**4. Results and discussion**

#### **4.1 Model validation**

Before performing the prediction of the annual thermal and electrical energy output, it is necessary to validate the accuracy of the numerical model. Hence, the comparisons between numerical and experimental results, in terms of the PV electrical energy production, PHE and thermal energy output from the heat pump, are analyzed based on the error analysis model from 01/Nov/2016 to 31/Jan/2017.

$$Error = \left| \frac{T\_{numerical} - \mathbf{T}\_{exp\,critical}}{T\_{numerical}} \right| \tag{27}$$

#### *4.1.1 Electrical energy production from PV array*

**Figure 5** displays the comparison of daily electrical energy output from PV array based on the simulation and test results. It is concluded that the error is up to 14.93% occurred at the termination of the operating phase, the mean error reaches 9.26%. Moreover, the experimental data demonstrated that the total electrical energy production could achieve 1125.89 kWh from 01/Nov/2016 to 31/Jan/2017 (228 days), by contrast, the numerical result exhibits close proximity of value, achieving 1247.51 kWh within a 10% error. This means that the numerical result is in very good agreement with experiment data, which validates the reliability of the numerical model.

#### *4.1.2 Thermal energy output from PHE*

It can be observed from **Figure 6** that the temperature variation between the experimental data and the numerical result has a similar trend. The highest thermal fluid temperature within the PHE reaches 15.75°C on 10/NOV/2016, by comparison, the lowest one is 0.75°C on 25/JAN/2017. And also, the minimum temperature difference was around 3.29% on 31/DEC/2016, the mean one being 9.11%, while the maximum temperature difference is approximately 14.72% on 14/NOV/2016.

**Figure 5.** *Electrical energy output from PV array.*

*Energy, Economic and Environmental (3E) Assessments on Hybrid Renewable Energy... DOI: http://dx.doi.org/10.5772/intechopen.102025*

**Figure 6.** *Thermal energy output from PHE.*

**Figure 7.** *Heat production from ground copper pipe.*

#### *4.1.3 Thermal output from ground copper pipe*

**Figure 7** displayed a similar temperature change tendency between the simulation and test results. Specifically, the temperature of the test could realize up to 14.23°C on 15/JAN/2017 whereas the lowest temperature could reach 0.89°C on 08/NOV/2016. Additionally, the maximum, minimum and average relative errors are 11.33% on 16/DEC/2016, 2.40% on 15/JAN/2017 and 6.36%, as clarified in **Table 1**.

#### *4.1.4 Thermal energy output from the heat pump*

**Figure 8** compared the thermal energy output from the heat pump system, and found that the daily maximum and minimum differences are about 9.30% appeared on 16/JAN/2017 and 5.49% occurred on 05/DEC/2016, respectively. Consequently, the numerical model could be employed to assess the annual thermal and electrical energy output of the hybrid renewable heating system over a year.

**Table 1** illustrated the relative error analysis of PV electrical, thermal, geothermal thermal and heat pump outputs between simulation results and experimental data. It is found that all error values are less than 15% which fulfill the requirement.

#### *Alternative Energies and Efficiency Evaluation*


#### **Table 1.**

*Relative error analysis of PV electrical, thermal, geothermal thermal and heat pump outputs.*

#### **Figure 8.**

*Thermal energy output from the heat pump system.*

#### **4.2 Year-round system performance assessment**

**Figure 9** depicts the monthly power energy production and efficiency from the PV array. It can be concluded that the minimum and the maximum monthly electrical energy generation are around 335.81 kWh with the lowest efficiency (about 14.85%) in December and 1830.35 kWh with the highest efficiency (about 15.9%) in June, respectively. And also, the overall electrical energy obtained from the PV array could reach 11,867 kWh during a year. This means that it not only can meet the power demand of the poultry shed, but also could supply around 43.5% power requirement of the heat pump compressor operating.

Additionally, diminishing the PV surface temperature contributes to increasing the voltage and electrical efficiency. The PHE under the PV array could help to decrease the PV surface temperature resulting in a PV electrical efficiency enhancement. **Figure 10** exhibits the monthly thermal energy output and COP variation of the heat pump unit. Results show that the highest and the lowest monthly thermal energy output could achieve 3848.77 kWh in July and 1610.77 kWh in February, respectively. And also, the overall thermal energy output is about 30210.98 kWh per annum. This means that some capacity of the gas burners would *Energy, Economic and Environmental (3E) Assessments on Hybrid Renewable Energy... DOI: http://dx.doi.org/10.5772/intechopen.102025*

**Figure 9.** *Monthly PV electrical energy production and efficiency.*

**Figure 10.** *Monthly thermal energy output and COP of heat pump system.*

be needed alongside the heat pump to warm the shed sufficiently, especially from December to February.

Furthermore, the highest and lowest PV/T thermal efficiency could reach 28.3% in June and 7.3% in December. When the PV/T operates in conjunction with the geothermal copper pipe array, the COP of the heat pump could achieve up to 5.01 in June, while a minimum COP of 2.17 can be achieved in December.

## **4.3 Economic assessment**

It can be observed from **Figure 11** that the comparison of gas and electricity cost between the current system and PV/T and heat pump system each period. Notably, the overall cost of the PV/T with heat pump system is lower than the gas burners system. To be more specific, the gas cost of the PV/T with heat pump system is approximately £319.74, which is significantly lower than that of the gas burner system (approximately £1083), saving about £763. Similarly, the electrical cost of the PV/T with heat pump system is approximately £128.52, which is lower compared to the gas burner system (approximately £893), saving about £750. Additionally, the payback period is about 5.5 years.

#### **Figure 11.**

*Comparison of gas and electrical cost between gas burners and hybrid renewable heating systems.*
