STIRLING_3_Estudio energia termosolar.pdf

PSA

Annual Report ‘95

2Technical description and project achievements...... 20

2.1Low Temperature Applications..............................20

2.2Parabolic Trough Technology................................28

2.3Dish/Stirling Systems..........................................43

2.3.1DISTAL I....................................................43

2.3.2DISTAL II...................................................45

2.3.3HYHPIRE...................................................47

2.4Central Receivers................................................49

2.5Solar Chemistry...................................................69

2.6Materials treatment.............................................81

Annual Report ‘97

PSA

2.3 Dish/Stirling Systems

Among the solar thermal systems for gener-

ating electricity, the parabolic concentrator

with Stirling engine is distinguished by its high

efficiency and the ease with which it can be

adapted to specific consumption structures.

Overall solar to electrical conversion efficien-

cies of up to 30% could be demonstrated. Due

to the small system sizes from 3 to 50 kW el

power generation plants containing several

units can be clustered and easily extended to

meet the local demand.

Since 1991, when Schlaich, Bergermann and

Partner (SBP) erected their first 9 kW el

Dish/Stirling units (DISTAL I) for long-term

testing, the PSA has been working successfully

in this field of investigation. Continuous opera-

tion since 1992 has resulted in about 29,000

hours of operation and more than 3,500 hours

in 1997. The other main event at the

Dish/Stirling test site was the startup and

testing of three new 10 kW el SBP systems

(DISTAL II), erected in late 1996. Including the

new systems, the PSA can now refer to more

than 30,000 hours of experience in the opera-

tion of Dish/Stirling systems.

Martin Stegmann

(until 31.10.97)

Peter Heller (since

1.11.97)

Wolfgang

Reinalter

Francisco Martín

2.3.1 DISTAL I

The DISTAL I test facility consists of three 7.5-m-

diameter single-faceted stretched-membrane concentra-

Table 2.3.1 SBP 9kWel DISTAL I Dish Stirling System specifications

CONCENTR ATOR

RECEIVER

STIRLING PCU

Manufacturer

SBP

Manufacturer

Solo

Manufacturer

Solo

Type

Single-

Facet,

Stretched

Membrane

Type

Directly

illumi-

nated

Tubes

Type Alpha-Type,

V 90°

Aperture Dia.

7.5m

Aperture Dia.

~12 cm

Displaced Vol.

160ccm

Reflecting Area

42 m 2

Totally

Swapped Vol.

226ccm

Focal Length Ca. 4.5 m

Working Gas

Helium

Concentration

Factor

> 2000

Peak Flux on

Surface

17 kW/cm

Max. Pressure

15 Mpa

Focal Ratio

0.6

Peak Temp.

on Surface

850°C

Max. Gas Temp.

~650°C

Output

34 kW th

Output

29 kW th

Output

9 kW el

Efficiency

81%

Efficiency

85%

Efficiency

29%

PSA

Annual Report ‘97

tors totaling 44 m 2

aperture area. The

concentrators are

mounted on a ‘polar’

axis, following the

sun at a constant

speed of rotation

throughout the day.

The Power Conver-

sion Unit (PCU) at

the focus uses a di-

rectly illuminated

tube receiver con-

nected to a SOLO

V160 Stirling engine

to produce an elec-

trical output power

of 9 kW el . in grid-

connected mode. In

1997 the facility was operated continuously and also

served as an EU-DGXII Training and Mobility of Research-

ers (TMR)’. test facility. The DISTAL I systems have now

accumulated 29,000 hours of operation.

In 1998, operation will continue as long as manpower is

available and no major problems occur. The facility will

also be accessible again for users of the TMR Program.

Three scientists have submitted proposals for a stay at the

DISTAL test site. Besides training at the facility, PCU proc-

ess parameter measurements will be integrated in a

simulation model for the design of a free-piston engine.

Fig. 2.3.1 Distal I test facility

Annual Report ‘97

PSA

2.3.2 DISTAL II

The erection of three new SBP 10-kW el Dish/Stirling sys-

tems was completed in 1997. Like DISTAL I, the systems

consist of a single-faceted stretched-membrane concentra-

tor with a Solo Stirling engine at its focus. The concentra-

tors were manufactured using a new laser welding method.

Tracking is done by

azimuth/elevation drive

system which is com-

puter controlled and

allows full automatic

operation. Due to the

stiff structure there are

no corrections needed

during the day. For op-

timization of the yearly

energy output the con-

centrator was enlarged

to a diameter of 8.5 m

which allows to reach

full power at about

850 W/m 2 .

Fig. 2.3.2 Distal II test facility (foreground)

The V160 Stirling engine was completely reworked by

Solo and optimized in respect to the manufacturing proc-

ess and the output power (now called ‘Solo V161’). The

highly stressed direct illuminated tube receiver is based on

the prototype with crossed tubes developed and tested in

the DISTAL I facility. On the surface of the receiver tem-

peratures up to 820°C are reached which lead to a working

gas temperature of about 650°C. As working fluid the sys-

tem uses helium with a maximum pressure of 15 MPa. At

insolation over 850 W/m 2 , when the working gas has

reached its maximum pressure and temperature, the re-

ceiver has to be cooled by a ventilation system to release

the excess energy collected by the enlarged concentrator.

During startup, many system settings could be defined

and performance tests made and evaluated. As observable

from the data plotted below, the system already shows

very good response, but system parameters still have to be

optimized to reach design performance. For this, further

qualification testing of major components was necessary

and additional measurement campaigns were started that

are to be continued in 1998.

PSA

Annual Report ‘97

Table 2.3.2 Data of SBP10 kW el Systems

CONCENTRATOR

RECEIVER

STIRLING PCU

Manufacturer

SBP

Manufacturer

Solo

Manufacturer

Solo

Type Single-Facet,

Stretched

Membrane

Type

Directly

illumi-

nated

Tubes

Type

Alpha-

Type,

V 90°,

crosshead

Aperture Dia.

8.5 m

Aperture Dia. ~18 cm

Displaced Vol. 160 ccm

Aperture Area

55 m 2

Complete Gas

Volume

250 ccm

Focal Length ca. 4.7 m

Working Gas Helium

Concentration

Factor

>2000

Peak Flux on

Surface

17 kW/cm

Max. Pressure

15 Mpa

Focal Ratio

0.55

Peak Surface

Temperature

850°C

Max. Gas

Temperature

~650°C

Output

45.8 kW th

Output £ 33 kW th

Output

10 kW el

Efficiency

81%

Efficiency

£ 85%

Efficiency

30%

With the help of SANDIA´s video-scanning system,

VSHOT, membrane quality was measured for two of the

three units. It showed slight deviations of the membrane at

the rim due to the manufacturing process and helped to

identify possibilities of improvement. A flux measurement

campaign was started and will be continued in 1998.

Several components, like the control and tracking sys-

tem, were able to be improved during startup. Their al-

ready very good performance will be optimized during fu-

ture operation. Up to now, the new dishes have been oper-

ated on-sun for about 1000 h.

Performance of Distal II

- Data of Dish North 31/11/97

- Values corrected according IEA Guidelines

200

400

600

800

1000

Direct Normal Insolation [W/m²]

Fig. 2.3.3 Performance data of DISTAL II

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