Harvesting Energy at Night: Solar Cell Keeps Working Long After Sun Sets
About 750 million people in the world do not have access to electricity at night. Solar cells provide power during the day, but saving energy for later use requires substantial battery storage.
In Applied Physics Letters. by AIP Publishing, researchers from Stanford University constructed a photovoltaic cell that harvests energy from the environment during the day and night, avoiding the need for batteries altogether. The device makes use of the heat leaking from Earth back into space – energy that is on the same order of magnitude as incoming solar radiation.
At night, solar cells radiate and lose heat to the sky, reaching temperatures a few degrees below the ambient air. The device under development uses a thermoelectric module to generate voltage and current from the temperature gradient between the cell and the air. This process depends on the thermal design of the system, which includes a hot side and a cold side.
“You want the thermoelectric to have very good contact with both the cold side, which is the solar cell, and the hot side, which is the ambient environment,” said author Sid Assawaworrarit. “If you don’t have that, you’re not going to get much power out of it.”
The team demonstrated power generation in their device during the day, when it runs in reverse and contributes additional power to the conventional solar cell, and at night.
The setup is inexpensive and, in principle, could be incorporated within existing solar cells. It is also simple, so construction in remote locations with limited resources is feasible.
“What we managed to do here is build the whole thing from off-the-shelf components, have a very good thermal contact, and the most expensive thing in the whole setup was the thermoelectric itself,” said author Zunaid Omair.
Using electricity at night for lighting requires a few watts of power. The current device generates 50 milliwatts per square meter, which means lighting would require about 20 square meters of photovoltaic area.
“None of these components were specifically engineered for this purpose,” said author Shanhui Fan. “So, I think there’s room for improvement, in the sense that, if one really engineered each of these components for our purpose, I think the performance could be better.”
The team aims to optimize the thermal insulation and thermoelectric components of the device. They are exploring engineering improvements to the solar cell itself to enhance the radiative cooling performance without influencing its solar energy harvesting capability.
Reference: “Nighttime electric power generation at a density of 50mW/m 2 via radiative cooling of a photovoltaic cell” by Sid Assawaworrarit, Zunaid Omair and Shanhui Fan, 5 April 2022, Applied Physics Letters.DOI: 10.1063/5.0085205
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9 Комментарии и мнения владельцев on Harvesting Energy at Night: Solar Cell Keeps Working Long After Sun Sets
Nothing new here folks. We were putting Peltier junction devices with heat sinks on the back our solar panels more than 20 years ago.
“The current device generates 50 milliwatts per square meter”
That is about what one can expect from a 2″x1″ photovoltaic cell in daylight. Not very much power!
Also, around sunset, there will be no thermal production because everything will be warm. Maximum thermal output will be just before sunrise, when most people will still be sleeping. If they live in a humid environment, it may never get cool enough to generate any usable power.
I was so excited when I saw this article but when I read 50miliwatts per m^2…Oh well, I wish them luck as it is a small step in the right direction. Literally any energy is a plus. I hope to see big improvements soon.
The efficiency of a TEG (Thermal Electric Generator) at these temperature differences is extremely poor. The payback time for the increased cost of the hardware is much longer than the expected life of the system.
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Its cool to hear about new efficient energy devices, I’ve got a few great ideas, one is a magnified solar system using the sun, the other is a centripetal oil and water displacement, I have a two cycle magnet engine, and a kinetic wind and water generator, also a theory how to harvest energy from lightning with the ground, but nobody wants to listen to me so I just make comic books
“… also a theory how to harvest energy from lightning with the ground, …”
Calculate how much power is in a lightning strike.
Don’t give up your day job.
Thermoelectric generators have been in use for at least a half-Century. They are known to be not particularly efficient in converting thermal gradients into electrical energy despite decades of efforts to make them more efficient. As pointed out in the article they are one of the most expensive components in the sandwich.
The magnitude of output is insignificant. The cost of the battery solution to store this amount of lighting energy to the night is far less than the additional costs described in their process.
This technology looks very efficient at generating research funding, but not much good for anything else.
Next-gen Solar farms that work at night, in the rain, and self-clean
With the worldwide roll-out of solar, raising the efficiency of energy conversion isn’t just about the materials science of PV cells. Douglas Broom, writing for the World Economic Forum, runs through three “add-on” innovations. Researchers have found a way to generate electricity in the dark as panels cool during the night. A low-cost thermoelectric generator works using the temperature difference between the cooling solar panels and the surrounding air. Next, friction generated by raindrops landing on and running off solar panels can create electricity using a triboelectric nanogenerator. Finally, automated robots trundle across acres of panels to clean them of the dust, water, sand and moss accumulating on the surface: dirty panels can reduce the output of solar panels by as much as 85%.
- Solar panels can traditionally only produce power when the sun shines, but new developments are changing that.
- Scientists have developed solar panels that can work in the dark and be powered by rain.
- These innovations could transform solar into a 24-hour power source, helping with the world’s transition to net-zero emissions.
The biggest problem with solar power is that the sun doesn’t always shine. If solar panels can’t produce power at night, or when it’s cloudy, how can we rely on them as a round-the-clock source of electricity?
This is a problem scientists around the world have been wrestling with, and some are now developing innovative ways to overcome the issue.
Solar energy has been recognised as one of the best ways to provide power to some of the world’s poorest people, with the price of panels down by 80% over the past decade. The World Economic Forum’s 2021 Energy Transition Index highlighted the potential of solar power to improve the lives of people in sub-Saharan Africa, where it says 44% of the population have no access to electricity.
These three innovations could help make more widespread solar power a reality.
Solar power in the dark
Who says solar panels don’t work in the dark? In a breakthrough promising 24-hour reliable renewable energy, scientists have tested panels that keep producing power even when the sun goes down.
Solar panels can now keep generating power even after sunset / IMAGE: Unsplash/Karsten Würth
Conventional solar panels only work in daylight, so you need expensive battery storage to enable solar-produced power to be used at night. Now a team at Stanford University in the US has tested solar panels that keep generating electricity round the clock.
Their innovation takes advantage of the fact that solar panels cool at night. Power can be generated from the temperature difference between the cooling panels and the still-warm surrounding air. This is done using a thermoelectric generator, which produces power as heat passes through it.
Thermoelectric generators can produce power using the temperature difference between cooling solar panels and the surrounding air / IMAGE: Applied Physics Letters
The panels were built using easily available components and the team says they offer the potential to provide a continuous reliable power source for the estimated 750 million people around the world who lack access to electricity at night.
The thermoelectric generator also boosts output from solar panels during the day by running in reverse, producing electricity as the panels heat up. It should be straightforward to upgrade existing panels in this way, the Stanford team says.
Rain-powered solar panels
The volume of power output from conventional solar panels varies with the intensity of sunlight, and it’s not just the sunset that can reduce their power. Heavy clouds and rain can make them less effective. But scientists from Soochow University in China believe they have solved this problem.
Anyone who has been caught in a downpour can attest to the impact of heavy rain. The Soochow team has taken the friction generated by raindrops landing on and running off solar panels, and used this to create electricity.
They placed a transparent layer containing a triboelectric nanogenerator (TENG) over a conventional solar panel. The TENG converts motion – in this case the impact of raindrops – into energy.
As well as boosting power output on rainy days, the friction-powered panels can also produce electricity at night if it rains. The scientists say their solar panels offer “an efficient approach to collect energy from the environment in different weather conditions”.
Robot cleaners for solar farms
Just as Cloud and rain can block out the light to solar panels, so too can dust and dirt. In fact, research shows that dust, water, sand and moss accumulating on the surface can reduce the output of solar panels by as much as 85%.
Cleaning a large solar installation is both time-consuming and expensive. Manual washing with a brush and water would cost 5000 million over a 10-year period, one study for a utility-scale solar plant estimates. But if it’s not done regularly, the grime will eventually become cemented to the panels, reducing solar generation.
Solar panels need to be cleaned regularly to ensure the highest possible level of power generation / IMAGE: Ecoppia
Step forward autonomous dry cleaning robots. Powered by an on-board solar panel, the robots work at night to limit disruption to the panels. Using microfibre cloths and jets of air, one year of their use has saved enough water to meet the needs of 220,800 people.
The robot cleaners’ performance is monitored by artificial intelligence software that plans preventative maintenance to avoid breakdowns. They are already being used to clean millions of solar panels at 30 large-scale solar projects, from Chile to India.
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Douglas Broom is a Senior Writer at Formative Content, writing for the World Economic Forum
Stanford’s solar panel breakthrough explained
As you can see, there’s no way for a PV panel to work without light. The moon and stars shed some light, but only enough to produce a tiny trickle of electricity. Because of this, most solar panels simply go into sleep mode at night.
But the new solar panels developed by Stanford don’t rely on photovoltaics. They use a completely different process called radiative cooling. It depends on the cold of outer space—which is always there, day or night.
How these solar panels can work at night
During the day, objects on Earth absorb heat from the sun. At night, any object facing toward the sky radiates that heat back out into space. In some cases, it loses heat so fast this way that it becomes colder than the surrounding air.
The researchers at Stanford found a way to exploit this temperature difference. They modified an existing solar panel by adding a thermoelectric generator—a device that converts heat flow into electricity. This generator produced electricity from the difference in temperature between the PV cell itself and the nighttime air.
The Stanford team wasn’t the first to try this. However, previous attempts produced only tiny amounts of electricity. The Stanford team’s breakthrough was its design, which generated 50 milliwatts of energy per square meter of panel size.
Of course, this is still a tiny fraction of the power a solar panel can produce from sunlight. A typical solar panel can generate around 200 watts per square meter—4,000 times as much. But even this small amount of electricity is enough for low-power jobs like lighting or recharging a phone. And future generations of this technology could do even better.
As a bonus, the thermoelectric generator also works in the daytime. It just runs in reverse, generating power as the panel heats up in the sun. This power adds a little boost to the energy the panel produces from sunlight.
When will these solar panels be available for public use?
This technology has a long way to go before it’s ready for real-world use. Shanhui Fan, the lead researcher on the Stanford project, says its goal wasn’t to build a device with practical applications. The team was only aiming to prove that it’s theoretically possible to generate power this way.
So don’t expect to see these solar panels for sale any time in the next several years. But do keep watching headlines for future advances in this technology that might someday lead to a commercially viable product.
Can this solar panel innovation help the transition to net-zero emissions?
The Stanford solar panel is unlikely to replace existing sources of electricity in the developed world. The amount of power it can produce is just too small. However, it could prove useful in developing countries, where people often have no reliable access to electricity at night.
The Stanford team’s paper about its research, published in Applied Physics Letters, offers a few examples. It says the new panels could “provide nighttime standby lighting and power in off-grid and mini-grid applications.” (Mini-grids are small, local power grids that aren’t connected to the central grid. They’re often used in rural communities too small or too remote to connect to a larger power network.)
Thus, these night-friendly panels could help developing countries electrify without needing to use fossil fuels for power generation. In this way, they can help prevent future greenhouse gas emissions.
What other new discoveries have been made in solar technology?
Most solar panels depend on bright sunlight. They’re much less effective on cloudy or rainy days. But a team of scientists at Soochow University in China has found a way around this problem. They’ve developed a new type of panel that’s actually powered by rain.
Like the Stanford team, the Soochow team built its panels by adding on to an existing solar panel. In this case, they added a clear layer containing a triboelectric nanogenerator, or TENG. It works by converting mechanical energy—motion—into electricity. When raindrops hit the panel, the TENG captures their energy and turns in into an electric current.
On rainy days, the electricity produced by the TENG boosts the panel’s reduced energy output. And the TENG can also produce power on rainy nights when there’s no sunlight at all. This offers yet another way to squeeze extra power out of solar panels at night.
Why these innovations are important for a sustainable energy future
For years, the fossil fuel industry has argued that we can’t give up coal and natural gas for power generation. They say we need these fuels as a backup for renewable energy sources like solar and wind energy. Without them, we’ll have no way to produce power when the sun isn’t shining and the wind isn’t blowing.
Discoveries like these prove they’re wrong. On one level, they show it’s possible to build solar panels that work at night or in the rain (or even transparent solar panels that may one day double as powerproducing Windows). But their impact goes far beyond this one discovery. They also demonstrate the huge, untapped potential of renewable energy.
The more ways we learn to produce power sustainably, the better our chances of reaching a 100% renewable energy future. And as these innovations show, when it comes to clean power production, we’ve only begun to scratch the surface.
What Happens at Night with Solar Panels?
Powering your home or business with solar energy has a lot of upsides. Solar panels can help you save money on your electric bills, avoid volatile electricity rates, and reduce your carbon footprint. But solar panels have one major downside—they don’t work at night.
Because solar panels don’t work without the sun, you can’t use them once it gets dark outside. But that doesn’t mean you lose power at night with solar panels.
Keep reading to learn more about what happens to solar panels at night.
How Do Solar Panels Work at Night?
Solar photovoltaic panels rely on sunlight to produce electricity. They work by absorbing light and using it to generate an electrical current. Sunlight is essential to this process, and your solar panels won’t work without it. But don’t worry—even though your solar panels will turn off at night, you’ll still have access to electricity. Solar homes have two options for nighttime electricity in Arizona:
A grid connection and/or solar battery storage give you access to electricity at night with solar panels so you can keep the power on around the clock.
Grid-Tied Homes Can Use the Electric Grid at Night
Unless you install an off-grid solar system, your solar panels will be connected to the electric grid in Arizona. This means you can use electricity from the grid whenever your solar panels are not meeting your energy needs. You will of course have to pay for the electricity you take from the grid—your electric meter will keep track of what you use and you’ll be billed monthly, the same way you would be if you didn’t have solar panels.
Net billing is a solar incentive system in Arizona that allows solar users to trade electricity with the grid. As a net billing participant, you’ll be able to send the excess electricity your solar panels generate during the day to the electric grid. In return, you’ll receive a credit on your account. You can use your credit to help pay for the electricity you buy from the grid when your solar panels are not producing energy. Net billing customers are unfortunately not credited at the retail rate of electricity, but at a lower Excess Electricity Generation Rate. Even with the lower rate, however, net billing can help you offset your electricity costs.
Solar Batteries Let You Use Solar Energy at Night
Solar panels may not work without sunlight, but solar battery storage has made it possible to use solar energy for power at night. Solar batteries work by storing the excess electricity your solar panels produce during the day. When the sun goes down, you can use your batteries for power.
If you want to go off-grid, you’ll need a large solar battery bank and a backup generator to ensure you have enough power at night. But for a grid-tied system, one or two batteries is usually enough. You won’t be able to run your entire home on stored solar power at night with just one or two batteries, but having some stored electricity will reduce the amount of power you have to buy from the grid.
And good news— solar batteries qualify for tax credits. including the 30% federal solar tax credit.
SouthFace Solar Electric installs grid-tied and off-grid solar energy systems in Arizona, and we can help you find the right fit for your home or business. We have over 35 years of combined experience and have completed solar projects throughout the entire state. If you’re interested in going solar, we’re here to help. Check out our frequently asked questions to learn more about solar installation in Arizona!