The solar panel efficiency can be found in the solar manufacturer’s datasheet. The amount of sunlight that the solar panels can convert into electricity determines the efficiency ratings of the panels. The first silicon solar cells that were manufactured in 195 by bell labs were about 6 percent efficient at converting the energy in sunlight into electricity. We have come a long way since then. Today’s panels available in the market can produce more than 20% efficiency of course this is only silicon-based solar panels as they dominate the current market compared to thin film and perovskite solar cells. The figure below shows the cell efficiency chart starting from 1975 within families of different semiconductors:
- Multijunction cells
- Single-junction gallium arsenide cells
- Crystalline silicon cells
- Thin-film technologies
- Emerging photovoltaics
Figure 1: NREL Research cell efficiency chart . Source: NREL
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. The efficiency of the panels varies according to the type of solar panel as mentioned before. The most common types of panels available in the market are monocrystalline solar panels, multi-crystalline solar panels, and thin film solar panels. 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 %. The world record for solar cell efficiency at 47.1% was achieved by using multi-junction concentrator solar cells, developed at National Renewable Energy Laboratory, Golden, Colorado, USA in 2019. As of 2022, The record lab cell efficiency is 26.7% for mono-crystalline and 24.4% for multi-crystalline silicon wafer-based technology. The highest lab efficiency in thin film technology is 23.4% for CIGS and 21.0% for CdTe solar cells. Record lab cell efficiency for Perovskite is 23.7%. These are official lab record efficiencies with a cell area of 1 m2. Several factors affect a cell's conversion efficiency value, including its reflectance, thermodynamic efficiency, charge carrier separation efficiency, charge carrier collection efficiency, and conduction efficiency values
Monocrystalline vs Polycrystalline panels
The PV market is currently dominated by monocrystalline and polycrystalline photovoltaic cells that are arranged on a module as monocrystalline or polycrystalline solar panels. This article will focus on the comparison of monocrystalline and multi-crystalline silicon panels under different weather conditions briefly. Before that, it is important to know the difference between monocrystalline and polycrystalline solar cells. Monocrystalline and polycrystalline solar panels essentially perform the same function, i.e., capture sunlight and turn it into electricity. The key difference is the type of silicon structure they use. 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.
Figure 2: Market share of crystalline silicon wafers. According to the ITRPV report, the market share of monocrystalline wafers is expected to increase driven by n-type wafers. Source: ITRPV.
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
Thin film solar panels
These kinds of solar cells are made by depositing thin layers on a substrate. Thin film solar panels are usually flexible and low in weight. Commercial thin-film solar cells available in the market include cadmium telluride (CdTe), copper indium gallium Diselenide (CIGS), and amorphous thin-film silicon (a-Si, TF-Si). Thin-Film solar panels are less efficient and have lower power capacities than mono and polycrystalline solar cell types
Figure 3: Thin film solar cells market share throughout the years.
Source : 2022, IEA.
Factors affecting solar panel efficiency
The efficiency of the panels will vary depending on the below-mentioned factors.
Temperature: We know that more is directly proportional to the amount of power produced, but solar panels tend to operate less efficiently after the panels reach a certain temperature. It is usually around 65֯ C where the efficiency begins to drop.
Shading: If a solar panel experiences any shading, it won’t produce as much electricity. Depending on the inverter you have, shading on one panel could impact the production of multiple panels
Weather: German Solar panels best operate on sunny and clear days. Cloudy days could impact the amount of irradiation on the solar panels. And snow accumulation can reduce power production altogether.
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.
According to the NREL, most solar panels installed in the world have an efficiency between 16% to 22%. Solar panel with higher efficiency rating comes with a higher price tag. When considering buying solar panels, it is not necessary to buy only those high-efficiency panels available in the market. The power rating of the panels gives you an overall picture of how many solar panels to buy and what should the efficiency be since the cost is an important factor Instead of just picking the panel with the highest efficiency, you should also consider how much the panel costs, and if the cost is worth the value the panel will provide. If you have much smaller roof space and don’t have the right orientation and you are willing to shell off a few bucks then installing fewer solar panels with higher efficiency could be a better option.