Solid state heat “engine”

This is interesting:

A new heat engine with no moving parts is as efficient as a steam turbine

Engineers at MIT and the National Renewable Energy Laboratory (NREL) have designed a heat engine with no moving parts. Their new demonstrations show that it converts heat to electricity with over 40 percent efficiency — a performance better than that of traditional steam turbines.

The heat engine is a thermophotovoltaic (TPV) cell, similar to a solar panel’s photovoltaic cells, that passively captures high-energy photons from a white-hot heat source and converts them into electricity. The team’s design can generate electricity from a heat source of between 1,900 to 2,400 degrees Celsius, or up to about 4,300 degrees Fahrenheit.

I’m annoyed they call this an “engine”. An engine outputs mechanical energy. This produces electrical energy. In reality it is “just” a photovoltaic cell that converts low energy photons into electricity at a remarkably good efficiency.

Still, it could be utilized to convert stored heat into electricity far cheaper than batteries:

The researchers plan to incorporate the TPV cell into a grid-scale thermal battery. The system would absorb excess energy from renewable sources such as the sun and store that energy in heavily insulated banks of hot graphite. When the energy is needed, such as on overcast days, TPV cells would convert the heat into electricity, and dispatch the energy to a power grid.

There are multiple interesting energy sources coming up that have the potential to reduce costs and pollution.

I like living in the future.


22 thoughts on “Solid state heat “engine”

  1. Being able to create electricity from a heat source is cool. I’m a bit concerned about the heat source though. They are looking for something over 1900C. Iron melts at 1538C and steel melts at a temperature not much higher.

    What are they going to be using as a heat source for this thing?

    We normally running steam turbines on super heated steam which is anything above 200C at 1 Mpa (Around 150psi).

    There is a huge difference between generating 200C and 1900C. I’m curious as to how they do it and what they are actually using.

      • I don’t think fission reactors run this hot, while (thermal) fusion reactors run very much hotter.
        This sort of device might work at the focal point of a mirror array solar oven system. Maybe. More likely it’s a nice bit of academic research that is only useful for generating Ph.D. theses and fleecing of the taxpayer.

  2. …inching closer to my goal of drilling in Idaho, Montana and Wyoming and putting huge bundles of thermovoltaic generators down into the Yellowstone magma reservoir. Generate electricity while reducing the chance of a mega-eruption.

    Yes, I know it would take a lot of them.

    • Geothermals are interesting. But having lived next to. And worked on them.
      I can tell you the releasing of trapped steam actually creates earthquakes. Albeit generally smaller, more numerous ones.
      Also, the power generating system would be very unsightly. Which in no way will ever match the Yellowstone motif.
      Good luck in your endeavors though.

    • That was my thought, too. Maybe every household could drill down to the point where subterranean heat reaches 200 C, and be off the grid forever. If this really is something usable, the power companies will lease them to their rate payers to maintain the cash flow. Like buying a TV on credit and still paying for it thirty years later.

      • What, you trying to bump up Haliburton stock? Drilling holes till the temp is 400F degrees is well below 5,000 ft.. Big rig stuff. Messy stuff.
        The biggest problem is drilling close enough to a magma chamber to supply a constant heat source. Or just as every passive system supply will be intermittent.
        If you can get close enough to a heat source. One can drill two wells. In geothermal, you use one to inject water into surrounding strata. And collect the steam that comes up out of the other well.
        Works good. But the collection/ turbine system is a pain. As a couple of wells is never enough to generate demand. Or justify cost.
        It’s not something that can be scaled down. Or improved on all that much.

  3. If they only had something similar that could work off of IR radiation, you could surround an exhaust pipe with these things, without touching it, and scavenge energy out of a system.

    The use for these might be in fusion. Once we have a stable fusion reaction at better than break-even, the next problem is how to get usable energy out of it on a longterm basis, not to mention just cooling the reaction chamber so it doesn’t melt. Heating steam to run a turbine is the old classic, but it’d be interesting to have a fusion lightbulb direct-to-electricity generator.

    • But do any of the major fusion projects actually have a realistic chance of running in production, above break-even, for less than the cost of a couple dozen fission reactors? It’s not clear.
      There are some interesting out of the mainstream concepts that, if they can be developed enough, would have really interesting properties. I’m fascinated by the direct conversion P-11B fusion scheme proposed by Robert Bussard in his Polywell reactor. You can’t do that reaction in a “thermal” fusion system like a Tokamak — too hot, you can’t get to break-even. But a Polywell isn’t a thermal reactor and can do it, though the ones that have been built are small lab demo units and you need something bigger than that. Anyway, that P+B reaction is really nice: you get electricity directly (no intermediate heat step) and no neutrons so the radioactive waste problem is basically not there — quite unlike D-T Tokamaks in spite of the “fusion is clean” stories you read in the popular press.

  4. The “between 1900 and 2400 celsius” bit seems to be not quite as the words in the top quote suggest. We’re not talking about recovering 40% of the heat energy corresponding to the delta between 1900 and 20 degrees. Rather, it’s talking about recovering 40% of the heat energy between 2400 and 1900 degrees. In other words, 1900 degrees corresponds to “discharged”. One wonders what the practically achievable heat loss rate is at 2400 C.
    Indeed this is not a heat engine; it’s an odd kind of battery. And interesting from a pure science point of view. Whether it is practically useful, or better than regular lithium batteries, never mind more exotic kinds like liquid sodium (which are quite cold compared to this device) is another question. Never mind large scale storage tricks like pumped hydropower.

  5. There very well maybe a 40% efficiency in the transfer of heat into energy. But storing that much heat would be a nightmare.
    The only insulator you could use would be a vacuum. On a large scale, would be next to impossible.
    Next up is the heat itself. That amount of heat in one place doesn’t come naturally.
    Nor can it be accumulated from lower amounts. So, the idea of rainy day storage totally escapes me.
    Something tells me their rating are not based in the creation of the heat. Only the use of something pre-existing.
    It seems a good intellectual exercise. But unless you plan to use them for a direct electrical conversion in a nuclear reactor. It doesn’t seem to me to going anywhere.
    To me the biggest hurdle to jump is the idea that CO2 is a problem in the atmosphere. Humans are never going to produce enough to be a pollutant. We just need to rise the efficiency of the way we produce it.

    • At these temperatures you have to be concerned about thermal radiation as well as conduction and convection losses. Hence, the containment system will also have to very good at reflecting the infra-red (and far-infra-red).

      That said, if you read the entire article you will find they claim they already have a way to store that energy, “The system would absorb excess energy from renewable sources such as the sun and store that energy in heavily insulated banks of hot graphite.” Also:

      With the new TPV cell, the team has now successfully demonstrated the main parts of the system in separate, small-scale experiments. They are working to integrate the parts to demonstrate a fully operational system. From there, they hope to scale up the system to replace fossil-fuel-driven power plants and enable a fully decarbonized power grid, supplied entirely by renewable energy.

      “Thermophotovoltaic cells were the last key step toward demonstrating that thermal batteries are a viable concept,” says Asegun Henry, the Robert N. Noyce Career Development Professor in MIT’s Department of Mechanical Engineering.

      • Not that I’m a big truster of science or anything. But storing that kind of heat in giant blocks of carbon? Not that it’s not possible. Just extremely difficult and expensive.
        The only solar plants that I know of that produce that much heat are all point focus collectors. Such as the one used in the plot of the movie, “Sahara”.
        They also had one down in the high desert above San Bernadino Ca. Not sure how much power it actually produced.
        And those systems are not exactly pocketbook friendly.
        Where it seems they would work is in space. As thermal graphite would not need to be insulated. As the vacuum of space would work as the insulator. Also the ability to not be effected by “night” would make it 24/7/365 power generation.
        Weren’t you talking about space/ electric generation once before?

        • Yes, I have posted about Space-Based Solar Power before (see here).

          I agree with you in regards to the point focus collectors being the only solar systems that could reach those temperatures.

          I think you misunderstand the thermal characteristics of space. Any warm object without a reflective barrier gets cold fast unless it has a heat source. The problem is the thermal radiation. Absent a heat source it will reach a temperature not far above absolute zero as the heat is radiated into space.

          There is a reason “Space Blankets” are shiny.

          • Yes, and the use of say, an atomic hydrogen torch. Recycling the same 100 gallons of water would generate a constant heat source.
            The point being that between the vacuum and cold. The insulation necessary is minimal. And the heat generation is constant.
            As it, “catches photons from a white hot heat source”. The real problem is generating that heat. Terrestrial based systems will need an extreme amount of insulation to get it passed the dark night.
            I’m positing that in space, not so much.
            I’m thinking like boiling water in a paper bag.
            Sorry if I wasn’t very clear.

          • MT, the issue is that a very hot object always loses energy through radiation. Vacuum makes no difference. Thermos bottles work because they prevent conduction and convection, and they limit radiation losses by being shiny.
            In this case, the heat sink is graphite, black for good radiation. The design problem is that you need to switch between letting that thermal radiation hit the IR solar cells (to get the electricity) and reflecting it back to the graphite (to retain the heat when you do not want to extract electricity right now). I suppose that’s doable, with an array of gold plated movable mirrors, perhaps venetian blind style. But even gold isn’t a 100% reflector, so the question is what the losses are in the idle (no current draw wanted) state.

          • A couple of things. Cold traps heat very well. And, “heat doesn’t transmit through a vacuum”. has been a principle in science for a 100 years or better. As indeed vacuum is what most thermos’s bottles use for insulation.
            But I agree that radiation does.
            Our earth is one such collector of said radiation.
            But all that aside. Heat storage would not be needed if you were someplace that didn’t have a nightside.
            You just need a glowing white hot photon emitting element. The radiation is what you want to create electromotive force right?
            One would seem to be better off running the system at a constant and using some other form of storage.
            And the whole problem is in using earth based solar.

  6. Yeah, scaling that up to municipal grid level capacities will be daunting.

  7. The problem, as always, isn’t the energy source, it’s the grid. Anything hooked to the grid is vulnerable and subject to (more) political manipulation by the watermelons. Out my way, they are protesting solar farms because of the desert tortoises. Their goal is to reduce overall energy consumption to the Middle Ages. If stuff is hooked to the grid it is much easier to monitor. In addition the watermelons oppose any and all improvements to the grid so you can have infinite energy but can’t deliver it anywhere. The future, if there is one, is locally produced and stored energy. I do get interested in affordable, personal storage gizmos.

    • As the WSJ pointed out in an editorial today, the left doesn’t like the grid. So when they claim to be in favor of green energy, just keep in mind that they really aren’t, because they don’t want any of that hypothetical energy actually to reach your house.

  8. A temperature of 2K Celsius is pretty damn hot. How well will this tech work at lower temperatures….if at all. Outside of a nuclear reactor it’s going to be pretty difficult to achieve and maintain such temperatures safely and efficiently.

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