinking water source. Digester effluent is further composted and then used as fertilizer on the fields.
Figure 2 Farm/ biogas/ fuel cell
facility flow diagram
Figure 1 gives one possible building layout that orients barns to minimize distance from barn to digester. The barns themselves are designed so that manure is easily collected at one end using a sloped subfloor or by some other means. In Figure 2 is shown a "conveyor" from animal barns to a manure holding tank. The intention is simply to design for easy movement of manure from the source (barns) to the holding tank (input to digester). This conveyance may be mechanical, manual, or likely a combination. The design of the animal barns and movement of manure from barns to holding tank is important. Proper design will allow for minimal effort, proper sanitation, minimal addition of undesired products (feed, straw, gravel, etc.), easy maintenance, and easy cleaning of floors and equipment.
The purpose of the holding tank is to allow for an unsteady influx of waste (as when a pond is cleaned and a large quantity of fish manure is collected). Manure is then fed to a pre-mixer where temperature, C/N ratio, pH, and other variables are monitored and adjusted. From there the manure is pumped to the digester. Making the digester perform well with a wide variety of inputs (different animals manure and vegetable matter) will be crucial to allowing this farm unit to be replicable while also meeting the desires of different villages for different animals and crops.
Biogas is taken off the top of the digester and scrubbed of sulfur and then fed either to village homes for cooking gas, or to the fuel cell. Biogas is first reformed from methane (plus inert gases) to hydrogen used by the fuel cell. The fuel cell generates electricity that is used to power the village. It also generates heat and water as byproducts, heat which can be used to warm the digester as well as used in other industrial processes or dumped to the air, and water for drinking or other purposes.
Important Design Issues
Sizing of farm to meet gas and electric needs of village and farm
A farm unit should be scaled to meet the needs of the village. Estimates of cooking gas requirements for a family are about 2 m3 for 2 meals.1 Therefore, at least 200 m3 of biogas needs to be produced daily to meet the cooking needs of villagers. Likewise, assuming a typical village home will have a small refrigerator, TV, and several fluorescent lights, one can estimate electric use of approximately 3 kWh per day (much less presently). Total village electric use, including farm, community center and businesses, will probably not exceed 500kWh in the near future. This translates to an average load of 20kW although peaks of 50 kW might be expected. Approximately 215 m3 of biogas per day would be required for a fuel cell (conversion efficiency 40%) to produce 500 kWh of electric energy.2 Therefore, the biogas requirements for cooking and for feeding the fuel cell are approximately the same, and a daily production of biogas of more than 400 m3 would be ideal. The farm unit depicted in Figure 1 will generate slightly less, as shown in Table 1. Increasing the number of pigs could raise the total biogas per day figure, as would making use of broiler excreta, pond scum, and vegetable matter. This same amount of gas could be generated with less land area if only pigs were used. Table 1 also gives a feel for the large number of animals on the farm. The farm layout of Figure 1 occupies approximately 30 mu (5 acres) of land.
Table 1 Animals and gas production of proposed Longju farm unit
These numbers are best estimates based on available data based on different conditions (e.g. animal size and digester efficiency) that are not always given.
* The 2 pig barns house a 150 sow unit with approximately 1200 pigs of varying maturity at any one time, with gas production approximately one half of an adult pig.
** Duck and geese biogas production estimates were based on body weight relative to chickens.
Choice of fuel-cell or alternative electric generator
The only presently deployable fuel-cell is a 200 kW unit from UTC Fuel Cells. This unit will provide approximately 10 times the needed average electric. The cost may be prohibitive. Ideally, a 20 kW unit could be used that fits the need of the village and meets the objective of being "village scale". Combining several 5 kW fuel cells might be the best strategy since many manufacturers are working on this size for near term production, and they may be available soon. This would keep investment cost low, while providing all of the electric power in the short term. If peak loads exceeded 20 kW, then the electric grid (electric service is already available in the village) could meet the demand, or else photovoltaic (solar) electric and batteries.
An alternative to a fuel-cell would be a diesel engine converted to burn biogas. The technology is not new, and would allow the engine to burn primarily biogas with only a small amount of diesel3. This engine would also produce heat useful for warming the digester. It would not produce drinking water as a fuel-cell would. Nonetheless, this option may be more cost effective, if not as technologically advanced or environmentally friendly. However, a diesel engine is much less efficient than a fuel cell such that generating 500 kWh of electricity would require approximately 400 m3 biogas plus 50 l diesel, or approximately 24% electrical efficiency. If the waste heat is used productively, the total efficiency is much higher. UTC states the PC25 fuel-cell efficiency (LHV) as "87% Total: 40% Electrical 50% Thermal". For reference, burning biogas directly as cooking gas gives a thermal efficiency of 55-60%.4
If the presently available PC25 200 kW fuel-cell is chosen, then some other alternatives to supplying it should be considered. It does not make sense to turn Longju village into "Longju Pig Farm" in order to feed biogas to the fuel-cell. That would be a commercial size pig operation and do away with the desired replicable village scale farm unit. Other alternatives include: piping in biogas from farm units in nearby villages, piping in city gas to feed this fuel-cell with the intent of using smaller fuel-cells in the future when they become available, or using some other fuel such as LPG to feed the fuel-cell. LPG is already in use with this same fuel-cell installed on a pig-farm in Guangzhou.5
Layout of biogas facility relative to village
There are many variables to consider in locating the farm/ digester/ fuel-cell relative to the village. The farm should be located with easy access to a road for bringing feed in and animals out. The farm should be located downwind of the main housing area to avoid obnoxious odor. The farm should also be close enough to the housing to minimize cost of laying gas pipe (and perhaps underground electric) to the homes. The fuel-cell should be located next to the biogas plant and also next to the electric transformer that brings electric to the village, since the fuel-cell now serves as a gateway, drawing power from the grid only when the fuel-cell itself cannot meet electric demand (either due to too high demand or a shortage of gas). An industrial area could be sited between the farm and the housing for easy access to fuel-cell heat and electric.
Selection of farm animals
The choice of which farm animals to include is one of villager preferences as well as of business and biogas economics. Having a steady uniform manure stream, say from 100% swine or cattle, would make the biogas operation easier to manage. However, the villagers of Longju wanted a mix of animals. The types of animals and estimated biogas contributions are listed in Table 1 above.
From Table 1, the "biogas per animal" clearly favors the pigs. Cows produce even more gas. From the perspective of barn floor space required per liter of biogas, the "biogas per m2 barn space" column shows that pigs and laying hens are the best performers. The rabbits are the worst performers in this respect (although their meat sells for a good price—the villagers motivation). Geese and ducks are also big space consumers since the required ponds were not included in the "biogas per m2 barn space" column. From a farm size perspective, cows and pigs are the best choices. Chicken manure is problematic with a mixed reactor due to feathers in the manure. The broilers (meat chickens) are on the litter system and the litter cannot be fed to the digester (at least if a mixed reactor design is chosen rather than a plug flow reactor), so that the broilers contribute nothing to the biogas production.
Design for ease of replication
Replication is a key concept along with "village scale". The goal is to have a farm that produces enough gas to provide gas and electric to a village. And the farm should be standardized as much as possible to allow easy replication.
Ideally, a farm unit should be designed in a way that can be easily built in different locations without needing large numbers of specialists for construction and commissioning. Different components of the farm and biogas facility need to be standardized: barn building design, manure collection and transfer design (building and pipe layout, the "conveyor" of Fig. 2), digester design, digester effluent handling, auxiliary motors/ pumps, gas distribution network, gas and electric metering, village home appliances (gas stove and lights, etc), fuel-cell/ batteries, composting, business model, training and operation procedures, etc.
The issue of designing a biogas digester that can perform well with varied inputs is important. The digester needs to perform well no matter if chicken manure or pig manure or fish pond scum is fed to it. The key to achieving this may be in control of the pre-mixer. Proper training and procedures need to be provided so that the facility manager can make necessary adjustments to digester input so as to maintain good digester performance.
Use of crop wastes in digester
Ideally, the digester design will allow for some vegetable waste as input. Soft waste (such as kitchen garbage) might go in with no problem. Perhaps woody stalks (e.g. rice straw) could be pre-treated to allow use in gas production. It may be that gas production can be boosted significantly by including crop waste into the digester.
Design of digester
The best choice of digester technology has not been specified. The digester should be designed to run efficiently, heated to maintain consistent gas production with a smaller tank volume. The most advanced technologies (pre-mixer, pumps, AD vessel design and mixer, gas scrubber) should be selected with the intention of being environmentally friendly, economical, and maximizing gas production.
Table 1 gives a liquid input to the digester of 11,000 l/day. For a 20 day hydraulic residence time this will require a digester volume of 220 m3. Alternatively, a chain of digesters in series could be selected, or a plug-flow reactor. A plug-flow reactor may allow for more easy handling of vegetable and chicken manure wastes since clogging is not a problem. Some simple method of seeding the input with bacteria would be necessary.
Simple operating procedures and technical support
The final facility design needs to have simple operating procedures and a plan for training so that managers and workers know how to operate and maintain the equipment, understand underlying principles, health and safety issues, the business model, and know how to manage the business and where to find help.
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Economic boost: The economy is further helped by the establishment of several new businesses. In addition to the farm, there is a straw board enterprise to make use of straw residue. This uses the village rice straw as input and makes a useful construction product while eliminating pollution from straw burning. Compressed earth block technology has been recommended to allow villagers to construct homes with village resources (dirt and manpower) and without the pollution that would be produced in the making of factory-fired bricks. This technology would remain as a village enterprise after construction of village homes. In addition, the fuel cell's got water output can run a small laundry business, the sale of the electricity produced by the fuel cell becomes an enterprise of its own. Likewise management and sale of biogas is a village enterprise. The village community center has a daycare service/ business as well as business opportunities associated with the internet connection there. Finally, the attractive village homes themselves present business opportunities. The homes have flexible building layouts that allow villagers to operate small shops to serve villagers and tourists. And solar water heaters and photovoltaic panels on homes required installation and maintenance.
The concept of recycling village resources has become central to making this a sustainable design, with renewable energy powering the village, and new technology introduced to support new enterprises; all leading to a healthier economy and environment. This sustainable village will serve as a model not only for villages in Sichuan, but throughout the developing world in agricultural based regions.
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1. "Country Analysis Briefs: China", US Energy Information Agency Office of Energy Markets and End Use (www.eia.doe.gov/emeu/cabs/china.html), April 2001.
2. "Carbon Dioxide Emission Factors for Coal," B.D. Hong and E.R. Slatick, Quarterly Coal Report, Jan-April 1994, DOE/EIA-0121(94/Q1).
3. "Biogas Digest" Volume I-IV, German Appropriate Technology Exchange (GATE) (http://www5.gtz.de/gate/id/publications.htm), GTZ-GATE, Eschborn, Germany, 1999.
4. Based on observations during site visit.
5. "Biogas Digest" GATE, 1999.
6. "Biogas technology: a training manual for extension," FAO/CMS (UN Food and Agriculture Organization, www.fao.org), 1996.
7. UTC Fuel Cells, United Technology Corp., PC25 200kW fuel-cell.
8. "China: Energy Efficiency and Pollution Control in Township and Village Enterprises (TVE) Industry" Report No. 168/94, Joint UNDP/ World Bank Energy Sector Management Assistance Programme (ESMAP), Dec. 1994.
10. Brick machine manufacturer estimate.
11. Honda website statement and data from "CA Exhaust Emission Standards and Test Procedures for 1995 and Later, Small Off-road Engines," CA Air Resources Board (http://www.arb.ca.gov/regact/sore), 1999.
12. PC25 fuel-cell specifications, (http://www.internationalfuelcells.com/commercial/pc25summary.pdf)
13. "Biogas Digest" Volume I-IV, German Appropriate Technology Exchange (GATE) (http://www5.gtz.de/gate/id/publications.htm), GTZ-GATE, Eschborn, Germany, 1999.
14. Based on UTC Fuel Cells, United Technology Corp., PC25 200kW fuel-cell specifications (http://www.internationalfuelcells.com/commercial/pc25summary.pdf), 2002.
15. "Biogas Digest", ibid.
16. "Improved Biogas Unit for Developing Countries," L. Sasse, C. Kellner, A. Kimaro, GTZ-GATE, Eschborn, Germany,1991.
17. News release of UTC Fuel Cells, Dec 17, 2001