Linear Fresnel Solar Concentrator - Revision history

Rasmus: fixed several typos

2016-03-01T21:01:08Z

fixed several typos

Andrea: /* Further steps */

2015-02-17T00:18:12Z

Further steps

← Older revision		Revision as of 00:18, 17 February 2015
Line 126:		Line 126:

	* [http://en.wikipedia.org/wiki/Concentrating_Linear_Fresnel_Reflector Wikipedia: Concentrating Linear Fresnel Reflector]		* [http://en.wikipedia.org/wiki/Concentrating_Linear_Fresnel_Reflector Wikipedia: Concentrating Linear Fresnel Reflector]

			=OSE Technical Requirements=
			as Open Source Ecologie team is moving forward developping the linear fresnel reflector is developing and request for your participation the complete set of technical requirements. the current work in progress is located [http://wiki.osefrance.org/doku.php?id=wiki:technical_requirements_english here]
			and [[http://opensourceecology.org/wiki/Solar_Concentrator/Research_Development here]]

Conor at 00:04, 16 February 2011

2011-02-16T00:04:01Z

← Older revision		Revision as of 00:04, 16 February 2011
Line 1:		Line 1:
			{{Category=Solar Turbine}}
	The solar concentrator arrangement proposed for the factor e farm [[solar turbine]] implementation is of the linear fresnel type. Linear, as it's focus is a line as opposed to a point, and fresenl as it is made of many small reflectors as opposed to a monolithic parabolic trough.		The solar concentrator arrangement proposed for the factor e farm [[solar turbine]] implementation is of the linear fresnel type. Linear, as it's focus is a line as opposed to a point, and fresenl as it is made of many small reflectors as opposed to a monolithic parabolic trough.

Line 125:		Line 126:

	* [http://en.wikipedia.org/wiki/Concentrating_Linear_Fresnel_Reflector Wikipedia: Concentrating Linear Fresnel Reflector]		* [http://en.wikipedia.org/wiki/Concentrating_Linear_Fresnel_Reflector Wikipedia: Concentrating Linear Fresnel Reflector]

	~~[[Category:Solar_Turbine]][[Category:Energy]][[Category:Solar Power]]~~

Rasmus at 02:55, 18 January 2011

2011-01-18T02:55:29Z

← Older revision		Revision as of 02:55, 18 January 2011
Line 126:		Line 126:
	* [http://en.wikipedia.org/wiki/Concentrating_Linear_Fresnel_Reflector Wikipedia: Concentrating Linear Fresnel Reflector]		* [http://en.wikipedia.org/wiki/Concentrating_Linear_Fresnel_Reflector Wikipedia: Concentrating Linear Fresnel Reflector]

	[[Category:Solar_Turbine]]		[[Category:Solar_Turbine]][[Category:Energy]][[Category:Solar Power]]

DavidCary: wall vs field of slats

2010-04-16T21:34:32Z

wall vs field of slats

← Older revision		Revision as of 21:34, 16 April 2010
Line 1:		Line 1:
	The solar concentrator arrangement proposed for the factor e farm implementation is of the linear fresnel type. Linear, as it's focus is a line as opposed to a point, and fresenl as it is made of many small reflectors as opposed to a monolithic parabolic trough.		The solar concentrator arrangement proposed for the factor e farm [[solar turbine]] implementation is of the linear fresnel type. Linear, as it's focus is a line as opposed to a point, and fresenl as it is made of many small reflectors as opposed to a monolithic parabolic trough.

	This is a discussion of the theory of linear fresnel solar ~~concnetrators~~, and a justification of the design decisions siezed upon by the factor e farm team.		This is a discussion of the theory of linear fresnel solar concentrators, and a justification of the design decisions siezed upon by the factor e farm team.


Line 52:		Line 52:

	Given this information, the factor e farm team has selected an east-west orientation.		Given this information, the factor e farm team has selected an east-west orientation.

			== wall vs field of slats ==

			With many slats and a single absorber, the question comes up:
			* put the absorber high in the air, and put a field of slats near the ground to the south (and possibly also to the north), or
			* use the slats to cover a south-facing wall, like the slats of a window blind, and put the absorber to the south (possibly on the ground, or possibly high in the air -- but not so high it shadows the slats in the winter).

			Mounting slats to a wall significantly reduces the cost of making the array hail-resistant or hail-proof.
			Mounting slats to a wall results in needing to clean the slats less often, because any given piece of dirt is more likely to fall off a near-vertical slat than a near-horizontal slat.
			Mounting slats to a south-facing wall seems like it would collect more sunlight in the winter.

			Mounting the slats near ground level puts the moving parts where they are easier to access and repair.
			Mounting the slats near ground level requires less structure cost per slat (if you ignore the cost of hail-proofing).
			Mounting the slats near ground level works fine even near the equator.

			For now we choose to put the absorber high in the air, and the slats near the ground, because that is a proven system.

	== Reflector Design ==		== Reflector Design ==
Line 107:		Line 123:

	and on from there...		and on from there...

			* [http://en.wikipedia.org/wiki/Concentrating_Linear_Fresnel_Reflector Wikipedia: Concentrating Linear Fresnel Reflector]

	[[Category:Solar_Turbine]]		[[Category:Solar_Turbine]]

WikiSysop: /* Further steps */

2009-01-31T02:32:53Z

Further steps

← Older revision		Revision as of 02:32, 31 January 2009
Line 107:		Line 107:

	and on from there...		and on from there...

			[[Category:Solar_Turbine]]

Offonoffoffonoff at 23:02, 22 August 2008

2008-08-22T23:02:29Z

← Older revision		Revision as of 23:02, 22 August 2008
Line 90:		Line 90:

	The conclusion of this report is that the Factor E farm linear fresenl collector should have an East-West axis and use 1/8th inch untempered glass mirrors. Mirrors closer to the absorber (<~14 ft) should be flat, whilst mirrors more distant should be curved so as to focus perfectly at ~11am half way between the equinox and the solstice. If at the time the mirrors are focused it happens to not be near that date, its alright because seasonal drift of the focus is minimal (1.8%).		The conclusion of this report is that the Factor E farm linear fresenl collector should have an East-West axis and use 1/8th inch untempered glass mirrors. Mirrors closer to the absorber (<~14 ft) should be flat, whilst mirrors more distant should be curved so as to focus perfectly at ~11am half way between the equinox and the solstice. If at the time the mirrors are focused it happens to not be near that date, its alright because seasonal drift of the focus is minimal (1.8%).

			== Further steps ==

			The use of a secondary reflector of the compound parabolic type would be highly beneficial, and inquiries should be made into its possible manufacture or purchase.

			Estimations of available insolation should be made for several specific days throughout the year, and for noon time throughout the seasons.

			Absorber height decided upon, which will be based upon available construction methods.

			A site chosen and roughly surveyed. (general strike and dip of the working surface)

			Details of the mirror row's positions should be sketched, with proper spacing for minimal shading in the winter with reasonably efficent land use for summer radiation considered.

			Expected system performance estimated.


			and on from there...

Offonoffoffonoff: /* the limits of concentration */

2008-08-22T22:53:10Z

the limits of concentration

← Older revision		Revision as of 22:53, 22 August 2008
Line 76:		Line 76:
	As light travels down different angles parallel to the axis of the concentrator, it travels different distances before reaching the absorber. Thus, if the array is in perfect focus at one angle, at another angle it will be out of focus. The percentage out of focus is inversely proportional to the amount of concentration possible. At twice the focal distance (%100 out of focus), the image is the same size as the width of the reflector. At 1.5 the focal length (%50), the image will be half the width of the reflector.		As light travels down different angles parallel to the axis of the concentrator, it travels different distances before reaching the absorber. Thus, if the array is in perfect focus at one angle, at another angle it will be out of focus. The percentage out of focus is inversely proportional to the amount of concentration possible. At twice the focal distance (%100 out of focus), the image is the same size as the width of the reflector. At 1.5 the focal length (%50), the image will be half the width of the reflector.

	In an east-west axis system, the sun moves from 45 degrees at 9 am to 0 at noon to 45 again at 3 pm. If this system were perfectly in focus at noon, the extra path length of Square root of two (~1.4) in the morning and evening would correspond to %40 out of focus or 2.5 times concentration. The best achievable theoretical fix would be to have the system focused perfectly at 22.5 degrees, so that the absorber is too close at noon and too far at 3pm, but neither as badly as if the system were in focus at noon. This corresponds to a maximum concentration of 3.27 (change in path length is 1/cos45 - 1/cos22.5 = 1.41 - 1.08 = .33 -> % out of focus of .33/1.08= %30.5). since the sine changes quickly around 45 degrees, ~~grester~~ ratios could be obtained by sacrificing efficiency at the extremes.		In an east-west axis system, the sun moves from 45 degrees at 9 am to 0 at noon to 45 again at 3 pm. If this system were perfectly in focus at noon, the extra path length of Square root of two (~1.4) in the morning and evening would correspond to %40 out of focus or 2.5 times concentration. The best achievable theoretical fix would be to have the system focused perfectly at 22.5 degrees, so that the absorber is too close at noon and too far at 3pm, but neither as badly as if the system were in focus at noon. This corresponds to a maximum concentration of 3.27 (change in path length is 1/cos45 - 1/cos22.5 = 1.41 - 1.08 = .33 -> % out of focus of .33/1.08= %30.5). since the sine changes quickly around 45 degrees, greater ratios could be obtained by sacrificing efficiency at the extremes.

	'''Perpendicular axis abberations'''		A north south axis orientation will experience this distortion less severely due to the fact that the seasonal angular deviation of the sun is much less than its daily variation.

			'''Perpendicular-axis abberations'''

			There are (at least) two parabolas passing through a given point that will focus perfectly at one point. (illustration soon). The first is a parabola has its axis parallel to the sun's rays with the absorber at its focus. The second is one with its axis at the half angle between the absorber and sun, with a focal length such that the absrober lays on the focal plane of the parabola (a plane perpendicular to the parabola's axis and passing through the focus. The image created by a parabolic reflector is undistorted on this plane). This second parabola will be useful in analyzing this type of distortion (and is also easier to implement)

			As the sun moves and the mirror moves to track it, the focal plane of our perfect reflector rotates around the reflector's pivot. thus, the absorber, once in the focal plane is there no longer. (illustration soon). The ideal focal length of our mirror would then be Cos(theta) of its previous value to maintain focus on the absorber. Because this effect depends upon the half angle, it is much less noticeable than the parallel axis phenomena. The maximum deviation in an east-west axis system is very small (1-Cos(11 degrees)=.018 or 1.8%), thus this effect is negligible in our system. It is more sever in the north-south system (1-cos(22.5) = 7.6%), but still hardly noticeable.


			== Recomendations ==

			The conclusion of this report is that the Factor E farm linear fresenl collector should have an East-West axis and use 1/8th inch untempered glass mirrors. Mirrors closer to the absorber (<~14 ft) should be flat, whilst mirrors more distant should be curved so as to focus perfectly at ~11am half way between the equinox and the solstice. If at the time the mirrors are focused it happens to not be near that date, its alright because seasonal drift of the focus is minimal (1.8%).

Offonoffoffonoff: /* Implementation dependant losses and issues */

2008-08-22T22:29:58Z

Implementation dependant losses and issues

← Older revision		Revision as of 22:29, 22 August 2008
Line 45:		Line 45:
	Also, the reflectors move between plus and minus 22.5 degrees of tilt from 9am till 3pm. Thus there will be a maximum half angle loss of cosine 22.5 and a total daily loss of the integral of cos (1/2 theta) from theta =-22.3 to 22.5		Also, the reflectors move between plus and minus 22.5 degrees of tilt from 9am till 3pm. Thus there will be a maximum half angle loss of cosine 22.5 and a total daily loss of the integral of cos (1/2 theta) from theta =-22.3 to 22.5

	The East-West orientation offers possibly the most complex tracking. The angle of the mirrors is determined by the vector towards the sun projected onto the vertical axis running north-south. During the winter, the mirrors tilt down towards the south, coming up till noon and decreasing again. The severity of this angular adjustment decreases from winter solstice till equinox, when no angular adjustment is needed (the plane of the sun's motion is co-incident with the plane of the parabolic trough), and reverses direction during the summer, as the sun rises slightly north and comes slightly south by noon. This tracking will likely need to be accomplished by sensors rather than formulas.		The '''East-West orientation''' offers possibly the most complex tracking. The angle of the mirrors is determined by the vector towards the sun projected onto the vertical axis running north-south. During the winter, the mirrors tilt down towards the south, coming up till noon and decreasing again. The severity of this angular adjustment decreases from winter solstice till equinox, when no angular adjustment is needed (the plane of the sun's motion is co-incident with the plane of the parabolic trough), and reverses direction during the summer, as the sun rises slightly north and comes slightly south by noon. This tracking will likely need to be accomplished by sensors rather than formulas.

	End losses in the east west orientation are maximum in the morning and evening, with almost none at noon. But as the sun is not inclined to the axis of the trough more than 45 degrees during the time of useable insolation, these losses are never as severe as winter end losses in the north south arrangement (where the noon sun is lower than 30 degrees, and the pre and post noon sun even lower. Thus, this arrangement will perform most satifactorily of the three in a flat on the ground implementation.		End losses in the east west orientation are maximum in the morning and evening, with almost none at noon. But as the sun is not inclined to the axis of the trough more than 45 degrees during the time of useable insolation, these losses are never as severe as winter end losses in the north south arrangement (where the noon sun is lower than 30 degrees, and the pre and post noon sun even lower. Thus, this arrangement will perform most satifactorily of the three in a flat on the ground implementation.
Line 52:		Line 52:

	Given this information, the factor e farm team has selected an east-west orientation.		Given this information, the factor e farm team has selected an east-west orientation.


	== Reflector Design ==		== Reflector Design ==

Offonoffoffonoff at 22:29, 22 August 2008

2008-08-22T22:29:17Z

@@ Line 10: / Line 10: @@
 ) total insolation
 ) air mass losses
 ) declination losses
@@ Line 17: / Line 19: @@
 == Implementation dependant losses and issues ==
 There a three common orientations:
 ) polar
 ) North-South axis
 ) East-West axis
-The Polar orientation focuses on a line parallel to the pole of the earths rotation, that is, inclined and running north-south.  Tracking here is the simplest, as the mirrors need only rotate at half the angular speed of the earths rotation.  However, due to the need to incline the absorber and reflectors, this orientation requires more structural considerations (and expenditures) than a flat (of the ground) approach.  Thus, the Factor E farm team has decided against this.
+Each of these three possible orientations has associated tracking issues and also efficency losses specific to that orientation (end losses and half angle losses).
-The North-South orientation is similar to the polar orientation, but may be flat on the ground.  Tracking may be as simple as in polar or it may have hidden complications (We don't know).  Due to the latitude of the Factor E farm, the end losses associated with the shallowness of the suns angle parallel to the axis of the collector would be severe in winter if this orientation were laid flat on the ground.  Since we do not wish to tilt the array towards the south for construction cost reasons (same as polar), and wish to collect energy during the winter, The factor E Farm team has shied away from this orientation as well.
+'''Perpendicular axis abberations'''