Category Archives: EuroSun2008-5

Hardware Structure

There are obvious advantages that the instrument based on PXI technology possesses a high speed, a small size and easy expansion, so the hardware structure will use PXI bus technology and relevant products based on the PXI bus. The system concludes PXI-1042 chassis, PXI-8186 Controller, PXI — 6221 multifunction data acquisition card, PXI-4351 high-precision temperature and voltage logger, PXI-6513 digital I/O card, and SC-2345 signal conditioning modules.

Fig. 3 shows the physical structure. PXI-1042 as chassis has 8 slots to comply with PXI and CompactPCI specifications with universal AC power supply. PXI-8186 as embedded controller can greatly improve the system scalability and integration. PXI-6221 multifunction data acquisition card can support two 16-bit analog outputs and has 24 digital I/O, 32-bit counters and digital triggering. PXI-4351 as high-precision temperature and voltage logger includes 8 digital I/O lines (TTL), 16 voltage or 14 thermocouple inputs and autozero and cold-junction compensation and its accuracy can reach 0.12°C for RTDs. PXI-6513 digital I/O card possess optical isolation in banks of 8 channels, 64

sink outputs. This card is a low-cost solution with advanced features for industrial control and manufacturing test applications and it is also a high-reliability industrial feature set. SC-2345 series have connector block and configurable connectors.

image033

Fig.3. Physical structure of hardware

The Solar Keymark Testing for Factory Made Systems by. Means of an Extrapolation Procedure

H. Kerskes*, B. Mette, H. Drtick, H. Mtiller-Steinhagen

Institute for Thermodynamics and Thermal Engineering (ITW),

University of Stuttgart, Pfaffenwaldring 6, 70550 Stuttgart, Germany
Tel.:++49-711-685-63534

Corresponding Author: kerskes@itw. uni-stuttgart. de
Abstract

System tests according to the EN 12976 test procedures are a basis for factory made Solar Keymark system certification. To obtain the Solar Keymark certificate, each system configuration of a solar domestic hot water system (DHW) has to be tested by an accredited testing laboratory. As companies often offer a product line of their solar DHW systems, it is desirable to have a calculation tool that is able to predict the thermal performance of the whole product line without the need to test each of the system configurations. This paper presents the main elements of the Solar Keymark certification program as well as a mathematical procedure developed at the ITW with which it is possible to extrapolate performance test results of one tested system to systems of the same product line.

Keywords: Solar Keymark certification, solar domestic hot water systems, DST

1. Introduction

With the implementation of Solar Keymark certification in the year 2003, a pan-European quality label for solar thermal products was established for the first time /1/.

The aim of the Solar Keymark label is to break the existing trade barriers within the European market. A solar thermal system or solar collector certified according to the Solar Keymark scheme rules fulfils the relevant European Standards and is hence qualified for acceptance by the national regulatory and financial authority, e. g. with regard to financial incentives.

Thereby it is avoided that a system already tested by an accredited testing laboratory has to be tested again by national laboratories. For manufacturers of solar thermal systems the Solar Keymark is an instrument to save time and money and to demonstrate the quality of their products. On the other hand customers benefit from the guarantee to buy an approved product.

In 2004 the first system tests according to the EN 12976 test procedures /2/ as basis for factory made Solar Keymark system certification were carried out at ITW. In the meantime about 35 factory made solar thermal systems are Solar Keymark certified by several European certification bodies and the number of requested system tests is growing rapidly.

Efficiency test results

The collector was tested according to both steady state test (EN 12975-2;section 6.1) and dynamic test (EN 12975-2; section 6.3) methods. The corresponding characteristic parameters are presented in Table 1.

Table 1. Efficiency curve parameters after steady-state test results

Steady-state test parameters

Dynamic test parameters

По

ai

[W/°C. m2]

a2

[W/°C2.m2]

П)ь

Ci

[W/°C. m2]

C2

[W/°C2.m2]

C5

[J/kg°C]

Kd(0)

0.725

3.599

0.007

0.794

3.483

0.010

13647

0.725

Incidence angle modifier (IAM) values obtained, after both test methodologies, for longitudinal and transversal incidences are presented in Table 2.

Table 2. Steady-state and dynamic test results for transversal and longitudinal incidence angle modifier values

Test

0

10

15

20

25

30

35

40

50

60

Steady

Kt(0)

0.990

0.999

0.949

0.887

0.632

0.494

0.481

0.482

Ki(0)

0.957

0.853

Dynamic

Kt(0)

0.966

0.992

0.931

0.840

0.529

0.362

0.328

0.057

Ki(0)

0.991

0.781

Longitudinal and transversal IAM functions were constructed after 2-points based and linear approximations, respectively (Carvalho et al, 2007). The composed IAM, illustrated in figure 2, follows the McIntire (1983) approximation:

K(9) = K(9l,9t )* K(9l,0)K(0,9t) (8)

The weighted average hemispherical IAM, calculated according to Eq.(7), yields Kdfh =0.529.

Comparison between QD and SS test results

From the test sequences obtained for QD test method, test periods according to SS test method conditions were selected and the parameters of efficiency curve determined (equation (3)). The values determined are listed in Table 2.

Table 2: Parameters of efficiency curve according to SS test method

Л0

a1

a2

0,688

4,140

0,005

Comparison of results between the QD and SS methods is presented in the form of an efficiency curve with respect to Tm* = (tm-ta)/G*, where G* is the global irradiance incident on the collector. The following values were considered:

G* = 1000 W/ m2; Gd = 150 W/ m2; 0: = 15°

according to the standard’s recommendations for the presentation of results.

image182

The above figure shows good agreement between the two test methods for the flat plate collector tested.

An evacuated tubular collector was also tested. It was a double glazed tubular collector and had as heat transfer device a heat pipe.

Test sequences were obtained but the identification of characteristic parameters was not successful since further development of the MLR tool was needed due to the fact that IAM can not be characterized by equation (7) for this type of collectors.

Also a strange behaviour of the collector was detected in the test sequences, showing that, after a certain time period the collector performance was enhanced, i. e, the outlet collector temperature raised in almost step wise way after a couple of hours, showing a different behaviour between morning and afternoon. The reason for this behaviour could not be determined.

5. Conclusion

The QD test methodology was implemented at LECS. For this implementation data acquisition programme and MRL tool were developed. First results were obtained for a flat plate collector and showed good results, although a better choice of test sequences is needed in order to incorporate a better weather variability, i. e., sequences with cloudy conditions.

For test of collectors with higher optical complexity, adaptation of the MLR tool is needed. This is the case of CPC type and evacuated tubular collectors.

References

[1] EN 12975 (2006), Thermal solar systems and components — Solar collectors — Part 2: Test Methods, Section 6.1. and Section 6.3, European Standard.

[2] Rojas, D. et al., Thermal performance testing of flat-plate collectors, Sol. Energy (2008), doi:10.1016/j. solener.2008.02.001

[3] Carvalho, M. J., P. Kovacs, Fischer, S., Project NEGST — New Generation of Solar Thermal Systems, "WP4-D2.1.k — Resource document — Definitions and test procedure related to the incidence angle modifier”, 2006, in http://www. swt-technologie. de/WP4 D2.1 ges. pdf

[4] Horta, P., M. J. Carvalho, S. Fisher (2008), Solar thermal collector yield — experimental validation of calculations based on steady-state and quasi-dynamic test methodologies, Submitted for presentation at Eurosun2008, Lisboa.

[1] Introduction

Solar water heating (SWH) systems are not usually equipped with any fault diagnostic system (FDS). Any faults are usually identified either by regular inspection by servicing personnel or when the system is not producing appropriate quantities of hot water, which is the most frequent. Usually people forget the existence of the solar system and this is inspected only after hot water is not available, indicating some problems. This results in problematic operation of the systems for long periods of time, which reduce the effectiveness and viability of the systems. Primarily works present the possibility of on-site determination of faults [1-2]. But the drifts were of a step-by-step

[3] Du to changes in the official CEN nomenclature the previously used abbreviation ENV for the indication of a preliminary standard is now replaced by the abbreviation CEN/TS (CEN: Comite Europeen de Normalisation — European Committee for Standardisation ; TS: Technical Specification).

[4] European Committee for Electrotechnical Standardization — Comite Europeen de Normalisation Electrotechnique

[5] Duff, W. S., Winston, R., O’Gallagher, J., Henkel T. and Bergquam, J., “Five Year Novel ICPC Solar Collector Performance”, 2003 American Solar Energy Society Solar Energy Conference, Austin TX, June 2003

[6] Duff, William, Roland Winston, Joseph

[7] The CSTG — method was originally developed within an European Project by the “Complete System

Testing Group” (CSTG). Today this method is standardised in ISO 9459-2

[9] DST: Dynamic System Test. The DST-method is standardised in ISO 9459-5.

[10] The collector performance calculated from the collector parameters gained under steady state conditions is only valid for the diffuse fraction prevailing during the measurements. The usage of these results leads to an under-estimation of the collector output for diffuse fractions smaller and to an over-estimation for diffuse fractions larger, than the values predominant during the steady state measurement.

[11] ++ well developed / can be applied directly, +- further research and development, — early R&D

[12] — not automated, +- partly automated, ++ fully automated

Description of the water heating system

Подпись: Fig. 1 Schematic diagram of the solar system

The solar system considered in this work is a large hot water production system suitable for a small hotel, blocks of flats, offices or similar applications. Although the FDS system developed can be applied to small systems as well it is thought that the expenditure required would not balance the extra benefits incurred in such cases and in domestic applications the users are usually more sensitive to the maintenance of their own system in comparison with the maintenance staff of a hotel for example or the tenants of a multi building installation where everybody but really nobody is responsible. The system schematic is shown in Fig. 1. The system consists of 40 m2 of collectors, a differential thermostat (not shown in Fig. 1) and a 2000 L storage tank. The system is also equipped with a data acquisition system which measures the temperatures at four locations of the SWH system; the collector array outlet (T1), the storage tank inlet (T2), the storage tank outlet (T3) and the collector array inlet (T4). The global solar radiation, the ambient temperature, and the pump state (on/off) are also recorded.

In fact, a TRNSYS model is used to simulate the system. Two draw off profiles have been used. The first one is repeated day after day, the second one is computed using the free generator developed at the Univeristat Marburg [7] and used in [8]. Being totally different, these profiles will show that the results do no depend on them. In a real application, the temperature readings would be affected by noise. So, it has been decided to add random noise to each computed temperature. It has to be noted that the time step is one hour.

Four drifts or defaults are taken into account in this study. For the collector, two parameters are considered: F’ (linked to the fin efficiency), and UL (linked to the thermal insulation); for details see TRNSYS manual. For F’, a progressive decrease is computed so that the value decreases from 0.7 to 0.6. For UL, a sudden increase is considered (from 3 to 4 W/m2.K) followed by a progressive increase (from 4 to 5 W/m2.K). For the connecting pipes, the variations of the U value are similar to the variations of the UL value. These drifts will be shown in the last section when presenting the results. It has to be noted that it has been necessary to write our own components for TRNSYS to be able to read the values from files, which allow continuous variations of the parameters (one value corresponding to one hour).

The drifts have been both considered separately and combined. In the latter case, which leads to the lowest performance of the system, the yearly increase of the auxiliary electrical power needed to deliver the hot water is less than 7.5%. It can be concluded that if the FDS is able to detect the faults before the end of the drifts, it is sufficiently efficient.

Thermal performance during the day

The power of the collectors during the day is studied to investigate the transient thermal performance of the ETCs. Figure 2 shows the collector power in an autumn day. In the morning, the direct flow ETC 7 starts up first, followed by the heat pipe ETC 4, ETC 2 and the double glass ETC with heat pipe. There is a sharp increase of the power of the heat pipe ETCs which is most likely caused by the late start-up of evaporation in the heat pipe causing “overheated” absorber temperatures. A possible explanation is that the upper part of the collector is heated up first, but the heat pipe will not be able to work until the bottom part of the heat pipe is heated up to the evaporation temperature. After 10:00 and before 15:00, the power of the ETC 6 levels out while the power of the other collectors increases in the morning and decreases in the afternoon. That can be explained by the cylindrical shape of the absorber of ETC 6. When there is almost no shadow on the tubes between 10:00 and 15:00, the irradiated surface area of the cylindrical absorber does not change significantly, therefore there is insignificant change of the collector power. The heat pipe ETC 2 and 4 and the direct flow ETC have a flat absorber, so the collector power will increase in the morning due to a decrease of incidence angle and an increase of irradiated surface area. In the afternoon the power will decrease due to increased incidence angle and reduced irradiated surface area.

The direct flow ETC 7 performs almost the same as ETC 4 but in the early morning and the late afternoon ETC 7 performs a bit better than ETC 4. The all-glass ETC 5 on the other hand starts up slowly and stops almost 1 hour later than the other collectors. This is due to its large thermal capacity since a large quantity of collector fluid is stored in the glass tubes.

image063 Подпись: 07:00 09:00 11:00 13:00 15:00 17:00 19:00 Time [h] Fig. 3: Collector power in a summer day in phase 3.

Figure 3 shows power of the collectors in a summer day. In the morning ETC 4, 6 and 7 almost start up at the same time. The power of the collectors increases gradually and smoothly. The power of ETC 6 is higher than ETC 4 and 7 in the morning and in the afternoon. That is because the cylindrical absorber of ETC 6 has a larger irradiated surface than a flat absorber in the morning and in the afternoon.

3.1. Long term thermal performance

The thermal performances of the seven ETCs are compared. Figure 4 shows relative thermal performances of the differently designed ETCs. The performance ratio is defined as the ratio between the weekly thermal performance of the collector in question and the weekly thermal performance of the reference collector shown in the figure. The mean solar collector fluid temperature during operation is given at the bottom of the figure.

Durability and reliability testing

In addition to the equipment required for thermal performance testing, the test facility is delivered with the complete equipment required for durability and reliability testing of solar thermal collectors according to EN 12975-2. This comprises test facilities for outdoor exposure, external and internal thermal shock, rain penetration, mechanical load test and internal pressure test.

Like for thermal performance testing, it is also possible to combine test facilities required for several durability and reliability tests into a single test facility. Figure 5 shows the test facility for the rain penetration which can also be used for performing external thermal shock tests.

For carrying out exposure tests, high-temperature resistance tests and internal thermal shock tests, the same test facility can be used since only the frame with the spray nozzles has to be moved sidewards.

image098

Fig. 5: Test facility for outdoor durability and reliability testing (here used for rain penetration test)

 

Furthermore, the collector test procedures related to the positive and negative mechanical load test, the internal pressure test, and the impact resistance test can be performed using only one single test facility. For this purpose, the collector is mounted on the mechanical load test facility; see figure 6.

image099

Fig. 6: The mechanical load test facility

 

Obviously, the mechanical load tests (negative and positive pressure) may be performed subsequently.

After connecting the equipment for the internal pressure test of the collector, the corresponding test can be performed on the mounted collector without any changes on the test facility.

According to EN 12975-2 two methods for performing the impact resistance test are specified. One method is using a steel ball and the other one ice balls.

Подпись: Fig 7: Push loading drawer including mounted collector pulled out of the mechanical load test facility.

For performing the impact resistance test by means of a steel ball, the collector does not need to be remounted since the collector is mounted stiff enough on the test facility. The supporting frame of the mechanical load test facility was designed by IAO as a push loading drawer. Due to this it is possible to pull out the support frame including the mounted collector underneath of the frame simulating the mechanical load; see figure 7.

Подпись: Fig. 8: Acceleration mechanism (“ice ball gun”) for carrying out impact resistance test
For performing the impact resistance test with ice balls, it becomes necessary to utilize a complete different test facility. Since the ice balls must have a certain speed at the time of the impact on the collector cover the application of a certain kind of acceleration mechanism (“ice ball gun”) is essential. Such an acceleration mechanism is shown in figure 8.

The performing of an impact resistance test according to this method makes it necessary to mount the collector vertically.

1.1 Patent

The mobile, stand-alone solar thermal test facility has been registered by SWT for patenting under the number AZ 102007018251.3 at the German Patent Office. Major issues of this patent are the mobile and stand-alone characteristics of the test facility combined with the possibility to perform tests according to three different standards with one single test facility.

Results for the base-cases and envelope changes needed to ensure compliance

The first stage of the calculations was to compute the main evaluation indexes (Nic, Nvc, Nac and Ntc) for the buildings with their base-case envelope, as described in section 2. Table 5 and Table 6 show the results of the heating and cooling needs for each of the 7 analysed locations. The results show that, with the base-case envelope, the heating needs are above the allowed limit if the buildings are located in the coldest regions — Bragan? a, Guarda, Penhas Douradas and Viana do Castelo (this later one only in the case of the dwelling). The cooling needs pose no problem in any of the studied locations.

Table 5: Results for the apartment with the base-case envelope — heating and cooling needs

Lisboa

Bragan^a

Faro

Evora

Guarda

Penhas

Douradas

Viana do Castelo

Nic

(kWh/m2.year)

55.5

161.8

51.6

67.4

169.3

200.8

73.6

Ni Max

(kWh/m2.year)

60.4

138.4

54.3

69.8

143.46

164.3

75.0

Nvc

(kWh/m2.year)

14.7

2.3

14.7

14.3

2.0

2.0

2.0

Nv Max

(kWh/m2.year)

32

18

32

32

18

18

18

Compliance

YES

NO

YES

YES

NO

NO

YES

Table 6: Results for the dwelling with the base-case envelope — heating and cooling needs

Lisboa

Bragan^a

Faro

Evora

Guarda

Penhas

Douradas

Viana do Castelo

Nic

54.6

165.9

51.3

66.8

173.8

207.2

93.7

Ni max

62.5

143.3

56.1

72.2

148.5

170.1

90.2

Nvc

14.1

1.9

14.1

14.0

1.6

1.6

1.6

Nv max

32

18

32

32

16

16

16

Compliance

YES

NO

YES

YES

NO

NO

NO

The second stage of the study consisted in identifying a minimum set of envelope changes that ensures compliance with the regulation in terms of heating and cooling loads. For each location there several sets of changes that can accomplish this goal, e. g. increasing the insulation, changing from natural to mechanical ventilation with lower air change rates or optimizing the window orientation and areas. Priority was given to measures that have no or little collateral impact with other architectural features. Table 7 summarises the main changes made to the base-case in order to fulfil the regulation demands in terms of heating and cooling needs. Table 8 and Table 9 show the results of heating and cooling needs plus the final energy for water heating and the total primary energy consumption (as a ratio between the actual result and the maximum allowed) as well as the resulting energy class. The results confirm that with the envelope changes identified it is now

possible to fulfil the heating and cooling requirements (first two lines). The results also show that the final result of (Ntc/Nt) and the corresponding energy class depends very strongly in the equipments used for heating, cooling and especially for DHW production. With the equipments scenario 3, which relies solely on electric resistance for DHW it is not possible to fulfil the regulation in any of the location, while with scenarios 2 and 6, which make use of solar collectors, all buildings become class A or A+.

Table 7: Changes in the envelope implemented to fulfil the regulation RCCTE.

Location

Apartment

Dwelling

Braganja

— Wall insulation increased to 6 cm (U= 0.41 W/m2.°C)

— Insul. of plan. th. br. increased to 3 cm (U=0.88 W/m2.°C)

— Floor slab insulation increased to 6 cm (U=0.53)

— Night occlusion device at kitchen window, U decreasing to 3.1 W/m2.°C.

— Wall insulation increased to 6 cm (U=0.45 W/m2.°C at walls and 0.52 at planar thermal bridges)

— Insulation of interior envelope walls increased to 6 cm (U=0.48 W/m2.°C)

— Natural ventilation air intake grills and windows with air tightness class 2, decreasing air change to 1.0 ach-1

Guarda

— Wall insulation increased to 6 cm XPS (U= 0.38)

— Insulation at planar thermal bridges increased to 3 cm XPS (U=0.81 W/m2.°C)

— Floor slab insulation increased to 6 cm (U=0.46)

— Window frames with thermal break + night occlusion devices, resulting in U=2.7 W/m2.°C.

— Wall insulation increased to 8 cm (U=0.37 W/m2.°C at walls and 0.41 W/m2.°C at planar thermal bridges)

— Roof slab insulation increased to 8 cm (U=0.32 W/m2.°C)

Penhas

Douradas

— Wall insulation increased to 7cm XPS (U= 0.34 W/m2.°C)

— Insulation at planar thermal bridges increased to 6cm XPS (U=0.49 W/m2.°C)

— Floor slab insulation increased to 7cm (U=0.48)

— Window frames with thermal break + night occlusion devices, resulting in U=2.7 W/m2.°C.

— Wall insulation increased to 8 cm (U=0.37 W/m2.°C at walls and 0.41 at planar thermal bridges)

— Insulation of interior envelope walls increased to 6 cm (U=0.48 W/m2.°C)

— Roof slab insulation increased to 8 cm (U=0.32 W/m2.°C)

— Night occlusion device of windows + rubber strips, resulting in windows with U=2.7 W/m2.°C

Viana C.

— Wall insulation increased to 5 cm (U=0.51 W/m2.°C)

Lisbon, Faro, Evora: No changes required

Table 8: Results for the apartment after the changes in the envelope to fulfil the regulation in terms of

heating and cooling needs.

Lisboa

Bragan^a

Faro

Evora

Guarda

P. Dour. as

Viana C. l°

Nic /Ni

92%

99%

95%

97%

95%

97%

98%

Nvc /Nv

46%

14%

46%

45%

15%

15%

12%

Eqpt. 1

Nac / Na

74%

74%

74%

74%

74%

74%

74%

Ntc /Nt

52% [B]

57% [B]

52% [B]

53% [B]

57% [B]

58% [B]

53% [B]

Eqpt. 2

Nac / Na

22%

26%

21%

21%

26%

27%

28%

Ntc /Nt

23% [A+]

32% [A]

21% [A+]

23% [A+]

32% [A]

35% [A]

26% [A]

Eqpt. 3

Nac / Na

68%

68%

68%

68%

68%

68%

68%

Ntc /Nt

136% [NC]

132% [NC]

137% [NC]

136% [NC]

129% [NC]

128% [NC]

137% [NC]

Eqpt. 4

Nac / Na

74%

74%

74%

74%

74%

74%

74%

Ntc /Nt

50% [A]

52% [B]

50% [A]

50% [B]

52% [B]

53% [B]

50% [A]

Eqpt. 5

Nac / Na

16%

20%

14%

15%

20%

21%

21%

image153

1st International Congress on Heating, Cooling, and Buildings, 7th to 10th October, Lisbon — Portugal /

Ntc /Nt

38% [A]

49% [A]

35% [A]

36% [A]

48% [A]

51% [B]

48% [A]

Eqpt. 6

Nac / Na

22%

26%

21%

21%

26%

27%

28%

Ntc /Nt

21% [A+]

27% [A]

19% [A+]

21% [A+]

27% [A]

29% [A]

24% [A+]

NC. = Not Compliant

Table 9: Results for the dwelling after the changes to meet the heating and cooling needs requirements

Lisboa

Bragan^a

Faro

Evora

Guarda

P. Dour. as

Viana C. l°

Nic /Ni

87%

100%

91%

93%

99%

99%

98%

Nvc /Nv

44%

16%

44%

44%

15%

14%

12%

Eqpt. 1

Nac / Na

74%

74%

74%

74%

74%

74%

74%

Ntc /Nt

53% [B]

61% [B]

53% [B]

54% [B]

61% [B]

62% [B]

56% [B]

Eqpt. 2

Nac / Na

26%

30%

24%

24%

30%

30%

31%

Ntc /Nt

27% [A]

39% [A]

26% [A]

28% [A]

40% [A]

42% [A]

33% [A]

Eqpt. 3

Nac / Na

68%

68%

68%

68%

68%

68%

68%

Ntc /Nt

134% [NC]

129% [NC]

135% [NC]

133% [NC]

127% [NC]

125% [NC]

133% [NC]

Eqpt. 4

Nac / Na

74%

74%

74%

74%

74%

74%

74%

Ntc /Nt

50% [A]

54% [B]

50% [A]

51% [B]

54% [B]

55% [B]

51% [B]

Eqpt. 5

Nac / Na

19%

23%

18%

18%

23%

24%

25%

Ntc /Nt

45% [A]

56% [B]

42% [A]

43% [A]

56% [B]

58% [B]

56% [B]

Eqpt. 6

Nac / Na

26%

30%

24%

18%

30%

30%

31%

Ntc /Nt

24% [A+]

33% [A]

23% [A+]

24% [A+]

33% [A]

35% [A]

29% [A]

Ten Year Study of a Novel ICPC Solar Collector Installation: Optical Modeling and Material Degradation

William S. Duff* and Jirachote Daosukho

Department of Mechanical Engineering, Colorado State University, Ft. Collins CO 80523
* Corresponding Author, bill@engr. colostate. edu

Abstract

A novel integral compound parabolic concentrator evacuated solar collector (ICPC) array has been in continuous operation at a demonstration project in Sacramento California since 1998. An ongoing study addresses the impact of optical, thermal, degradation and component failure factors on array performance over the ten years of operation. This paper reports on the ray trace modeling for the vertical and horizontally oriented fined absorber tubes and the degradation of the reflector in the tubes of the array. The paper will include a review of collection system performance and reliability over the ten years of operation, the design of the simulation, animations of rays striking at various angles, the incidence angle evaluation and the design of the laser device.

Keywords: ICPC, Optical Modeling, Materials Degradation, Reliability

1. Background

1.1 Development of the Novel ICPC

Research on CPC solar collectors has been going on for almost thirty years. See Garrison [1] and Snail et al [2]. In the early 1990s a new ICPC evacuated collector design was developed. The new ICPC design allows a relatively simple manufacturing approach and solves many of the operational problems of previous ICPC designs. The design and the fabrication approaches are described in Winston et al [3] and Duff et al [4].

Comparison with Parabolic Trough Collector

Based on the project results Fraunhofer ISE together with the partners DLR and PSE performed a technology comparison between Linear Fresnel-Collector (LFC) and Parabolic Trough (PT) for a 50 MW solar power station. Due to the lower collector efficiency (cosine, shading and blocking losses) of the LFC a larger aperture area is needed than for the PT. For optimized optical and thermal performance it seems completely feasible that due to lower investment costs per aperture area the levelised electricity costs (LEC) for the LFC are appreciably lower than for the PT.

image081

relative change of parameters

Figure 8: Break-even-costs for LFC compared to PT (assumed specific costs 275 €/m2) Starting point for LFC design is the prototype collector performance — 25% thermal loss would require vacuum tube receivers

We have calculated break-even-costs for the LFC against a Eurotrough collector with assumed specific costs of 275 €/m2. As can be seen from Figure 8 careless optical design and lower quality components should be avoided due to the economical sensitivity for a variation of optical efficiency. Thermal losses should be lower further which is possible with increased concentration ratio, lower emissivity or

vacuum receivers. In previous studies e. g. [1] specific investment costs of 117 €/m2 for the LFC were compared to 220 €/m2 for PT, resulting in lower LEC for the Fresnel technology consistent with this new comparison. The question, whether for the Fresnel technology lower O&M costs which are a relevant parameter for LEC may be expected is still under discussion.

5 Summary and Outlook

The influence of optical quality on the energy and cost performance requires a careful control and optimization of the collector components. We have developed methods to characterize the key optical components as well as single components as in overall collector performance. All these methods are quite flexible and can be used — with necessary adaptations — also for other concentrating optics. The results obtained so far from different Linear Fresnel Collectors showed were positive concerning optical concentrator quality.

Looking at the results and the large impact of optical quality, thermal losses, tracking and O&M on the economics of concentrating collector in solar power applications, it seems justified and necessary to build a complete solar power plant using Fresnel technology to prove expectations on electricity price. Smaller projects are under way meanwhile.

6 Acknowledgements

The authors gratefully acknowledge the financial support for the research and development projects »FRESQUALI« and »FRESNEL2«, funded by the German Ministry of Environment, Nature Conservation and Nuclear Safety (BMU) under the numbers FKZ 16UM0079 and FKZ 16UM0050.

7 References

[1] Haberle A., Zahler Ch., Lerchenmuller H., Mertins M., Wittwer Ch., Trieb F., Dersch J., The Solarmundo line focussing Fresnel collector. Optical and thermal performance and cost calculations. Proceedings of the 11th SolarPACES International Symposium, (2002)

[2] Mertins M., Lerchenmuller H., Haberle A. Geometry Optimization of Fresnel-Collectors with economic assessment, 5th ISES Europe Solar Conference, EuroSun2004 (2004)

[3] Bernhard R., Laabs H.-G., de Lalaing J., Eck M., Eickhoff M., Georg A., Pottler K., Morin G., Heimsath A., Haberle A.: Linear Fresnel Collector demonstration on the PSA Part I — Design, Construction and quality control, Proceedings of the 14th SolarPACES International Symposium, Las Vegas, USA (2008)

[4] Bernhard R., Hein S., de Lalaing J., Eck M., Eickhoff M., Pfander M., Morin G., Haberle A.: Linear Fresnel Collector demonstration on the PSA Part II — Commissioning and First Performance Testing, Proceedings of the 14th SolarPACES International Symposium, Las Vegas, USA (2008)

[5] Heimsath A., Bothe Th., Li W., Tscheche M., Platzer, W.: Characterization of Optical Components for Linear Fresnel Collectors by Fringe Reflection Method, Proceedings of the 14th SolarPACES International Symposium, Las Vegas, USA (2008)

[5] Morin G., Dersch J. et. al.: Bewertung der linearen Fresnel-Kollektor-Technik und technisch-wirtschaftlicher Vergleich mit Parabolrinnen-Kollektoren, Teilbericht Projekt Fresnel II, Freiburg (2008)