Editing Solar thermal collector (section)

====Bowl collectors====
A ''solar bowl'' is a type of solar thermal collector that operates similarly to a [[#Parabolic dish|parabolic dish]], but instead of using a tracking parabolic mirror with a fixed receiver, it has a fixed spherical mirror with a tracking receiver. This reduces efficiency but makes it cheaper to build and operate. Designers call it a ''fixed mirror distributed focus solar power system''. The main reason for its development was to eliminate the cost of moving a large mirror to track the sun as with parabolic dish systems.<ref name="solarbowl">{{cite book |url=https://books.google.com/books?id=giwEAAAAMBAJ&q=crosbyton%20solar%20bowl&pg=PA199 |title=Duel for the Sun |last=Calhoun |first=Fryor |series=[[Texas Monthly]] |date=November 1983 }}</ref>

A fixed parabolic mirror creates a variously shaped image of the sun as it moves across the sky. Only when the mirror is pointed directly at the sun does the light focus on one point. That is why parabolic dish systems track the sun. A fixed [[Curved mirror|spherical mirror]] focuses the light in the same place independent of the sun's position. The light, however, is not directed to one point but is distributed on a line from the surface of the mirror to one half radius (along a line that runs through the sphere center and the sun).{{citation needed|date=January 2021}}

[[File:Sphericalmirrorimage.jpg|thumb|Typical energy density along the 1/2 radius length focal line of a spherical reflector]]

As the sun moves across the sky, the aperture of any fixed collector changes. This causes changes in the amount of captured sunlight, producing what is called the ''sinus effect'' of power output. Proponents of the solar bowl design claim the reduction in overall power output compared with tracking parabolic mirrors is offset by lower system costs.<ref name="solarbowl" />

The sunlight concentrated at the focal line of a spherical reflector is collected using a tracking receiver. This receiver is pivoted around the focal line and is usually counterbalanced. The receiver may consist of pipes carrying fluid for thermal transfer or [[Solar cell|photovoltaic cells]] for direct conversion of light to electricity.

The solar bowl design resulted from a project of the Electrical Engineering Department of the Texas Technical University, headed by Edwin O'Hair, to develop a 5 MWe power plant. A solar bowl was built for the town of [[Crosbyton, Texas]] as a pilot facility.<ref name="solarbowl" /> The bowl had a diameter of {{convert|65|ft|m|abbr=on}}, tilted at a 15° angle to optimize the cost/yield relation (33° would have maximized yield). The rim of the hemisphere was "trimmed" to 60°, creating a maximum aperture of {{convert|3318|sqft|m2}}. This pilot bowl produced electricity at a rate of 10&nbsp;kW peak.{{Citation needed|date=August 2011}}

A {{convert|15|m|adj=on}} diameter Auroville solar bowl was developed from an earlier test of a {{convert|3.5|m|adj=on}} bowl in 1979–1982 by the [[Tata Energy Research Institute]]. That test showed the use of the solar bowl in the production of steam for cooking. The full-scale project to build a solar bowl and kitchen ran from 1996 and was fully operational by 2001.{{Citation needed|date=August 2011}}

In locations with average available solar energy, flat plate collectors are sized approximately 1.2 to 2.4 square decimeter per liter of one day's hot water use.