Consumers must make sure whether switching to solar panels is worth going through the hassle. Typically, it is determined by how much energy rooftop panels will produce and if it is enough to meet the energy needs of a house or a commercial building in the longer term. As this regulates what kind of panels with what efficiency one should buy ultimately deciding the price factor.
The Power Rating
The power rating of individual solar panels can be found in the manufacturers' data sheet. They are measured in Watts. Usually, they are in the range of 100 W to 500W. What this means is that the panel produces this much amount of power in one hour under ideal conditions (Direct sunlight with perfect weather conditions). The value mentioned in the data-sheet is measured under standard testing conditions (STC). As one would expect, the higher the power rating of the solar panels, the more expensive the solar panel will be, this gives us a good indicator of how expensive it will be.
How is it calculated?
The energy measured in watts is calculated by multiplying the current and total voltage produced. When sunlight hits the panels DC (Direct current is generated) flows due to the potential difference (Voltage) and this current encounter resistance. The work done to counter this resistance is power.
P (Power) = I (current)* V (Voltage)
Figure 1: Aurora Solar panels series with a power rating ranging from 485 – 510 W. Maximum power rating can be found in the data sheet under electrical specifications.
The power rating of a solar panel only refers to the amount of power it can produce while operating in ideal conditions. The actual power output of a solar panel will depend on several factors.
Solar Panel Efficiency Solar panels' efficiency is usually tested under standard conditions known as STC. Under these conditions with a temperature of 25°C and an irradiance of 1,000 W/m2 a solar panel efficiency of 15% with a 1 m2 surface area would produce 150 Watts. It is important to understand that solar cell efficiency is different from solar panel efficiency. The solar cell efficiency can go as much as up to 40 %. Today’s silicon panels can produce up to 22 % efficiency which leads to a total power rating of around 220 W/m2. Monocrystalline solar panels are relatively a premium product compared to their polycrystalline counterpart as they are expensive to make so for this reason for the same wattage monocrystalline panels are a bit more expensive than polycrystalline panels.
- No. Of Solar Cells
Usually, most solar panels have 60 cells, or 72 cells connected in series. Solar panels with 72 cells are usually bigger and have a higher power rating as it has more no of cells which in turn produces more power compared to solar panels with 60 cells. After that half-cut solar panels emerged which can accommodate up to 144 half-solar cells.
Figure 2: Comet Solar panels series with a power rating ranging from 560 – 580 W. Half cut the bifacial panel with 110 cells as mentioned in the spec sheet.
The PV market is currently dominated by monocrystalline and polycrystalline photovoltaic panels. Monocrystalline solar cells are made from a single crystal of silicon. As a single continuous crystal, the electrons inside the cell can move quite easily generating more current and giving out higher cell efficiency. In the case of polycrystalline solar cells, they are manufactured with a nonregular silicon structure as monocrystalline, then electrons cannot move quite easily which leads to reduced cell efficiency. The number of cells for rooftop panels is usually either 60 or 72 cells. For commercial projects, these panels can have more than 72 cells. As shown in figure 2 the comet solar panel series manufactured by AE Solar are half-cut bifacial panels that produce power from both the front and back side of the solar panel has 110 solar cells and can produce power ratings ranging from 560 to 580 Watts.
- Shading: Shading on the solar panels will reduce the total power output of the panel. The power rating in the spec sheet does not consider shading.
- Angle Installation and orientation: For rooftop panels, the slope of the roof will impact how much sunlight is hitting the panels throughout the day. Large commercial systems have tracking systems installed so that they can be optimized at providing maximum power output. Dust and debris accumulation on the panels is also one of the factors that can reduce the solar panel power output greatly.
- Hours of Sunlight:The longer the sun is out the better it is as your solar panels can absorb irradiation for longer hours.
Why does it matter?
The power rating is an important metric for your home or commercial solar panel system. When you buy or install a solar photovoltaic (PV) energy system, the price you pay is typically based on the solar panel output of your system. The power rating is not itself the only indicator of panel quality and performance. Some panels’ high power output rating is due to their larger physical size rather than their higher efficiency or technological superiority. In conclusion, while it is always important to keep an eye on power ratings and efficiency ratings, they are not the only factors that will determine how much power your solar power system can generate. There are many things you can control to make sure your solar panels are working at their highest potential.