10.07.2015   Sonar-Collecttors

Solar Only Plant and Gas Co-firing

From the starting point of a 50 MWei Solar Only steam plant, it will be analysed how natural gas co-firing influences the electrical yield, the solar share and the costs of the plant. For this analysis 240 plant configurations with different solar fields (210’000 m2 — 617’000 m2) and boilers (0 MWth — 150 MWth) were examined.

2.1 Technical Description

Power Cycle

The 50 MWel power cycle is equipped with sea water cooling and the feed water storage tank as single preheater (see figure 5). Its net efficiency is 32.8% (at a water temperature of 14°C, for warmer water temperatures and at part load the efficiency drops). [4]

The steam is produced by the solar field. If it does not reach the maximum turbine load it is supported by a parallel gas boiler. As opposed to the biomass variant, it was taken into consideration that the solar share should remain high. The assumed operation mode is that gas will be co-fired, once the solar collector can provide more than one kg/s steam.[5] An exemplary day (July, 13) is given in figure 6. The boiler’s thermal energy production is limited either by its thermal capacity or by the nominal mass flow of the turbine. For technical reasons the boiler operates between 20% and 100% of its nominal capacity.

time

Figure 6: thermal energy to power block by solar field (453600 m2) and gas burner (Pth, n=70 MW), july, 13