By Kayla Wiles
What if paint could cool off a building enough to not need air conditioning?
Purdue University engineers have created white paint that can keep surfaces up to 18 degrees Fahrenheit cooler than their ambient surroundings – almost like a refrigerator does, but without consuming energy.
According to the researchers, the paint would replace the need for air conditioning by absorbing nearly no solar energy and sending heat away from the building. Without the building heating up, air conditioning wouldn't have to kick on.
"It's very counterintuitive for a surface in direct sunlight to be cooler than the temperature your local weather station reports for that area, but we've shown this to be possible," said Xiulin Ruan, a Purdue professor of mechanical engineering.
The paint would not only send heat away from a surface, but also away from Earth into deep space where heat travels indefinitely at the speed of light. This way, heat doesn't get trapped within the atmosphere and contribute to global warming. A video about this project is available on YouTube.
"We're not moving heat from the surface to the atmosphere. We're just dumping it all out into the universe, which is an infinite heat sink," said Xiangyu Li, a postdoctoral researcher at the Massachusetts Institute of Technology who worked on this project as a Ph.D. student in Ruan's lab.
Earth's surface would actually get cooler with this technology if the paint were applied to a variety of surfaces including roads, rooftops and cars all over the world, the researchers said.
An infrared camera image shows that white radiative cooling paint developed by Purdue University researchers (left, purple) can stay cooler in direct sunlight compared with commercial white paint. Purdue University image / Joseph Peoples
In a paper published Wednesday (Oct. 21) in the journal Cell Reports Physical Science, the researchers show that compared with commercial white paint, the paint that they developed can maintain a lower temperature under direct sunlight and reflect more ultraviolet rays.
Their proof is infrared camera images taken of the two paints in rooftop experiments.
"An infrared camera gives you a temperature reading just like a thermometer would to judge if someone has a fever. These readings confirmed that our paint has a lower temperature than both its surroundings and the commercial counterpart," Ruan said.
Commercial "heat rejecting paints" currently on the market reflect only 80%-90% of sunlight and cannot achieve temperatures below their surroundings. The white paint that Purdue researchers created reflects 95.5% sunlight and efficiently radiates infrared heat.
Developing this paint formulation wasn't easy. The six-year study builds on attempts going back to the 1970s to develop radiative cooling paint as a feasible alternative to traditional air conditioners.
The researchers considered over 100 different material combinations, narrowed them down to 10 and tested about 50 different formulations for each material. They landed on a formulation made of calcium carbonate, an earth-abundant compound commonly found in rocks and seashells.
This compound, used as the paint's filler, allowed the formulation to behave essentially the same as commercial white paint but with greatly enhanced cooling properties. These calcium carbonate fillers absorb almost no ultraviolet rays due to a so-called large "band gap," a result of their atomic structure. They also have a high concentration of particles that are different sizes, allowing the paint to scatter a wider range of wavelengths.
According to the researchers' cost estimates, this paint would be both cheaper to produce than its commercial alternative and could save about a dollar per day that would have been spent on air conditioning for a one-story house of approximately 1,076 square feet.
"Your air conditioning kicks on mainly due to sunlight heating up the roof and walls and making the inside of your house feel warmer. This paint is basically creating free air conditioning by reflecting that sunlight and offsetting those heat gains from inside your house," said Joseph Peoples, a Purdue Ph.D. student in mechanical engineering and a co-author of the work.
Cutting down on air conditioning also means using less energy produced by coal, which could lead to reduced carbon dioxide emissions, Peoples said. The researchers have further studies underway to evaluate these benefits.
The researchers are working on developing other paint colors that could have cooling benefits. The team filed an international patent application on this paint formulation through the Purdue Research Foundation Office of Technology Commercialization. For further discussion on this intellectual property, please contact D.H.R. Sarma at [email protected] and reference track code 2020-ABDE-68815.
Reposted with permission from Purdue University.
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Solar power has been an energy source of growing importance in recent years, as technology has advanced and the cost of solar panels has declined sharply. As a result, many smaller sun-powered products have become available, from solar phone chargers to solar generators to outdoor solar lights.
Whether you're looking for ground lights or flood lights, illuminating your outdoor spaces with a wired system can be both an electrical challenge and an eyesore. Convenience, sleekness and sustainability are just a few reasons so many people are looking for the best outdoor solar lights.
In this article, we'll go over how solar lights work, show you some of the best solar lights available and help you decide whether solar-powered lighting is a good choice for your home.
6 Best Outdoor Solar Lights
The below table provides a quick summary of our recommendations for the best outdoor solar lights across six unique categories. We chose these products based on criteria including durability, ease of installation, ease of use, run time, cost and more.
|Best Outdoor Solar Lights||Our Award||Buy Now|
|Solpex Solar Ground Lights||Best Overall||Check Price|
|Brightech Ambience Pro||Best String Lights||Check Price|
|Beau Jardin Solar Pathway Lights||Best Path Lights||Check Price|
|AmeriTop Motion-Sensor Lights||Best Flood Light||Check Price|
|Brightown Solar-Powered Fairy Lights||Best Fairy Lights||Check Price|
|Sunnest Stainless Steel Outdoor Solar Lights||Best Lights Under $20||Check Price|
To dig into the advantages and disadvantages of each of these models specifically, keep reading.
Best Overall: Solpex Solar Ground Lights
Solpex's outdoor in-ground solar lights provide bright illumination without getting in the way or even really being noticeable until they're turned on. The high-quality system is designed to be exceedingly easy to install, is extremely durable in material and operates with ease, turning on automatically and running from dusk to dawn. Solpex's bright LED bulbs are perfect for providing your yard with guiding light year-round.
- Easy to install
- Weather-resistant and durable
- Efficient and effective
- More expensive than some competitors' models
- In-ground lights need more maintenance to keep clean and clear
Why Buy: If you're looking for an in-ground solar garden light that will truly wow your guests when they turn on, the Solpex Solar Ground Lights could be your best pick.
Best String Lights: Brightech Ambience Pro
String lights can be the perfect mood-setter, and using the Brightech Ambience Pro solar powered string lights ensures that you brighten your space reliably and efficiently. With a thorough two-year warranty and extensive weatherproofing and shatterproofing, these lights will hold up through most weather conditions while still appearing delicate enough for any setting — romantic, celebratory, relaxed or otherwise.
- Long lifetime
- Flexibility in installation and design thanks to clip-on bulbs
- Decorative cozy feel
- May not provide enough light for safety or security applications
- Heavier than non-solar string lights
Why Buy: To fill your outdoor space with a warm ambiance, Brightech's solar-powered outdoor string lights are a great option. The Edison bulbs give off a vintage feel that your guests are sure to appreciate.
Best Path Lights: Beau Jardin Solar Pathway Lights
To dot a pathway, garden or outdoor patio, using solar outdoor lighting eliminates the need for fragile and cumbersome wiring, and the Beau Jardin Solar Pathway Lights are some of the best ones out there at an affordable price. These solar path lights take seconds to install — simply use the spike to insert them directly into the ground — and are built to last for years.
- Easy installation
- Great value for money
- Extensive battery life
- Stylish appearance
- Made of plastic, so not as durable as more robust materials
- Provide accent lighting rather than full illumination that may be needed for some pathways
Why Buy: The Beau Jardin Solar Pathway Lights are the best outdoor solar lights if you're looking for affordability and quick installation. They're ideal for accent lighting during the darker hours, and buying multiple packs can allow you to light up a wider area.
Best Flood Light: AmeriTop Motion-Sensor Lights
Floodlights are critical for outdoor security, but if the lights burn out or aren't illuminating enough, then they can't do their job. That's why solar floodlights, and specifically the AmeriTop Motion-Sensor Lights, get high marks from us. They provide a wide angle of light to illuminate an expansive area brightly, and they do so using motion sensors in durable, waterproof fixtures.
- Wide angle is great for security
- Built-in motion sensor requires no additional power
- Highly durable, weatherproof design
- Designed for function rather than decoration, so they may not fit into your outdoor style
- Doesn't provide constant light (only on a motion sensor basis) so may not work for steady light applications
Why Buy: Floodlights can be critical for outdoor safety, and the AmeriTop Motion-Sensor Lights accomplish that efficiently with solar energy and built-in motion detection. We recommend them as the best outdoor lights to illuminate your entire yard for safety.
Best Fairy Lights: Brightown Solar-Powered Fairy Lights
Fairy lights provide the perfect touch of style and design to an outdoor area, and moving to solar lights eliminates the frustrating constraints of having to plug them in. We recommend the Brightown Solar-Powered Fairy Lights because of their quick charging, flexible design and warm light that's perfect to decorate for holidays, barbecues, parties, weddings and more. They also have eight light modes that range from slow fades to steady twinkling.
- Easy to shape into different designs
- Multiple lighting modes and patterns for customizability
- Great price
- More delicate in construction
- May not hold up as well in heavy snow or flooding
Why Buy: Solar-powered fairy lights are the perfect decorative addition to a yard or patio, and the flexibility the Brightown Solar-Powered Fairy Lights offer in design and operation can't be beaten for the price.
Best Lights Under $20: Sunnest Stainless Steel Outdoor Solar Lights
The best solar-powered outdoor lights don't have to break the bank. Sunnest's stainless steel landscape lights come in a pack of 12 for under $20 yet still deliver great functionality, appearance and ease of use. They can be installed to illuminate pathways, gardens or other outdoor areas.
- Attractive in design with cool white lights
- Ready to install in seconds
- Cheaper price means less durable over the long term when up against the elements
- Provides accent levels of lighting rather than full illumination
Why Buy: If you want to dip your toes into the solar outdoor light area without investing a lot of money right away, the Sunnest Stainless Steel Outdoor Solar Lights are your best bet to enjoy that initial experience and get hooked into more solar light solutions.
How Do Outdoor Solar Lights Work?
When choosing the best outdoor solar lights for your yard, it may be helpful to understand how these solar panels work.
You may have seen traditional solar panel installations on the rooftops of homes around you, businesses at which you shop or even installed in large outdoor solar farms owned by utilities. What's particularly intriguing about solar lights is that the technology used is more or less the same as these large-scale panels that are powering entire buildings.
Regardless of the size of a solar panel, it contains solar cells, which are made up of unique semiconductor materials like silicon. When sunlight strikes the cell, some of that energy is absorbed by the material via electrons being knocked loose and being able to flow freely (otherwise known as electricity!).
While standard types of solar panels may contain 36 to 48 solar cells connected together, solar lights are smaller in size and require much less electricity to run (particularly when paired with energy-efficient LED lights). The typical solar light will therefore use just four solar cells, but that's really the only difference from a solar technology basis.
The rest of the solar light comprises a battery, controller board, photoresistor and the light itself. During the sunny daytime hours, the four-cell solar panel will charge up the battery, typically receiving more than enough juice to run for the entire night.
The photoresistor's job is then to detect when light is no longer hitting the solar panel, at which point two things will happen: 1) the battery will stop getting charged, and 2) the controller board will tell the light to turn on. In that way, the solar light is always either charging or illuminating.
When morning strikes and the sun hits the photoresistor once again, the controller board will send a message to turn off the light, and the battery will begin accepting its daytime charge.
Types of Outdoor Solar Lights
Outdoor solar lights are a broad category, filling lots of niche needs and popping up in new opportune areas as the technology continues to improve. Because of their low installation threshold, falling prices and efficiency, solar outdoor lighting solutions can be ideal for countless scenarios, including (but not limited to) the following:
- Ground lights
- Path lights
- Landscape lights
- Motion or security lights
- Fairy lights
- String lights
- Hanging lights
- Post lights
Homeowners deciding which style of outdoor solar light they want to install should consider all the same factors as they would with traditional lighting technologies: What areas do they need to be illuminated for safety? What fits into the aesthetic of the outdoor area? What security needs can lights fill?
The advantage is that homeowners wise enough to go the route of solar lights will have fewer headaches with installation, will have their lighting last for a longer period of time before it needs to be replaced and can easily change their minds on lighting locations because no wiring is needed.
How Much Do the Best Outdoor Solar Lights Cost?
You may be sold on the technology and ease of outdoor solar lights, but how much will it set you back to purchase the best option out there? As with any advancing technology, the answer to that question can vary significantly depending on the choices you make. The answers to these questions, for example, will all have a material impact on price:
- How bright (i.e., how many lumens) do you need the lights to be?
- How efficient do you want the lights to be?
- How durable do you need the lights to be?
- How top-of-the-line do you want the materials and decorative nature to be?
For the bulk of the outdoor solar light market, regardless of your answers, each light system will typically cost between $20 and $50. If you really want to go with a high-tech system (which could mean higher-capacity batteries, more intelligent functionality, intricate customizations and more), it could end up costing over $200.
The best approach is to analyze your specific needs and then purchase accordingly.
Choosing the Best Outdoor Solar Lights for Your Home
According to the U.S. Department of Energy, outdoor solar lighting works quite well in most areas of the U.S., as it doesn't require an excessive amount of sunlight to charge up and work. This means that even on cloudy days or during winter, you'll still be able to light your way. Solar light adopters aren't only helping the environment, but they're also saving money via reduced energy consumption.
If you're ready to make the switch, identifying the best solar lights for your specific home and need is no small task. When picking the best outdoor solar nights for your need, some characteristics you're going to have to make decisions on include:
- Design, style and aesthetics
- Size of fixture
- Ease of use and control after installation (remote-controlled, connected to in-home smart device, manually controlled, etc.)
- Durability to weather and general wear and tear
- Expected lifetime before replacements are needed
- Overall system cost
FAQ: Best Outdoor Solar Lights
What are the brightest outdoor solar lights?
If you want the brightest outdoor solar lights, you'll want to look at floodlights or spotlights. These often have a higher lumen count and can light spaces better than string or ground lights. Our pick for the best solar-powered floodlight is the AmeriTop Motion-Sensor Light.
What is the best outdoor solar lighting?
We named the Solpex Solar Ground Lights the best overall choice for outdoor solar lighting. These lights are easy to install, ultra-efficient and hold up well in the elements.
What should I look for in outdoor solar lights?
When choosing the best outdoor solar lights for your home, consider factors such as design, brightness, durability and cost.
Do outdoor solar lights really work?
Yes, outdoor solar lights work just as well as traditional outdoor lights. According to the DOE, solar-powered outdoor lights work well in most areas of the U.S. because they don't require much sunlight. This means that even if you live somewhere with more gray days than sunny ones, you can still harness the sun's power to light your outdoor space.