There are betavoltaic generators [1] that directly produce electricity from decay electrons using p-n junctions (similar to photovoltaic cells). However, in the vast majority of applications, they get outperformed by modern lithium batteries (i.e. coin cells).

[1] https://en.m.wikipedia.org/wiki/Betavoltaic_device

How can you compare a generator to a battery? How do you charge the battery without a generator?

I believe GP means a disposable battery that you replace with a new one when it's empty. Not a rechargeable battery.

Betavoltaics aren't really either - they provide a constant, slowly-over-years declining flow of power. They can't be recharged, they _could_ be refueled (don't know if it's economic though), and are mostly used when you need a small flow of power and a long period of time between maintenance (think pacemakers, weather buoys, some satellites or probes).

A bettery, from the viewpoint of a circuit, is just another source. So we could call them chemical electricity generators, if we're brave enough to indulge the confusion

I still don't quite understand it. Where does the battery get the energy? I understand that there's no difference in a circuit, but why is this comparison relevant? Many power sources are way less efficient that using a battery, but we need to charge the battery.

For low-enough-power applications and sufficiently long-lasting batteries, charging is just another step in production.

Betavotaic generators usually produce extremely low power. A similarly sized battery can last for decades at the same power output.

Alkaline batteries are never charged, per se. The energy comes from the one-way chemical breakdown of cathode and the anode.

Are there already solid state ones that use the heat from radioactive decay and the Peltier principle? I assume your idea, if feasible, might be more efficient?

Yes they exist, though I don't think they are Peltier devices: https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_ge...

If you want a "zero moving part reactor," what you are really looking for is: https://en.m.wikipedia.org/wiki/Fission_fragment_reactor

And its spaceflight cousin: https://www.projectrho.com/public_html/rocket/enginelist2.ph...

Though they are not peltier devices either.

We already have a fusion reactor at a relatively safe distance called the sun.

We also have this thing called night, as well as weather and seasons.

And we also have this looming thing called climate emergency, which should conceivably motivate us to forge ahead with renewables and adjust our energy usage patterns to match production peaks, lest we doom humanity to extinction

I feel like this is one of the biggest missed opportunities. Why do we insist on our energy system to be infinitely flexible and full power available 24/7? Is a habit of doing the laundry at night worth more than additional millions of tons of CO2 in the atmosphere?

I understand convenience, laziness and inertia (resisting change) but I also think changing the times when we click "power on" is a simpler solution than mining millions of tons of more lithium, no?

You would have to retrofit every residence to handle daily brownouts (circuits for lights, furnaces and medical equipment stay on, everything else off).

You would have to completely rebuild most of the manufacturing industry, as many plants have startup times measured in hours or days.

It'd be cheaper to just build nuclear.

Industry uses most of the energy. The industry is already moving towards their own price optimizing energy usage and/or storage.

Like computing, having high uptime has a value all its own compared to an unreliable system. Countries which do have regular brownouts you find people buying their own (inefficient, polluting) generators to get round it.

Smart demand-response may yet become a thing, but it's not yet a commodity product. You need a system to send out "turn off" notifications, and a system for measuring that in realtime, and a system for paying people. Some grids _do_ have this, but only for very large consumers.

Many grids do have this for normal residences, but it only covers your air conditioner not everything (and maybe water heater). By running your AC on half duty cycle all day your house still stays cool enough and they are able to reduce substantial peak demand. For most people HVAC and water heating are the two biggest demands, and also ones where simple management can result in a substantial changes in demand without affecting your comfort.

Making thermostats that are aware of dynamic energy pricing or, better yet, are in part controlled by the energy company (I want my house to be 21-24 C, I don't care when the cooling happens) would give us massive flexibility.

All power hungry devices should at least have that capability (maybe other than the kettle, lol). This is literally a cost of $20 hardware in many cases.

In most houses the HVAC and water heater are the only devices that the user can accept not being in full control. Everything else is like the kettle: when you turn it on you want it on now.

> Why do we insist on our energy system to be infinitely flexible and full power available 24/7?

I like to heat my home during winter. We have a (modern, highly efficient) heat pump, so we need most electricity during January, just when the least amount of solar insolation is available [1] and when it sometimes stays cloudy and below 0°C continuously for days. But I guess we'll just have to be more flexible and turn off heating, light, and electricity in general for a week, no big deal.

[1] I wonder if there's a causal relation between cold weather and low solar insolation?

Regarding [1] - are you being sarcastic?

Is that a serious question?

Yes. The dominant (essentially only at the surface) source of heat on the planet is the Sun?

Of course it was sarcasm. I meant to highlight the major problem for using renewables for heating: you'll need most of the power when the least amount of daily solar insolation is available – in winter. This means you either need a lot of storage capacity, or a lot of transfer capacity from far away places, to cover several days of dunkelflaute [1]. This problem is solvable, but it's hard and expensive to solve in practice.

[1] https://en.wikipedia.org/wiki/Dunkelflaute

I couldn’t tell because many people make arguments (or imply) that it doesn’t matter with an apparently straight face all the time! Including large scale gov’t programs.

Including other comments on this exact thread where people did exactly that.

You don't actually need your heat pump 24x7 even on those cold days, if you can run for 15 minutes one, 15 off that would make a big difference to the grid (your neighbor running the same schedule but opposite times) without making your house too cold. Managing the above is tricky though.

> You don't actually need your heat pump 24x7 even on those cold days, if you can run for 15 minutes one, 15 off that would make a big difference to the grid

That's already the case – the actual heat pump only runs intermittently, on demand. This happens quasi-randomly, so you automatically get some load balancing across a city.

The problem is that this is intra-day load balancing, which doesn't help one bit if there are several days of low supply (windless winter days).

What your thermostat does is not synchronized with your neighbors, so the peak load is not managed.

It also isn't synced to supply, instead most people have it set to different temperatures based on when they are home. It would be better to cool or heat the house based on supply. You want the house between 21 and 24c, you don't care when the system is on.

It's often >90 degrees Fahrenheit at night in for months on end where I live, and houses are built cheaply and in a style completely unfitting a hot climate (that is, thin walls, dark roofs, fully aboveground, thoughtless window placement, etc. Standard American Dumbass style). It's unhealthy to sleep in these conditions without AC, even fatal for some.

So yes, we could survive without power at night. We just have to rebuild every building.

As a long-term ideal I don't disagree with you. We should be building for resilience. But that's not a solution to climate change.

Demand shaping is part of the plan, but opportunities are currently limited. For most applications demand can only be shifted by a short time.

Water heating, AC, fridges and freezers, maybe even EV charging (in some cases) could be done at any time during the 24 hour period, if setup with proper hysteresis.

Shifting some load by a couple of hours is indeed often possible, shifting it by 12 hours is already difficult.

Interesting, I would have thought in many cases it is maybe not trivial, but easily doable at worst. Do you have some personal experience with that?

A friend is working at Siemens R&D on this topic.

Renewables alone won't let us decarbonise, they are too expensive and intermittent. We need lots of nuclear if we want to stand a chance.

I don't know why people always comment this on posts about renewables as if it's some kind of gotcha.

When there's no sun, then other countries probably have sun. When there's no sun, there's hydro. When there's no hydro there's wind. When there's no wind, there's tidal. When there's no tidal there's geothermal. And when there's none of those, there's stored energy in batteries.

And if for some reason all of those combined can't satisfy the demand, then there's nuclear as a last resort.

And if there's none of any of those at all, then we've probably got bigger problems anyway

Those things don't add up - there's often no wind, no sun, no hydro. Energy storage is also orders of magnitude too small to store reasonable amounts of energy. I would argue we should start with the cleanest source of energy (which is nuclear, of course) and fill the gaps with renewables.

Many of the plans for the future involve drastically undersized battery storage and decommissioning nuclear. That’s why.

So... my point still stands even without nuclear?

I can’t tell what your point is, frankly. That everything is fine until it isn’t, then we’re boned? Or that it will never go wrong, unless we have ‘bigger problems’? (Which are what exactly? alien invasion?)

Lack of power either way certainly won’t help!

If by design nuclear is offline, fossil fuels are offline, and battery capacity (or other storage) is insufficient for known (but infrequent) weather events, then we’re designing an inevitable and destructive catastrophe as we have no Plan B for when realtime production is insufficient.

And that will happen some day, regardless of how much capacity we build. It’s currently the norm on many days.

One that will kill a lot of people, especially the physically weaker ones, and be very destructive economically.

One that will also play out randomly based on weather, and for which we’ll have no real Plan B.

Being flippant about it seems rather macabre.

While other countries have sun when it is night here, realistically we cannot build the needed wires to get that energy here. We need 20,000km of wire to get power around the earth at the equator.

Wind suffers the same problem as the sun in that sometimes there is no wind anyplace close, and it is even less predictable. While tide power is predictable and consistent, I don't live anywhere close to the ocean so we still need 2000km of wire to get it to me. Geothermo is useful when lava is close to the surface, but I don't live in such an area.

Note that my power is 80% wind, but it was done via several decades of building wind turbines, and I live in Des Moines which nobody would call a big city, if you live in a big city you have even more work to build it (you are both way behind us in building wind, and have a lot more to build)

But you've just done exactly what I said people do wrong. Why do people only consider absolutes when talking renewables. We're not relying on a single source, and we're not relying on countries exactly the other side of the world.

Sure you don't have to have a single wire from one side of the planet to the other, but that's the point in a power grid. Even connecting two solar farms to the grid a time zone apart provides an extra hour of power to each of those time zones and reduces the risk of a single cloud bringing the country down

And as for the rest, you know what the electricity grid is right? Cables already run around the country, and if anything this reduces the strain on single connection as there are lots of smaller generators dotted around the country rather than a huge point of failure connected to a single power plant

> realistically we cannot build the needed wires

On the contrary, Europe, Africa, Asia, the Americas are all wide enough that they can do plenty of solar trading during the daytime. Of course that does not provide energy in the night and that's OK.

We also have space lasers and mirrors.

I can imagine some sort of orbital parabolic mirror setup that keeps a few acres at 2000C in the dead of winter and vaporizes any birds that fly over the power plant site.

We're nowhere near the point where that would make sense, but it could let us harness more than the earth's surface area of sunlight for energy production.

It will probably have to wait until after we plunge ourselves into some a perpetual winter trying to mitigate climate change. Of course, a ring world or dyson sphere would make it obsolete.

This looks like it has about 100x higher power density than what solar PV gives at peak. Combine that with 100% uptime and deployment pretty much anywhere, that are some pretty compelling advantages.

How could that possibly be the case? The current best commercially-available solar panels are 20% efficient. Last-gen stuff is 10-15%.

Well if you put those solar panels right up against the sun, they'd be much more power dense. But for the moment building a nuclear reactor on earth is a significantly easier engineering challenge than building a solar plant on the sun.

Isn't the thing running the Voyager space probe one of these? https://en.wikipedia.org/wiki/Voyager_2#Power

Sure, on paper.

One of the proposed ideas for nuclear rocket propulsion would contain a fissioning gas cloud inside a fused-silica glass blub. At a temperature of several thousand degrees (5,000 - 20,000 K), incandescent light escapes the glass, and gets absorbed by the hydrogen propellant (with bits of solid dust flowing through it as an opacifier). That's one-half of your idea: there's no photovoltaic component, but it does examine the "nuclear fission reactor as an optical light source" half.

https://en.wikipedia.org/wiki/Nuclear_lightbulb

https://sci-hub.se/10.2514/6.1991-3512 (pdf) ("Summary of nuclear light bulb development status" (1991))

excerpt:

- "The gas core Nuclear Light Bulb (NLB) propulsion system could provide both the desired thrust and specific impulse. Initial gas core nuclear rocket (GCNR) investigations started in the 1950s when two somewhat different concepts emerged; an open-cycle GCNR and a closed-cycle GCNR (named the Nuclear Light Bulb). The open cycle configuration (Fig. 1) isolates hot fissioning gas from the chamber walls by flowing cooler propellant around the hot gas. Although some nuclear fuel will diffuse into the propellant and exhaust into space, the theoretical amount was considered too small to be of consequence. NASA-Lewis pursued the open cycle by both analysis and laboratory experiments from the ’50s through the early ‘70s.’"

- "At the same time, United Technologies Research Center, then United Aircraft Research Laboratory, explored the closed cycle NLB concept (Fig. 2).[2,3] Hot fissioning fuel in a gaseous state is confined within a transparent wall of fused silica by a vortex of tangentially injected buffer gas that is also transparent to thermal radiation. Hydrogen propellant, seeded with micron-size tungsten particles to absorb the thermal radiation from the hot fuel, flows axially outside the fused silica wall and is exhausted through thrust nozzles. Complete fuel containment requires continuous withdrawal of a small fraction of the mixture of fuel and buffer gas for reprocessing and reinjection into the vortex flow."

Yeah, that’s a radioisotope thermoelectric generator:

https://en.m.wikipedia.org/wiki/Radioisotope_thermoelectric_...

There’s a story about some loggers finding an abandoned RTG in Siberia and sleeping next to it for warmth. They woke up with severe radiation burns.

That's different, isn't it? An RTG only produces heat via radioactive decay. A nuclear reactor is a controlled chain reaction.

Yes, those aren't nuclear reactors. However nuclear reactors with thermoelectric converters for power generation have been built before. There were the Soviet TOPAZ reactors and the US SNAP-10A reactor.

You'll find a similar story (minus the burns) in The Martian!

https://www.amazon.com/Martian-Andy-Weir/dp/0553418025

No-moving-parts is probably not realistic - the core would be much hotter than the radiating surface due to the thermal resistance of the shielding. More likely, you would have a working fluid to transfer the heat. Most nuclear reactors operate at much lower temperatures where TPV wouldn't be efficient or cost-effective. It's certainly possible to go much higher. Nuclear-thermal rocket propulsion tests ran with exhaust temperatures up to ~2200 C [0]. Whatever fluid is used, you would need to avoid radioactivity in it, b/c that would probably degrade the TPV. Also you would probably want to avoid having heat exchangers because each one incurs a temperature drop. So helium would fit that bill. That's what the "high temperature gas reactors" use [1]. IDK if helium-compatible plumbing/pumping could be made to work at >2000 C though.

Edit: BTW, there are radioisotope thermoelectric generators used for space applications primarily, but they are not true nuclear reactors - they produce short-range radiation that doesn't require much shielding. Nuclear reactors produce neutrons and gammas that require thick shielding.

[0] https://en.wikipedia.org/wiki/Project_Rover#Kiwi_A

[1] https://en.wikipedia.org/wiki/High-temperature_gas_reactor