*4.3.1 Overview of photo thermal energy production*

Up to date, the primary energy supplied for human needs comes from fossil and nuclear resources. These can be harmful to environment because they cause global warning, ozone layer depletion, biosphere and geosphere destruction, and ecological devastation [86]. These drawbacks have geared the attention towards cleaner energy. Solar energy is one of the most promising amongst them not only because its exploitation can fulfill the entire world demand in energy, but more importantly it is one of the cleanest source or energy [87].

**145**

*Nanocomposite and Nanofluids: Towards a Sustainable Carbon Capture, Utilization, and Storage*

*Silicated-gel formed from Si-NP and polyvinyl alcohol without (a) porous medium and (b) in a porous* 

Solar thermal energy consists in transforming photons into heat, which is collected and distributed by the means of devices called solar collectors [88]. A solar system usually has at least three components including the solar collector, a heat

Solar collectors use working fluids exposed to the solar irradiation. One of the most attractive candidates working fluid is water, given its price, its availability, and its eco-friendliness. The optimal temperature that can be obtained from a solar system depends on the type of solar collectors, which include flate-plate, parabolic

The efficiency of a solar thermal systems is strongly related to the thermal efficiency of the working fluid, which is the ratio of useful energy effectively transferred. Ideal working fluids should exhibit peculiar thermophysical properties such as low viscosity, high thermal conductivity and high specific heat capacity, in addition to chemical stability [91]. The interest of MO-NPs for solar applications lies on their ability to enhance of the properties, which results in a significant improvement of the outlet temperature and the net power produced within a solar thermal system.

The literature reports that MO nanofluids have a higher thermal conductivity than that water taken alone [92]. The replacement of water as Heat Transfer Fluid (HTF) by a SiO2-water based nanofluid has demonstrated the ability to enhance the performance of a FP collector through the reduction of the viscosity, the enhancement of the specific heat capacity and the rise of the temperature of the HTF at the

exchanger, and a thermal storage system (**Figure 16**).

*Schematic representation of a thermal solar system for water heating applications.*

through and parabolic dish collectors [89, 90].

outlet temperature of the solar system [93].

*4.3.2 Relevance of MO-NPs in solar thermal systems*

*DOI: http://dx.doi.org/10.5772/intechopen.95838*

**Figure 15.**

*medium.*

**Figure 16.**

**Figure 14.** *Conceptual enhancement of CO2 sequestration by Si-NF injection.*

*Nanocomposite and Nanofluids: Towards a Sustainable Carbon Capture, Utilization, and Storage DOI: http://dx.doi.org/10.5772/intechopen.95838*

#### **Figure 15.**

*Advances in Microfluidics and Nanofluids*

Mineral trapping, which is the slowest of the processes, is the final phase. It results from the geochemical reactions of carbonic acid (H2CO3) and the native minerals of the formation. This trapping mechanism is dependent on the rock minerals, the pressure of the gas, temperature and porosity of the host formation [85]. However, if mineral trapping is hastened, it may weaken the cap rock and the overlying formation causing a serious leak in CO2. From above, it appears that the extent to which the CO2 reacts with the formation water (dominated by its solubility) will vary according to factors such as pressure, temperature, the solubility of CO2, the fluid and fluid/rock chemistry. The selection of a proper MO-NF could enhance the

trapping mechanisms, and ultimately ensure an efficient CO2 sequestration. This is potentially achieved by injecting a nanofluid that buffers the acidity within the host formation (**Figure 14b**), but more importantly will yield a gel-like material (**Figure 14a**), denser than the resident fluid in the host formation.

Increasing the load in Si-NP yields a rigid gel (**Figure 15**).

temperature, and pressure) alter the gel formation.

*4.3.1 Overview of photo thermal energy production*

it is one of the cleanest source or energy [87].

*Conceptual enhancement of CO2 sequestration by Si-NF injection.*

**4.3 Renewable energy production**

In this study, it was found that formulating a nanofluid from Si-NP and polyvinyl alcohol under CO2 bubbling would lead to the formation of silicated gels.

The results suggest that condensation of SiO2-NF depends rather on the load in Si-NP than the concentration in PVOH. However, further investigations are required to understand the extent to which the host formation-fluid chemistry alters the solubility of CO2, and the host formation parameters (fluid chemistry,

Up to date, the primary energy supplied for human needs comes from fossil and nuclear resources. These can be harmful to environment because they cause global warning, ozone layer depletion, biosphere and geosphere destruction, and ecological devastation [86]. These drawbacks have geared the attention towards cleaner energy. Solar energy is one of the most promising amongst them not only because its exploitation can fulfill the entire world demand in energy, but more importantly

**144**

**Figure 14.**

*Silicated-gel formed from Si-NP and polyvinyl alcohol without (a) porous medium and (b) in a porous medium.*

**Figure 16.** *Schematic representation of a thermal solar system for water heating applications.*

Solar thermal energy consists in transforming photons into heat, which is collected and distributed by the means of devices called solar collectors [88]. A solar system usually has at least three components including the solar collector, a heat exchanger, and a thermal storage system (**Figure 16**).

Solar collectors use working fluids exposed to the solar irradiation. One of the most attractive candidates working fluid is water, given its price, its availability, and its eco-friendliness. The optimal temperature that can be obtained from a solar system depends on the type of solar collectors, which include flate-plate, parabolic through and parabolic dish collectors [89, 90].

#### *4.3.2 Relevance of MO-NPs in solar thermal systems*

The efficiency of a solar thermal systems is strongly related to the thermal efficiency of the working fluid, which is the ratio of useful energy effectively transferred. Ideal working fluids should exhibit peculiar thermophysical properties such as low viscosity, high thermal conductivity and high specific heat capacity, in addition to chemical stability [91]. The interest of MO-NPs for solar applications lies on their ability to enhance of the properties, which results in a significant improvement of the outlet temperature and the net power produced within a solar thermal system.

The literature reports that MO nanofluids have a higher thermal conductivity than that water taken alone [92]. The replacement of water as Heat Transfer Fluid (HTF) by a SiO2-water based nanofluid has demonstrated the ability to enhance the performance of a FP collector through the reduction of the viscosity, the enhancement of the specific heat capacity and the rise of the temperature of the HTF at the outlet temperature of the solar system [93].

A theoretical model assessing the performance of a solar thermal system using Al2O3-water based nanofluid as Direct Absorber Solar Collector (DASC) has shown an increase of 10% of the collector efficiency compared to water-based flat plate solar collectors operating in the same conditions [94]. However, the optical performance of MO-NF as DASC depends of the volume fraction of MO-NPs [95]. MO-NP can also be associated with photovoltaic devices within hybrid Photovoltaic Thermal (PV/T) systems.

In such configurations, the electrical and thermal energy are simultaneously generated by a photovoltaic module and the working fluid, respectively [96]. Furthermore, nanofluids, exhibiting magnetic properties, offer the possibility to increase the thermal conductivity of a working fluid upon the application of a magnetic field [97, 98]. Nano ferrofluids, standing amongst, were found to improve significantly the efficiency of the photothermal or PV/T systems [99].

However, the major challenge with such types of nanofluids is the formulation of stable working fluid. This is so because nano ferrofluids have the propensity either to agglomerate in solution [100] or to suffer from chemical instability [101]. The combination of Fe3O4 with other MO-NP in composite materials usually allows to overcome those limitations. Therefore, exploration of the thermophysical features of composite MO nanofluids is an interesting direction aiming at the optimization of solar thermal systems.
