# Solar Hybrid Micro Gas Turbine Based on Turbocharger
## 2 Design, Operation, and Performance Aspects
### Economic Aspects  
Competitiveness and thus attractiveness of a plant are judged in terms of its economic performance. The economic performance of an installation is best expressed using the levelized electricity cost (LEC). Here, LEC is computed using Equation (1) below, which was derived from taking into account the discussion in the literature [29; 30; 31; 32]. \[LEC=\frac{PI-\sum\limits_{t=1}^{N}\left(\frac{DEP+INT}{(1+r)^{t-0.5}}\cdot TR \right)+\sum\limits_{t=1}^{N}\left(\frac{DPT+INT}{(1+r)^{t-0.5}}\right)+\sum \limits_{t=1}^{N}\left(\frac{OP}{(1+r)^{t-0.5}}\cdot(1-TR)\right)}{\sum \limits_{t=1}^{N}\left(\frac{E}{(1+r)^{t-0.5}}\cdot(1-TR)\right)} \tag{1}\]  
where: _DEP_: Depreciation; _DPT_: Loan Dept; _INT_: Loan Interest; _N_: Plant's Life; _t_: Time; _OP_: Operating Cost; _PI_: Privet Investments; _r_: Discount Rate; _TR_: Tax Rate; E: Energy. This formula has some advantages compared with others (e.g., [30]), because it takes into account accounting factors, such as the investment source type (private and/or loan), and the depreciation and tax rate. Thus, plant economic performance can be determined for a variety of financing cases. In order to apply this formula to compute LEC, economic data of the used components are necessary. They include the cost for acquiring the installation (investment cost) and the cost \begin{table}
\begin{tabular}{c c} \hline
**Parameter** & **Value** \\ \hline Heliostats & \\ \hline Reflectivity & 0.97 \\ Heat interception & 1 \\ Shading–Blocking & 0.98 \\ Aperture [m\({}^{2}\)] & 64 \\ \hline Receiver & \\ \hline Absorptance & 0.95 \\ Optical efficiency & 0.96 \\ Emissivity & 0.05 \\ \hline Engine Components & \\ \hline Ducts pressure drop & 0.02 \\ Receiver pressure drop & 0.02 \\ Burner pressure drop & 0.02 \\ Shaft/Generator efficiency & 0.98 \\ TIT [\({}^{\circ}\)C] & (a) 400, (b) 600, (c) 800 \\ \hline Hybrid Setup & \\ \hline Fuel Lower Heating Value [M]/kg] & 42.6 \\ CO\({}_{2}\) emissions [kgCO\({}_{2}\)/M]\({}_{\text{fuel}}\) & 0.07315 \\ \hline \end{tabular}
\end{table} 
Table 2: Added components design specifications. needed for operation (operational cost). Data for investment and operational cost were drawn from publications of international organizations (e.g., IEA--International Energy Agency, NREL--National Renewable Energy Laboratory, EIA--Energy Information Administration) [15; 16; 25], as presented by [PERSON] et al. [33], as well as communication with manufacturers. Annual operational cost equal to 2% of investment cost for turbomachinery components were considered, as proposed in the literature [25]. For components that are already mass produced and used in existing applications (e.g., turbomachinery, generator, etc. ), the investment and operational costs are not expected to significantly change over time. On the other hand, solar components are not yet mass produced, and thus the advancement and penetration of solar thermal technology is expected to lead to lower costs. This applies in particular to the case of air type receiver, which is today in a rather experimental stage, while mirrors are already used in commercial solar Rankine plants, with water/steam or molten salts type receiver. In the particular application examined here, the relative low pressure and temperature at the receiver would permit the selection of cost values lower than the ones used for this component, which are current figures and obtained for receivers with pressure input from 10-bar and above. Fuel cost can be the dominant factor to determine if a plant based on renewable energy sources is more profitable compared with a conventional one, based on fossil fuel. As a result of a variety of reasons, fuel price can change dramatically over time. For example, in the period 2012-2017, diesel price has fluctuated between 0.98 $/gallon and 3.3 $/gallon [34]. Furthermore, the fuel cost can significantly rise for remote locations because of the added transport cost. In this study, carbon emissions cost is also taken into account.