10 ms·

For anybody who is interested in this stuff, I was the CTO of a Canadian geothermal company, and I became convinced that it was folly to dig 4km down to get hot

by rfrey 6y ago

For anybody who is interested in this stuff, I was the CTO of a Canadian geothermal company, and I became convinced that it was folly to dig 4km down to get hot water when we are surrounded by waste heat in large industrial plants that is largely untapped. By way of example, I was working on a geothermal plant in Alberta that would generate 5MW and cost $60 million (CDN) to build. Similar heat can be found everywhere at surface, especially in Alberta which has a heavy industrial base. Harnessing the heat from industrial sources is exactly the same as a geothermal plant: only the source of heat is different. For example, I scoped a project on a natural gas pipeline compressor station. It used a RB211 gas turbine to drive the compressor. Capturing the waste heat from the exhaust stack of that engine gave us 7MW of net generation, at a cost of $30 million, and much lower operating expenses to boot. 58% of the energy we generate each year is lost, much of it (upwards of 20%) as industrial waste heat. That's terajoules of electrical generation potential globally, just from the easily captured stuff. It's not exactly like geothermal energy, because you have counterparty risk in that the cement factory (or whatever) might close. But the tech is identical to geothermal, and there's no exploration risk or digging expense.

JoeAltmaier 6y ago
Sounds like low-hanging fruit. But not really scalable. A 7MW plant sounds OK for some applications. But a really big geothermal plant might compete with nuclear.
- rfrey 6y ago
  It's a good point, but there are many grid experts who argue that smaller, distributed generation is more robust and reliable than larger, 500MW+ plants. Outside a few areas, most geothermal plants are quite small: I doubt we'll ever see one over 15MW in Canada, for example. A 7MW plant doesn't sound like much, but if you're cookie-cuttering 9 of them along a line, costs come way down since they're all essentially identical. I did some back-of-the-envelope calculations and if we did all the larger (over 15000hp) natural gas compressor stations in the US and Canada, we'd be looking at something like 42TWh per year of generation. That compares to 68 TWh for all deployed utility solar (2018 tho). That's just gas compressor stations, which are about 15% of the industrial heat generated in the US.
- rfrey 6y ago
  Responding specifically to the competition with nuclear: you're absolutely correct: the Geysers geothermal complex (which is actually about 22 power plants) is about 1.6GW. That's easily the world's largest though: I don't think there's another one over a gigawatt anywhere. And you need really special conditions for that kind of power - specifically really hot geological conditions. The problem, as always, is that jerk Carnot and his limit. Most accessible geothermal fluid is <150C except in very geologically active areas. That puts a pretty hard limit on plant efficiency.
epistasis 6y ago
I'm surprised that the waste heat is enough to drive a turbine and generate electricity! How much waste heat is that hot? Combined cycle natural gas turbines already do this. Natural gas combustion drives a turbine, then the "waste heat" drives a steam cycle. Even though that steam cycle is less than 50% efficient, I'm guess the wasted heat there can't be used, right? How high of a COP would it take to make a heat pump a feasible way to make lower temperature waste heat a source? Or is this where the thermodynamics breaks down?
- colechristensen 6y ago
  You won’t be able to take waste heat economically from a power plant, they’re generally designed to capture more and more heat until diminishing returns take over. There are a lot of other industrial processes though that don’t do any heat capturing. Something left out though is that you might have lower capital costs but if you try tacking a power plant on somebody else’s factory, they’re going to want a cut. Efficiency is dictated by temperature differences, you get a bigger cut for less investment when the temperature difference between heat source and environment is largest.
  - brundolf 6y ago
    What if you just sold the equipment (+ setup services) to the plants directly? They could turn around and reuse the recovered energy themselves, or sell it on down the line, but there would be no coordination/mixed-incentives problem.
    - sroussey 6y ago
      Probably best to sell a kit of a few designs, equipment, project management, and financing (avoid capital costs) that shares in income but also has contractual obligations for length of running.
    - colechristensen 6y ago
      Then you're the one taking the cut, still an additional cost that needs to be considered when doing a comparison with digging a hole for geothermal energy.
foobarian 6y ago
Thinking about this with a software engineering hat on I am breaking out in cold sweat. You attach these waste heat generators to random other industrial machinery and now suddenly you can't do any maintenance or power cycling for fear of disrupting the power supply to whole regions. It also seems organizationally very complicated to have co-located hardware owned by completely unrelated organizations. I guess if it was all nationalized or belonged to one huge multinational it may be less of a concern.
- TeMPOraL 6y ago
  > You attach these waste heat generators to random other industrial machinery and now suddenly you can't do any maintenance or power cycling for fear of disrupting the power supply to whole regions. It's not that you can't. But you have to coordinate with another party, particularly if you're generating large amounts of energy this way. But the grid is evolving towards increased storage to accommodate renewables, so this will mitigate the impact of shutting generation down to run maintenance on the heat source. But if we don't want to couple random industrial plants to the supply side of the power grid, I wonder if we couldn't be using this with some self-contained carbon recapture devices. Heat -> power -> less CO₂ in the air. If that kind of tech will ever be workable, that is. All this to say, when I put my software engineering hat on, I'm starting to get sick thinking of all that capacity being wasted.
- dundarious 6y ago
  I’m ignorant on the topic, but seems more like a great cost- & carbon-reduction technology for the industrial plants, rather than a power generation technology for the masses. For what it is, it sounds great though.
  - rfrey 6y ago
    It never meets economic hurdle rates for industrials on their own, which is why we're building them as independent power plants. We prefer to sell the electricity back to the host facility, but we often sell into the grid.
pfdietz 6y ago
Waste heat is one of the markets Climeon is going after. They've had success in exploiting waste heat on ships, for example. https://climeon.com/ https://climeon.com/
- rfrey 6y ago
  They're a great, innovative company. They're mostly focused on smaller stuff - 150kW and below, although I think they did some larger bespoke projects earlier. For larger stuff my favourite company is Exergy (www.exergy.it). They resurrected a format of turbine - a radial outflow configuration - that lost to axial turbines in the early 1900s, recognizing that it had special advantages when used with organic fluids rather than steam.
trhway 6y ago
> It used a RB211 gas turbine to drive the compressor. Capturing the waste heat from the exhaust stack of that engine gave us 7MW of net generation, at a cost of $30 million, and much lower operating expenses to boot. the main issue here is actually such a low efficiency turbine - an efficient one wouldn't have such an easy capturable exhaust heat to start with. One can understand that a gas turbine on a plane for example has weight limits so you can't tack on additional turbine stages, etc. to increase efficiency, yet for ground based it would only be about increased capital costs of such a turbine - so that means that running inefficient turbine is cheaper, i.e. the energy/fuel is still very cheap.
- rfrey 6y ago
  My understanding is that the most efficient turbines top out at about 40%. Reciprocating engines are better, but even they can't get much above 50%. There's still lots of heat there even in the most efficient engines. You're absolutely right about the efficiency being just fine -- especially when you're a pipeline company and you just pull fuel for free out of the pipeline to run the turbine. That's a big reason why these companies haven't built these plants already.
  - trhway 6y ago
    >pull fuel for free out of the pipeline to run the turbine. yep. The situation here and globally would be completely different if to the price of fuel, however low one can get it, the price of the emitted carbon were added. That would in particular have leap frogged our civilization efficiency.
  - jjk166 6y ago
    Rankine cycle tops out at 40%, gas turbines are more like 50%, and combined cycle, which is really what's being implemented here, can reach around 60%. When the gas is essentially free, there's not much incentive for efficiency, but they could have powered the compressor with a smaller yet more efficient combined cycle system. If you can economically extract power from a powerplant's waste heat, the original power plant was suboptimally designed.
ilaksh 6y ago
The article suggests that the trick to high profits is really getting the depth for higher temperatures without melting the equipment. Because getting lower with higher temperatures dramatically increases the energy generation. As opposed to sort of current minimal viable depth/temperatures. So is it possible that with some significant engineering advances the costs would go down and generation would go up quite a bit? To me the article is suggesting research investment to improve the materials and technology to go deeper less expensively. Can you provide any insight into the feasibility of that type of research paying off? Do you know of any promising techniques, materials, designs? Or maybe you feel like they are insurmountable challenges? Thanks for any details.
- rfrey 6y ago
  You can go deeper, but in most regions you'll be into impermeable rock by the time you get usable temperatures. You need the rock to be permeable so brine can flow from your injection site to the extraction well. Companies like Eavor claim a closed loop in impermeable rock will work, but then you're limited by the thermal conductivity of the rock around your pipe. You can only pull out as much heat as can flow through the rock around the pipe. Our simulations on Eavor's system showed they would work for about a couple months before they started dropping off. Fracking seems like a more promising avenue, and it might work. A ton of political challenges there though.
  - neltnerb 6y ago
    Interesting, when I studied these a long time ago they talked about mining geothermal energy in these kinds of deep rocks but having to move the "heat mine" after it got cool due to the lack of heat transfer through the solid rock. I got the impression that heat flows into the hot rock are orders of magnitude lower than the heat flows out required to make power generation efficient and useful. The radiator design is interesting but ultimately it's a heat sink and power output will be limited. Initially I bet the power output is great, and as the area cools they tap it out. Who knows how long it'd last, you'd think the higher the power capacity the faster it would cool down underneath. So really you need to be able to build new mines cheap enough to justify doing such a hard mine knowing it'll only last for 22 years.
vmception 6y ago
good points, did you notice that you can also get investors and pay yourself a modest salary for 10 years?
jonstewart 6y ago
The Washington, DC wastewater treatment plant figured out how to generate methane from sewage, which they then burn to drive turbines. They get 10MW of net electricity out of it, which they use themselves (sounds like their electric usage is 30MW). It would seem that a lot of industry installations with waste heat sources likely also use a lot of electricity and could benefit from doing something similar. https://www.dcwater.com/whats-going-on/news/dc-water-leverages-technology-first-north-america-generate-clean-renewable https://www.dcwater.com/whats-going-on/news/dc-water-leverag...
- nullc 6y ago
  Even ignoring the energy savings, methane is a potent greenhouse gas so you'd much rather it be burned than just released. Though I wonder if there isn't an opportunity to sequester a lot of carbon being missed by digesting sludge instead of ... say, dumping it into a deep injection well.
- why_only_15 6y ago
  10MW ~= $3M/yr @ $30/Mwh (going by https://www.eia.gov/electricity/wholesale/xls/ice_electric-2020.xlsx https://www.eia.gov/electricity/wholesale/xls/ice_electric-2... )
- tobinfricke 6y ago
  I think this is pretty common at sewage treatment plants. Our local plant (EBMUD in West Oakland) does this too. In fact it seems they import additional organic waste to throw into their methane digester, with the resulting generation covering all of the plant's needs: https://www.ebmud.com/wastewater/collection-treatment/wastewater-treatment/ https://www.ebmud.com/wastewater/collection-treatment/wastew...
kumarvvr 6y ago
Unlike geothermal heat, Industrial heat is too spread out. The quantity of heat may be comparable, but because of wide area of distribution, it is not practical to tap it. By wide area, I mean the various sources of heat in any industrial plant. Also, industries would not really prefer if you want to have equipment to tap waste heat at various points in their shops. Even in the example you give, of a turbine outlet, it is economical and practical, only because the heat is concentrated in the exhaust. However, most plants that have turbines, do recoup energy from turbine exhausts.
- 01100011 6y ago
  You could say the same about solar. Personally, I think residential solar is less preferable than commercial installations where you can benefit from greater centralization, but that said, residential solar seems to have done fine. Now on the other hand, solar has less moving parts, so the reliability is greater and the distributed nature may be less important.
  - novok 6y ago
    Doesn't having electricity generation distributed reduce transmission loss although?
  - kumarvvr 6y ago
    In solar, there are no naturally occurring concentrated sources of energy. We have to concentrate it in certain ways, or use solar panels. Residential solar will definitely reduce load and transmission losses. However a broad strategy must be required by governments to plan and establish solar plants. For example, it makes sense to have a coherent solar planning policy taking into account the huge consumers of electricity (cities and industries) and planning solar plants near them, reducing the losses in transmissions (which can go upto 33% or more). Additionally, if the production and consumption are close by, transmissions can be made with lower voltage and higher currents, perhaps even HVDC, to unlock even more efficiencies.
umvi 6y ago
Seems like it would be better to directly use the heat i.e. for desalination vs. trying to turn it into electricity. i.e. build a nuclear power plant near the coast, use piped in sea water to cool it, use hot sea water to desalinate with heat gradient
- Mountain_Skies 6y ago
  Can the problems encountered with the Fukushima nuclear plant being located on the coast be overcome?
  - Baeocystin 6y ago
    What led to the Fukushima reactors failing the way they did was that their emergency generators were situated in low-lying, tsunami-reachable areas. Simply relocating/elevating them, and the whole mess wouldn't have happened. https://news.usc.edu/86362/fukushima-disaster-was-preventable-new-study-finds/ https://news.usc.edu/86362/fukushima-disaster-was-preventabl... (There's more to it than this, of course, but it's an accurate first-pass summary.)
rebuilder 6y ago
How long will the industrial plants that produce such heat be able to operate? The geothermal plants are being built as we try to address climate change, with many countries aiming for carbon neutrality by 2035. How much room is there for fossil fuel powered plants in that?
- alvah 6y ago
  That is an interesting question, as a world without large industrial plants will not resemble the world we live in today, in all kinds of ways. Any sensible plan to reduce emissions will need to provide for industry (most industrial processes involve heat), otherwise we're all going back to living in caves.
rojobuffalo 6y ago
long-term probably both are good ideas. i would think geothermal would be more stable over a long period of time.
pontifier 6y ago
This is making me wonder how much fuel savings you'd get by replacing an alternator with a peltier effect generator.
- raverbashing 6y ago
  No fuel savings. Peltiers are very inneficient
fulafel 6y ago
This sounds good for low hanging fruit in cases where industrial waste heat and local population have an auspicious ratio, but probably rare. In metro areas the required scale is different... Eg here's a 100x bigger (150 MW electricity + 350 MW) district heating generating CHP plant in Stockholm, serving a fraction of the city: https://dcd.events/conferences/energysmart2018/benefits/visit-stockholm-exergis-kkv8-chp-plant https://dcd.events/conferences/energysmart2018/benefits/visi...
jillesvangurp 6y ago
That big industry that you talk about needs to actually switch to clean energy sources as well. It needs to happen for environmental reasons. But the reasons it is actually happening are more related to cost. There are a few aluminium and steel plants coming online running on hydrogen recently. With clean sources for hydrogen coming online as well, that puts us on a track to cleaning up energy in heavy industries. Right now natural gas is still cheaper but that may not last that long as prices for wind and solar continue to trend down and as there are ongoing improvements in cost of producing hydrogen. Geothermal could be part of the solution for that. But the price has to be right and I have a hunch that there are some challenges there long term. With geothermal the innovation is not necessarily in building huge plants in geologically unstable areas, which in other places indeed requires drilling quite deep, but in using heat pumps to work with small temperature differences you get by digging only a few tens to hundreds meters deep. This is currently quite popular in northern Europe as a way of cheaply heating/cooling houses and reducing cost relative to burning natural gas. The main cost is putting pipes in the ground. In any case, the main challenge with any energy generation project is cost and amortizing that over its lifetime. There are a few things on the market that have come down in price by orders of magnitude and are on track for more improvements in the next decades. This puts any predictions about cost and profitability at risk. In the case of coal, people came out on the wrong side of the equation and a lot of plants are being shut down ahead of their scheduled end of life. IMHO the same will happen to gas plants in the next decades. That makes investments in large scale geothermal very risky. Which is perhaps why there is far less of it than you would expect given that we've known how to build such plants for a very long time. The combination of cheap storage and low cost solar panels or super efficient 10-20 MW wind mills is becoming quite hard to compete with and you see this stuff popping up in formerly very fossil fuel friendly places because it makes sense right now from a cost perspective. Even Iceland is investing in offshore wind.
01100011 6y ago
That sounds a lot like cogeneration. I remember 25 years ago there was a plant near LA that produced steam to process oranges while also generating power. I think you're right though, there is a lot of untapped waste heat out there.
Kosirich 6y ago
Were the projects you mention that used waste heat and generated electricity based on (ORC) Organic Rankine Cycle?
notabee 6y ago
That sounds like a good efficiency measure to use in addition to adding new zero/low carbon energy sources. If you only capture waste heat, the net total is still all coming from carbon-based sources. Maybe it's the low hanging fruit for now, but it's not enough. We need to tap every feasible alternative energy source.

by rfrey 6y ago

JoeAltmaier 6y ago

Sounds like low-hanging fruit. But not really scalable. A 7MW plant sounds OK for some applications. But a really big geothermal plant might compete with nuclear.

rfrey 6y ago
It's a good point, but there are many grid experts who argue that smaller, distributed generation is more robust and reliable than larger, 500MW+ plants. Outside a few areas, most geothermal plants are quite small: I doubt we'll ever see one over 15MW in Canada, for example. A 7MW plant doesn't sound like much, but if you're cookie-cuttering 9 of them along a line, costs come way down since they're all essentially identical. I did some back-of-the-envelope calculations and if we did all the larger (over 15000hp) natural gas compressor stations in the US and Canada, we'd be looking at something like 42TWh per year of generation. That compares to 68 TWh for all deployed utility solar (2018 tho). That's just gas compressor stations, which are about 15% of the industrial heat generated in the US.
rfrey 6y ago
Responding specifically to the competition with nuclear: you're absolutely correct: the Geysers geothermal complex (which is actually about 22 power plants) is about 1.6GW. That's easily the world's largest though: I don't think there's another one over a gigawatt anywhere. And you need really special conditions for that kind of power - specifically really hot geological conditions. The problem, as always, is that jerk Carnot and his limit. Most accessible geothermal fluid is <150C except in very geologically active areas. That puts a pretty hard limit on plant efficiency.

epistasis 6y ago

I'm surprised that the waste heat is enough to drive a turbine and generate electricity! How much waste heat is that hot? Combined cycle natural gas turbines already do this. Natural gas combustion drives a turbine, then the "waste heat" drives a steam cycle. Even though that steam cycle is less than 50% efficient, I'm guess the wasted heat there can't be used, right? How high of a COP would it take to make a heat pump a feasible way to make lower temperature waste heat a source? Or is this where the thermodynamics breaks down?

colechristensen 6y ago
You won’t be able to take waste heat economically from a power plant, they’re generally designed to capture more and more heat until diminishing returns take over. There are a lot of other industrial processes though that don’t do any heat capturing. Something left out though is that you might have lower capital costs but if you try tacking a power plant on somebody else’s factory, they’re going to want a cut. Efficiency is dictated by temperature differences, you get a bigger cut for less investment when the temperature difference between heat source and environment is largest.
- brundolf 6y ago
  What if you just sold the equipment (+ setup services) to the plants directly? They could turn around and reuse the recovered energy themselves, or sell it on down the line, but there would be no coordination/mixed-incentives problem.
  - sroussey 6y ago
    Probably best to sell a kit of a few designs, equipment, project management, and financing (avoid capital costs) that shares in income but also has contractual obligations for length of running.
  - colechristensen 6y ago
    Then you're the one taking the cut, still an additional cost that needs to be considered when doing a comparison with digging a hole for geothermal energy.

foobarian 6y ago

Thinking about this with a software engineering hat on I am breaking out in cold sweat. You attach these waste heat generators to random other industrial machinery and now suddenly you can't do any maintenance or power cycling for fear of disrupting the power supply to whole regions. It also seems organizationally very complicated to have co-located hardware owned by completely unrelated organizations. I guess if it was all nationalized or belonged to one huge multinational it may be less of a concern.

TeMPOraL 6y ago
> You attach these waste heat generators to random other industrial machinery and now suddenly you can't do any maintenance or power cycling for fear of disrupting the power supply to whole regions. It's not that you can't. But you have to coordinate with another party, particularly if you're generating large amounts of energy this way. But the grid is evolving towards increased storage to accommodate renewables, so this will mitigate the impact of shutting generation down to run maintenance on the heat source. But if we don't want to couple random industrial plants to the supply side of the power grid, I wonder if we couldn't be using this with some self-contained carbon recapture devices. Heat -> power -> less CO₂ in the air. If that kind of tech will ever be workable, that is. All this to say, when I put my software engineering hat on, I'm starting to get sick thinking of all that capacity being wasted.
dundarious 6y ago
I’m ignorant on the topic, but seems more like a great cost- & carbon-reduction technology for the industrial plants, rather than a power generation technology for the masses. For what it is, it sounds great though.
- rfrey 6y ago
  It never meets economic hurdle rates for industrials on their own, which is why we're building them as independent power plants. We prefer to sell the electricity back to the host facility, but we often sell into the grid.

pfdietz 6y ago

Waste heat is one of the markets Climeon is going after. They've had success in exploiting waste heat on ships, for example. https://climeon.com/ https://climeon.com/

rfrey 6y ago
They're a great, innovative company. They're mostly focused on smaller stuff - 150kW and below, although I think they did some larger bespoke projects earlier. For larger stuff my favourite company is Exergy (www.exergy.it). They resurrected a format of turbine - a radial outflow configuration - that lost to axial turbines in the early 1900s, recognizing that it had special advantages when used with organic fluids rather than steam.

trhway 6y ago

> It used a RB211 gas turbine to drive the compressor. Capturing the waste heat from the exhaust stack of that engine gave us 7MW of net generation, at a cost of $30 million, and much lower operating expenses to boot. the main issue here is actually such a low efficiency turbine - an efficient one wouldn't have such an easy capturable exhaust heat to start with. One can understand that a gas turbine on a plane for example has weight limits so you can't tack on additional turbine stages, etc. to increase efficiency, yet for ground based it would only be about increased capital costs of such a turbine - so that means that running inefficient turbine is cheaper, i.e. the energy/fuel is still very cheap.

rfrey 6y ago
My understanding is that the most efficient turbines top out at about 40%. Reciprocating engines are better, but even they can't get much above 50%. There's still lots of heat there even in the most efficient engines. You're absolutely right about the efficiency being just fine -- especially when you're a pipeline company and you just pull fuel for free out of the pipeline to run the turbine. That's a big reason why these companies haven't built these plants already.
- trhway 6y ago
  >pull fuel for free out of the pipeline to run the turbine. yep. The situation here and globally would be completely different if to the price of fuel, however low one can get it, the price of the emitted carbon were added. That would in particular have leap frogged our civilization efficiency.
- jjk166 6y ago
  Rankine cycle tops out at 40%, gas turbines are more like 50%, and combined cycle, which is really what's being implemented here, can reach around 60%. When the gas is essentially free, there's not much incentive for efficiency, but they could have powered the compressor with a smaller yet more efficient combined cycle system. If you can economically extract power from a powerplant's waste heat, the original power plant was suboptimally designed.

ilaksh 6y ago

The article suggests that the trick to high profits is really getting the depth for higher temperatures without melting the equipment. Because getting lower with higher temperatures dramatically increases the energy generation. As opposed to sort of current minimal viable depth/temperatures. So is it possible that with some significant engineering advances the costs would go down and generation would go up quite a bit? To me the article is suggesting research investment to improve the materials and technology to go deeper less expensively. Can you provide any insight into the feasibility of that type of research paying off? Do you know of any promising techniques, materials, designs? Or maybe you feel like they are insurmountable challenges? Thanks for any details.

rfrey 6y ago
You can go deeper, but in most regions you'll be into impermeable rock by the time you get usable temperatures. You need the rock to be permeable so brine can flow from your injection site to the extraction well. Companies like Eavor claim a closed loop in impermeable rock will work, but then you're limited by the thermal conductivity of the rock around your pipe. You can only pull out as much heat as can flow through the rock around the pipe. Our simulations on Eavor's system showed they would work for about a couple months before they started dropping off. Fracking seems like a more promising avenue, and it might work. A ton of political challenges there though.
- neltnerb 6y ago
  Interesting, when I studied these a long time ago they talked about mining geothermal energy in these kinds of deep rocks but having to move the "heat mine" after it got cool due to the lack of heat transfer through the solid rock. I got the impression that heat flows into the hot rock are orders of magnitude lower than the heat flows out required to make power generation efficient and useful. The radiator design is interesting but ultimately it's a heat sink and power output will be limited. Initially I bet the power output is great, and as the area cools they tap it out. Who knows how long it'd last, you'd think the higher the power capacity the faster it would cool down underneath. So really you need to be able to build new mines cheap enough to justify doing such a hard mine knowing it'll only last for 22 years.

vmception 6y ago

good points, did you notice that you can also get investors and pay yourself a modest salary for 10 years?

jonstewart 6y ago

The Washington, DC wastewater treatment plant figured out how to generate methane from sewage, which they then burn to drive turbines. They get 10MW of net electricity out of it, which they use themselves (sounds like their electric usage is 30MW). It would seem that a lot of industry installations with waste heat sources likely also use a lot of electricity and could benefit from doing something similar. https://www.dcwater.com/whats-going-on/news/dc-water-leverages-technology-first-north-america-generate-clean-renewable https://www.dcwater.com/whats-going-on/news/dc-water-leverag...

nullc 6y ago
Even ignoring the energy savings, methane is a potent greenhouse gas so you'd much rather it be burned than just released. Though I wonder if there isn't an opportunity to sequester a lot of carbon being missed by digesting sludge instead of ... say, dumping it into a deep injection well.
why_only_15 6y ago
10MW ~= $3M/yr @ $30/Mwh (going by https://www.eia.gov/electricity/wholesale/xls/ice_electric-2020.xlsx https://www.eia.gov/electricity/wholesale/xls/ice_electric-2... )
tobinfricke 6y ago
I think this is pretty common at sewage treatment plants. Our local plant (EBMUD in West Oakland) does this too. In fact it seems they import additional organic waste to throw into their methane digester, with the resulting generation covering all of the plant's needs: https://www.ebmud.com/wastewater/collection-treatment/wastewater-treatment/ https://www.ebmud.com/wastewater/collection-treatment/wastew...

kumarvvr 6y ago

Unlike geothermal heat, Industrial heat is too spread out. The quantity of heat may be comparable, but because of wide area of distribution, it is not practical to tap it. By wide area, I mean the various sources of heat in any industrial plant. Also, industries would not really prefer if you want to have equipment to tap waste heat at various points in their shops. Even in the example you give, of a turbine outlet, it is economical and practical, only because the heat is concentrated in the exhaust. However, most plants that have turbines, do recoup energy from turbine exhausts.

01100011 6y ago
You could say the same about solar. Personally, I think residential solar is less preferable than commercial installations where you can benefit from greater centralization, but that said, residential solar seems to have done fine. Now on the other hand, solar has less moving parts, so the reliability is greater and the distributed nature may be less important.
- novok 6y ago
  Doesn't having electricity generation distributed reduce transmission loss although?
- kumarvvr 6y ago
  In solar, there are no naturally occurring concentrated sources of energy. We have to concentrate it in certain ways, or use solar panels. Residential solar will definitely reduce load and transmission losses. However a broad strategy must be required by governments to plan and establish solar plants. For example, it makes sense to have a coherent solar planning policy taking into account the huge consumers of electricity (cities and industries) and planning solar plants near them, reducing the losses in transmissions (which can go upto 33% or more). Additionally, if the production and consumption are close by, transmissions can be made with lower voltage and higher currents, perhaps even HVDC, to unlock even more efficiencies.

umvi 6y ago

Seems like it would be better to directly use the heat i.e. for desalination vs. trying to turn it into electricity. i.e. build a nuclear power plant near the coast, use piped in sea water to cool it, use hot sea water to desalinate with heat gradient

Mountain_Skies 6y ago
Can the problems encountered with the Fukushima nuclear plant being located on the coast be overcome?
- Baeocystin 6y ago
  What led to the Fukushima reactors failing the way they did was that their emergency generators were situated in low-lying, tsunami-reachable areas. Simply relocating/elevating them, and the whole mess wouldn't have happened. https://news.usc.edu/86362/fukushima-disaster-was-preventable-new-study-finds/ https://news.usc.edu/86362/fukushima-disaster-was-preventabl... (There's more to it than this, of course, but it's an accurate first-pass summary.)

rebuilder 6y ago

How long will the industrial plants that produce such heat be able to operate? The geothermal plants are being built as we try to address climate change, with many countries aiming for carbon neutrality by 2035. How much room is there for fossil fuel powered plants in that?

alvah 6y ago
That is an interesting question, as a world without large industrial plants will not resemble the world we live in today, in all kinds of ways. Any sensible plan to reduce emissions will need to provide for industry (most industrial processes involve heat), otherwise we're all going back to living in caves.

rojobuffalo 6y ago

long-term probably both are good ideas. i would think geothermal would be more stable over a long period of time.

pontifier 6y ago

This is making me wonder how much fuel savings you'd get by replacing an alternator with a peltier effect generator.

raverbashing 6y ago
No fuel savings. Peltiers are very inneficient

fulafel 6y ago

This sounds good for low hanging fruit in cases where industrial waste heat and local population have an auspicious ratio, but probably rare. In metro areas the required scale is different... Eg here's a 100x bigger (150 MW electricity + 350 MW) district heating generating CHP plant in Stockholm, serving a fraction of the city: https://dcd.events/conferences/energysmart2018/benefits/visit-stockholm-exergis-kkv8-chp-plant https://dcd.events/conferences/energysmart2018/benefits/visi...

jillesvangurp 6y ago

That big industry that you talk about needs to actually switch to clean energy sources as well. It needs to happen for environmental reasons. But the reasons it is actually happening are more related to cost. There are a few aluminium and steel plants coming online running on hydrogen recently. With clean sources for hydrogen coming online as well, that puts us on a track to cleaning up energy in heavy industries. Right now natural gas is still cheaper but that may not last that long as prices for wind and solar continue to trend down and as there are ongoing improvements in cost of producing hydrogen. Geothermal could be part of the solution for that. But the price has to be right and I have a hunch that there are some challenges there long term. With geothermal the innovation is not necessarily in building huge plants in geologically unstable areas, which in other places indeed requires drilling quite deep, but in using heat pumps to work with small temperature differences you get by digging only a few tens to hundreds meters deep. This is currently quite popular in northern Europe as a way of cheaply heating/cooling houses and reducing cost relative to burning natural gas. The main cost is putting pipes in the ground. In any case, the main challenge with any energy generation project is cost and amortizing that over its lifetime. There are a few things on the market that have come down in price by orders of magnitude and are on track for more improvements in the next decades. This puts any predictions about cost and profitability at risk. In the case of coal, people came out on the wrong side of the equation and a lot of plants are being shut down ahead of their scheduled end of life. IMHO the same will happen to gas plants in the next decades. That makes investments in large scale geothermal very risky. Which is perhaps why there is far less of it than you would expect given that we've known how to build such plants for a very long time. The combination of cheap storage and low cost solar panels or super efficient 10-20 MW wind mills is becoming quite hard to compete with and you see this stuff popping up in formerly very fossil fuel friendly places because it makes sense right now from a cost perspective. Even Iceland is investing in offshore wind.

01100011 6y ago

That sounds a lot like cogeneration. I remember 25 years ago there was a plant near LA that produced steam to process oranges while also generating power. I think you're right though, there is a lot of untapped waste heat out there.

Kosirich 6y ago

Were the projects you mention that used waste heat and generated electricity based on (ORC) Organic Rankine Cycle?

notabee 6y ago

That sounds like a good efficiency measure to use in addition to adding new zero/low carbon energy sources. If you only capture waste heat, the net total is still all coming from carbon-based sources. Maybe it's the low hanging fruit for now, but it's not enough. We need to tap every feasible alternative energy source.