**4.4 System fabrication**

478 Solar Radiation

The thermocouple wires (Type E) made of different metal alloys (Nickel-Chromium copperconstantan) is joined together by soldering. The number of thermocouples required to generate an output voltage of 15V is required. Knowing the output voltage of one thermocouple (type E) given as 153mv (0.153v), dividing 15 by 0.153 to give 98.04 = 98 junctions. There are six modules with 15 junctions each (Fig 9). These thermocouples were joined together in series to form cascaded thermopile consisting of a number of

The construction of the solar power module was simple and convenient employing modular approach in which the entire system is divided into modules. The design is to generate high voltage, thus the cells are connected in series in the module. The voltage is a function of the cell's physical composition, while the amperage is affected not only by the area of the cell,

**4.3 Construction of thermocouple circuit** 

thermocouples.

Fig. 9. Thermocouple solar panel

but also by the amount and intensity of light falling upon it.

The entire system is divided into modules as shown in Figure 11. Vero board is used as the circuit boards for the solar panel and the charge control system.

Fig. 11. Block diagram of the system

The charge control system uses the LED control charging system to charge a 12v lead Acid battery. An electrical diode, D1 ensures unidirectional voltage flow when battery is under charge (Fig 10). For simplicity of construction and convenience the modular approach of constructing solar energy harvest modalities is used. Photovoltaic conversion provides the highest power density, which makes it the modality of choice to power an embedded system using reasonably small harvesting module.

Fig. 11. Circuit Diagram of the solar power supply

The components of the electrical circuit and ratings are as follows:

D1, D2 = Diode (MA2J728 or MA3x704), Q1, Q2 = FET transistor (IRFZ44), R1 = Resistor =220k, R2 = Resistor = 12k, R3 = Resistor = 2.7k, R4 = Resistor = 4.5k, R5 = Variable Resistor = 1000k, LED (Green/Red), Battery = 12V Rechargeable Lead Acid.

Since the thermocouple array is expected to charge the battery on sunny days when output exceeds the load, but on cloudy days or at night, the load is expected to exceed the array output and drain the battery- Hence the array must be sized to ensure that the balance is positive and the battery is recharged when discharged. The array delivered an average daily output equal to the average daily system load (including all losses) plus approximately 10% to ensure that the battery is recharged.

#### **5. System test result**

#### **5.1 Collector surface temperature**

The daily total solar energy Qt received per unit surface area of the absorber at the location (Ishiagu, South East Nigeria) as evaluated by Bello and Odey (2009) is 747.67 W/m2. The useful components of the global solar radiation at the location are: direct solar radiation qD = 680.67 W/m2, diffuse solar radiation qd = 64.21 W/m2 and ground reflected radiation qr = 2.34 W/m2. The collector heat transfer coefficient between the absorber and cover expressed as the heat loss per unit area of the collector surface per temperature change is 3.06 W/m2 oC. Total absorbed heat energy per unit surface area of absorber qu = 592.43 W/m2

Fig. 11. Circuit Diagram of the solar power supply

to ensure that the battery is recharged.

**5.1 Collector surface temperature** 

**5. System test result** 

LED (Green/Red), Battery = 12V Rechargeable Lead Acid.

heat energy per unit surface area of absorber qu = 592.43 W/m2

The components of the electrical circuit and ratings are as follows:

D1, D2 = Diode (MA2J728 or MA3x704), Q1, Q2 = FET transistor (IRFZ44), R1 = Resistor =220k, R2 = Resistor = 12k, R3 = Resistor = 2.7k, R4 = Resistor = 4.5k, R5 = Variable Resistor = 1000k,

Since the thermocouple array is expected to charge the battery on sunny days when output exceeds the load, but on cloudy days or at night, the load is expected to exceed the array output and drain the battery- Hence the array must be sized to ensure that the balance is positive and the battery is recharged when discharged. The array delivered an average daily output equal to the average daily system load (including all losses) plus approximately 10%

The daily total solar energy Qt received per unit surface area of the absorber at the location (Ishiagu, South East Nigeria) as evaluated by Bello and Odey (2009) is 747.67 W/m2. The useful components of the global solar radiation at the location are: direct solar radiation qD = 680.67 W/m2, diffuse solar radiation qd = 64.21 W/m2 and ground reflected radiation qr = 2.34 W/m2. The collector heat transfer coefficient between the absorber and cover expressed as the heat loss per unit area of the collector surface per temperature change is 3.06 W/m2 oC. Total absorbed Measurements were taken on a clear day without cloud cover and surface temperatures were measured at five different spots every hour. According to measured temperature data, the average daily surface temperature increases with increase in sunshine hour reaching its peak between 1300hr and 1400hr (Fig 12) and then decline. On the average, 10hrs of sunshine hours is available per day, but for useful solar harvest, 8hrs of sunshine may is assumed because of difference in temperature between the collector surface and the ambient. The full sun (peak sun) hour value monitored at the site during raining season and dry season were found to be 4hrs and 5hrs respectively, agreeing with Onojo *et al.,* (2004).

Fig. 12. Average daily temperature in collector

Three surface areas were used for the test as follows 0.6m2, 1.0m2 and 1.5m2. There appeared to be no significant difference in spot temperatures in each of the surfaces per hour (Fig 12), it can be concluded that the surface temperature is independent of surface area. There appeared to be no significant difference in spot temperatures measured in each of the collectors per hour (TAV1, TAV2, TAV3), hence, it can be concluded that the surface temperature is independent of surface area. The average cell surface area used in computation is 1.03 m2 and the total surface area of the module is 6.2 m2.

Material density constitutes to heat retention within the system and hence increases in surface temperature and higher potential difference. The collector compaction test shows that a densely packed material retains more heat and hence increases surface temperature, which obviously will produce higher potential difference.
