# Techno-Economic Assessment of an Innovative Small-Scale Solar-Biomass Hybrid Power Plant
## 2 Materials and Methods  
### Plant Location Characterization  
The development of the feasibility analysis for the hybrid plant under study required the characterization of both the available solar resources and the biomass production. However, these two parameters are strongly dependent on the selected plant location. Therefore, the decision made regarding the chosen location for this study is justified below. While selecting a location for a conventional power plant is always a critical decision, the complexity of this decision increases in the case of a CSP-biomass hybrid power plant. This added complexity arises from the need for high availability of both of the two primary energy sources used for electricity generation. In other words, in the case of the plant under study, high levels of both annual irradiation and biomass production had to be ensured. For this reason, the region of Andalusia (southern Spain) was selected as an optimal location for a plant of this type. From the perspective of solar resources (Figure 1), the most attractive areas in Andalusia are the Guadalquivir Valley (western Andalusia) and the province of Almeria (eastern Andalusia), both of which have annual direct normal irradiation values exceeding 1900 kWh/m\({}^{2}\). Figure 1: Average daily global horizontal irradiation (kWh/m\({}^{2}\)) [28]. On the other hand, Andalusia is a region with a high capacity for biomass generation with an estimated annual production of 20.1 million tons, encompassing sources such as agriculture, forestry, industry, energy crops, and urban and industrial waste. However, the technical characterization of the hybrid plant required the selection of a specific type of biomass, as this aspect greatly influences the design of critical components such as biomass boilers. Agricultural biomass represents 33% of the total energy potential of biomass produced in Andalusia, with olive crop residues (2.5 million tons/year) being particularly significant. However, due to its lower chlorine content, which allows for higher working temperatures in the boilers, the chosen biomass type corresponded to forest residues. This type, consisting of residues from the maintenance (pruning and cutting) of forest stands mainly composed of pine (pinus), eucalyptus (eucalyptus), and oak (quercus), has an annual production of 1.3 million tons, with the province of Huelva (western Andalusia) contributing 50% of it (Figure 2). The combined analysis of available solar resources and biomass led to the conclusion that the western region of Andalusia combines high levels of both resources. For this reason, a site corresponding to the latitude 37.25\({}^{\circ}\) north and longitude 6.50\({}^{\circ}\) west was chosen as the hypothetical plant location. Once the exact location of the hybrid plant under study was determined, a typical design year was developed based on the information available in the NSRDB (NREL) [30; 31], which provides representative values of various meteorological variables. Among these variables, direct normal irradiance (DNI) is worth noting, and its annual evolution is shown in Figure 3. The typical design year had a resolution of 10 min, as can be observed in Figure 4, which displays the temporal evolution of DNI for the four days corresponding to the two equinoxes and the two solstices. Lastly, the typical design year revealed an annual direct normal irradiation of 2150 kWh/m\({}^{2}\) with an uncertainty of less than 10%, making it highly suitable for the implementation of a CSP plant. Figure 3: Direct normal irradiance (DNI, W/m\({}^{2}\)) of the design year. Figure 2: Forest biomass production in Andalusia (green: pinus, orange: eucalyptus, brown: quercus) [29]. Regarding the impact of the hybrid plant's location on the availability of forest biomass, it is worth noting that within a radius of 25 km, a production of 146 kton/year was quantified.