Heat island effect of solar cell modules
In the design process of solar LED lighting systems, monolithic solar cells are generally not used, and solar cell modules are used in practice. A solar cell module is composed of multiple solar cells to achieve a desired voltage value. During the use of a solar cell module, if a single solar cell is shaded, such as leaves, bird droppings, etc., the shaded solar cell will be heated and damaged under strong sunlight, thus causing damage to the entire solar cell module. This is the so-called heat island effect. In order to prevent the heat island effect, the solar cells are generally placed obliquely so that leaves and the like cannot be attached, and bird-proof needles are installed on the solar cell modules.
In general, when calculating the power generation of solar cells, it is obtained on the premise that the solar cell square is completely free of shadows. Therefore, if the solar cell cannot be directly illuminated by sunlight, only scattered light is used to generate electricity, and the power generation at this time is about 10%~20% less than that without shadow. In this case, the theoretical calculation value should be corrected. Usually, when there are objects such as buildings and mountains around the solar cell array, after the sun comes out, there will be shadows around the buildings and mountains, so try to avoid shadows when choosing a place to install the solar cell array. If it is impossible to avoid it, it should also be solved from the wiring method of the solar cell, so that the influence of the shadow on the power generation is minimized. In addition, if the solar cell array is placed in front and back, the shadow of the front solar cell array will affect the power generation of the rear solar cell array after the distance between the rear solar cell array and the front solar cell array is close. If there is a bamboo pole with height L1, the shadow length in the north-south direction is L2, the sun height (elevation angle) is A, and when the azimuth angle is B, assuming that the shadow magnification is R, then
R=L2/L1=cotA × cosB
The above formula should be calculated on the day of the winter solstice, because that day has the longest shadow. For example, the height of the upper edge of the solar cell array is h1, and the height of the lower edge is h2; then the distance between the arrays is
When the latitude is higher, the distance between the solar cell arrays should be increased. For the square array with anti-snow measures, the inclination angle is large, so the height of the solar cell square is increased. In order to avoid the influence of shadows, the distance between the solar cell squares is correspondingly increased. Usually, when arranging solar cell arrays, the construction size of each solar cell array should be selected separately, and its height should be adjusted to an appropriate value, so as to use its height difference to minimize the distance between solar cell arrays. The specific solar cell array design should be comprehensively considered while the azimuth angle and the inclination angle are reasonably determined, so that the solar cell array can reach the best state.
Solar LED lighting systems generally require light-controlled switches, and some designs often use photoresistors to automatically switch lights on and off. In fact, the solar cell itself is an excellent photosensitive detector. Using it as a photosensitive switch has better characteristics than a photoresistor. The application of solar LED street lights and garden lights is not a big problem, but for solar lawn lights that only use a 1.2V Ni-Cd battery, the solar cell element is composed of four solar cells connected in series, and the voltage is low. The voltage is lower under weak light, so that the voltage is lower than 0.7V in the absence of darkness, causing the light control switch to fail. In this case, the problem can be solved as long as a first-stage transistor is directly coupled to the amplifier circuit.