# Biomass District Heating Systems Based on Agriculture Residues
## 3 Methodology
#### 5.3.3 Straw  
In the case of using straw as fuel, the process of obtaining the biomass has a different impact in the cost and in the relative effect over the total fuel cost. The transport costs required to perform these tasks are taken into account. It is also important to note that in the case of straw, there are different final geometries of packaging the biomass, and it affects to the final price in each case as it affects to the transport and management. Three different tables (Tables 4-6) [21] are presented with the differential costs for different final geometries of fuel compilation. This procedure can be extrapolated for the evaluation of the costs of other of agriculture biomasses. Step 6. Cost and benefit evaluation  
At the BioDH system level, viability is evaluated through a Cost-Benefit analysis [8]. It involves the analysis of: \begin{table}
\begin{tabular}{c c c} \hline \hline
**Costs Category (Operation)** & **Costs (\(\ell\)/b)** & **Costs Structure (\%)** \\ \hline Bailing & 8.70 & 21.48 \\ Materials & 21.70 & 53.58 \\ Manipulation & 3.60 & 8.89 \\ Storage & 6.50 & 16.05 \\
**Total costs** & **40.50** & **100.00** \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Differential costs of briquetting per ton of briquettes produced [21]. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Spain as Base** & **Correction Factor** & **Sweden as Base** & **Correction Factor** \\ \hline Spain & 1.000 & Sweden & 1.000 \\ France & 1.121 & Austria & 0.985 \\ Italy & 1.169 & Denmark & 1.124 \\ Greece & 0.851 & Finland & 0.979 \\ Portugal & 0.820 & Germany & 1.057 \\ - & - & Norway & 1.245 \\ - & - & Poland & 0.514 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Correction factors used for the extrapolation of the basic costs calculated for Spain and Sweden (data extracted from [20]). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Costs Category (Operation)** & **Costs (\(\ell\)/b)** & **Costs Structure (\%)** \\ \hline Bailing & 1.90 & 17.27 \\ Materials & 1.90 & 17.27 \\ Loading & 1.20 & 10.91 \\ Transportation & 3.00 & 27.27 \\ Manipulation & 1.20 & 10.91 \\ Storage & 1.80 & 16.36 \\
**Total costs** & **11.00** & **100.00** \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Calculation of differential costs of energy use with straw prepared in small square bales [21]. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Costs Category (Operation)** & **Costs (\(\ell\)/b)** & **Costs Structure (\%)** \\ \hline Bailing & 2.30 & 26.44 \\ Materials & 0.50 & 5.75 \\ Loading & 3.10 & 35.63 \\ Transportation & 0.60 & 6.90 \\ Manipulation & 0.80 & 9.20 \\ Storage & 1.40 & 16.09 \\
**Total costs** & **8.70** & **100.00** \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Calculation of differential cost of energy use with straw collected in the form of cylinder-shaped bales is used [21]. _(i) CAPEX._ It includes all the required investments to start up each of the subsystems: biomass thermal power station (\(CAPEX_{TP}\)), distribution network (\(CAPEX_{N}\)) and energy transfer stations (\(CAPEX_{ETS}\)). \[CAPEX_{BioDH}=CAPEX_{TP}+CAPEX_{N}+CAPEX_{ETS} \tag{4}\]  
Thermal plant investment for BioDH systems is in the range of 855 \(\upxi\)/kW to 1453 \(\upxi\)/kW of the total plant capacity [22; 23]. For a power range of 8 MW to 50 MW, higher than those expressed in [22; 23], reduces the capital investment to a much lower range, 200 \(\upxi\)/kW to 250 \(\upxi\)/kW, due to economies of scale. The cost of the distribution network must be evaluated according to its length and specific diameter. The specific pipe diameter for each BioDH network can be calculated using [24]:  
\[d_{a}=0.0486\cdot\ln(D/L_{P})+0.0007 \tag{5}\]  
where \(d_{a}\) is the pipe diameter (m), and \(L_{P}\) the network pipe length (m), together with \(D\), forms \(D/L_{P}\) the linear heat density (GJ/m).