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“Efficient” and “efficiency” are such commonly used words that it’s easy to forget that, in many contexts, efficiency measures a mechanical, physical, or chemical phenomenon mathematically.
We’ve all tried to become more efficient at work or in our personal lives.
Merriam-Webster’s definition says, “Efficient most often describes what is capable of producing desired results without wasting materials, time, or energy.”
Obviously, efficiency applies differently to individuals, organizations, and machines.
The same is true for solar products such as photovoltaic (PV) modules — like solar panels — and Smart Devices that run on electricity generated from sunlight.
Read on to find out more about solar product efficiency and the most efficient solar products for home use.
What is Energy Efficiency for Solar Products?
Products that run on solar energy — like solar generators and Smart Devices — are often referred to as being “energy-efficient.”
While it’s true that you can substantially reduce or eliminate utility grid electricity consumption and bills with PV systems that generate electricity from sunlight using the photovoltaic effect, solar products are energy efficient in comparison to more conventional methods of producing power — like burning fossil fuels.
Because solar power is clean and renewable, it’s more “energy efficient” because it generates electricity without consuming finite resources like gas, oil, or coal.
EnergyStar defines energy efficiency as “using less energy to get the same job done – and cutting energy bills and reducing pollution in the process.”
Solar products meet that definition because there are no ongoing costs for generating electricity from sunlight — and no harmful greenhouse gas emissions.
However, the “efficiency” of solar products — and other machines like car engines or refrigerators — typically measures how well a device performs its primary function without wasting energy.
For example, a car or truck’s fuel efficiency technically measures the ratio of chemical energy converted into kinetic energy by burning gasoline or diesel.
However, you’re probably more familiar with that formula being expressed as miles-per-gallon (mpg) or how far you can go on a tank of fuel.
Measuring the efficiency of a solar product varies based on the device’s primary function.
For example, the energy efficiency of a solar refrigerator is measured based on how cold it can make the interior vs. how much power it consumes.
The most commonly used solar products — by far — are photovoltaic modules like solar panels, rooftop tiles, and shingles.
The primary function of each is to generate electricity by capturing energy from sunlight and converting it to electricity.
So, how do you measure the efficiency of solar panels?
Let’s take a closer look…
What is Solar Panel Efficiency?
The efficiency of solar panels — and other photovoltaic modules that generate electricity from sunlight — is a specific measurement determined in a laboratory under Standard Test Conditions (STC).
Standard Test Conditions for Photovoltaic Modules
| Condition Type | Standard Test Condition | Real-World Conditions |
| Solar Incident Angle | Always zero, irradiation beam always normal to the PV panel* | Variable, and depends on time, date, and site latitude. In the case of rooftop systems, roof orientation, and inclination govern system capacity. |
| Solar Irradiation | Always equal to 1000 Watts/m²* | Variable and depends on the time, date, and site latitude. Limited sunshine hours bound system capacity. |
| Ambient Temperature | Always 25°C* | Variable and depends on the time, date, weather condition, and site latitude. Higher ambient temperature degrades PV panel efficiency and reduces system output. |
| Air Mass Coefficient (AM) | Always equal to 1.5* | Variable and depends on the time, date, and site latitude. Higher AM with higher latitudes. |
| System Losses (e.g., Wiring, Inverter) | Always Zero* | Variable and depends on the design and location of PV panels, inverter, and grid meter. |
*Cannot be achieved in real operation (Source: ResearchGate)
It measures the percentage of solar energy a PV module can convert into direct current (DC) electricity per square meter (m2) of photovoltaic cells under laboratory conditions that simulate peak sunlight.
STCs are rarely—if ever—achieved in the real world, but they provide an industry standard for measuring PV module performance under ideal conditions.
It’s essential to consider efficiency when shopping for solar panels — or other PV modules — primarily because it determines how much electricity you can generate per square meter of photovoltaic material.
If you’re mounting solar panels on a rooftop, the PV module efficiency indicates how much surface area receiving direct sunlight you require to generate the desired amount of electricity on an average day.
Many additional factors affect how much electricity you can generate at your location with solar panels and a balance of system…
But a basic understanding of solar panel efficiency is essential for making an informed purchase decision.
The more efficient the solar panels, the less installation space — and potentially fewer PV modules — you’ll need.
Most Efficient Solar Products of 2025
EcoFlow’s mountable and portable solar panels offer industry-leading efficiency ratings of up to 25%.
Efficiency is particularly critical in applications with limited installation space and lower levels of solar irradiance.
Because all solar products rely on the efficiency of photovoltaic modules like solar panels to function, we’ve listed the ratings of EcoFlow’s portable, rigid, and flexible solar panels below.
Portable Solar Panels
| Product Name | EcoFlow 45W Portable Solar Panel | EcoFlow 110W Portable Solar Panel | EcoFlow 160W Next-Gen Portable Solar Panel | EcoFlow 160W Portable Solar Panel | EcoFlow 220W Bifacial Portable Solar Panel | EcoFlow 400W Portable Solar Panel |
| Rated Power: | 45W | 110W | 160W (±5W) | 160W | 220W Front Side/155W Rear Side | 400W |
| Efficiency: | 25% | 22.8 % | 25% | 21 % – 22 % | 22 % – 23 % | 22.6 % |
| Solar Cell Type: | N-Type TOPCon Monocrystalline Silicon | Monocrystalline Silicon | N-Type TOPCon Monocrystalline Silicon | Monocrystalline Silicon | Monocrystalline Silicon | Monocrystalline Silicon |
Mountable Solar Panels
| Product Name | EcoFlow 100W Flexible Solar Panel | EcoFlow 100W Rigid Solar Panel | EcoFlow 175W Rigid Solar Panel | EcoFlow 400W Rigid Solar Panel |
| Rated Power | 100W | 100W | 175W | 400W |
| Efficiency | 23% | 23% | 25% | 23% |
| Solar Cell Type | Monocrystalline | Monocrystalline | N Type TOPCon Monocrystalline Silicon | Monocrystalline |
Most Energy Efficient Types of Solar Products
Solar Panels
All devices that use electricity generated from sunlight do so using photovoltaic cells, also known as solar cells.
Over 90% of solar panels currently available or in use rely on crystalline silicon solar wafers as the primary semiconductive material required to generate electricity from visible light using the photovoltaic effect.
According to the International Energy Agency, crystalline silicon (cSi) “remains the dominant technology for PV modules, with a market share of more than 97%.”
Other types of PV cells currently in use include:
- Passive Emitter and Rear Contact (PERC)
- Thin Film
- Perovskite
Pure monocrystalline silicon solar panels are the most efficient, but the tradeoff is that they’re typically more expensive than polycrystalline solar panels with the same rated power wattage.
For example, the EcoFlow 175W Next-Gen Rigid Solar Panel has an efficiency rating of 25%.
Many 175W polycrystalline solar panels have an efficiency rating of ~15%.
Depending on the application, you’ll likely require 67% more surface area for installation — and 67% more polycrystalline PV cells — to generate the same amount of electricity from available sunlight.
It’s essential to weigh the long-term benefits of higher efficiency against the lower price tag of less efficient solar panels to make the best decision for your specific application.
Solar Generators
Solar generators are plug-and-play solutions that include PV modules and all the other balance of system components required for you to produce electricity from sunlight in portable applications or at home.
Depending on whether you opt for a grid-connected photovoltaic system without storage or go off-grid or hybrid, you’ll need the following components.
- PV modules (solar panels, roof tiles, or shingles)
- Solar inverter
- Solar battery*
- Charge controller*
- Battery management system*
- Cables and wiring
- Transfer switch**
* Not required for grid-tied PV systems
** For home wiring integration (Optional)
It’s possible to purchase each balance of system component separately, but many prefer an all-in-one option like EcoFlow’s DELTA Pro 3 and portable/mountable solar panels.
Going plug-and-play eliminates compatibility headaches, which can be costly and potentially dangerous.
Solar generators make your home more energy-efficient by reducing your electricity consumption by 75% or more or enabling you to go completely off-grid.
However, efficiency isn’t a specification that applies to solar generators — only to the PV modules that provide the DC electricity that makes them operate.
The essential specs to focus on with solar generators are:
- AC output (starting and running watts)
- Battery storage capacity
- Solar charging input (in watts, volts, and amps)
Solar Batteries
Because all renewable energy sources are intermittent, storage is essential unless you’re connected to the utility grid.
Wind turbines don’t generate electricity on still days.
Solar panels don’t work at night.
Grid-tied PV systems use PV modules and an inverter to supply your home with electricity during daylight hours and auto-switch to grid power at night or when consumption exceeds the supply from your solar panel array.
However, it’s essential to note…
On-grid solar panel systems don’t work during a blackout.
Grid-tied PV systems rely on a bi-directional connection that transmits and receives electricity from the grid.
During a power outage, grid-connected systems auto-shutdown to eliminate the possibility of injuring workers trying to restore electricity and further damage to infrastructure.
Being grid-connected can have advantages, such as participating in net metering programs — a billing mechanism that allows you to sell the electricity your system generates in excess of consumption back to the grid.
However, net metering isn’t available everywhere…
And even if it is, you’ll typically pay a significantly higher price for the utility electricity you consume than the credits you earn from selling power to the grid.
Instead, consider taking measures to increase self-consumption of solar power by storing the electricity generate in a solar battery and making your home itself more energy-efficient.
The federal government currently offers Energy Efficient Home Improvement Credit, which offers a 30% federal income tax credit towards qualified expenses, including:
- Qualified energy efficiency improvements installed during the taxable year
- Residential energy property
- Home energy audits
According to the IRS, improvements covered by the credit include:
- $2,000 per year towards qualified heat pumps, water heaters, biomass stoves or biomass boilers
- $1,200 for energy-efficient property costs and certain energy-efficient home improvements, with limits on exterior doors ($250 per door and $500 total), exterior windows and skylights ($600), and home energy audits ($150)
The maximum credit you can claim each year is $3,200, but there’s no limit to how many times you can claim it between now and 2033.
Hybrid solar power systems, like EcoFlow DELTA Pro Ultra, which provide solar power and storage, are eligible for the 30% solar tax credit.
The Residential Clean Energy Credit offers homeowners a credit for 30% of the total purchase and installation costs of eligible small wind, solar thermal, home battery backup, and solar photovoltaic systems against their federal income tax liability.
If the credit exceeds your tax liability for the year of purchase and installation, you can roll the balance over to the following years.
Even if you don’t owe taxes, you may be able to collect the credit in the future.
Learn more about the Federal Solar Tax Credit here.
Smart Devices
As photovoltaic cell efficiency and performance increase, more and more products are available that have all the necessary components to run on solar power built in.
For example, EcoFlow Glacier Portable Refrigerator offers the fastest cooling in the industry and can keep food and beverages cold for up to 40 hours without recharging.
EcoFlow WAVE 2 is a portable air conditioner/space heater that can cool or heat a space by 18°F in 5 minutes. It has 5100 BTUs of cooling and 6100 BTUs of heating power.
Both EcoFlow WAVE and Glacier are highly efficient Smart Devices that support direct solar panel charging.
You can even wear solar power now!
EcoFlow Power Hat offers UPF50+ sun protection from UV rays and heat. It can recharge your phone in as little as two hours of direct sunlight.
It even has dual ports for charging two devices at once.
Like all EcoFlow solar products, the Power Hat uses high-performance monocrystalline solar cells with an efficiency rating of 23-24%.
What Factors Determine the Efficiency of Solar Products?
The primary factor determining the efficiency of solar products is the type of photovoltaic cells used to generate electricity from sunlight…
But numerous other factors affect both efficiency and performance.
If you want a pro-level understanding of solar panel efficiency, you must understand the difference between efficiency and performance regarding how much electricity a PV module will generate.
For example, the 23% efficiency rating of an EcoFlow 400W portable solar panel doesn’t change at night, but it won’t generate any power without sunlight.
With that in mind, here are the main factors that impact the energy efficiency and performance of photovoltaic modules, such as solar panels and products with direct solar charging capabilities.
Sunlight Exposure
The amount of direct sunlight — technically known as solar irradiance — a PV module receives doesn’t affect its efficiency…
However, it’s the primary factor in determining a solar product’s performance.
Because efficiency is determined in a lab under ideal conditions, a solar panel’s efficiency rating doesn’t change, even when it’s pitch dark.
But solar products can’t generate any electricity at all without visible light.
Along with ultraviolet (UV) and infrared (IR), visible light makes up a significant proportion of the solar spectrum — the lightwave energy from the sun that reaches the Earth.
Solar products can generate electricity from any visible light — including moonlight, street lamps, and artificial light from incandescent, fluorescent, and LED light sources.
Small solar products like LCD calculators can operate on artificial light alone.
But PV modules — like solar panels — require high-intensity sunlight to generate sufficient electricity to make them practical for high-wattage applications.
The peak sunlight hours your solar product receives is the number one determiner — not of efficiency — but of performance.
Monocrystalline or Polycrystalline?
Most solar products rely on pure monocrystalline or polycrystalline solar cells to generate electricity using the photovoltaic effect.
Other PV cells are available or in development, but are largely unsuitable for portable or residential use.
Polycrystalline solar products tend to be cheaper but far less efficient than monocrystalline PV modules.
Any savings you get on the sticker price will likely be outweighed by inferior efficiency and performance over the mid to long term.
Monocrystalline solar panels achieve efficiency ratings of up to 25% and can help you achieve solar payback more quickly.
The more electricity your solar products can generate from available sunlight, the greater your return on investment (ROI) over time.
Direction, Angle, and Tilt
Where and how you position your solar panels and products also has a significant impact on performance.
In the northern hemisphere, PV modules should ideally face south during peak sun hours to maximize exposure to direct sunlight.
Positioning solar panels to optimize performance is an art in itself, which is why many homeowners choose to work with a reputable installer to mount their PV modules, particularly for fixed rooftop PV arrays.
If you’re using portable solar panels, you can easily change the direction, angle, and tilt of the unit to maximize sun exposure throughout the day.
Temperature
It may be surprising but solar panel efficiency actually declines in extreme heat.
Solar farms in locations that get extreme amounts of direct sunlight — like in a desert — actually have cooling systems to reduce the temperature of solar panels to optimize efficiency.
The ideal ambient temperature for solar panels is 25°C (77°F), but efficiency isn’t noticeably impacted by temperatures between 59°F and 95°F.
Solar panels perform well in cold and heat, although efficiency decreases at extremes.
Age
Considering the direct exposure to extreme weather that solar panels must endure in order to function, they’re surprisingly durable.
High-quality solar panels with an IP68 rating can last for 25 years or more without requiring replacement.
For reference, that’s longer-lasting than most home roofs.
However, photovoltaic cells do experience a minimal decrease in efficiency over time — approximately 0.5% or less a year — barely noticeable for decades or more.
Final Thoughts
From Smart Devices to solar generators, there’s never been a better time to take advantage of the sun’s endless supply of clean, renewable energy.
The industry-leading efficiency rating of 25% for solar panels and products may seem low…
But it’s essential to realize that it measures a unique property of photovoltaic modules, completely different from the energy or fuel efficiency of home appliances or vehicles.
EcoFlow offers a wide variety of solar products for portable and residential use.
Check out our selection today.