Solar cells output power, efficiency and voltage rating are given at standard test conditions (T=25°C). So, it clears that the cell voltage, efficiency, and output power depends on cell temperature. In practical applications, the operating temperature of solar cells may be different from 25°C. The cell temperature varies due to ambient temperature and in practice, the solar cells encapsulated (in PV module) with glass which results in heating of solar cells. Due to encapsulation solar cell temperature increases. The change in temperature from standard operating temperature directly affects the output voltage, efficiency, and power. Normally, when a solar cell operates at the temperature above 25°C; the voltage, efficiency and output power of a solar cell reduces.It may seem counter-intuitive, but solar panel efficiency is affected negatively by temperature increases which affect the performance of solar power plant.
The decrease in voltage, power, and efficiency with temperature is different for different type of solar cells, for crystalline Si solar cells, for every 1°C increase in temperature above 25°C, the decrease in value of voltage, power and efficiency is given as below
Parameter of crystalline Si solar cells Decrease /°C rise in cell temperature from standard test condition(STC)value of 25°C
The angle of sunlight with respect to solar cell greatly affects the output power. The solar cell produces maximum power (for given light intensity) when sunlight falls perpendicular to the surface of solar cells. When the light does not fall perpendicular to solar cells, it always gives less output power than maximum possible output power affecting the performance of solar power plant. This is because when light falls at a particular angle, some part of light falling on the solar cell is reflected. Hence, the actual light utilized by a solar cell is less than the amount of light falling on it.
Therefore, one should always try to install a solar cell or module in such a way that most of the time sunlight is close to perpendicular, especially in the afternoon time when the intensity of light is high.
Change in solar cell area(A)
The maximum output current (Isc or short circuit current) of a solar cell depends on the area of solar cells. The current output is directly proportional to the cell area. So, when solar cell area is large, the amount of electric current generated will be large and vice versa.
For a given amount of sunlight if 100cm2 cells produce 2A current, then a 200m2 will produce 4A and 50cm2 will produce 1A current.
Change in amount of input light(Pin)
We would get maximum output from solar cell when the sunlight falling on it must be equivalent to 1000W/m2. The current generated by a solar cell is directly proportional to the amount of sunlight falling on it. Suppose a solar cell produces 1A current under 1000W/m2 radiations then under 500W/m2, it will produce 0.5A current.
Voltage doesn’t depend on the intensity of solar radiation much. But still, the amount of power generated (Current x Voltage) is proportional to the light falling on it. As the power generated by the solar cell depends on solar radiations it keeps changing with the radiations density. More the intensity of light more the power will be generated.
Of the total energy falling on a solar cell, only some fraction of the light energy gets converted into electrical energy by the solar cells. The ratio of electrical energy generated to the input energy is referred as conversion efficiency of the cells. The conversion efficiency of solar cell is fixed, based on the material and the manufacturing process. Once a solar cell of given material is manufactured, its efficiency value becomes fixed and it cannot be changed.
The efficiency of a solar cell is given in terms of maximum power that solar cell can generate for a given input solar radiation. The maximum power output (Pmax or Pout) of solar cells depends on the voltage developed across cell terminals and the current it can supply.
To get the most from solar panels, you need to point them in the direction that captures the most sun. During the course of a day, the sun passes through the sky in an arc that varies throughout the year due to the earth’s orbit (see image). The arc is always symmetrical from East to West, measuring out from the center point, which would be midday.
It is simplest to mount your solar panels at a fixed tilt and just leave them there. But the sun is higher in the summer and lower in the winter; you can capture more energy during the whole year by adjusting the tilt of the panels according to the season.
It is always considered as the best practice during installation of solar power plants to orient solar panels in the south-west direction at an angle equal to the latitude of the location to get maximum output at a fixed tilt.
Most panels can withstand winds up to 90 mph (or more), so barring the occasional hurricane, you have virtually nothing to worry about.
Wind causes forced convection heat transfer with the atmosphere. Wind influence remains low but not really negligible.