How Efficient Are Solar Panels?

Investing in solar energy is a significant financial decision that lowers your electricity bills. Installing high-efficiency solar panels means your home can produce the same amount of electricity with fewer panels, lowering your project costs. So, just how efficient are solar panels? Discover factors affecting solar panel efficiency and how evaluating efficiency factors improve your bottom line.   

How Do Solar Panels Work?

Photovoltaic PV panels harness the sun’s energy to generate electricity through the photovoltaic effect. The sun shines on your solar panel, which absorbs the light photons through photovoltaic cells. The solar cells lay between layers of semiconducting material like silicon. When hit with sunlight, the material energizes, releasing electrons and creating an electric field. 

Your solar panels generate direct current and pair with a solar inverter. The direct current passes through your inverter, and the inverter converts the direct current to alternating current. Leftover usable electricity is then stored in your solar battery bank or fed back into the national electricity grid.

What is Solar Panel Conversion Efficiency?

Solar panel efficiency measures how effectively a solar panel captures light and generates power proportional to the amount of sunlight it receives. Solar companies express efficiency as a percentage showing the measure of sunlight the panel converts into electricity. 

If a solar panel has an efficiency rating of 15%, it means that the panel converts 15% of the sunlight that hits its surface into electricity, while it reflects the remaining 85% of the sunlight or dissipates it as heat. 

Higher-efficiency panels generate more electricity with less surface area, making them more effective in various applications and small spaces. 

Calculating The Efficiency of Solar Panels

Experts calculate solar panel efficiency using a simple formula where electrical energy output refers to the amount of electrical energy generated by the solar panel expressed in kilowatt-hours and solar energy is the amount of sunlight that falls on the solar panel’s surface expressed in kilowatt-hours. 

Efficiency (%) = (Electrical energy output in kWh) / Solar energy output in kWh) x 100

All solar panels receive a baseline efficiency from the manufacturer. However, factors like temperature, shading, orientation, and more affect the real-world efficiency of your solar system. 

Factors Affecting Solar Panel Efficiency

Determining your landscape’s impact on your photovoltaic system’s maximum efficiency involves assessing your home’s solar potential. Factors like sunlight intensity, shading, roof orientation, and the average number of cloudy days in your local climate all influence cell efficiency.

Sunlight Intensity and Orientation

Your roof’s orientation: north, south, east, or west, along with the intensity of sunlight your home receives during different times of the day, affects the efficiency of your system. South-facing roofs capture the most sunlight in the northern hemisphere, while north-facing roofs receive the least direct sunlight, making them less efficient. 

Materials

The materials used in your solar panels play a large role in their efficiency, durability, and cost. High-quality materials, like silicon, contribute to better efficiency and longevity. The primary materials and components of a PV panel include:

• PV cells are the heart of your solar panel and are responsible for converting sunlight into electricity thanks to semiconductor materials that generate electric current when exposed to light. 
• Encapsulation shields the solar cells from the environment, moisture, dust, and mechanical stress inside protective layers composed of tempered glass or ethylene-vinyl acetate (EVA).
• Backsheets protect the backside of your solar module, comprising polyester or fluoropolymer.
• The frame provides structural support and is generally made from aluminum. It protects your solar panel and maintains its integrity under mechanical stress. 
• The junction box houses the electrical connections and wiring at the back of your panel and offers electrical insulation and protection. 
• Wiring connects the solar cells within your panel and transfers the generated electricity to the junction box. High-quality connectors ensure efficient and reliable energy transmission and are typically composed of copper. 

Roof Angle, Shading, and Obstructions

Your roof’s angle and type affect your solar potential. Solar installers adjust and align solar panels to the optimal angle for energy production, between 30 to 45 degrees in the northern hemisphere. 

Like roof angle and orientation, shading from nearby trees and structures can diminish your solar output. Assess potential shading throughout the day and identify obstructions, including chimneys and vent pipes, before installing solar panels. 

Roofs with too much shade or too many obstructions limit the size and efficiency of a solar energy system and are not good candidates for solar installation.  

Temperature

Solar technology advancements have improved solar panel performance across a range of temperatures, but each panel has its own temperature coefficient. Overall, solar panels become less efficient as temperatures increase, and high temperatures reduce output and efficiency. 

Lower temperature coefficients coincide with higher efficiency, and performance impacts from temperature shifts are smaller. 

Environmental Conditions

Harsh weather, such as humidity and exposure to saltwater or pollutants, affects the longevity and efficiency of your solar panels. 

• Humidity can lead to moisture infiltration, damaging the internal components of your panels. High humidity levels increase the risk of corrosion and decrease panel efficiency. 
• Snow and ice accumulation cover the surface of your panels, reducing sunlight exposure. Solar installers position panels at an angle to encourage snow to slide off, and some have built-in heating elements. 
• Hail impact damages glass surfaces, solar cells, and coatings, affecting efficiency and structural integrity. 
• Air pollution degrades the surface of your solar panels, reducing their transparency and efficiency. 
• Saltwater exposure speeds up corrosion, leading to decreased efficiency.
• Higher altitudes receive more direct sunlight but experience more extreme temperature fluctuations, reducing efficiency. 

Dirt, Dust, and Debris

The accumulation of dirt, dust, or debris on the surface of your solar panels significantly impacts their efficiency and energy production. Dirt creates a barrier that obstructs sunlight from reaching your solar cells, reducing sunlight absorption and casting a shading effect. 

Shading one cell on a silicon solar panel’s surface causes a noticeable decrease in energy production, leading to a 20% to 30% reduction in output. 

Dust and debris increase the reflectivity of your panel’s surface. Instead of absorbing sunlight, your panel reflects it away, lowering energy conversion. Additionally, dust shading creates hotspots that cause localized overheating, leading to damage and reducing the lifespan of the affected cell.

Routine Solar Panel Maintenance for Dirt, Dust, and Debris

Mitigate the negative effects of dirt, dust, or debris with regular solar panel cleaning and maintenance. 

• Develop a regular maintenance routine based on your environmental conditions. Depending on your area’s dust levels, this includes monthly, quarterly, or bi-annual cleaning. 
• Use proper cleaning techniques such as brushes, sponges, and microfiber cloths to remove dirt and debris. Avoid abrasive materials that can scratch the panel’s surface. 
• Avoid hard water and opt for deionized or distilled water to prevent mineral deposits from clouding the panel.
• Skip harsh chemicals and replace them with mild detergents designed for solar panels. 
• Ensure safe access and consider professional cleaning services for homes with two or more stories. 
• Rinse thoroughly to remove residue and prevent buildup that could reduce your panel’s efficiency. 

Regular maintenance improves your energy production and extends the lifespan of your solar panels. 

Do Solar Panels Lose Efficiency?

Solar panels degrade over time because of various factors like normal wear and tear, their environment, material quality, and temperature. The rate of degradation varies among types and brands, and most solar panel manufacturers provide a degradation rate under their specifications. 

A degradation rate shows how much the manufacturer expects the panel’s efficiency to decrease each year under standard test conditions. Most solar panels have a degradation rate of around 0.5% to 1% per year. This means that after the panel’s productive period, between 25 to 30 years, its efficiency has increased by 20% to 30%.  

Compare the degradation rates and efficiency of some of the most popular solar panels on the market: 

Brand of Solar Panel	Conversion Efficiency	Degradation Rate After First Year	Annual Degradation Rate For Years 2 to 25
Panasonic EverVolt	21.6% – 22.2%	2%	0.25%
Q Cells Q.Peak	19.5% – 21.4%	2%	0.5%
REC Alpha Pure	20.7% – 22.3%	2%	0.25%
SunPower M Series	21.2% – 22.8%	2%	0.5%
Tesla Module	19.3% – 19.8%	2%	0.54%

What Types Are The Most Efficient Solar Panels?

There are two major categories of solar panels: crystalline and thin-film. Different types have varying levels of efficiency because of their design, materials, and manufacturing processes. 

Monocrystalline Solar Panels

Monocrystalline solar panels are the most efficient type of solar panel. Their efficiency typically ranges between 15% to 25%. Solar manufacturers construct mono panels from single silicon crystal structures that offer high efficiency and a sleek black appearance. They are perfect for small roof spaces and perform well under various light conditions.  

Polycrystalline Solar Panels 

Polycrystalline solar cells have a lower efficiency than monocrystalline but are more efficient than thin-film varieties. Their efficiency ranges between 14% to 17% and the panels comprise multiple silicon crystals. They have a blue appearance and are less expensive than monocrystalline panels.

Thin-Film Solar Panels

Manufacturers craft thin-film solar cells by depositing thin layers of semiconductor material onto a substrate. Thin-film panels are lightweight and flexible, making them well-suited to solar shingles and complex roof shapes. Unfortunately, these panels are the least efficient, ranging from 13% to 15% efficiency, but are also the most affordable. 

How to Choose the Best Solar Panels for Your Home

Choosing the best solar panels for your home involves several considerations, including: 

1. Understand your energy needs by using your utility bills to determine your monthly energy consumption to estimate how many solar panels you need. 
2. Evaluate your available space and consider factors like shading, orientation, and angles to select the best type of solar panel.
3. Research solar panel types to understand brands, aesthetic characteristics, cost, efficiency, and more. 
4. Compare efficiency ratings to select higher efficiency panels to balance your budget and output. 
5. Check warranties and look for panels with comprehensive coverage for performance and workmanship. 
6. Request multiple quotes to compare costs, system designs, and potential savings. 
7. Read reviews and get references from neighbors and reputable sites like Trustpilot, BBB, and Consumer Affairs.
8. Evaluate financing options to select an option based on your financial situation. 
9. Calculate your payback period and analyze your potential energy savings. Consider incentives, rebates, and tax credits. 

Use the National Renewable Energy Laboratory’s (NREL) PVWatts Calculator to help estimate the output and consumption of the home.  

Federal Solar Tax Credit

Solar panels are eligible for the Investment Tax Credit (ITC). Systems installed between 2023 to 2032 are eligible for a 30% credit. There is no maximum amount a homeowner can claim and expenses include: 

• Solar panels or cells 
• Contractor labor costs, including permitting fees and inspection costs
• Balancing equipment, including wiring, mounting equipment, and inverters
• Energy storage devices with a capacity rating of 3 kilowatt-hours or greater
• Sales tax on expenses

Tax incentives apply to residential and commercial installations to encourage solar adoption. It reduces the amount of federal income tax you owe, resulting in substantial savings when installing solar.  

The Future of Residential Solar Panels

Solar advancements continue to improve solar panel efficiency and bridge the gap between efficiency and panel type. New technologies like perovskite solar cells, passivated emitter and rear cells, and bifacial solar panels have emerged to change the landscape of residential solar in the next few years. 

Perovskite Solar Cells

Perovskite solar cells use a unique solar crystal structure constructed of perovskite as the light-absorbing material. They are the highest efficiency solar panels in development, reaching efficiency ratings over 30% under standard test conditions. 

Perovskite cells have low manufacturing costs and use simpler materials and processes. Unfortunately, the new clean energy producers are in the development phase and lack stability, durability, and scalability.  

Passivated Emitter and Rear Cell (PERC)

Passivated emitter rear cells improve traditional silicon solar cells, including mono and polycrystalline cells. The technology adds a passivation layer to the rear of the solar panel to reduce energy loss.

PERC enhancements increase solar cell efficiency without changing the fundamental materials of traditional solar panels. 

Bifacial Solar Panels

Bifacial solar panels capture sunlight from the front and back sides of the solar panel, using reflected and diffused light. The dual-sided design increases energy generation and can lead to a faster return on investment (ROI). Unfortunately, these solar panels have different spacing requirements and are traditionally best for ground-mounted systems. 

FAQ About Solar Panel Efficiency

Connect With a Solar Panel Installer

The question, “How efficient are solar panels?” is fundamental when choosing the best solar system for your home. It is essential to consider your location, roof style, maintenance commitment, and solar panel materials when making your decision. 

If you’re ready to learn more about solar panel efficiency, let RoofGnome connect you with a local expert, so you can start saving on your utility bills. 

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