Evaluation of test results

From the experimental data the receiver module efficiencies were derived based on incident flux measurements. Measured efficiencies ranged between 68% and 79%. The pressure drop through the receiver cluster was about 120 mbar, which corresponds well with the design data. The solar fractions reached up to 70%; the remaining contribution comes from fuel combustion. The SOLGATE solarized turbine efficiency, at nominal conditions of 230 kWe, was about 20%. The maximum receiver outlet temperature reached 960°C before stopping the tests due to the necessary gas turbine maintenance. Test data for the day with the highest air outlet temperature is given here as an example. About 45 heliostats were used at a solar irradiation of about 770 W/m2 . Air temperatures in the receiver modules were increased from about 300°C compressor discharge temperature to about 960°C in the high temperature receiver outlet. By mixing with the bypass air stream the air temperature dropped to 800°C which is the limit of the current combustor.

The gas turbine system performance for design conditions is shown in Fig. 6.

The electrical power production at the 960°C situation was about 190 kWe (with 130 kWe due to solar contribution). The estimated overall thermal efficiency of the receiver cluster was 77% for 800 °C and 70% for 950 °С.

Layout, Optimization and Performance Calculation

Modern computer based simulation models have been developed, adapted and validated to analyse the performance of solar-hybrid gas turbines in commercial system size,. The design of the optical part of the tower system (concentrator field arrangement and size, secondary acceptance angle, receiver aperture and orientation and tower height) can be cost-optimized using an adapted version of the HFLCAL code [5]. For the annual

performance calculation of the thermal power system the simulation environment TRNSYS with the model library STEC is used [7], [8].

Results for two industrial gas turbine systems as potential solar-hybrid prototype plants are presented here:

• Solar Mercury 50 — recuperated single shaft gas turbine. ISO rating 4.2 MW, thermal

efficiency 40.3%

• PGT 10 — gas turbine with bottom cycle. ISO rating 16.1 MW, thermal efficiency

44.6%

The solarization adds a receiver cluster directly before each combustion chamber for solar preheating of the compressed air. The receiver exit temperature under design conditions is 800°C or 1000°C. The receiver design temperature rules the maximum solar share. Data is presented for the site Daggett (California, USA, 34.9°N, annual DNI 2790 kWh/m2).More details will be published in [9]. Table 1 summarizes the cost-optimized layout of the prototype plants. Fig. 7 shows the layout of the solarized gas turbine plants. Each receiver zone consists of a group of single receiver modules connected in parallel. Receivers are subdivided into low-temperature (up to 600°C), medium-temperature (up to 800°C) and high-temperature modules (up to 1000°C). According to their temperature level, receiver zones are located in the low, medium and high flux region of the focal spot.

gas turbine system

Mercury 50

PGT10 CC

PGT10 CC

solar design temperature

800°C

800°C

1000°C

design point solar share

38%

58%

88%

total receiver aperture

12.18 m2

54.60 m2

82.32 m2

tower height

50.6m

100.2 m

130.2 m

total reflective area

8615 m2

37615 m2

62733 m2

total plant area2

7.2 ha

37.4 ha

46.5 ha

Table 1: Results of layout and cost-optimization of prototype plants.

The annual performance of the prototype plants was calculated using a typical meteorological year on hourly basis. The results for day time operation are summarized in Table 2. The solar incremental electricity is the basis for the other incremental figures of merit. It is defined as the amount of net electricity produced by the solar-hybrid plant compared to the pure fossil reference plant using the same amount of fuel.

The incremental solar share varies according to the receiver inlet and outlet temperatures between 17.8% and 52.5% for daytime operation. The incremental solar to electric efficiency is the fair basis for comparison with other electricity generating technologies like PV. Values of 15% to 19% are reached with the prototype plants analyzed here. These

values will be even better when higher power levels with more efficient cycles are considered.

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