Kevin Kilty
Crises produce a lot of dubious effort to supposedly solve them. The long past energy crisis of the 1970s for example, the one that actually started as a utility crisis in the 1960s, caused many completely mad proposals for how to generate useful energy without using petroleum liquids. Limestone caverns filled with air during high pressure, let back out through a turbine when pressure is low; air foils propelled by wind around an elongated railroad track; magnets placed on automobile fuel lines to do something, never clearly explained, with the electrons in gasoline to improve mileage – that sort of stuff.
That 1960s-1970s crisis ended, I would argue, once we began burning coal in great quantities to generate electrical energy. We solved the crisis by simply substituting a plentiful fuel without having to adopt complicated schemes. Yet, those less-than-useful ideas live on and we see some of them today now proposed to solve the alleged CO2 crisis.
Unworkable schemes come in two flavors. The first involves schemes too mad capped to work because they have no principle of operation behind them or they violate how the universe works – they violate one of the laws of thermodynamics, for example. The second includes schemes that could work in principle, but could never be made to operate economically.
When I read this headline in the Cowboy State Daily “Research Shows Solar Panels Can Also Generate Electricity At Night”; I figured this to be a routine bout of physics madness. It turns out, though, that this is a case of saying it’s a solar panel that works at night, when, in fact, it is a totally different device. Let’s figure this out.
How does a solar panel work?
Figure 1 shows the cross section of a crystalline silicon solar cell. There are five layers of material; 1) a conductive surface to make device contact; 2) a thin layer of n-type silicon (silicon doped with a bit of phosphorus); 3) a space charge region created at the interface of p-type and n-type material (a pn junction) by diffusion of charge carriers from concentration gradient; 4) a p-type silicon (silicon doped with a bit of boron); 5) finally a lower layer of conductive material to make device electrical contact.
Reading from left to right, Figure 1 illustrates a minimal explanation of solar cell operation. In its equilibrium state on the left, the space charge region sports an electric field that acts counter to the diffusion of charge carriers to establish equilibrium. A photon of sunlight enters the device, and if absorbed delivers enough energy to lift an electron from the valence (bonding) band into the conduction (mobile) band. Raising this electron into a mobile state leaves behind an empty mobile charge known as a hole. The internal electrical field separates the paired electron and hole to prevent them from recombining (maybe 90% effective at this task). Finally, on the right side of the diagram the electron is able to join a current flow through an external load to recombine with the hole.
Figure 1 shows plainly why solar cells don’t work at night. Photons from sunlight provide the fuel to produce mobile charge pairs. There are none at night.
As an aside, knowing that there is an intense radiative flux from the sky to ground during all hours (the greenhouse flux), why don’t the photons in this flux generate an electrical current?
The answer here lies in how much energy a photon absorbed can deliver in relation to the valence to conduction band gap. In a silicon solar cell this band gap energy is about 1.1 electron volts (eV). The energy a photon carries is E=hc/λ; where h is Planck’s constant, c is the speed of light, and λ is the wavelength of the photon. A photon of 1.0 micrometer wavelength, which is in the near infrared part of the spectrum, carries energy of 1.24eV, enough to create a conduction charge pair. A photon from the peak of the Planck function at a temperature of 288K, on the other hand, has wavelength (per Wien’s law) of 10 micrometers and carries energy of only 0.124eV, far too little to create a pair. No photons coming from terrestrial radiation ever supply 1.1eV. These photons can only interact with lattice vibrations (phonons) in the solid material to maintain temperature equilibrium with its surroundings.
Figure 1. The space charge region at the pn junction balances the tendency of charge carriers to diffuse in response to concentration gradient against a growing internal electric field. It is essential to the separation of mobile charge carriers (red/blue dots) once an absorbed photon creates a pair.
Adding a Completely Different Device to Generate at Night
This should put to rest any notion that the solar panels generate energy at night from, what the article says, and the Stanford PR amplifies, radiation. What our researchers have done is to add a separate device to the solar panel, one that operates with temperature differences, and the journalists call it a solar panel for nighttime operation. It’s a collision of science with journalism.
This device is actually a thermoelectric generator. It produces electrical energy from heat flow, or from a temperature difference. The physical basis of this is the Seebeck effect, a voltage that appears along with a difference in temperature – i.e. V=B(Th-Tc), where B is the Seebeck coefficient.
The Seebeck coefficient in metals is small, less than a limiting value of 87 microvolts per Kelvin (uV/K). So metal junctions are used only for temperature measurement as the lower part of Figure 2 shows. Some semiconductors, on the other hand, have much larger Seebeck coefficients (300 uV/K), making them useful for energy generation in some situations; mainly where waste heat is available and when no other, less expensive, method of producing a small amount of electrical energy is available.
For example, the Galileo mission to Jupiter in 1989 used a thermoelectric generator powered by the radioactive decay of plutonium 238. The 41 kg system in this case produced 5W per kg and ran flawlessly for 7 years. No other system available from 1980 era technology could have done the same.
The upper part of Figure 2 shows a long series of pn junctions connected in series to produce a voltage large enough to be useful. This is a thermoelectric generator.
Figure 2. The thermocouple is very widely used to measure temperature in industry and consumer goods.
Since a thermoelectric generator operates from heat flow, it is subject to a maximum efficiency that includes the Carnot factor. Neff=K(1-Tc/Th); where the K factor involves what is known as the figure of merit, ZT, of the thermoelectric materials. Current thermoelectric materials have a poor figure of merit, and then considering the small temperature differences in the Carnot factor on a typical solar panel, almost everything works against this energy scheme.
Although no diagram of the “night-time solar panel” was available in the news article, Stanford PR, or other PR, a person can surmise that the device would resemble Figure 3.
Figure 3 shows a solar panel. Heat fins on the lower face of the panel maintain a temperature near ambient. Sandwiched in between is a thermoelectric generator like that in Figure 2. The upper surface of the panel might have a temperature 40C above ambient when exposed to the full day sun. Or, it might have a temperature 10C below ambient on a clear night in the arid and elevated portions of the West and Southwest. The temperature difference powers the thermoelectric circuitry.
There is no doubt the additional equipment will produce some power in addition to or in place of the solar generator. But this is not a solar panel that works at night. It doesn’t use starlight or moonlight. It doesn’t even necessarily use radiation as some of its PR claims. It works from a temperature difference.
Figure 3. Points labeled ‘A’ are the power circuit for the thermoelectric generator.
In what I view as a misleading claim, the press release states this (bold text is mine):
Advantages
- Low cost, off-grid
- Nighttime 2.2 W/m2 power density
- Outperforms other ambient energy harvesting techniques like wind or radio frequency
- Daytime performance estimated to be 3-4x higher than nighttime
Wyoming wind plants currently dedicate about 100 acres, or about 40 hectares, to each MW of nameplate wind. Since wind plants have an annual average capacity factor of about one-third, the power density computed from dedicated land area is about 0.7W/m2. So, the claim that this 2.2W/m2 of thermoelectric power exceeds the power density of wind is true. Yet, then what must also be true is that the panels having thermoelectric generators must cover the entire 40 hectare area with modified panels to “outperform wind”.
Even though the PR says that the thermoelectric modules need only cover 1% of the solar panel area, many must be connected in series to reach a usable voltage. It seems like a lot of trouble and expense in a weak attempt to address the intermittency of solar energy.
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Can they generate electricity from moonshine? 😉
Of course, but not enough to be useful.
Ethanol IS one of the better biofuels….still about 30% short of gasoline….and it’s general use would drive the cost of tortillas through the roof…
I once worked on an industrial design to collect the ethanol from fermenting potato peels and use it to fire the boilers in the French fry factory…
https://www.forbes.com/sites/michaellynch/2022/06/06/ethanol-is-cheaper-than-gasoline-well-5-of-the-time/
A few years back, a friends adult children were trying to leave the Beaumont area during a hurricane approach. Traffic was bumper to bumper, and the kids were worried about running out of gas, My buddy told them to pull over at the first package store and buy all the everclear and high proof vodka they could find–worries over, and soon out of the traffic mess and on their way home.
I was trying some time to use E85 in California, my car was Flexfuel, designed to properly burn it. It was cheaper than gas, but consumption was horrible. I got around 23l/100km (10.2MPG) ethanol vs. 15l/100km (15.7MPG).
Anyway I liked smell of ethanol every morning after cold engine start….
No, but moonshine can get you you “lit”.
Electricity is everywhere….just suspend a 100 foot copper wire vertically above the ground and connect a voltmeter between the wire and ground. A few years ago, a satellite recorded a lightning bolt that extended for over 400 miles.
Hmmmm . . . I guess I need to quit throwing away my “dead” batteries.
Yes, I was thinking to use that, problem is that this energy density is really low, you got very very low amperage.
To get some usable power from this you would need monstrous metal energy exchanger in air very high altitude.
How you will get 100m2 of metal sheet hanging 100m high in the air? How long will it last high winds?
In theory you can put such structure on hill above your house and use cable to transfer power from there to your house.
But this would be magnet for lightning.
Only if you burn the moonshine.
Yes but! Extracting sunbeams from cucumbers is the method of choice – as Dean Swift demonstrated!
Just like hydrogen powered planes, this Rube-Goldberg arrangement will fade into history never to be heard about again.
Getting down in the weeds is necessary.
Those weeds are known, in the biz, as agrivoltaics.
Smoking and eating the weed is more satisfying though.
Thermoelectric systems are extremely low yield, and depend on a high temperature difference between the hot and cold side of the cell. Maybe a triple junction cell (extremely expensive) absorbing at IR wavelengths could maybe generate a few milliamps per sq. meter = useless.
The only solar panels that work at night that I’ve heard of was in spain where people used
diesel powered generators to illuminate their solar cells at night because the generated current
was highly subsidized by the government to make it economically viable for them (but not the taxpayer).
I think I heard about that, but its such crazy stuff that I’d put it far out of my immediate memory. Subsidies cause idiocy.
Any idea on how much this changes the cost per KW/H from the “solar” panels?
Why not use a Sterling Engine instead and working with an attached generator?
🤣😁
Gas fired appliances of all types have incorporated thermo-electric generators (thermopiles) with standing pilot lights to power the appliances operating thermostatic and safety valve. They typically produce power of ~0.25 to 0.75 v and about 200 mA. The input is an open gas flame ~ 800 BTU/h. This device allows for appliance operation with electrical power and provides a critical safety function assuring gas cannot flow without a proved ignition source. It has saved countless lives and prevented fires and explosions for many decades. Of course the anti fossil fuel fanatics have pushed to outlaw standing pilot control systems.
While thermoelectric generators are very useful devices for small scale applications, they are not a viable method of generating grid scale energy.
I think they just ran the diesel generators to feed the grid thru their solar farm connection … got paid the solar rate for diesel electricity …
Solar panels worked very well, at night in Spain.
Until they were caught…!
https://theecologist.org/2010/apr/16/spanish-nighttime-solar-energy-fraud-unlikely-uk
Ralph
403 error on the link.
Very doubtful the same PV inverter can be connected to the thermopile, the operating V-I window would be completely different. Inverters have a minimum voltage below which they can’t operate, this why a PV system doesn’t start producing power as soon as the sun is over the horizon.
That’s why I put a different load in my Figure 3. At some point, however, a person realizes they are putting too much thought into an idea that might be nothing more than a way to build an IP portfolio.
A fundamental hurdle is that the Seebeck effect voltage is 3-orders of magnitude smaller than the photovoltaic effect voltage.
With PV inverter you are always using MPPT controller between panels and inverter. This device is changing any combination of voltage and current (within its maximum limits) to provide stable nominal voltage and dynamic current. This must be connected to battery or grid to smooth power output.
So there would be absolutely no problem to connect such thermopile to existing PV system.
One time I was already thinking about such solution. There is not enough energy from my PV during Winter, so I was thinking about using thermoelectric elements on my wood stove, but after counting expenses and gained power I gave up.
On the other side, wood powered steam engine running electric generator is still on my possible to do list.
If the thermopile voltage is below the inverter’s voltage threshold, it will be off — no max power tracking is possible.
There is a WUWT article from 2014 reporting on the results of an inquiry in Spain as to how “solar panels” could generate electricity at night back in 2010.
From that inquiry, as summarised (in English) and cited in that article :
A FiT that is six times the market rate => buying diesel generators and arc-lights to shine high-intensity light onto solar panels 24 hours a “day” becomes economically feasible.
.
Part of human nature is that most people have an incredible lack of imagination … unless we’re talking about coming up with ways to
avoid paying taxescollect government subsidies / obtain research grants.NB : There is probably a disconnect between what the researchers actually wrote in their submitted papers and what some administrative intern at Stanford put into that “Press Release”, let alone the end result of journalists “hyping it up”.
The researchers won’t have been paid anything like as much as the Spanish “entrepreneurs” raked in back in 2010, but they will at least be able to pay their bills and put food on their families tables.
I don’t think they bothered with arc lights. Just connect the diesel generator output downstream of the inverter ahead of the meter on a two way switch.
In my first link there is a link to the original WUWT article in 2010 that repeated what Bishop Hill wrote at the time.
.
This would indeed be a more efficient way of “rigging the system” …
… however these are people who did not stop and think that, as the subsequent inquiry report put it :
Some of those “entrepreneurs” may not have had (competent) electrical engineers to advise them, and may thus have stuck to an “arc-lights (24/7)” option.
Funny you should mention that. I think this solar farm in Scotland, whree an annual load factor above 10% is rare, may have questions to answer:
https://www.ref.org.uk/generators/view.php?id=G01532PVSC&tab=lf
Green solutions are always just around the corner. Except in the real world they are not and never will be.
I’m amazed anyone truly believes in them.
So best performance would be Summer with hot solar panels providing the nighttime heat above and a cool evening breeze keeping the time cooler at night. But what about winter when solar panels are cold from snow cover and electric demand increases for electric heating??
Best performance would be hot solar panel surface in daylight against cooler ambient air. Best in wintertime is cold solar panel radiating to a clear night sky against slightly warmer ambient air below the panels shielded from the night sky. Best of these “best” cases is still none too good.
Does the polarity of the voltage depend on which plate is hot, and which one is cold?
If it does, you are going to add some complexity to your input circuitry to handle this reverse in voltage going between night and day.
Yes. Polarity follows heat flow vector. More complexity? Yes.
Absolutely pointless, actually. As you mention, the temperature differential between the hot and cold junctions produces the current flow. If both are either boiling hot or 40 below, no current flows.
I remember seeing other “research” from a prestigious body, which claimed that a special coating allowed more energy to be emitted than absorbed, and purported to show measurements that the more sunlight a panel absorbed, the colder it became – a reverse GHE effect, I suppose. Free air conditioning for the downtrodden masses?
Like much well-funded “research” the magical one-way reverse insulation seems to have faded from view. People still seem to believe in an atmosphere which admits more energy than it allows to exit, causing heating! The Earth seems to have cooled in spite of the passionate beliefs of GHE enthusiasts.
‘As an aside, knowing that there is an intense radiative flux from the sky to ground during all hours (the greenhouse flux), why don’t the photons in this flux generate an electrical current?’
As an aside, I’ll throw out that this is a statement of fact not in evidence given that in the lower troposphere IR active (greenhouse) gases in an excited state are predominantly thermalized by collisions with other gases before they can emit photons.
This is not to say that there is no downward radiative flux in the lower troposphere, but rather that it originates from the thermal emissions of condensed matter (e.g., water droplets, ice and dust particles, etc.) that emit outside the frequencies of the so-called greenhouse gases.
But such a situation would be nonequilibrium and would lead to temperature change. The principle of detailed balance is that at equilibrium each elementary process is in equilibrium with its reverse process. In other words, the collisions would also excite molecules to emit photons.
I hope this does not generate the usual argument that leads to dozens of dueling comments…
‘But such a situation would be non-equilibrium and would lead to temperature change.’
Which is exactly the point of ‘Shula & Ott’ that Andy May and some others here find interesting, if not compelling, i.e., thermal energy from the surface that is absorbed by IR active gases is converted to sensible heat and then transported aloft by convection, not by radiative transfer.
Frank, all gases are “IR active”. All of them. In fact, all non-excited gases at the same temperature emit exactly the same frequency photons in a practical sense. Not only that, but gold, paper, carpet, bricks at the same temperature cannot be distinguished by the frequency of the emitted radiation.
I await with interest the barrage of semantic gymnastics which my comment might generate.
I can only ask: “Where is the predicted “hot spot” of the enhanced greenhouse gas theory? People can argue pro and con until they are blue in the face, but facts on the ground will out.
Which statement itself is not in evidence due to the fact that ALL atmospheric gases, even after being thermalized with IR-active gases, do continuously emit thermal radiation (photons) across a wide spectrum because they have a temperature above absolute zero.
‘…ALL atmospheric gases…continuously emit thermal radiation (photons) across a wide spectrum because they have a temperature above absolute zero.’
I’d like to see a citation for that. Also keep in mind that we’re talking about the IR part of the spectrum here, for which the bulk of atmospheric gases, i.e., O2 and N2 are completely transparent.
Is this the same Peltier cell used by those little fans you can put on top of a woodburning stove?
The Peltier effect is the inverse of the Seebeck effect in Onsager’s irreversible reciprocal relationships.
Peltier: Electric current coupled to heat transport. electric current=cause, heat transport=effect.
Seebeck: Heat transport coupled to charge transport.
Often referred to as the Peltier-Seebeck effect. The same physical process is involved. I tend to separate them depending on whether the desired outcome is heat or electricity.
If your doodad produces electricity from heat differential, I’d call it a Seebeck doodad myself – but it doesn’t really make a difference, does it? Just more opportunities for people to play semantic games, more’s the pity.
There are different optimizations of the materials for Peltier (heat pump with power) and Seebeck (power from temperature differential) devices but they’ll both work the opposite way, just not as well.
The heat powered fans are misusing cheap Peltier devices. They produce enough power to run a small motor. Dunno how much good they do kicking a bit of air sideways from above a wood stove or other heater.
Peltier devices have dropped a huge amount in price. They’re cheap as chips on Temu.
They produce more heat than the amount of heat they move, so the energy output on the hot side is quite a bit more than what they’re absorbing on the cold side. The amount of energy moved VS power input gets less with more power input – and if you put too much power in without enough heat sink capacity on the hot side, you melt the Peltier. Even with really good cooling it’s still possible to exceed the damage temperature, especially with the ones that have sealed edges for condensation corrosion protection. The unsealed ones can have air blown through.
What most YouTuber Peltier experiments goof on is the devices are most efficient at around 50% of their rated power input. In other words use them in pairs in series instead of all in parallel. There’s one guy who stacked three or four Peltiers, in decreasing size, and achieved some crazy low temperature at the top of the pyramid, but it was in a postage stamp sized area and the power used was pretty high.
Seebeck devices prices remain rather high. If they were priced as low as Peltier I’d be buying a batch to experiment with building an exhaust heat power recovery tube to put in the exhaust on an old truck. Wire up the modules to produce 14 volts DC so it can take some load off the alternator. Put an air conditioner compressor clutch on the alternator to disengage it when/if the exhaust power generator keeps up with the draw on the battery.
Even if you do get the panels to be sensitive enough to detect moonlight the power available from the moonlight would not be enough to even power the inverter to turn on let alone produce power.
A full moon provides about 0.05–0.1 lux illumination, while direct sunlight is 120,000 lux
This has already been Origen in Spain where a solar plant actually produced more electricity at night than during the day.
The key was rigging huge arc lights over the array at night, fed by cheap rate electricity, then sold at much higher feed-in tariffs. A nice little earner.
It works, but what are the capital and maintenance costs?
Maybe the next CoP should run a competition for the best “Rube Goldberg” inspired green energy generation invention?
https://en.wikipedia.org/wiki/Rube_Goldberg
Mr. Mr: (Always wanted to do that!) Too complicated, can’t compete with the simple efficiency of that bar bird that dips its beak. It would help if I could do images, but hook that bird up to a dynamo and power up!
🙂
News tip
https://www.energylivenews.com/2025/04/22/gores-climate-tracker-sets-out-to-tell-true-picture-on-emissions/
One to watch
Another big problem here. The hotter the solar panel is, the faster it breaks down.
This “solution” requires you to keep the solar panels themselves as hot as possible, so that you can get the most power out of the thermocouples.
It’s quite likely that the cost of the shortened lifespan of the solar panels will exceed the benefit of a small amount of extra power.
And that’s before you start considering the capital cost of the thermocouples.
A better solution would be to just bolt the heat sinks to the back of the solar panels in order to increase their effective lifespan.
There’s one guy on YouTube who demonstrated increasing the power output of a PV panel simply by running a thin film of water over its top surface. Kept it cooler so it was more efficient.
There are commercially produced PV panels that have water cooling channels bonded to their back sides. They’re markets as combination for generating electricity and for heating, but circulating water through and dumping the heat elsewhere (like in water to air radiators on the shady side of a house, with separately PV powered fans) should help the panels produce more electricity.
I say separately PV powered fans for a good reason. Most PV systems I see use one panel array and tap the power for monitoring, control, tracking motors, pumps etc from that array and battery bank. It should be more efficient to stick on extra, small panels to directly run tracking motors, fans, pumps, the control electronics, and other accessories. Then all the power from the big array can go into the battery back to be run through AC inverters for the house power.
If the motor to move a PV panel to track the sun uses 10 watts, bolt a little 15~20 watt panel onto the top edge of each large panel.
So much added expense, all to try and squeeze a few more percent out of those poor panels.
Photovoltaic is also αβγ(alpha, beta, gamma)-voltaic. Dump a cell in radioactive material, and it will also generate electricity.
And just as practical! Which is, like every con, why there isn’t a normalized cost-per-watt-hour even estimated in the report.
“Research shows….” makes it sound like it always worked that way and nobody knew.
No, see, what you do is have a bank of high intensity lights pointed at the solar panels, and hooked up to a diesel-powered generator. Then, when the sun goes down, fire that baby up. Boom! Done.
Maybe the thermopiles can work off the waste heat of the diesel generators used to power the nighttime arc lamps shining on the solar panels. Everybody’s happy and pseudo-useful.
Very nice Kevin. Wind and solar have already proved they are not a substitute for fossil fuel, hydro and nuclear. Time to move on the other side has list.
Research projects like this, which could have been demonstrated to not generate practical real-world results before they were ever started, are a necessary part of the climate-government-academic-industrial complex. They help to use up the torrent of taxpayer money that flows into the pockets of Big Green.
Without these non-starters (or projects that essentially repeat prior studies), much of the climate research budgets would be unused and would have to be returned to the taxpayers, or used to maintain infrastructure, beef up the military, etc. etc.
The takeway message from this post is that research grant applications need to be rigorously reviewed by specialists in the field, ideally those with hands-on experience in the real world.
hell … given the latest technology its possible the themoelectric generator could generate more power in sunlight than the actual solar panel … but both will generate nothing usefull at night …
Hmm….so adding something else that is useless to solar panels which are essentially of little use. Great idea.
hell I can think of a scheme where you install a bunch of solar panels and a diesel generator … run the generator all day (sunlight hours) sell all the output from the generator and the solar panels back to the “grid” as “solar” energy and reap a tidy profit … my 10,000 watts of solar panels could “generate” 20,000 watts of power all day … does anyone really check the “capacity” of a solar farm ?
At least one cunning chap used off-peak power at night to charge a battery bank of discarded deep-cycle cells (big, heavy – but free), and then sell the power back to the “grid” during the day – receiving a large government subsidised profit per kWh. Apparently nobody actually checks whether the batteries were charged by the sun, as long as the paperwork looks to be in order.
I notice feed-in prices for solar power have dropped markedly in some Australian states. No need to wonder why.
Try this one:
https://www.ref.org.uk/generators/include/graph_monthly.php?id=G01532PVSC
In Fife, Scotland!