Solar Power System Calculator
A solar cell / photovoltaic cell is a p-n junction diode, which converts the energy of light directly into electrical energy. On a clear day, solar radiation received on a earth surface oriented normal to the Sun rays at noon is in the order of 1000 watts per square metre. Considering the 19% efficiency of solar cell, solar panel of one square metre gives output power of 190 watts (or 18 watts per square feet) on a clear day. Selection of adequate solar panel size, battery bank & inverter power rating based on the latitude value of place and connected load is very important for a user and described below:
#Note: Please read 'Technical Info : Technical Terms' section of this website for more details about various terms & angles related to Solar Power System and used in this simulation tool.
1. A single junction silicon crystal solar cell can produce a maximum open circuit voltage of approximate 0.5 to 0.6 volts, 42mA/cm2. Solar cell has efficiency of 16 to 22%. Output of a solar panel depends on the solar radiation collected by that panel.
2. In order to capture the most solar radiation, the solar panel surface should be perpendicular to the Sun’s rays each instant during the day. To achieve this at every moment of the day, tracking needs to be used. Since tracking mechanisms are expensive, fixed solar panels are used for most solar panel installations. Further, a fixed solar panel tilt angle can be optimized yearly, seasonally, or monthly to obtain maximum output energy from solar panel throughout the year.
3. The two angles define the orientation of the solar panel are tilt angel and azimuth angle. Tilt angle is angle between solar panel plane and the horizontal earth surface. Azimuth angle is angle between due south and a projection of the panel’s surface normal onto a horizontal plane.
4. The solar cells are connected in series to provide a desired output voltage and in parallel to supply required output current. Generally, a series-parallel combination of solar cell is used inside solar panel to obtained required voltage and current at output.
5. This calculation is based on the assumption that user is adjusting solar panel tilt angle minimum two times in a year as per Summer and Winter season requirements. A margin of 20% in equipment rating calculation is considered on account of future extension.
6. Average power factor of 0.65 is considered for calculation of 'Inverter' capacity calculation. User is advised to input the wattage rating of the load for calculation i.e. Ceiling fan - 40 watts, Tube light - 40 watts or as mentioned on equipment name plate.
7. Cloudy weather condition is not consider for calculation. Therefore, the capacity of solar panel system may degraded during foggy and cloudy weather conditions.
8. If a lead-acid cell has nominal rating of 2V, 150AH; then series connection of six cells will make a battery of 12V, 150AH. Further, combination of two 12V, 150AH batteries in series will make a battery bank of 24V, 150AH and combination of two 12V, 150AH batteries in parallel will make a battery bank of 12V, 300AH.
9. Battery capacity factor as per C5 discharge rate, battery ageing factor, inverter efficiency and design margin of 20% have been considered for calculation. Battery storage room temperature is considered 27°C. Lower ambient temperature decreases the battery Ah capacity and vice versa.
10. No other electricity source is considered for charging of battery connected with Solar Panels. If other electricity source is also available for charging of battery, required size of solar panel will be comparatively less.
11. The output voltage and efficiency of a solar panel decreases with increase in its temperature and vice versa. Commercially available monocrystalline silicon solar panel has efficiency in the range of 20 to 22%.
12. The value of solar radiation outside the earth's atmosphere is 1367 W/m2 (the value when the Earth–Sun distance is 1 astronomical unit), then the direct sunlight at Earth's surface when the Sun is at the zenith is about 1000 W/m2, but the total amount (direct and indirect from the atmosphere) hitting the ground is around 1120 W/m2. In terms of energy, sunlight at Earth's surface is around 52 to 55 percent infrared (above 700 nm), 42 to 43 percent visible (400 to 700 nm), and 3 to 5 percent ultraviolet (below 400 nm).
13. Standard Test Conditions (STC): STC is an industry-wide standard to indicate the performance of Photovoltaic / solar modules and specifies a cell temperature of 25°C and an irradiance of 1000 W/m2 with an air mass 1.5 (AM1.5) spectrum. Air mass (AM) refers to the path length of sunlight through the atmosphere normalized to that when sun is directly overhead (at Zenith). Solar panel available in market gives rated output under standard test conditions.
14. It is not necessary to adjust the tilt angle of solar panels in every season. If solar panel size is selected as per requirement of summer load, which is oversized to meet the requirement of winter load. In this case, it may be possible that solar power system will work properly in winter season without any tilt angle adjustment.