When solar radiation strikes a surface, a portion of it is transmitted or absorbed, while the rest is reflected. Solar wall system absorbs solar radiations with high absorbency panel, and heats the plenum by conduction and convection. When the suction fan is operated, fresh air is introduced to the plenum through the tiny holes on the panel. The air thus absorbs the heat stored in the plenum. The efficiency of energy transformation of solar panel is expressed by the following Eq.1.

П = pm *Cp (T0ut — Tn)/AI (1)

In this equation m* is the mass airflow rate Cp. is the specific heat of air at constant pressure, Tout is the plenum temperature, Tin is the ambient temperature, A is the cross-sectional area of the solar collector in m2 and I is irradiance in W/m2.

Replacing m by AV in Eq.1 we get Eq.2 n = pVsCp(Tou, — Tn)/1 (2)

where Vs means the velocity of air which goes through a hole of the panel and it is expressed the flow rate in m3/sec. The values for air density (p) and specific heat under constant pressure (Cp.) used in our work were p =1.167 kg/m3and Cp=1007J/Kg-k respectively. The efficiency of the solar panel was calculated by using Eq.2, at different airflow rates under no­wind, low-wind and high-wind conditions as mentioned earlier.

1. Experiment

A solar collector, with a corrugated steel absorber sheet (Table1. and Fig.1), with perforations covering 1% of its surface was selected for experimental purposes. Its area was 1m2 with a duct of diameter 0.06m which was connected by a fan used to vent out heated air for outlet temperature (plenum temperature) measurements (see Fig.2). Measuring duct airflow rate, ambient and plenum temperatures, and the solar irradiance monitored the collector performance. For the experimental work, the duct airflow rate was measured with a digital blade anemometer, the temperature conditions were measured with a Type T thermocouple (Omega. co USA).

The primary components of the indoor test facility system included, (a) a solar simulator, (b) an air suction system for drawing air through holes of the absorber plate at different known rates, and (c) an open-ended wind deflector to allow the wind to flow over the absorber plate. A model M11 Kipp and Zonen (Holland made) calibrated pyranometer connected with a high-precision millivoltmeter (see Fig.3) was installed near the collector at a distance of 2m from the artificial irradiance source. An irradiance level of about 300W/m2 was delivered to

the entire test plate by the sun-simulator, which was consisted of an Osram halogen light bulb with highly reflective metal laminate. The irradiance level was uniform over the plate’s test area, excluding the part with in 0.01m of the plate edge. The experiment was designed to measure the efficiency dependent wind conditions under different suction velocities.

As can be seen from the defining equation for efficiency Eq.2, determining the efficiency requires only the measurement of two temperatures. Four thermocouples were thus fixed at different locations on the test plate, so that the average plenum temperature Tp could be measured. The temperature of the approaching wind was measured inside the duct at the top center of the plate. After a steady state was reached, measurements were made for different wind velocities and suction airflow rates.