Before investing thousand of dollars in buying a solar power system, it is a good idea to know a bit about the most important component in the system that is SOLAR PANEL.
One should choose a panel that not only meets the energy needs within one's budget but also is profitable in long term, offering good returns. For this, one should understand the specifications of the solar panel that are printed on its back. But Solar panel specifications are full of technical jargon, electrical ratings, mechanical specifications, various certifications ,and more. And Understanding all of them can be a bit scary. Fortunately, there are only few important specifications that can help the home-owner to choose the right solar panel matching her/his energy needs.
Let's understand them:
Solar Cell
A solar cell is an electrical device that converts sunlight into electricity.
When the photons of light (packets of light) fall on the solar cell, the outermost electrons absorb that energy and get excited. They jump from valence band to the conduction band and the flow of electrons start that we call electric current. The solar cells are generally made of silicon (a semi-conductor) element doped with impurities of similar electronic structure. A normal silicon solar cell generates a maximum voltage of 0.5 volts to 0.6 volts. When number of solar cells are joined together in a frame to get higher voltage an power, Such arrangement is called a solar panel. Types of Solar Panels
You'll find 2 types of solar panels in the market:
Mono-crystalline solar cells are made from unbroken and single crystal of silicon cell On the other hand, Poly-crystalline solar cells are also made of silicon but in this smaller and broken fragments of silicon are joined together to form a silicon wafer.
Ideal Conditions: STC (Standard Test Conditions)
The solar panel manufacturers rate the power output of the solar panels under Standard Test Conditions (S.T.C), which are:
You can see that the Rated Maximum Power (Pmax) output of Panasonic N340 solar panel is 340 watts under STC.
Panasonic HIT+ Photovolataic module data sheet
But
The Standard Test Conditions conditions generally do not reflect typical environmental conditions in which we live where cell temperature is generally higher than 25° C and we don't get sunlight of 1000 W/m² every time. Therefore, the output power of Panasonic N340 solar panel would be somewhat less in the actual environmental conditions. In short, Pmax of any solar panel gives you the rated maximum power output under ideal conditions which we call STC. We know that Power (P) = Voltage (V) x Current (I) Or P(max) = V(max) x I(max) When a solar panel is operating under its maximum rated power capacity under STC, the voltage we measure across the connected load at that time is called V(max) and the current measured at that time is called I(max) Open Circuit Voltage (Voc): The maximum voltage that a solar panel can produce when no load is connected to it. When you connect 2 panels in series then their Voc will add up. The open circuit voltage is important for sizing of the solar charge controller. The Voc of the panels + safety margin of 10% must be less than the the maximum voltage permitted by the solar charge controller. In the above table of N340, the open circuit voltage is 71.3 volts. Then your solar charge controller should have voltage rating of: Voc + 10% of Voc (safety margin) = 71.3 volts + 7.13 volts = 78.43 volts Short circuit current (Isc): It is the current that flows out of the solar panel when its positive and negative terminals are connected directly without a load. It is important to determine the current holding capacity of the solar charge controller. The Isc is the highest current that a solar panel can produce under Standard Test Conditions. The Isc in the N340 solar panel specifications is 6.13 Amperes. You should choose a solar charge controller with current holding capacity of Isc + 20% of Isc (safety margin) = 6.13 A + 20% of 6.13 A = 6.13 A + 1.226 A = 7.35 A Real Conditions: (NOCT) Nominal Operating Cell Temperature
The NOCT standards reflect real world conditions that represent how your solar panel will perform under these set of standards.
In short, the NOCT standards are better representation of solar panel performance than than that of STC. NOCT standards use following test conditions:
Kindly note that STC standards use cell temperature (25° C)
whereas NOCT standards use ambient temperature (20° C). There is a key difference between the two. Let me explain you with the help of an example: Have you ever touched the wind screen of the car on a clear sunny day? You might have noticed that it is hotter than the surrounding temperature. Same is the case with the solar panel, Although, the ambient air temperature is low but the solar cell in the panel might be performing under hotter temperature than the surroundings. And this difference could be as high as 30° C. An ambient air temperature of 20° C might mean the cell temperature near to 45° C. And the performance of the panel decreases with the increase in the cell temperature. Let's see the piece of specification chart of LG 375 W high efficiency solar panel. You can spot the difference:
{*NOCT is sometimes referred as NMOT (Nominal Module Operating Temperature)}
Electrical Properties of 375 W high efficiency LG NeON under STC and NOCT respectively.
The maximum power under NOCT is low than that of under STC.
Let's find some relation between the 2 terms by doing a little MATH: P(max) NOCT/P(max)STC x 100% = 282 W/375W x 100% = 75.2% The NOCT Pmax is 75% of STC Pmax In general, you'll find NOCT P(max) as 70% - 80% of STC P(max) "Higher is the percentage, better is the panel performing under NOCT." Understanding Temperature Coefficients
It is found that the solar panel performance decreases with the increase in the temperature.
The manufacturers specify the loss in power in panel using temperature coefficient called temperature coefficient of P(max). Its value reflects the percentage loss in power with every degree rise in the temperature above 25° C. The temperature coeff of P(max) along with NOCT are used to compare panels performance under high temperature. Let us understand with the help of an example: 
Canadian Solar High Density Mono-Perc 400 W solar module
Solaria Power XT 400 W solar panel
Power Loss under NOCT
If you're living in a hotter climate then you should go for a panel that has low NOCT temperature and low Power degradation coefficient
Strength of the Solar Panel (Snow load and wind load ratings)
If you're living in a extreme climate like frequent hurricanes or heavy snowfall then the strength of the solar panel could be the deciding factor for choosing the solar panel.
The Snow load and Wind load ratings are the ones on which you should pay attention while choosing a solar panel. The Snow load rating (How much snow weight the solar panel can withstand) is often called a front side rating while the wind load rating is often called as rear side rating. You might be wondering why the rear side of the solar panel is specified for wind load rating? In any solar power system, the panels are installed and fitted on the roof by giving some angle with the horizontal. Even if the panels are placed horizontally, there is a small gap between the roof surface and the rear of the panel. When a strong blow of wind passes between this gap, it creates a huge upthrust that can sail the panel along with it. These mechanical load ratings give you an idea whether a solar panel will withstand in extreme weather conditions or not. The higher are the rating, the stronger is the panel. It is common to see 2400 Pascal rating for Wind load and Snow load. Let's see the mechanical ratings of Canadian Solar Panel.
Mechanical load ratings of Canadian Solar Module
The mechanical rating of Solar Power solar module are:
Mechanical load ratings of Solaria Power Solar Module
You can see that both are equally strong from front side in withstanding the snow load
But Solaria Power module is stronger from rear side in terms of handing the wind load.
Therefore, Solaria Power solar panel is preferred for regions with high wind speeds
Whereas, Canadian solar panel performs well in hotter climate. Solar Panel Efficiency (Ƞ)
How much amount of sunlight is converted into electricity, is usually referred as the efficiency of the solar panel and it is written in percentage.
This efficiency is calculated under STC when solar radiations are 1000 W/m². You can easily find the efficiency of any panel if you know its dimensions and Pmax. Kindly see the datasheet of Solaria XT 400 W solar panel that shows its efficiency as 20.2%. 
Solar Power XT 400 W solar module efficiency
Let's do a little MATH.
The dimensions of this panel are: 1644 mm x 1204 mm x 40 mm (Length) (Breadth) (Height) We need area (L x B), not height, for calculating the efficiency because it is the area of the panel that receives sunlight. Input (sunlight) = 1000 W/m² Efficiency (Ƞ) = {Pmax/Area x Input sunlight under STC} x 100 % = {400 W/ (1.644 m x 1.204 m x 1000 W/m²)} x 100 % = 20.2 %
When you take 2 solar panels of same Pmax but different efficiencies, the one with higher efficiency has less surface area than that of one with lower efficiency.
The efficient solar panels occupy less area but are costly. But you can save on labor cost, installation cost, and racking material cost that are proportional to the area of the panel. A few years back, the 15% efficient solar panel was a norm. But The efficiencies have improved a lot and now you can find solar panels having efficiencies over 20%. The most efficient solar panels are from SunPower having efficiency over 22%. Warranties
A Solar Power System is an investment, as a home-owner you must pay attention to the solar panel warranties which come in 2 forms.
One is warranty on material and workmanship and another is power output warranty. The material and workmanship warranty protects your panel from manufacturing defects, early wear and tear, environmental issues. You'll generally find it for 10 years. While the other warranty covers the performance of the solar panel. The power output of the panel gradually starts decreasing due to exposure of UV light and high temperature. The solar panel manufacturers give a warranty that solar panel would still generate certain percentage of the maximum power even after 25 years. It is generally 80% of the Pmax in the 25th year. The higher is the better.
Let's look at the Product and Performance Warranties of Canadian Solar Panel.
It is offering 15 years limited product warranty which says that the product shall be free from defects in materials and workmanship. And 25 years Performance Warranty that the panel output will not be less than 97.5% of maximum power rating in the first year and thereafter, it will decrease at the rate of 0.6% per year till 25th year and it will not be less than 83.1% of the maximum power rating of the panel. 
Canadian Solar: Product and Performance Warranties
For example, you have a 400 W Canadian Solar Panel then its performance under STC will decrease as follows:
Performance degradation of 400 W Canadian Solar Panel
You can see that with this degradation rate, the power output would be 84.4% of Pmax that is more than the minimum power output warrantied by the manufacturer.
And It is a good thing. By comparing the performance degradation rates of 2 panels, you can choose the one with low degradation rate than the other. This will give you more current in the long term. Let's Summarize
You can choose the right solar panel matching your needs if you know the following technical specifications:
The output power of the panel is the function of the irradiance. The slight haze due to cloud, dust and humidity, in the atmosphere can affect the efficiency of the solar panels. Keep cleaning your panels regularly :) Related Articles:
1 Comment
Charu
29/3/2021 08:28:15 pm
Brilliant explanation of every basic related to solar panel, keep sharing.. Leave a Reply. |
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