4.2 Absorber
Material of the absorber:　　　　　　　　　 n/a (MS)
Kind/Brand of selective coating: 　　　　　　sputtered (MS)
Absorptivity coefficient : 　　　　　　　　　　93% (MS)
Emissivity coefficient ": 　　　　　　　　　　 > 6.5 % (MS)
Material of the absorber pipes:　　　　　　　 copper (MS)
Layout of the absorber pipes: 　　　　　　　　parallel, heat pipes (MS)
Number of absorber pipes: 　　　　　　　　　18 (MS)
Outer diameter:　　　　　　　　　　　　　　 8 mm (MS)
Inner diameter:　　　　　　　　　　　　　　 6.8 mm (MS)
Distance between the pipes:　　　　　　　　 80 mm (MS)
Material of the header pipe: 　　　　　　　　　copper (MS)
Outer diameter of the header pipe: 　　　　　　22 mm (MS)
Inner diameter of the header pipe: 　　　　　　1 mm (MS)
Material of the contact sheets:　　　　　　　　 aluminium (MS)
Thickness of the contact sheets: 　　　　　　　0.2 mm (MS)
4.3 Insulation and Casing
Collector dimensions
Height, width, depth: 　　　　　　　　　　　　2.100 m; 1.487 m; 1.560 m
Medium between the inner and
outer tubes of the vacuum flask:　　　　　　　＝＜3* 10-2 Pa (MS)
Material of the casing: 　　　　　　　　　　　　high-grade steel (MS)
Sealing material: 　　　　　　　　　　　　　　silicon (MS)
4.4 Limitations
Maximum pressure: 　　　　　　　　　　　　　800 kPa (MS)
Operating pressure:　　　　　　　　　　　　　 6 bar (MS)
Maximum service temperature: 　　　　　　　　125oC
Maximum stagnation temperature: 　　　　　　　250oC
Flow range recommendation:　　　　　　　　　　 1.1 l/m2h (MS)
4.5 Kind of mounting
Flat roof, mounted on the roof:　　　　　　　　　 yes (MS)
Tilted roof, mounted on the roof:　　　　　　　　　 yes (MS)
Tilted roof, integrated:　　　　　　　　　　　　　no (MS)
Free mounting:　　　　　　　　　　　　　　　　 yes (MS)
Fassade:　　　　　　　　　　　　　　　　　　　 yes (MS)

4.6 Picture and cut drawing of the collector

Figure 1: Picture of the collector SPA-58-1800-18-C mounted on the test facility of Fraunhofer ISE

Figure 2: Cut drawing of the vacuum tube KTB Nr.

5 Collector efficiency parameters
5.1 Test method
Outdoor, steady state according to EN 12975-2:2006
Thermal solar systems and components, solar collectors, test methods
5.2 Description of the calculation
The functional dependence of the collector efficiency on the meteorological
and system operation values can be represented by the following
mathematical equation:

5.3 Instantaneous efficiency parameters based on aperture and absorber area and
mean temperature of heat transfer fluid
Boundary conditions:
Test method: 　　　　　outdoor, steady state
Latitude:　　　　　　　 48.0o
Longitude:　　　　　　 7.8o
Collector tilt:　　　　　 tracked between 40oand 50o
Collector azimuth:　　　 tracked
Test conditions:
Mean irradiation : 　　　986 W/m2
Mean wind speed: 　　　3 m/s
Mean flow rate: 　　　　　124 kg/h
Kind of fluid:　　　　　　 water
Results:
The calculated parameters rely on following areas1:
aperture area absorber area
(1.706 m2): (1.451 m2):

The determination for the standard deviation (k=2) was performed
according ENV 13025 (GUM). Based on this calculation the uncertainty is
less than 2%-points of the efficiency values over the complete measured
temperature range ( η0a = 0.573 +/- 0.02). Based on our experience with
the test facilities the uncertainty is much smaller and in a range of
+/- 1%-point. The standard deviation of the heat loss parameters resulting
from the regression fit curve through the measurements points is:
a1a = 2.085 +/- 0.087 and
a2a = 0.0083 +/- 0.0012 .
1absorber area - projected area of absorber tube,
aperture area - projected area of inner diameter of cover tube