By Marco Poliafico, MEng GradEI

By allowing CSP to compensate for some of the greatest challenges facing the technology including high costs, bankability and the provision of a continuous supply of energy, it is no surprise that hybrids are gaining traction. 

But just how cost effective is CSP hybridization (specifically ISCCs)? And how much CO2 reduction do ISCCs achieve? CSP Today examines the integration between gas and solar to show that whilst ISCCs may be more expensive than conventional plants, they are considerably cheaper than stand-alone CSP plants and achieve significant reductions in CO2 when compared to conventional Natural Gas Combined Cycles.

The CSP Today Global Tracker has around 40 hybrid CSP plants listed in its database including in Algeria, Morocco, Egypt, Iran, Israel, Turkey, India, Australia, China, Italy, Chile, Mexico and the USA. India has recognised the value of integration between CSP and other resources to promote CSP energy generation with the Ministry of New and Renewable Energy (MNRE) launching its hybrid capital support programme for CSP.

The below case study shows the results of a Life Cycle Assessment (LCA) methodology applied in 2011 to an ISCC plant located in Morocco (Rabat, Nominal Irradiance 900 W/m2) [01]. The installed capacity of the ISCC plant is 150 MWe with the solar field contributing 20MWe with a potential of 1h Thermal Energy Storage (TES). All the technical assumptions employed for the separate solar installation are derived from the Andasol-I CSP plant. The comparison carried out is between the ISCC described above and a corresponding Natural Gas Combined Cycle (NGCC) plant of 150 MWe installed capacity. The results of the economic and environmental assessment carried out at the Ecole Polytechnique Federale de Lausanne are displayed in figures 1 to 3 [01].

Figure 1 shows the contribution of the solar field in terms of Installed Capacity (column on the left) and Solar Fraction (portion of electricity generated in one year from the CSP part) of the ISCC plant.

Figure 1: Percentage of Installed Capacity from the CSP Plant and Solar Fraction (Electricity Generation per year from the CSP part) of the ISCC Plant in Rabat, Morocco

(Source: Own Production based on [01])

Figure 2 shows the cost comparison of the ISCC plant and the corresponding NGCC plant. The third column on the right refers to the solar part of the ISCC whilst the middle column refers to the entire ISCC. From the values reported the ISCC project requires a higher capital cost (152.95% when compared to the corresponding NGCC). However this is well below the capital cost associated with the CSP part of the plant (the ISCC specific cost is 46.49% of the cost of the solar system). The conclusion according to this study is that the most economic investment is a conventional combined cycle power station. This said, a hybrid plant costs only a fraction of the CSP facility.

Figure 2: Investment Costs and LCOE of the ISCC Plant in Rabat, Morocco

(Source: Own Production based on [01])

The red columns indicate the LCOE of the three options and follow the vertical axis on the right. According to the findings of the research [01] the LCOE of the ISCC plant is124.68% of the LCOE of the corresponding NGCC facility. However this cost is only 32.43% of the LCOE of the solar system considered (9.6 c$/KWhe vs 29.6 c$/KWhe). Although the percentage varies, the conclusion is in line with that remarked above, namely that conventional plants are currently less expensive than ISCC plants but these in turn are a more cost effective solution when compared to a CSP energy plant.

So if an ISCC is not yet competitive with a NGCC in terms of cost, where can it compete? One potential area is in CO2 reductions.

Figure 3 compares the environmental performance of the three options. The layout of the graph is the same as in figure 2. The blue columns follow the left vertical axis and indicate the CO2 emission avoided. Leaving aside the data related to the solar system which is of course close to zero, it is interesting to compare the emissions produced by the other two options. The ISCC plant produces 91.70% of the emissions of a conventional combined cycle plant, confirming that the solar system contributed to the reduction in its environmental impact.

The red columns (right vertical axis) indicate the embedded energy of the plant, namely how many MJ have to be invested to produce each kWhe. As before, the relevant comparison is between the ISCC and the NGCC alternatives. The hybrid plant needs 91.63% of the resources required by the fossil fuel facility, completely in line with the previous result.

Figure 3: Environmental Performance of the ISCC Plant in Rabat, Morocco

(Source: Own Production based on [01])

Whilst ISCCs have some way to come to achieve competitiveness on a cost level, the environmental benefits are clear. As ISCCs, and hybridisation in general, gain a larger portion of the CSP market it is likely that new technology innovations and tried methods will lead to improved cost levels not only for hybrid CSP, but for CSP as a whole. 

LIST OF REFERENCES

1 Canedo, M. (*), 2011. Economic and Environmental Assessment of an Integrated Solar Combined Cycle (ISCC). conference Poster, (*) Laboratoire de Bioénergie et Planification Énergétique, Ecole Polytechnique Federale de Lausanne.