How Efficient Are Solar Panels: A Brief Guide
Sep 5th 2022
Considering a DIY Solar System or looking to upgrade your current system? The first step in choosing the right equipment is understanding the basics of how solar works. This post will provide an overview of how solar panels convert light into usable electricity and solar panel efficiency.
What is solar panel efficiency?
First of all, what are solar panels? Look at the picture below and you will find how they look like.
A solar panel is the most important component of a photovoltaic system and is responsible for absorbing sunlight and converting it into DC currents. The panels are usually made of a sheet of soldered solar cells, glass panel, aluminum frame, EVA film, and TPT backsheet.
How does a solar panel work and how do solar panels convert energy?
A single solar panel consists of multiple photovoltaic (PV) cells, commonly referred to as solar cells. These wafer-like silicon cells are semiconductors that create electrical current when exposed to sunlight.
Solar cells typically have multiple silicon layers like a sandwich. These include a p-type silicon layer (or positive layer) and an n-type silicon layer (or negative layer). When the sun shines on a solar cell, it transfers the sun’s energy to negatively charged particles called electrons. The electrons flow between the p and n layers creating electric current. This process is known as the Photovoltaic Effect.
(Fig 1. Identifying parts of P-N junction in a silicon solar cell.)
This current is then extracted through conductive metal contacts or electrodes. Individual solar cells are wired together to make a solar panel or module. Solar panels in-turn can be wired together to form a solar array to meet the energy needs of a home or vehicle.
To conclude, solar panel efficiency, or solar panel conversion rate, refers to the portion of sunlight (irradiation) that can be converted into electricity via the solar cells in the solar panels.
Solar panel efficiency comparison: now and then
Now that we’ve covered how solar panels create usable electricity, the next step is to understand how much power they produce. This will help you identify how many panels you’ll need to meet your energy needs.
So are solar panels efficient? Today you can find a wide variety of solar panels with efficiencies ranging between 15 and 22 percent. The efficiency of current solar panels has increased significantly in recent years with advances in materials and technology, and the efficiency percentage of the most efficient solar panels can achieve about 22.8 percent. The first selenium solar cell developed in 1883 by American inventor Charles Fritts, had an efficiency of just 1 percent. And for decades after that, advances were minimal.
(Fig 2. 1956 Bell Labs ads for solar battery system. Source: Sensei Alan from Flickr)
But in 1954, Daryl Chapin, Calvin Fuller, and Gerald Pearson developed a practical silicone cell that changed the game. This new silicone cell could convert enough solar energy into electricity to power electrical devices. Before long, Bell Laboratories invented a new silicone cell that initially achieved 4 percent efficiency but soon was up to 11 percent. Since then, new and better solar technologies have been introduced, such as half-cut and diode designs. These and other technologies are driving big advances in solar efficiency.
To conclude, solar panel efficiency, or solar panel conversion rate, refers to the portion of sunlight (irradiation) that can be converted into electricity via the solar cells in the solar panels. Due to insurmountable technology barriers so far, 100 percent efficient solar panels are not yet able to come true.
Solar efficiency over time
Why does the efficiency of solar panels matter?
Efficiency ratings can be tough to get your head around, even for the most knowledgeable solar consumers. Let’s take a look at how efficiency plays a central role in planning solar projects.
Using panels with higher efficiency lets you save space by using fewer panels to generate the same amount of power. That means you can fit a larger system with more power on the same available roof space.
(Fig 3. Comparing the roof space installed with PV module of different efficiency.)
The image above shows two different 1300W solar arrays. The right one uses 3 of Renogy’s latest 450W solar panels, which are one of the most efficient solar panels on the market, with an efficiency of up to 22.8%. It covers an area of 70 square feet. The one on the left uses 13 of Renogy’s classic 100W solar panels with efficiency of up to 22% and covers an area of 78.8 square feet. As you can see, higher efficiency panels save you roof space. That means you can fit a larger system with more power on your roof.
Cost and Environmental Impact
Choosing highly efficient solar panels is also beneficial to you and the environment. Using fewer panels means fewer resources for manufacturing and reduced impact of disposal. Processing silicon and turning it into wafers requires large amounts of energy.
When panels produce more energy your payback period is also shorter. According to Dutch researcher E.A. Alsema, it takes approximately 4 years for current multi-crystalline solar panels with 12% efficiency to achieve return on investment. In comparison, the payback time is reduced to only 2 years for solar panels with 14% efficiency.
(Fig 4. Energy payback for PV Modules of different efficiency. Data from https://www.nrel.gov/docs/fy04osti/35489.pdf)
Although the upfront investment for a complete solar power system is significant, don’t forget that a solar panel usually lasts 20-30 years. Keep in mind how much you can save on utility bills by going solar. Once you consider how much you’re saving, it’s easy to see how your investment in solar will pay for itself in just a few years.
How Solar Panel Efficiency is Calculated
You may be wondering how efficiency is calculated and how solar companies use them as a selling point. Below is a step-by-step demonstration of how to calculate the efficiency of a solar panel.
Calculating efficiency ratings is easy. You can do it with a simple math equation. It’s really just the ratio of a panel’s power output to the solar energy absorbed on the surface of a panel under standard testing conditions. The equation below shows just how easy it can be.
Module efficiency VS. Cell efficiency
To understand solar panel efficiency, first we need to understand solar cell efficiency. We know module efficiency is the ratio of the power a module can produce to the solar energy hitting the surface of a panel under standard testing conditions. But for solar cells, efficiency is calculated using the same ratio but there’s a gap between these two efficiency ratings. There’s a gap because the cell efficiency is calculated with the area of a single cell. In contrast, the module efficiency includes other aspects of a panel’s construction. This includes shading that may come from other components in the panel such as busbars, or space between cells that may lead to energy loss.
At Renogy, we refer to cell efficiency when talking about solar panel efficiency since cells are the fundamental components of a module. You can also find cell efficiency ratings in the specification section of a module.
(Fig 7. Comparing the area of a solar cell and a PV module.)
Breakdown of calculation
Let’s use what we’ve learned to calculate efficiency with our popular 100W Monocrystalline Solar Panel (Compact Design)
Step 1. Determine the module’s maximum power output under optimal conditions
To get the maximum power output of a solar panel (Pmax), we use the maximum power output of a module before the encasing process. After encasing solar cells in glass, the extra layer reduces sunlight absorption, leading to a lower efficiency rating. This figure should be in Watts (W). In the case of our 100W monocrystalline solar panel (compact design), the maximum power output of the module before encasing is 108W after testing in the lab.
To get the maximum power output of a solar cell, divide maximum power output by the number of the solar cells in the module. In this case, the maximum power output a solar cell can deliver is:
Step 2. Find the dimensions of the solar cell
You can find the dimensions of a module in its the specifications. The size information is either in millimeters (mm) or inches (in). You’ll need to convert these figures into meters (m) for other calculations.
The dimensions of this 100W solar panel are: 41.8 x 20.9 x 1.4 in / 1.06 x 0.53 x 0.035 m
The dimensions of its solar cells are: 6.5 x 3.3 in / 0.1651 x 0.08382 m
Step 3. Determine the module’s maximum absorbed power at standard testing conditions (STC)
First let’s look at the definition of standard testing conditions for the factors considered in panel efficiency.
- Irradiance 1000W/m2: This means 1000W of solar energy is absorbed by a square meter on a module at a given time.
- Temperature 25°C: Solar cells are tested at 25°C. Note that this does not refer to the ambient temperature.
- Air Mass 1.5: This metric is related to the angle the sunlight hits a given spot on the earth. The smaller the number, the smaller the distance sunlight needs to travel to reach the earth’s surface.
To get the maximum absorbed power at standard testing conditions, multiply the irradiance 1000W/m2 and the solar panel/solar cell area. In this case, the calculation is:
1000W/m2 x (1.06 x 0.53 m)=561.8W
1000W/m2 x (0.1651 x 0.08382 m)=13.8W
Step 4. Calculate cell efficiency
The final step is to divide the total power output by the absorbed energy of the panel/solar cell.
The module efficiency of this 100W solar panel:
100W/1000W/m2 x (1.06 x 0.53 m) ≈ 18%
The solar cell efficiency of this 100W solar panel:
3W/1000W/m2 x (0.1651 x 0.08382 m) ≈ 22%
Efficiency of Solar Panels
The more efficient the photovoltaic solar panel, the more energy output it will have per amount of light energy hitting the cell, which will in turn take up less surface area to meet your energy requirements.
Today, most solar panels provide an energy efficiency rating between 11 and 15 percent, which is the percentage of solar energy that is being converted into useable electricity.
While it may seem like a low percentage, advancements in solar energy technologies are continually being made, and modern panels can more than cover the energy requirements of most commercial and residential needs.
Today, researchers are continually trying to improve the efficiency of photovoltaic technology. Scientists have now achieved a record of 40 percent efficiency by utilizing multi junction cells that are tuned to capture different frequencies of light on the electromagnetic spectrum. While these are currently the most efficient solar cells that have been created, they are not yet available to the general public.
If you have a smaller roof and limited space, a more efficient solar panel may be the right choice for you. Because of their higher efficiency, these panels may be slightly more expensive, but they will still meet the energy requirements you need.
However, if you have a larger amount of space, you may be able to achieve your energy needs with less efficient and less expensive panels to help save on your installation costs. Considering the overall cost of the panels and the kilowatt production can help you pick which is best for your installation.
Photovoltaics and Types of Solar Panels
The industry standard for solar electric systems is based on photovoltaic, or PV, technology, which converts sunlight into electricity. Multiple solar cells are interconnected to create a module, which comprises the panel.
Each panel is usually connected together in a system in which electricity is sent to an inverter to provide the power needed to run household electric devices. Efficiency is often dependent on the design of the panel and how it is engineered to capture different frequencies of light energy. Consider the following designs:
- Monocrystalline Silicon Panels. The most efficient type of photovoltaic solar panel available today is currently monocrystalline, or single, silicon panel. Because of the higher silicon content used in the design, they are more expensive than alternative types of panels. energy is converted into electricity, so fewer panels are needed in most roof installations to meet the same power requirements. These types of square-shaped panels are ideal for roof mounted solar electric systems.
- Polycrystalline Silicon Panels. With lower amounts of silicon utilized in polycrystalline, or multi-layered, silicon panels, they are often cheaper than their more efficient counterparts. They implement a design to help reduce this efficiency loss, allowing them to be utilized on roof mounted systems. This makes them ideal for larger projects and installations because they cost less. Polycrystalline silicon panels are also resistant more resistant to heat.
- Building Integrated Photovoltaic Panels. Appearance is an important aspect of a building. As with many historic buildings, or ones that feature unique architectural designs, owners might be hesitant to alter the distinctive character of a structure by installing a solar electric system. To help mitigate the aesthetic changes that solar panels might bring, building integrated photovoltaics are available. While they may be able to keep the look of traditional roofing, these types of panels are more costly and less efficient than the alternatives.
- Thin-Film Solar Cell Technology – Thin film cells are a newer photovoltaic technology that consists of one or multiple layers of thin films of photovoltaic cells that are laminated to existing material, such as metal roofing or glass Windows. These photovoltaic films are very thin allowing them to be lighter and more flexible compared to other PV systems. While thin-film technology is extremely versatile, it comes at a cost. Thin-film systems are less efficient and can degrade faster than conventional solar systems, but are improving with technology advancements.
Factors That Can Impact Efficiency
Solar power efficiency depends on a variety of factors including proper installation and assessment of the structure. Hiring a professional to inspect the structural design and location of your building is essential in determining what type of installation will best meet your requirements and provide you with the long-term economic benefits of solar power. Empire Renewable Energy offers a range of services for commercial and residential applications:
- Most solar panels are designed with a layer of protective glass over the cells, which sunlight must pass through. The amount of energy harnessed is dependent on the angle in which light is passing through, as well as the reduction of reflectivity of the glass.
- Proper installation of a solar panel is significant to capturing the maximum amount of sunlight. The angle of the panel and the amount of light hitting it are both important factors that will help you maximize efficiency.
- For roof mounted panels, the slope of the roof will impact how much sunlight is hitting the panels throughout the day. Large commercial installations can compensate for the movement of the Earth by installing solar tracking systems, but due to the expense, they are not typically installed for residential use.
- Temperature can impact the overall output of a solar cell. Higher temperatures can reduce output and lower efficiency. Some solar panels are designed for warmer climates, where efficiency must be maintained as temperatures climb. Ensure you select the right panel that is best suited to your climate, so you can enjoy a better return on your investment.
- Even a small shaded area on solar panels can greatly reduce their output. Since panels are often wired together in a system, even a small shadow on one panel can drastically reduce the system’s overall energy production. It is ideal to install panels in a way that no shadows will fall on any of them. In some situations this may be difficult to avoid, so alternatives are available to help maintain efficiency.
1) Off-Grid Solar Systems
MPPT solar inverters at 48V are ideal for standalone, off-grid installations where no utility grid connection is available. They efficiently manage energy flow from solar panels to batteries, ensuring optimal charging and usage.
2) Hybrid Solar Systems
These inverters can be integrated into hybrid systems that combine solar power with grid electricity or other renewable energy sources. The 48V MPPT inverter optimizes the solar input and seamlessly switches between energy sources as needed.
3) Remote Locations
48V MPPT solar inverters are used in remote areas or places with unreliable power, offering reliable and independent electricity generation.
PSW6K-PRO 48v hybrid solar inverter 6000 watt with mppt 100 amp
PSW1K-Pro mppt dc to ac single phase off-grid 1000w solar inverter
PSW8K-PRO 96v mppt solar power energy 8000 watt inverter generator
PSW3K-Pro 24v pure sine wave mppt off grid solar 3kva inverter
a) System Sizing
Properly sizing the solar panel array, battery bank, and inverter is crucial for achieving optimal performance and maximizing energy harvest.
b) Quality and Reliability
Choose reputable brands and reliable products to ensure long-term performance and protection against potential faults or failures.
MPPT solar inverters operating at 48V bring significant advantages to solar power systems. With enhanced efficiency, wide input voltage range, battery charging capabilities, monitoring features, and scalability, these inverters maximize solar power utilization and improve system performance. As the demand for renewable energy continues to grow, MPPT solar inverters at 48V are playing a crucial role in harnessing the full potential of solar energy and paving the way towards a sustainable future.
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