Solar-Hybrid Gas Turbine Technology

Solar gas turbine systems use concentrated solar power to heat the pressurized air in a gas turbine before entering the combustion chamber (Fig. 1). The solar heat can therefore be converted with the high thermal efficiency of a modern recuperated or combined gas turbine cycle. The combustion chamber closes the temperature gap between the receiver outlet temperature (800-1100°C at design point) and the turbine inlet temperature (950- 1300°C) and provides constant turbine inlet conditions despite fluctuating solar input. The solar power tower technology is used with concentration ratios up to 1000 suns to achieve the high receiver temperatures.

Status of Solar-Hybrid Gas Turbine Technology

A pressurized volumetric air receiver with secondary concentrator has been developed and successfully tested as the so-called REFOS receiver technology in the scope of several German national and international R&D projects [2], [3]. In 2002, three receiver modules have been coupled in series to a 240 kWe gas turbine and successfully operated at receiver temperatures of up to 800°C [4]. More detailed information about the receiver development and recent test results with receiver temperatures up to 960°C can be found in [3]. This section gives an overview over the recent results.

To make use of this promising technology a high temperature volumetric pressurized receiver had been developed in the past by DLR and successfully tested up to a temperature of 800°C and 15 bars [5]. Within the SOLGATE1 project a test system was operated, consisting of a solarized gas turbine connected to a pressurized receiver. The system was set up at the solar tower test facility of the Plataforma Solar de Almeria (PSA), Spain, at 60m height. The test setup consists of 3 receiver modules, a helicopter engine with modified combustor and a generator. In the receiver cluster the air from the compressor of the turbine is heated from 290°C to 1000°C with solar energy. A bypass allows to reduce the temperature at the combustor inlet to 800°C, due to current limitations of the combustor design. The combustor can be fed also with gas. The two-shaft turbine is driving the compressor and the generator which is connected to the grid.

Power Conversion Unit

The Power Conversion

Unit included the gas turbine, a converted helicopter engine and the balance of plant systems.

The gas turbine was installed on a stationary skid and integrated with a generator and auxiliary systems (Fig. 3). A separate oil cooling system and a new electric and control system were added as

Co-funded by the EC under contract no. ENK5-CT-2000-00333.

well as a more powerful starter. The new super alloy combustor included larger diameter inlet flanges to allow for air to enter at over 800°C compared to 300°C in the original combustor. The injector and the igniter were purposely designed to allow continuous operation at elevated air inlet temperatures. Furthermore, the injector had to function at a wide range of air-to-fuel ratios without flameout. A fuel shut off valve and a metering valve were added for fuel flow control. The solar test loop introduced the receiver array between the compressor and the combustor, the dead volume was increased from a few litres to about 3 m3 and the pressure drop was also significantly higher. This had to be taken into account in the control logic.