*Solar Energy in Industrial Processes DOI: http://dx.doi.org/10.5772/intechopen.97008*

**Figure 9.**

*Series of* n *collectors.*

**Figure 10.** *Structure of a solar collector network with 16 units.*

Several solar collectors, *Nc*, make up the structure of the solar collector network as show Eq. (7)

$$N\_c = N\_p N\_s \tag{7}$$

*Ns* is the number of series collectors and *Np* is the number of parallel branches.

In **Figure 10** the arrangement of a network of 16 collectors in a 4 x 4 arrangement (parallel series) is displayed. Generalising the arrangement for any collector network it can be denoted as *mxn*, where the lines in parallel to be placed (*m*) and the number of collectors connected in series (*n*) are shown. In this way, it is possible to meet the temperature level and the thermal load required for the process, of these, the first is achieved by connecting n collectors in series and the second is achieved through the determination of branches given by Eq. (6).

The absorber surface of the solar collector network is calculated from Eq. (8)

$$A\_{\rm SCN} = L\rmWN\_c \tag{8}$$

Where *ASCN* is the area of the solar collector network (m<sup>2</sup> ), *Nc* is the number of collectors, *L* is the length (m), and *W* is the width of the solar collector (m).

Then we proceed to determine the cost of the collector network, *CSCN* (USD), using Eq. (9) reported in [17]:

$$\mathbf{C\_{SCN}} = \mathbf{N\_c} \left[ \chi\_0 + \frac{\mathbf{A\_l} N\_t}{\pi} \left( \chi\_1 d + \chi\_2 + \frac{\chi\_3}{d} \right) + \mathbf{WL} \chi\_4 + \chi\_{10} \frac{\dot{m} \mathbf{L} \mu}{\pi \rho d^4} \right] + \chi\_5 \left( \frac{\dot{m} \mathbf{H}\_b}{e\_{fl}} \right) \tag{9}$$

Where *Nc* is the number of collectors, *At* is the lateral area of the tube, *Nt* is the number of tubes, *d* is the internal diameter of a tube, *W* and *L* are the width and length of a solar collector, *Hb* and *eff* are the load and pump efficiency, respectively. The *γ<sup>i</sup>* terms are as follows: 6,768.82 (USD); 202,822.47 (USD/m<sup>3</sup> ); �1,576.96 (USD/ m2 ); 32,576 (USD/m); 994.1 (USD/m<sup>2</sup> ); 3.52 (USD h m�<sup>1</sup> kg�<sup>1</sup> ); 0.14 (h2 /m<sup>5</sup> ); 0.45 (h/m<sup>2</sup> ); 1 dimensionless, 0.54 (m) and 261.61 (USD m h2 /kg), respectively.

network are the operating conditions of the process (temperature and required thermal load), the environmental parameters (irradiance and ambient temperature), geometric dimensions and characteristics of the flate-plate solar materials, the properties of the working fluid, and the network operating conditions (flow and

<sup>Δ</sup>*<sup>T</sup>* <sup>¼</sup> *<sup>T</sup><sup>n</sup>*

outlet temperature of one minus to the *n-th* element (°C) (**Figure 9**). The number of branches or lines in parallel is calculated by Eq. (6)

The minimum number of collectors connected in series can be calculated considering that the minimum difference between the outlet temperature of the fluid from the collector,*T0* (°C), and the temperature of the fluid at the entrance to the collector,*Ti* (°C), is equal to or greater than 1 °C. Generalising this difference for

Where *n* refers to outlet temperature of the *n-th* element and *n-1* refers to the

*Np* <sup>¼</sup> *Qi*

*Qi* is the thermal load provided by a series of *n* collectors connected in series (kW) and *Q* is the total thermal load (kW) required by the process, whether to

*<sup>o</sup>* � *<sup>T</sup><sup>n</sup>*�<sup>1</sup> *<sup>o</sup>* (5)

*<sup>Q</sup>* (6)

feed temperature).

**Figure 7.**

**Figure 8.**

*Annualised total cost from heat recovery network against ΔTmin.*

*Solar Cells - Theory, Materials and Recent Advances*

any collector or series have Eq. (5)

*Irradiance throughout a year for clear sky days.*

cover partially or totally.

**464**

For the estimation of the costs of the solar collector network, they can also be annualised, a 25-year amortisation period of the investment is considered with fixed interest of 5%, as shown in Eq. (10)

$$\mathbf{C}\_{\text{TA SCN}} = f\_{\mathcal{A}} \mathbf{C}\_{\text{SCN}} \tag{10}$$

In **Figure 11** the annualised cost of the thermal storage system is shown as a function of the accumulation time, costs increase the longer the storage time. **Figure 11** shows the annualised cost of the thermal storage system for a load of 339,812 kW, which corresponds to the total heating service. If we assume that this thermal load is stored for 23 hours, the cost would be 8669.73 USD/year, compared

The total cost of the solar thermal installation (USD) includes: the total cost of the solar collector network and the total cost of the thermal storage system that represents around 80% of the total, the rest corresponds to the control and pumping system. The costs are also annualised at a fixed interest rate (5%) for a repayment

To evaluate the total cost of the integrated system, the costs of each of the components must first be updated: the heat recovery network, the solar field, and the thermal storage system. In this case the values of the equations are calculated for the year 2010. To obtain the updated cost values, the costs obtained must be multiplied by the value of the ratio that exists between the cost index for 2019 (*IC* 2019) and the 2010 cost index

> *IA* <sup>¼</sup> *IC* <sup>2019</sup> *IC* <sup>2010</sup>

One method of comparing the magnitude of a dollar equity investment with a future stream of income is to convert the cost of capital into a future annual charge. The calculation is done with Eq. (15) [15], where *i* is the annual interest and *n* is the number of years of useful life of a piece of equipment or of a network of equipment or process in general. According to IRENA, solar plants have a useful life of 25 years.

*<sup>f</sup> <sup>A</sup>* <sup>¼</sup> *CT* <sup>∗</sup> *<sup>i</sup>* <sup>∗</sup> ð Þ <sup>1</sup> <sup>þ</sup> *<sup>i</sup> <sup>n</sup>*

ð Þ <sup>1</sup> <sup>þ</sup> *<sup>i</sup> <sup>n</sup>* � <sup>1</sup>

(15)

(14)

to the cost of the solar collector network, this represents 32%. To define the operation and size of the storage system, the process conditions and the costs

*Annualised cost of the thermal storage system as a function of accumulation time.*

period of 25 years and the costs are obtained per year for that period.

(*IC* 2010), which are 607.5 and 550.8, respectively [15] as seen in Eq. (14).

associated with them must be considered.

*2.6.1 Cost evaluation*

**467**

**Figure 11.**

*Solar Energy in Industrial Processes*

*DOI: http://dx.doi.org/10.5772/intechopen.97008*

**2.6 Total cost of the solar thermal installation**

**Table 3** shows the arrangement area, and costs of the flat solar collector network where two scenarios are analysed. In scenario 1, it is considered that solar thermal energy supplies the entire thermal load required for the process at a temperature of 101 °C. In scenario two, a limitation of 50% is considered in the area available for the installation of the solar collector network in the plant. The first scenario would be the most desirable where it seeks to substitute the use of fossil fuels in a profitable way. In this scenario, it is also considered that there are no restrictions on available area or capital investment. Scenario 2 has a lower investment, however, there are still emissions to the environment.

### **2.5 Thermal storage system**

The cost of the thermal storage system represents 30% of the cost of the solar thermal installation [17] and its operation is essential to store heat, also to dampen fluctuations in environmental variability, and increase the solar fraction of the process, when there is a gap between energy production and demand.

To determine the size of the thermal storage system, *VTS* (m3 ), we have Eq. (11) [18]:

$$V\_{\rm TS} = \frac{\text{3600 Q}\_{\rm TS} \, t}{\text{C}\_{\rm p} \Delta T\_{\rm TS} \, \rho \, \text{eff}\_{\rm TS}} \tag{11}$$

In Eq. (11), *QTS* is the total heat load to be stored in the day (kW), *t* is the storage time of the system (h), *Cp* is the heat capacity of the working fluid (kJ/kg °C) and *ρ* is the density of the thermal fluid (kg/m<sup>3</sup> ), in this case water, *ΔT*TS and *eff*TS are the temperature variation of the thermal storage system (°C) and its efficiency (dimensionless).

The size, storage time and cost of the storage system is conditioned by the sizing of the collector network and the operation of the solar thermal device. Next, Eq. (12) used to determine the cost of storage, *CTS* (USD) [18].

$$C\_{\rm TS} = \textbf{5800} + \textbf{1600} \ V\_{\rm TS} \,\text{^{0.7}} \tag{12}$$

The cost of the thermal storage system is also annualised with an interest of 5% in a period of 25 years, this function is by Eq. (13) where the cost of the thermal storage system is multiplied by the annualisation factor, *fA*.

$$\mathbf{C\_{A\ T S}} = f\_{\ A} \mathbf{C\_{T S}} \tag{13}$$


**Table 3.**

*Results of the design of the solar collector network for different operating conditions.*

*Solar Energy in Industrial Processes DOI: http://dx.doi.org/10.5772/intechopen.97008*

**Figure 11.**

For the estimation of the costs of the solar collector network, they can also be annualised, a 25-year amortisation period of the investment is considered with fixed

**Table 3** shows the arrangement area, and costs of the flat solar collector network where two scenarios are analysed. In scenario 1, it is considered that solar thermal energy supplies the entire thermal load required for the process at a temperature of 101 °C. In scenario two, a limitation of 50% is considered in the area available for the installation of the solar collector network in the plant. The first scenario would be the most desirable where it seeks to substitute the use of fossil fuels in a profitable way. In this scenario, it is also considered that there are no restrictions on available area or capital investment. Scenario 2 has a lower investment, however,

The cost of the thermal storage system represents 30% of the cost of the solar thermal installation [17] and its operation is essential to store heat, also to dampen fluctuations in environmental variability, and increase the solar fraction of the

*VTS* <sup>¼</sup> <sup>3600</sup> *QTS <sup>t</sup>*

temperature variation of the thermal storage system (°C) and its efficiency

of the collector network and the operation of the solar thermal device. Next,

*CTS* ¼ 5800 þ 1600 *VTS*

The cost of the thermal storage system is also annualised with an interest of 5% in a period of 25 years, this function is by Eq. (13) where the cost of the thermal

> **ASCN (m<sup>2</sup> )**

339.81 101.20 23x29 1293.98 1 5 367,412.97 26,068.85 169.91 101.20 12x29 675.12 0.5 5 204,448.15 14,506.10

Eq. (12) used to determine the cost of storage, *CTS* (USD) [18].

storage system is multiplied by the annualisation factor, *fA*.

**Solar collector network array**

*Results of the design of the solar collector network for different operating conditions.*

*Cp*Δ*TTS ρ eff TS*

In Eq. (11), *QTS* is the total heat load to be stored in the day (kW), *t* is the storage time of the system (h), *Cp* is the heat capacity of the working fluid (kJ/kg °C) and *ρ*

The size, storage time and cost of the storage system is conditioned by the sizing

process, when there is a gap between energy production and demand. To determine the size of the thermal storage system, *VTS* (m3

*CTA SCN* ¼ *f <sup>A</sup>CSCN* (10)

), we have

), in this case water, *ΔT*TS and *eff*TS are the

*CA TS* ¼ *f <sup>A</sup> CTS* (13)

**f Supply period (h)**

<sup>0</sup>*:*<sup>7</sup> (12)

**CSCN (USD)**

**CTA SCN (USD/y)**

(11)

interest of 5%, as shown in Eq. (10)

*Solar Cells - Theory, Materials and Recent Advances*

there are still emissions to the environment.

is the density of the thermal fluid (kg/m<sup>3</sup>

**Temperature level (°C)**

**2.5 Thermal storage system**

Eq. (11) [18]:

(dimensionless).

**Heat load to supply (kW)**

**Table 3.**

**466**

*Annualised cost of the thermal storage system as a function of accumulation time.*

In **Figure 11** the annualised cost of the thermal storage system is shown as a function of the accumulation time, costs increase the longer the storage time. **Figure 11** shows the annualised cost of the thermal storage system for a load of 339,812 kW, which corresponds to the total heating service. If we assume that this thermal load is stored for 23 hours, the cost would be 8669.73 USD/year, compared to the cost of the solar collector network, this represents 32%. To define the operation and size of the storage system, the process conditions and the costs associated with them must be considered.

#### **2.6 Total cost of the solar thermal installation**

The total cost of the solar thermal installation (USD) includes: the total cost of the solar collector network and the total cost of the thermal storage system that represents around 80% of the total, the rest corresponds to the control and pumping system. The costs are also annualised at a fixed interest rate (5%) for a repayment period of 25 years and the costs are obtained per year for that period.

#### *2.6.1 Cost evaluation*

To evaluate the total cost of the integrated system, the costs of each of the components must first be updated: the heat recovery network, the solar field, and the thermal storage system. In this case the values of the equations are calculated for the year 2010. To obtain the updated cost values, the costs obtained must be multiplied by the value of the ratio that exists between the cost index for 2019 (*IC* 2019) and the 2010 cost index (*IC* 2010), which are 607.5 and 550.8, respectively [15] as seen in Eq. (14).

$$I\_A = \frac{I\_{C\ 2019}}{I\_{C\ 2010}}\tag{14}$$

One method of comparing the magnitude of a dollar equity investment with a future stream of income is to convert the cost of capital into a future annual charge. The calculation is done with Eq. (15) [15], where *i* is the annual interest and *n* is the number of years of useful life of a piece of equipment or of a network of equipment or process in general. According to IRENA, solar plants have a useful life of 25 years.

$$f\_A = C\_T \* \left[ \frac{i \* \left(\mathbf{1} + i\right)^n}{\left(\mathbf{1} + i\right)^n - \mathbf{1}} \right] \tag{15}$$

#### *2.6.2 Environmental impact assessment*

Currently, solar thermal technology is competitive against those that operate with fossil fuels, however, the negative environmental impact generated by these energy sources is global and tangible. One of the most well-known parameters is the quantification of CO2 emissions as greenhouse gas, however, they are not the only gases emitted, in addition, there are other no less important parameters that are not considered. In this study, only the tons of CO2 that are ceased to be emitted into the atmosphere are quantified when integrating solar thermal energy into the process. The factor of 0.203 kg CO2/kWh is considered for fixed combustion equipment that works with natural gas as fuel, this data is reported for the European Union [19].

**4. Chemical vapour deposition as a route to improve solar technology**

Other solar technology that is heading the solar integration to industry in a big part of world, are the photovoltaic solar panels. Photovoltaics (PV) implies the direct conversion of sunlight into electricity by mean of semiconducting materials with a photovoltaic effect. Solar panels are widely used because its property of magnify the inlet micro-power, by the relatively constant production of electricity and by the possibility to use the stored electrical energy even in the absence of sunlight. Each solar panel is made up of a multitude of solar cells which manufacturing is, in this moment, in a high-tech period (third generation) of research (i. e. Dye-sensitised solar cells, DSSC, Perovskite solar cells, PVSC, Polymer hetero-junction solar cells, PSC, among others) [4]. Function, materials, characteristics, power-conversion-efficiency of solar cells are widely described in meticulous reviews and papers [4, 22–23]. The aim in this paragraph is to display the benefits that use of Chemical Vapour Deposition, CVD, has implied to improve solar cells performance and to present the novelties in evacuated solar tubes.

Among the most used thin film deposition processes to manufacture solar cells, are: evaporation, sputtering technique and chemical vapour deposition (CVD), with some variants in each technique. Briefly, they can be described as follows [24]: Evaporation. The source material is evaporated in vacuum, this lets vapour particles to travel until the substrate, then, they condense to a solid state. Unfortunately, could occur that the different components of an alloy vaporise at different speeds, which will cause the composition of the deposited layer to be different from

Sputtering deposition or Physical Vapour Deposition. The source materials are sputtered by the hitting of high energy ions in an oxidising atmosphere and depos-

Chemical Vapour Deposition (CVD). The CVD technique consists of the reaction of a gas mixture inside a vacuum chamber followed by diffusion of reactants to a heated substrate to produce a material in the form of a thin layer. A useful variant is the reaction of metal–organic precursors (MO-CVD) because these ones improve

Using CVD and PVD techniques give added value to solar cells with not too high costs, thanks to these techniques the efficiency of solar cells has increased from 10% in the 70ies to 20% today, since the different thin films that can be deposited perform various functions such as: antireflection, passivation layers, thickening of

It is important to mention that exists an innovative report in literature about the use of CVD technique to deposite selective coating in evacuated solar tubes. The novel absorber layers have a base of carbon nanotube sheets that have showed their capability to converting solar radiation into electricity and heat [25], this is a

the absorbent layer, among others that have not yet been explored [24].

The proposed methodology allows integrating solar thermal energy, in a

In the event of any restriction such as an available space of 50% respect scenario 1 (scenario 2), cost savings can be up to 12% during the two hours that the thermal load can be supplied directly, with a payback time of the solar device of 2.61 years, eliminating completely the use of thermal storage. The reduction of the requirement

profitable way, and replace, totally, the use of fossil fuels (scenario 1).

of hot utility was 80.62% being 19.40% by integration from solar energy.

promising result in increasing the efficiency of evacuated tubes.

ited on a heated substrate, following the growth of thin films.

the original composition.

*Solar Energy in Industrial Processes*

*DOI: http://dx.doi.org/10.5772/intechopen.97008*

the efficiency of solar cells.

**5. Conclusions**

**469**
