【文章內(nèi)容簡介】 e two phototransistors covered with a small plate to act as a shield to sunlight, as shown in Fig. 1. Fi g. 1 Alternative solar tracking method When morning arrives, the tracker is in state A from the previous day. The left phototransistor is turned on, causing a signal to turn the motor continuously until the shadow from the plate returns the tracker to state B. As the day slowly progresses, state C is reached shortly, turning on the right phototransistor. The motor turns until state B is reached again, and the cycle continues until the end of the day, or until the minimum detectable light level is reached. The problem with a design like this is that phototransistors have a narrow range of sensitivity, once they have been set up in a circuit under set bias was because of this fact that solar cells themselves were chosen to be the sensing devices. They provide an excellent mechanism in light intensity detection – because they are sensitive to varying light and provide a nearlinear voltage range that can be used to an advantage in determining the present declination or angle to the a 5 result, a simple triangular setup was proposed, with the two solar cells facing opposite directions, as shown in Fig. 2. Fig. 2 Setup of solar reference cells Fig. 3 Solar reference cells at rest position In its rest position, the solar cells both receive an equal amount of sunlight, as the angle of incidence, although not 90 176。 , is equal in both cases as seen in Fig. 3. Fig. 4 Solar reference cells at a significant angle to the sun It can be seen in Fig. 4 that as the sun moves in the sky, assuming that the solar tracker has not yet moved, the angle of incidence of light to the reference panels will cause more light to fall on one cell than the other. This will obviously cause a voltage difference, where the cell that is facing the sun will have higher potential than the other. This phenomenon will result in a detectable signal at each cell, which can be processed by a suitable circuit. III. A PROTOTYPE SOLAR TRACKER The final stage involved coupling the circuitry to the motor and mounting it onto the bracket. The final product is seen plete . It has a Solarex 9W solar array made of polycrystalline silicon mounted on the flanges, which was borrowed from the teach officers. Quite simply having two test subjects carried out testing. The first scenario involved removing the panel from the tracker and laying it in a flat output was connected to a load that would dissipate 9W that would match the panel‘s at 12V 6 corresponds to a current of , so by Ohm‘s law。 a load resistance was calculated as being 16Ω . 15 Ω 50W resistor was the closest value found and was connected to the tracking device still requires power, but a 12V battery that is connected in a charging arrangement with the solar panel supplies it. The voltage across and current through the load was monitored using two separate multimeters, and was recorded every halfhour on a clear day into an Excel spreadsheet. The readings were taken on a span of days that possessed similar conditions including no cloud cover. The readings are shown below in a graph generated by Excel. 7 Fig. 6 Experimental results of power increase for tracked panel It is possible to calculate a percentage increase and an average increase by writing the appropriate calculations in excel. It was found that in this case, the fixed panel provided an average of 39% of its 9W, or , calculated over a 12hour period. By contrast, the tracked solar panel achieved an overall 71% output, or over the same time frame. At the earlier and later hours, the power increase over the fixed panel reached up to 400%. This amounts to an average 30% increase in power simply by maintaining the solar panel as perpendicular as possible to the sun. To ensure that power was not being wasted, the device itself was also monitored for current drawn to power itself. When the device was at rest, an ammeter was placed in series with the battery. The total current at 12V was measured as only 4mA, which corresponded to a power dissipation of 48mW under no load. IV. DISCUSSION A solar tracker was proposed, designed and constructed. The final design was successful, in that it achieved an overall power collection efficiency increase from only 39% for a fixed panel to over 70% for the same panel on the tracking device. In terms of real value, this means that the overall cost of a system can be reduced significantly, considering that much more power can be suppl ied by the solar array coupled to a solar tracking device. By extracting more power from the same solar panel, the cost per watt is decreased, thereby rendering solar pow