An autonomous house or off-the-grid (OTG) house is designed to be operated independently from infrastructural support services ("grids") such as the mains electricity grid, water supply system, sewage/excreta disposal system, centralised food production system, gas grid, and in some cases, storm drains, mains electricity grid-connected communication services and public roads.
An autonomous neighbourhood is a collection of houses which together work autonomously (as one unit). Some of the houses may be completely autonomous on one aspect (e.g. electricity production) but not on other aspects (e.g. sewage disposal)
The phrase "off the grid" has also entered popular language as a related but distinct concept of generally independent lifestyles or desire to be low-profile. For example: "I'm not on social media because I prefer to stay off the grid."
This article focuses on the housing and appliances of autonomous houses. Sustainable city living discusses some of the areas of action specific to green living in a urban environment.
An example of a sustainable city is a 6.5-MW microgrid was built by AlphaStruxure. For it’s a joint venture of Schneider Electric and the Carlyle Group. That’s a global private equity firm, under a long-term energy-as-a-service (EaaS) agreement the company has with the county. Located at the Brookville Smart Energy Bus Depot, it will power the Montgomery County Department of Transportation’s Ride On transit electric buses.
Overview[edit | edit source]
One of the major drawbacks of centralised systems (e.g. municipal sewage systems, mains electricity grids) is that they require long water piping/cabling, towers, etc. These components tend to increase the cost of the system, which is ultimately charged to the users of the system. In addition, besides increasing cost, it also decreases efficiency (e.g. a lot of energy is lost in the longer cabling)
Autonomous houses however have very short piping/cabling. This has several advantages including reduced environmental impacts, increased security, and lower costs of ownership. Autonomous houses often rely very little on civil services and are therefore safer and more comfortable during civil disaster or military attacks. This is because the houses would not lose power or water if public supplies were compromised for some reason.
The basic functions performed by the solar batteries.
With battery storage, you are in a position to:
- Daytime storage of surplus solar production for use at night
- Manipulate time-of-use tariffs (TOU) when it’s cheaper to buy power at off-peak rates and store it for peak hours.
- Providing your home with backup power
- Selling energy back to the grid for a premium rate at peak days
In a broad sense, solar energy operates rather well. It processes the surplus solar energy from the PV device for overnight consumption. This helps create more cash reserves. It becomes a very beneficial long-term investment with the reasonable prices of current export customs duties.
Another important feature of storage systems is that it serves to protect your house from power cuts and lessen grid supply reliance.
However, it would be very hard to impossible for every house to attain autonomous operation on all aspects (e.g. food production, water supply, sewage, energy production) Even if it were possible, then systems in which autonomous operation is assured per neighbourhood (so say per 10 houses or per street -exact size depends on the region-) are still cheaper. This is because when we arrange autonomous operation per neighbourhood, 1 single (larger) unit (e.g. wind turbine, water treatment plant) can serve much more people, hereby lowering the cost (e.g. when compared to each house requiring its own (smaller) unit). However, by nonetheless reducing the amount of people served compared to a municipal (or even nation-wide) system, we still increase self-sufficiency/security and also still increase the efficiency of the system.
Another major advantage of autonomous neighbourhood systems is that the tasks for maintaining the autonomy can be shared among much more people, hereby decreasing the effort required considerably. For example, food can be grown by one family and preserved by another. Sewage can be handled by yet another family, for example.
Some sustainable households may choose to produce their own renewable energy, while others may choose to purchase it through the grid from a power company that harnesses sustainable sources (also mentioned previously are the methods of metering the production and consumption of electricity in a household). Purchasing sustainable energy, however, may simply not be possible in some locations due to its limited availability. 6 out of the 50 states in the US do not offer green energy, for example. For those that do, its consumers typically buy a fixed amount or a percentage of their monthly consumption from a company of their choice and the bought green energy is fed into the entire national grid. Technically, in this case, the green energy is not being fed directly to the household that buys it. In this case, it is possible that the actual amount of green electricity that the buying household receives is a small fraction of their total incoming electricity. This may or may not depend on the amount being purchased. The purpose of buying green electricity is to support their utility's effort in producing sustainable energy. Producing sustainable energy on an individual household or community basis is much more flexible, but can still be limited in the richness of the sources that the location may afford (some locations may not be rich in renewable energy sources while others may have an abundance of it).
Ultra-low energy house[edit | edit source]
A ultra-low energy house is a house built using low energy methods, and allows a very low and very efficient use of energy. Several types of ultra-low energy houses exist. A energy-neutral or energy-positive house is even more energy efficient, the latter even producing more energy than it consumes.
Common techniques include insulation, thermal mass and passive solar heating and cooling. Examples of these are trombe walls and other technologies as skylights. Earth sheltering and windbreaks can also reduce the absolute amount of heat needed by a building, while rounded, aerodynamic buildings also lose less heat.
Systems[edit | edit source]
In most aspects, autonomous houses/neighborhoods tend to implement use reduction. This as it is a cost-effective approach (they limit the needed investments on the equipment).
Water supply[edit | edit source]
Although covering some 70% of the Earth's surface, most water is saline. Freshwater is available in almost all populated areas of the earth, although it may be expensive and the supply may not always be sustainable.
There are many methods of collecting water. The most common methods are the use of a well or the use of rainwater harvesters. When filtered, it becomes potable water which can be drunk.
Sources where water may be obtained include:
- Ground sources such as groundwater, hyporheic zones and aquifers.
- Precipitation which includes rain, hail, snow, fog, etc (see rainwater harvesting) Even humid air can be used as a source for water, see Fof nets and Atmospheric water generator (the latter extracts moisture from dry desert air and filters it to pure water).
- Surface water such as rivers, streams, glaciers
- Biological sources such as plants (See Gathering water from plants) and animals (urine)
- The sea through desalination
- Water supply network
In addition, greywater (water from washing machines, sinks, showers and baths) may be reused in landscape irrigation and toilets as a method of water conservation.
Sewage/excreta disposal[edit | edit source]
Some of the oldest pre-system sewage types are pit toilets, latrines, and outhouses. These are still used in many developing countries but do not allow composting, incineration or any other method of destroying pathogens. As such, there is a serious risk of microbial and viral contamination and thus can cause the operator of becoming ill.
The standard system used today is a flush toilet with drain leach field and a septic tank. They however require huge amounts of water (although some tweaks can reduce water use for these, see flush toilet) to operate and can be -relatively- complicated. Incinerator systems are also quite practical. The ashes are biologically safe, and take up less than 1/10 the volume of the original waste.
The approaches above however treat human excrement as a waste rather than a resource. Composted human excrement can be used to provide (or return, ie if the garden is used to grow food) nutrients to a garden. Recycling human excrement requires minimal life-style changes. In this context, Composting toilets are a better choice as they allow reuse of the human excrement, in a safe manner. They also reduce water use by half, and eliminate the difficulty and expense of septic tanks.
Food production[edit | edit source]
Food production has often been included in historic autonomous projects to provide security. Skilled, intensive gardening can support an adult from as little as 100 square meters of land per person, possibly requiring the use of organic farming and aeroponics. Some proven intensive, low-effort food-production systems include urban gardening (indoors and outdoors). Indoor cultivation may be set up using hydroponics, while outdoor cultivation may be done using permaculture, forest gardening, no-till farming, and do nothing farming.
Greenhouses are also sometimes included (see Earthship Biotecture). Sometimes they are also outfitted with irrigation systems or heat sink-systems which can respectively irrigate the plants or help to store energy from the sun and redistribute it at night (when the greenhouses starts to cool down).
Electricity[edit | edit source]
Besides energy conservation, we also need to generate power, preferably in a way that it can be sustained infinitely. This means the energy source must preferably be renewable, and must not harm the environment or the people working under it. The most commonly used renewable sources of energy are: biomass, waterW, geothermalW, windW, and solarW.
Solar power harnesses the energy of the sun to make electricity. Two typical methods for converting solar energy into electricity are photo-voltaic cellsW that are organized into panels and concentrated solar power, which uses mirrors to concentrate sunlight to either heat a fluid that runs an electrical generatorW via a steam turbineW or heat engine, or to simply cast onto photo-voltaic cells.
The energy created by photo-voltaic cells (which are preferably placed on the roof) is a direct current and has to be converted to alternating current before it can be used in a household. Solar tile roofs have the potential to be more cost-effective than retrofitted solar power, because buildings need roofs anyway. A downside however is that they can not rack the sun during the day, and are hard to access in case they need repairs/cleaning. Modern solar cells last about 40 years, which makes them a reasonable investment in some areas. Solar cells have only small life-style impacts: The cells must be cleaned a few times per year.
Direct current can be either stored in batteries for later use, or we can use an AC/DC inverter for immediate use. To get the best out of a solar panel, the angle of incidenceW of the sun should be between 20-50 degrees. Solar power via photo-voltaic cells are usually the most expensive method to harnessing renewable energy, but is falling in price as technology advances and public interest increases. It has the advantages of being portable, easy to use on an individual basis, readily available for government grants and incentives, and being flexible in regards to location (though it is most efficient when used in hot, arid areas since they tend to be the most sunny).For those that are lucky, affordable rental schemes may be found.Concentrated solar power plants are typically used on more of a community scale rather than an individual household scale, because of the amount of energy they are able to harness but can be done on an individual scale with a parabolic reflectorW.
A number of areas that lack sun have wind. In these cases, wind turbines may be a solution. Wind power is harnessed through turbines, set on tall towers (typically 20' or 6m with 10' or 3m diameter blades for an individual household's needs) that power a generator that creates electricity.They typically require an average of wind speed of 9 mi/hr (14 km/hr) to be worth their investment (as prescribed by the US Department of Energy), and are capable of paying for themselves within their lifetimes. Wind turbines in urban areas usually need to be mounted at least 30' (10m) in the air in order to receive enough wind and to be void of nearby obstructions (such as neighboring buildings). Mounting a wind turbine may also require permission from authorities. Wind turbines have been criticized for the noise they produce, their appearance, and the argument that they can affect the migratory patterns of birds (their blades obstruct passage in the sky). Wind turbines are much more feasible for those living in rural areasand are one of the most cost-effective forms of renewable energy per kilowatt, approaching the cost of fossil fuels, and have quick paybacks.For those that have a body of water flowing at an adequate speed (or falling from an adequate height) on their property, hydroelectricity may be an option. On a large scale, hydroelectricity, in the form of dams, has adverse environmental and social impacts. When on a small scale, however, in the form of single turbines, hydroelectricity is very sustainable. Single water turbines or even a group of single turbines are not environmentally or socially disruptive. On an individual household basis, single turbines are the probably the only economically feasible route (but can have high paybacks and is one of the most efficient methods of renewable energy production). It is more common for an eco-village to use this method rather than a singular household.Geothermal energy production involves harnessing the hot water or steam below the earth's surface, in reservoirs, to produce energy. Because the hot water or steam that is used is reinjected back into the reservoir, this source is considered sustainable. However, those that plan on getting their electricity from this source should be aware that there is controversy over the lifespan of each geothermal reservoir as some believe that their lifespans are naturally limited (they cool down over time, making geothermal energy production there eventually impossible). This method is often large scale as the system required to harness geothermal energy can be complex and requires deep drilling equipment. There do exist small individual scale geothermal operations, however, which harness reservoirs very close to the Earth's surface, avoiding the need for extensive drilling and sometimes even taking advantage of lakes or ponds where there is already a depression. In this case, the heat is captured and sent to a geothermal heat pumpW system located inside the shelter or facility that needs it (oftentimes, this heat is used directly to warm a greenhouse during the colder months).Although geothermal energy is available everywhere on Earth, practicality and cost-effectiveness varies, directly related to the depth required to reach reservoirs. Places such as the Philippines, Hawaii, Alaska, Iceland, California, and Nevada have geothermal reservoirs closer to the Earth's surface, making its production cost-effective.Biomass power is created when any biological matter (e.g. bagasseW, biogas, manure, stoverW, straw, used vegetable oil, wood) is burned as fuel. As with the case of using green materials in a household, it is best to use as much locally available material as possible so as to reduce the carbon footprint created by transportation. Although burning biomass for fuel releases carbon dioxideW, sulfur compounds, and nitrogen compounds into the atmosphere, a major concern in a sustainable lifestyle, the amount that is released is sustainable (it will not contribute to a rise in carbon dioxide levels in the atmosphere). This is because the biological matter that is being burned releases the same amount of carbon dioxide that it consumed during its lifetime.However, burning biodiesel and bioethanol (see biofuel) when created from virgin material, is increasingly controversial and may or may not be considered sustainable because it inadvertently increases global poverty, the clearing of more land for new agriculture fields (the source of the biofuel is also the same source of food), and may use unsustainable growing methods (such as the use of environmentally harmful pesticides and fertilizers).Digestion of organic material to produce methane is becoming an increasingly popular method of biomass energy production. Materials such as waste sludge can be digested to release methane gas that can then be burnt to produce electricity. Methane gas is also a natural by-product of landfills, full of decomposing waste, and can be harnessed here to produce electricity as well. The advantage in burning methane gas is that is prevents the methane from being released into the atmosphere, exacerbating the greenhouse effect. Although this method of biomass energy production is typically large scale (done in landfills), it can be done on a smaller individual or community scale as well.During times of low demand, excess power can be stored in eletrochemical batteries for future use. However, batteries need to be replaced every few years. Microbial fuel cells allow the generation of electricity from biomass. Unlike direct incineration of biomass however, the method using a microbial fuel cell is completely emissionless. The plant can be chopped and converted as a whole, or it can be left alive so that waste saps from the plant can be converted by bacteria.
In addition, recent advances in passively stable magnetic bearings may someday permit inexpensive storage of power in a flywheel in a vacuum, and some other types of fuel cells may also be useful for storing power. Other possible options are Earth batteries.
In many areas, battery expenses can be eliminated by attaching the building to the electric power grid and operating the power system with net metering. Utility permission is required, but such cooperative generation is legally mandated in some areas (for example, California).
A (semi-)grid-based building is less autonomous, but more economical and sustainable with fewer lifestyle sacrifices. In rural areas the grid's cost and impacts can be reduced by using single wire earth return systems (for example, the MALT-system).
In areas that lack access to the grid, battery size can be reduced by including a generator to recharge the batteries during extended fogs or other low-power conditions. Auxiliary generators are usually run on biofuel or petrofuel. An hour of charging usually provides a day of operation. Modern residential chargers permit the user to set the charging times, so the generator is quiet at night. Some generators automatically test themselves once per week.
Heating and cooling[edit | edit source]
Heating[edit | edit source]
Passive solar heating can heat most buildings in even the coldest climates. In colder climates, extra construction costs can be as little as 15% more than new, conventional buildings. In warm climates, those having less than two weeks of frosty nights per year, there is no cost impact.
Electric heaters and electric stoves may provide pollution-free heat (depending on the power source), but use large amounts of electricity. If enough electricity is provided by solar panels, wind turbines, or other means, then electric heaters and stoves become a practical autonomous design.
Radiator reflectors can be made and placed behind your radiators and the walls. They can be made DIY from sticking aluminium kitchen foil unto pieces of cardboard. The reflectors improve the efficiency of your radiators greatly as they avoid that any heat generated goes into the walls. Perhaps surprisingly, heat that goes into the inner or outer brick walls of your house is lost and does not contribute to heating the house (unlike e.g. with glass bottle walls, which do radiate this heat back).
An increasing number of commercial buildings use a combined cycle with cogeneration to provide heating, often water heating, from the output of a natural gas reciprocating engine, gas turbine or stirling electric generator.
The domestic water can be heated using either the same heating system (e.g. gas or firewood can also be used to heat the domestic water, by using a heat exchanger). In addition, solar water heating can be incorporated (often as a additional technology).
Solar thermal energy is harnessed by collecting direct heat from the sun. One of the most common ways that this method is used by households is through solar water heatingW. In a broad perspective, these systems involve well insulated tanks for storage and collectors, are either passive or active systems (active systems have pumps that continuously circulate water through the collectors and storage tank) and, in active systems, involve either directly heating the water that will be used or heating a non-freezing heat-transfer fluid that then heats the water that will be used. Passive systems are cheaper than active systems since they do not require a pumping system (instead, they take advantage of the natural movement of hot water rising above cold water to cycle the water being used through the collector and storage tank).
Other methods of harnessing solar power are solar space heatingW (for heating internal building spaces).
Some authorities advocate that bottled gas or natural gas be replaced by biogas. However, this is usually impractical unless live-stock are on-site. The wastes of a single family are usually insufficient to produce enough methane for anything more than small amounts of cooking.
Cooling[edit | edit source]
Windows can be shaded in summer. Eaves can be overhung to provide the necessary shade. These also shade the walls of the house, reducing cooling costs.
Another trick is to cool the building's thermal mass at night, and then cool the building from the thermal mass during the day. It helps to be able to route cold air from a sky-facing radiator (perhaps an air heating solar collector with an alternate
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- Gipe, ibid.
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