# Techno-Economic Assessment of an Innovative Small-Scale Solar-Biomass Hybrid Power Plant
## 2 Materials and Methods
### Technical Characterization
Additionally, this compensates the limitation of the maximum allowable temperature of the synthetic oil employed as heat transfer fluid in current parabolic trough solar power plants. One disadvantage of series hybridization is that the biomass boiler and the solar steam generator must operate simultaneously, limiting the operating time of the hybrid plant and linking its operation to the availability of solar radiation. This does not improve the dispatchability of the energy supplied to the electrical distribution grid and negatively affects the profitability of the plant. * Although parallel hybridization designs do not improve the efficiency of the hybrid plant compared to conventional parabolic trough solar plants, this configuration allows the hybrid plant to operate during periods of null or low solar radiation [36]. This improvement has a very positive influence on the dispatchability of the electrical supply, decoupling it from the random nature of solar resources. Additionally, the increase in operating hours of this configuration has a positive impact on the profitability of the plant. While initially considering only the possibility of choosing between series or parallel hybridization between the solar steam generator and the biomass boiler, a more complex configuration was ultimately adopted, consisting of a mixed series/parallel hybridization (Figure 5). It can be observed that the SSG was supported by a biomass boiler in parallel (Boiler 2). In this way, Boiler 2 compensated for fluctuations in solar resource availability. Additionally, an additional biomass boiler (Boiler 1) was proposed in the series with the \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Value** & **Units** \\ \hline Aperture width & 5.77 & m \\ Aperture area & 817.5 & m\({}^{2}\) \\ Focal length & 1.71 & m \\ Absorber radius & 3.5 & cm \\ Concentration factor & 82.43 & - \\ Peak optical performance & 0.73 & - \\ Fouling factor & 0.90 & - \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Main characteristics of the of the parabolic trough collectors. SSG and Boiler 2 to improve the quality of the generated steam. The combustion products used in the superheater of Boiler 1 came from a furnace, which needed to be cooled. For this reason, the furnace of Boiler 1 also acted as an evaporator located in parallel with the evaporators of the SSG and Boiler 2. Finally, the thermal energy from the combustion products at the outlet of the superheater of Boiler 1 was utilized in an economizer located upstream of the SSG and Boiler 2. This achieved higher process efficiency by reducing the stack temperature of the flue gases in Boiler 1. The proposed configuration, although more complex than traditional hybridizations, simultaneously allowed for control of the dispatchability of the power plant and for the improvement of the live steam parameters, resulting in improved thermal performance. Furthermore, the proposed hybridization scheme enabled a significant increase in the operating hours of the hybrid plant compared to a conventional CSP plant, without the need for expensive thermal energy storage systems. Lastly, compared to conventional biomass plants, the proposed hybrid plant reduced biomass consumption, thereby reducing its global carbon footprint. Although the present study did not consider it, in the future, the possibility of extending the hybridization to include biomass treatment will be evaluated, for instance, through the use of solar-based drying technologies as proposed by [PERSON] et al. [37]. The following economic analysis took into account different designs of CSP-biomass hybrid power plants, all based on the previously described concept of mixed hybridization. The various designs considered variations in the size of the solar field, characterized by the Solar Multiple (SM); as well as the thermal power of Boiler 2, characterized by the Biomass Fill Fraction (BFF).