Couldn't we have a lead box lined with these radiation to electricity converters with a small amount of radioactive material in the center, and have an energy generating device that would last for thousands or even millions of years? Imagine putting the sun in a box lined with solar cells, but on a much smaller scale.
Is there a reason this wouldn't work?
Yep, it's called a "radioisotope thermoelectric generator". Mostly used on satellites.
Related accident: https://en.wikipedia.org/wiki/Lia_radiological_accident
Three men in forest in Georgia during winter found mysterious sources of heat and decided to warm up using them. They turned out to be unlabeled RTG cores. One of the three died as a result of exposure.
The youtube channel @PlainlyDifficult has a whole playlist about "sources in the wild" that also covered this one and many other nuclear accidents and incidents.
Betavoltaic devices are exactly what you’re describing. They convert beta radiation (energetic electrons) into electricity in the same way that photovoltaic cells (solar panels) convert photons into electricity. You can create a nuclear battery by putting some radioactive material that decays via beta emission in one of these.
The downside of these devices is that they generate very little power. It takes a dangerous amount of radioactive material to generate the power needed for say a phone or laptop. Commercial betavoltaic devices generate ~tens of microwatts. They’re useful if you need a low power battery somewhere that you don’t want to replace, like in a remote sensor.
I wonder sometimes about the efficiencies/outputs of some technologies lagging because other technologies are plentiful and easier, even if the potential is there for a better system.
Obviously internal combustion engines come to mind, and the reliance on fossil fuel. I guess it only took us 10 focused years to get to the moon once upon a time, so humanity will pull it off at the last minute.
With betavoltaics it’s more a matter of physics than lack of engineering refinement. Even assuming 100% efficiency, you would need something like 250 gallons (1000 liters) of tritium gas at atmospheric pressure to power a 100 Watt lightbulb.
Nuclear reactors, however, absolutely should be supplying a larger fraction of our electrical grid. Traditional, large reactor facilities have such a high cost and long timescale for permitting/construction that it’s difficult to get newer, more modern reactors built in the US. There are some exciting developments in small, modular reactors that would sidestep these issues. I believe a few designs are in the process of being built for full scale testing.
So you need to consider the relationship between the amount of decay radiation and how long a substance lasts. The more radiation, the faster the fuel will decay. If you want something to last a long time this way it will probably be too stable to generate a lot of energy.
Lot of comments about RTGs, but I don't think that's what OP is asking. RTGs convert heat to electricity, same as a conventional power plants
they just do it in a solid state way instead of steam. In RTGs it doesn't matter where the heat comes from; they are not really analogous to solar cells, as the title asks.
In fact, there are consumer products that use the same technology
you can buy a little electric fan that sits on top of a wood stove and, once up to temp, will start spinning. The electricity is generated by the thermal gradient using heat from the stove, essentially the same as an RTG.
You can buy Sterling engines for that too and skip the electric phase.
Yup, RTGs are still subject to the second law of thermodynamics.
This article has a good breakdown. The biggest issue is efficiency. RTGs are around 5-9% efficient. Standard steam cycle generators are around 30% (see this article ) . You get much more usable energy from fuel used in a commercial reactor vice a RTG.
From the article it looks like RTGs are just converting the heat energy into electricity. Seems like there's a lot unused potential being missed.
Yes, I don't think RTGs are really what you're asking about. It's just a solid state way of turning heat into energy instead of using steam.
Can you ELI5 why the efficiency is so low on the RTGs?
RTGs aren't radioactive-specific, they are just a solid state way of turning a temperature difference into electricity. The better way to do this (at scale) is e.g. a steam engine, which is what big power plants do.
Thank you so much. I think I’m kind of getting but you have some to ing I can do some more research on.
You might be interested about this, too: https://en.m.wikipedia.org/wiki/Ocean_thermal_energy_conversion
Very much so! Guess I’m going down this rabbit hole before bed tonight haha. Thanks for the extra info.
Wow! I think is a subject that I’d going to occupy my downtime for awhile. Thanks for the in depth info, also relevant username?
They take the waste heat from nuclear decay and convert it to electricity through the use of a peltier device. Those work off of differential temperature and are pretty inefficient to begin with. Unmderated Nuclear decay doesn't produce a lot of heat at one time, which is why reactors use a moderator to increase the power output.
What the hell is this thumbnail?
A box of science.
Looks like some imitative ML hallucinated it.
The doodad is working at peak efficiency
It works, but if I remember well my material science course, the yield is pretty bad compared to a simple steam-turbine. Therefore engineer chose the simplest and most efficient design. And this is how the most advanced energy source humanity have end-up being controlled by a good old steam machine
No one has directly answered your question.
The answer is yes, you can create photovoltaic cells better optimise to pick up high energy light such as that from nuclear decay (gamma radiation). However, the power generated by photovoltaics is limited more by intensity of the light, and not the energy per photon (wavelength). For physical reasons is hard to capture the energy of high energy light, so gamma photovoltaics are low power concepts.
There is an idea going around to grow diamond with c14 and also harvest that c14 decay with a diamond based photovoltaic. Making everlasting batteries, albeit radioactive and microwatt. (Specifics are probably wrong, working from memory.)
Just mentioned the diamond thing in another comment, assuming you're also talking about the nano/nuclear diamond battery thing
Yup, RTGs exist, but they're impractical for most terrestrial use cases. The problem is that any isotope that's energetic enough to generate meaningful amounts of energy is also going to be somewhere between quite dangerous and insanely dangerous if the container is breached. And unless there are very strong protocols in place for handling the RTG, on a long enough timeline, there's basically guaranteed to be a nuclear accident.
Since they also rely on the radioactive decay, the power output isn’t constant. It will also decay as time goes on. Sure, it will stay hot (not to mention completely lethal) for a very long time, but that might not be enough for all applications.
Maybe it was enough to keep a lighthouse operational for decades, but eventually it won’t be enough for that. What do you do with an RTG like that? Instead of powering a large light with that, you could probably power a smaller light or a small water pump. After a few more decades, that small pump is once again too powerful for your legacy RTG, so you’ll have to settle for running a smaller pump or a street light with it. It’s going to take a very long time until you get to that point, so it’s highly likely that the RTG will be forgotten, abandoned or stolen by then.
Looking into it, it should be theoretically possible to get a material that decay into beta particles trapped in sphere that would gather these particles and thus electrically charge the sphere.
I don't see how you turn it on or off though, which might be a problem.
I think there a similar concept for providing energy to space missions built around a plutonium isotope.
And why turn it off? Even if the maximum output was only seldomly required, convert the excess energy into a reserve (like green hydrogen) would make sense.
Yes, with RTGs. They are used on mars rovers, for example.
There is the nano/nuclear diamond battery thing too, which is supposed to work like this but apparently produces very little energy if any
I worked up the energy to google. Turns out it's not a photovoltaic (gamma-voltaic?) anyway, it's a betavoltaic. I guess that makes more sense than the rubbish capture cross section of high energy light.
Yes and we already have and use them. Albeit only on NASA probes leaving earth.
Both of the curiosity rovers use this as their power plant. A bunch of plutonium sits in that little tail like stub on them and generates perpetual power for them.
To add to your answer, the reason they're not used on Earth, besides the radioactivity dangers, is that they just can't produce very much power.
Would it be a way to reuse nuclear waste?
The recycling process that France currently uses recovers about 96% of the radioactive material remaining in nuclear waste and produces new fuel rods usable in conventional reactors. Spent fuel rods from conventional reactors can also be used in other types of reactors. For whatever reason, we in the US just shove all of our nuclear waste in old mines like it's still 1950 but technology has continued to develop and places that are more invested in nuclear energy have much better ways of dealing with the waste.
On of the fusion reactor designs works this way. Sorta.
The reactor creates a magnetic field, then fusion happens, creating a magnetic (or electric… iono. Not a nuclear engineer) field flux in the same coils that created the initial field. Fusion stops, then the flux is ‘harvested’ somehow to generate electricity directly. Then the field is primed again, and fusion happens again. It’s pulsed and happens 60-100 times a second.
I think the company working on this is called Helion.
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