Thermal collector could be used ultimately to power steamplant to produce electricity. Collector would consist of two major subsystems: (1) series of segmented tracking mirrors with two axes of rotation and (2) absorber mounted on centrally located tower

Brantley, L. W., Jr.

English

NASA Technical Reports Server

fune 1975	 B75-10098 
NASA TECH BRIEF 
Marshall Space Flight Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Large-Scale Solar Thermal Collector Concepts 
Marshall Space Flight Center has conducted a 
study to. define quantitatively a large-scale solar 
thermal collector that could be used ultimately to 
power a steamplant to produce electricity. The 
collector would consist of two major subsystems: (1) a 
series of segmented tracking mirrors with two axes of 
rotation and (2) an absorber mounted on a centrally 
located tower. A collector for an installation 
producing 100 kW of electricity (running continu-
ously) was studied first, and the technique was then 
extended to the design of a system to produce 
100 MW of electricity throughout a 12-hour day. 
Several computer programs were written to aid in 
calculating the optimal mirror size, type, geometry, 
and placement. Other programs were used to 
determine the resulting performance of the system. 
The mirror configuration found to be best was a field 
of flat-plate reflectors oriented so that the reflected 
rays arrive at a single point, where the absorber is 
From Absorber
Inlet (Day) 
2500 psia 
10000
 F
placed. This configuration is frequently referred to as 
an approximated paraboloid. Each mirror can be 
rotated about two axes to follow the position of the 
Sun. 
The absorber studied consisted of a low-
temperature preheater section and a high-
temperature section. Incoming radiation is directed to 
the preheater where it is reflected along a light pipe 
with walls having low solar-spectrum absorbance and 
high infrared absorbance. The light is then reflected 
to the high-temperature section which has high 
solar-spectrum absorbance and low infrared emission. 
The absorber working fluid first passes through the 
preheating section and then circulates through the 
high-temperature section. 
The calculated absorber efficiency was 90 percent, 
but 80 percent was used in the study to allow for 
possible losses in heat tratjsfer. If water is used as the 
fluid, about 50 percent of the energy is used to heat it, 
Regulating
To Turbine 
— Outlet (Night)
1900 psia 
9500 F 
Liquid Level Inert 
Solidified	 Gas 
Level i
Metal-Filled 
Steel Bail
eo%z 'J()UJ 
40% Al Q.,dli 95? F
Zn 70% 	
SW  
OoJ 
%Zn
 g
85?F 
10% Al
	 I 75? F 
99PF 
95%p5
65?F 
? 0)4
Volume of Spheres-
300 ft3 
OW F 
Insulated Piston 
	Volume of Water- 
Water  _0 I'	 1	 365 ft' 
To Absorber Feed Pump
	 ,.,...._- From Conversion System Feed Pump 
Energy Storage System
(continued overleaf) 
This document was prepared under the sponsorship of the National
	
Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19750000098 2020-03-19T20:06:52+00:00Z
25 percent to boil it, and 25 percent to superheat it to different-melting-point metal mixtures. It is finally 
1,000° F at 2,500 psia (540° C at 17X10 6 N/rn2). condensed in the lower zone. To discharge the 
The energy storage concept is shown in the figure. module, the pressure is lowered, and the condensed 
Energy is stored first as the heat of fusion of metal water begins to boil. The steam is superheated by the 
mixtures contained in steel-walled spheres and second metal spheres as it passes up through the module. The 
in condensed water. To charge the module, steam following table is a summary of the characteristics of 
entering the top gives up its energy and is cooled as it electrical generating	 plants	 designed	 to	 produce 
passes through mutually insulated zones of spheres of 100 kW (continuous) and 100 MW (12 hours). 
100-kW Plant	 100-MW Plant 
CHARACTERISTICS (Continuous)	 (12 hours/Day Only) 
Reflector Field 
Land Area .2 acres	 640 acres 
Surface Area 328,000 ft2	 13,000,000 ft2 
Mirror Diameter 15 ft	 15 ft 
Number of Mirrors 185	 70,000 
Mirror Spacing (N-S/E-W) 25-32/16-23 ft	 25-45/16-30 ft 
Reflector Surface/Pointing Accuracy 1/40/ 1/40	 1/10° / 1/10° 
Reflector Efficiency 80%	 - 80% 
Total Thermal Power 2 MW (average)	 600 MW (average) 
Tower Height 150 ft	 1,500 ft 
Absorber 
Diameter (Flat/ Spherical) 28/20 ft	 70/50 ft 
Efficiency 80%	 .	 90% 
Solar Flux Peak 5,000 W/ft2	 100,000 W/ft2 
Energy Storage 
Efficiency 80%	 90% 
Capacity	 .	 . . 18 hours	 6 hours 
Al-Zn and Pb-Na Alloys 300/67 (ft 3/tons)	 72 K/16.1 K (ft3/tons) 
Pressure Water Volume 365/11.5 (ft 3/tons)	 87.5 K/2.75 K (ft3/tons) 
Conversion System Efficiency
	 . 30% (assumed)	 35% (assumed) 
Turbine Inlet Temperature 	 . 950° F	 1,000° F
B75-10098
Note: 
Requests for further information may be directed 
to
Technology Utilization Officer 
Marshall Spaôe Flight Center 
Code ATO1 
Marshall Space Flight Center, Alabama 35812 
Reference: TSP75- 10098 
Patent status: 
Inquiries concerning rights for the commercial use 
of this invention should be addressed to: 
Patent Counsel 
Marshall Space Flight Center 
Code CCO1 
Marshall Space Flight Center, Alabama 35812 
Source: L. W. Brantley
Marshall Space Flight Center 
(MFS-23167) 
Categories: 03 (Physical Sciences)

-	 06 (Mechanics) 
02 (Electronics Systems) 


Large-scale solar thermal collector concepts

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