I assume you mean a concentrating solar plant by CSP. The combined cycle power plant should be able to approach 60% efficiency (based on higher heating value/gross calorific value) when fired with natural gas and assuming you have reasonable cooling water available. It should have very high (90%+) availability. The CSP plant is highly location, weather, and season dependent and, since you state it will not have storage, will be a highly intermittent source of steam. Candidly, the only redeeming feature of such a plant is its low CO2 output - in all other ways (cost, efficiency, reliability, etc.) it is likely to be poor. The IGCC plant also can approach 60% (again HHV) efficiency on paper but in practice will achieve only 40% at best. Furthermore, the pressurized gasifier will require continuous expert attention to maintain a reasonable availability. The CO2 emissions from the IGCC plant will be more than double those of a natural-gas-fired combined-cycle plant given the combination of the fuel C intensity and the difference in efficiency. However, the fuel should be inexpensive. Quantitative comparisons vary widely, but a consensus view is that power from CSP is more expensive than IGCC which is more expensive than coal which is more expensive than NGCC. However, you appear to only want the heat from CSP, not power, in which case it probably makes more sense if your demand can tolerate the intermittency of supply. Depending on the temperature of the heat you want from CSP, I presume you are aware that there will large quantities of low-grade heat available from the NGCC that is essentially free and not intermittent. 

Thank you for your inputs. Yes, I'm trying to operate on a model where there is a lot of components involved and I can play with it for optimization. The CHP plant models I shortlisted were Combined cycle power plant, IGCC, Fuel cell CHP and CSP combined cycle hybrid. So, my major concern is CSP combined cycle CHP a good model to work with?Or should i go for other plants?

Dear Pru

the storage is a very important factor, especially for isolated rural villages. You can see example on how to optimize in this paper

https://www.researchgate.net/publication/303256411_Discrete_cogeneration_optimization_with_storage_capacity_decision_support_for_dynamic_hybrid_solar_combined_heat_and_power_systems_in_isolated_rural_villages

Article Discrete cogeneration optimization with storage capacity dec...