Editing Autonomous building (section)

===Electricity===
[[File:Green Building by Terry Farrel and Partners 394640345.jpg|thumb|right|Wind turbine on the roof in [[Manchester]], UK]]
[[Image:Solar panels on house roof.jpg|thumb|right|A PV-solar system]]
{{Further|Zero emissions|Zero-energy building}}
Since electricity is an expensive utility, the first step towards autonomy is to design a house and lifestyle to reduce demand. [[LED light]]s, laptop computers and gas-powered refrigerators save electricity, although gas-powered refrigerators are not very efficient.<ref>Sunfrost rates {{convert|15|cuft|L|abbr=on}}. refrigerators at [http://www.sunfrost.com/extreme_efficiency.html 0.27 kWh/day] (2007-12-27), while Dometic brand (formerly Servel brand) gas refrigerators cool only {{convert|8|cuft}} for [http://www.sunfrost.com/extreme_efficiency.html 325 W continuous] (i.e. 7.8 kWh/day) ALternatively, they use about {{convert|8|USgal}} of LP gas per month, which in most places is more expensive than the equivalent electricity.(2007-12-27)</ref> There are also superefficient electric refrigerators, such as those produced by the Sun Frost company, some of which use only about half as much electricity as a mass-market [[energy star]]-rated refrigerator.

Using a solar roof, [[solar cell]]s can provide electric power. Solar roofs can be more cost-effective than retrofitted solar power, because buildings need roofs anyway. Modern solar cells last about 40 years, which makes them a reasonable investment in some areas. At a sufficient angle, solar cells are cleaned by run-off rain water and therefore have almost no life-style impact.

Many areas have long winter nights or dark cloudy days. In these climates, a solar installation might not pay for itself or large battery storage systems are necessary to achieve electric self-sufficiency.<ref>{{Cite journal|last1=Ramirez Camargo|first1=Luis|last2=Nitsch|first2=Felix|last3=Gruber|first3=Katharina|last4=Dorner|first4=Wolfgang|date=2018-10-15|title=Electricity self-sufficiency of single-family houses in Germany and the Czech Republic|journal=Applied Energy|language=en|volume=228|pages=902–915|doi=10.1016/j.apenergy.2018.06.118|issn=0306-2619|doi-access=free|bibcode=2018ApEn..228..902R }}</ref> In stormy or windy climates, [[wind turbine]]s can replace or significantly supplement solar power.<ref>{{Cite journal|last1=Ramirez Camargo|first1=Luis|last2=Nitsch|first2=Felix|last3=Gruber|first3=Katharina|last4=Valdes|first4=Javier|last5=Wuth|first5=Jane|last6=Dorner|first6=Wolfgang|date=January 2019|title=Potential Analysis of Hybrid Renewable Energy Systems for Self-Sufficient Residential Use in Germany and the Czech Republic|journal=Energies|language=en|volume=12|issue=21|pages=4185|doi=10.3390/en12214185|doi-access=free}}</ref> The average autonomous house needs only one [[small wind turbine]], 5 metres or less in diameter. On a 30-metre (100-foot) tower, this turbine can provide enough power to supplement solar power on cloudy days. Commercially available wind turbines use sealed, one-moving-part AC generators and passive, self-feathering blades for years of operation without service.

The main advantage of [[wind power]] is that larger wind turbines have a lower per-watt cost than solar cells, provided there is wind. Turbine location is critical: just as some locations lack sun for solar cells, many areas lack enough wind to make a turbine pay for itself. In the [[Great Plains]] of the United States, a 10-metre (33-foot) turbine can supply enough energy to heat and cool a well-built all-electric house. Economic use in other areas requires research, and possibly a site survey.<ref name="Gipe">Paul Gipe, "Wind Power for Home and Business"</ref>

Some sites have access to a stream with a change in elevation. These sites can use [[Micro hydro|small hydropower systems]] to generate electricity. If the difference in elevation is above 30 metres (100 feet), and the stream runs in all seasons, this can provide continuous power with a small, inexpensive installation. Lower changes of elevation require larger installations or dams, and can be less efficient. Clogging at the turbine intake can be a practical problem. The usual solution is a small pool and waterfall (a penstock) to carry away floating debris. Another solution is to utilize a turbine that resists debris, such as a [[Gorlov helical turbine]] or [[Ossberger turbine]].

During times of low demand, excess power can be stored in batteries for future use. However, batteries need to be replaced every few years. In many areas, battery expenses can be eliminated by attaching the building to the [[distributed generation|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).<ref name="Gipe"/>

A 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 (electricity system)|MALT]]-system).

In areas that lack access to the grid, battery size can be reduced with a generator to recharge the batteries during energy droughts such as extended fogs. Auxiliary generators are usually run from [[propane]], [[natural gas]], or sometimes [[Diesel fuel|diesel]]. 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.<ref>[http://www.eaton.com Eaton power]; see the specifications and manuals. Referenced 2007-12-27</ref><ref>[http://www.KohlerSmartPower.com Kohler Generators]; see the specifications and manuals. Referenced 2007-12-27</ref>

Recent advances in [[magnetic levitation|passively stable magnetic bearings]] may someday permit inexpensive storage of power in a [[flywheel]] in a vacuum. Research groups like Canada's [[Ballard Power Systems]] are also working to develop a "[[regenerative fuel cell]]", a device that can generate hydrogen and oxygen when power is available, and combine these efficiently when power is needed.

[[Earth battery|Earth batteries]] tap electric currents in the earth called [[telluric current]]. They can be installed anywhere in the ground. They provide only low voltages and current. They were used to power [[Telegraphy|telegraphs]] in the 19th century. As appliance efficiencies increase, they may become practical.

[[Microbial fuel cell]]s and [[thermoelectric generator]]s<ref>{{cite web|title=Biolite Portable Stoves|url=https://www.bioliteenergy.com/collections/stoves|website=bioliteenergy.com|publisher=Biolite|access-date=12 May 2018}}</ref><ref>{{cite web|title=Firebee:Charge your USB Device!|url=http://firebeecharger.com/|website=firebeecharger.com|publisher=Firebee|access-date=12 May 2018}}</ref> allow electricity to be generated from biomass. The plant can be dried, chopped and converted or burned as a whole, or it can be left alive so that waste saps from the plant can be converted by bacteria.