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How can you burn fossil fuels to produce electricity, to use to turn the combustion byproducts back into fuel at any reasonable level of efficiency? Some people

by eloff 9y ago

How can you burn fossil fuels to produce electricity, to use to turn the combustion byproducts back into fuel at any reasonable level of efficiency? Some people here are saying the electricity doesn't matter, because it is from renewable sources - but then you could just shut down that dirty coal plant and use the renewable energy directly. Something doesn't add up here.

a3n 9y ago
The CO2 is already there, now. Might as well use it.
- jcranberry 9y ago
  I think the worry is that it might cost more energy to process the CO2 than it actually produces. In which case the energy would be more of a byproduct of removing the CO2 from the atmosphere, I guess?
  - notabee 9y ago
    No, the worry is that without negative emissions, there's no realistic way to head off worst case climate change. The IPCC scenarios that have us averting disaster already assume that we're going to develop carbon sequestration technology that is beyond what we can currently do. There will inevitably be some inefficiency in the conversion, but even a fairly inefficient process that is still carbon negative is desirable.
    - mkempe 9y ago
      And what will you do when the current interglacial ends? the last one --the Eemian-- was much warmer, and it did end. Or do you believe that this particular interglacial will, somehow, never end?
      - kmonsen 9y ago
        It seems like we have the technology to warm up the planet within reach already
        mkempe 9y ago
        You believe that you can control the cycles of the changes in orbit and axis of our planet, as well as the cycles of solar activity? Or do you have evidence for other primary cyclical causes of ice ages, interglacials, and glaciations?
  - jtbayly 9y ago
    Might? I’m pretty sure that’s not a question. If they were claiming it would generate more energy than it took, this article would have been about a perpetual motion machine.
allthenews 9y ago
The advantage of fossil fuels in this case is energy storage density, and potentially longer engine life than that afforded by modern batteries.
derekp7 9y ago
The renewable power source for the electricity isn't close enough to where it is needed (hydro-electric), or not stable enough (wind, solar). And the fuel produced can be used for applications other than power generation. And used as a storage medium to even out the bumps in solar/wind. For that last category, this process needs to be more effective than battery storage.
- ttul 9y ago
  And if there is a price on carbon pollution that is high enough, that would help make the case.
  - ebbv 9y ago
    It wouldn’t help because at best this is carbon neutral. But in reality it’s unlikely to be anywhere close to carbon neutral, in which case a tax on carbon makes this much more costly than battery storage.
    - usrusr 9y ago
      And if it was carbon-neutral, it would also be energy neutral, at best (realistically: much worse). But there is a time-shift opportunity in there, capture the CO2 when renewable output is lower than demand, recycle the CO2 into fuel when renewable energy is abundant. Retrofitting existing gas peaker plants into giant flow batteries would be the holy grail of grid scale energy storage.
      - ebbv 9y ago
        Except we know that existing fossil fuel burning plants are about 30% efficient. No battery is that bad. This is a really weak idea that only sounds good if you don’t think about the details at all. (And remember that 30% is only on the recovery side, you’d have to factor in any inefficiencies on the storage side before getting a final efficiency number to compare against other means such as batteries.)
kragen 9y ago
Basically this is a reasonable idea for transport fuels. Sunlight gives you 1000 W/m², or 160 W/m² at 16% photovoltaic efficiency. A Boeing 777 has a surface area on top of something under 1000 m², and so if you cover it with solar panels, you get 160 kW when the sun is shining directly on it. But its engines produce somewhere between 700 and 1100 kN at a cruising speed of 900 kph, or 250 m/s, which if you work it out means it would need 175–275 MW if the engines are 100% efficient, a bit over 1000 times what it can gather from the sun. (A bit less since it's not running the engines at full power when it's cruising, but a lot more when you take into account that the engines are quite inefficient.) There are ways you can design the plane to use less power, and Solar Impulse 2 demonstrated that it is in fact possible to fly on solar power alone, but Solar Impulse 2 also took 23 days to go around the world, has a maximum speed of 140 km/h, and has a maximum passenger capacity of 1, rather than a few hundred. Design compromises like these are necessary to lower the power intensity of flight to a solar-feasible level. So, it's likely that liquid-fueled aircraft (the 777 burns kerosene) will continue to have substantial advantages over solar aircraft for the foreseeable future. The obvious solution is to use some 10⁸ m² of area on the ground — something like a 10 km by 10 km square for each 777 in flight — to generate electricity to produce the liquid fuels for the liquid-fueled aircraft. That sounds like a ridiculous thing to do, building a city-sized solar plant for a single airplane, and today it would be — the photovoltaic modules would cost US$5 billion and installing them would cost another US$5 billion, for a total of US$10 billion. The entire Boeing 777 development cost was only US$5 billion, and each plane sells for US$300M or so. So the cost of the power plant would be something like 30× as high as the cost of the airplanes themselves. From an exponential point of view, though, that's only 5 doublings. If the price-performance of photovoltaic modules improves by a factor of 2 five times, the power plant falls to the cost of the plane. If PV modules continue dropping in price by 30% per year, as they have been for the last four years or so, that crossover happens in 2028; if they continue dropping in price by 20% per year, as they have been over a somewhat longer period, it happens in 2033. It's only in a scenario where PV modules effectively stop dropping in price where this remains a ridiculous idea. The same logic applies, but in a weaker form and a nearer crossover, for other challenging transport fuel uses such as ships and trucking.
- entee 9y ago
ebbv 9y ago
Your suspicion is correct. This is a film flam. At best this is an extremely inefficient way to store energy.
skybrian 9y ago
This is for soaking up renewable energy that either isn't connected to the grid yet, or is being generated at the wrong time. Since there's no fuel cost for wind or solar, you might as well do something with it. Anyone willing to buy electricity at inconvenient places or times will help make renewable energy generation more profitable, so more will be built. There are lots of potential competitors, though: other kinds of energy storage (such as charging a battery), industrial users that can run in the off hours, or maybe generating Bitcoin. It's probably too soon to say whether this technology will win. Buying electricity at a low price and selling it at a different time or place at a higher price is basically a form of arbitrage. Hopefully energy storage will become more efficient at getting electricity to customers when they need it, so they can outbid things like Bitcoin mining.
- eloff 9y ago
  That makes sense, I was struggling to grasp how it could be economical.
- Gravityloss 9y ago
  Demand elasticity. We are still really far from reasonable deployment. Talking to a friend who worked for a power utility here, it's a very foreign concept. Some room for disruption there.
- Gravityloss 9y ago
  For this you would need to store the CO2. For each ton of coal burned you generate about 3 tons of CO2. At atmospheric pressure thats 1500 cubic meters. A small 200 MW power plant could burn 80 tonnes per hour. Thats 120 000 cubic meters. That is a building 12 m high and 100 m square. I guess everything is possible given the right subsidies...
  - ajnin 9y ago
    You wouldn't store the CO2 gaseous at atmospheric pressure, you'd use the energy to compress it, presumably liquefying it. Liquid CO2 has a density of around 1100kg/m3, according to a quick Google search, so your example power plant would need only about 200m^3 to store the CO2 produced in one hour, or a cube of about 6m wide. Or 120m wide per year. Still seems like a lot, and I don't know how much energy is needed to compress and cool all that CO2 but it's dubious the surplus renewable energy would suffice to compress all the CO2 produced by fossile-burning power plants.
myrryr 9y ago
Time... It is all about when you want to use the electricity.
philwelch 9y ago
This could be useful for developing countries, if the following supply chain became feasible: 1. Rich country builds nuclear reactors to generate power 2. Rich country uses nuclear power to synthesize hydrocarbons for export 3. Developing country imports hydrocarbons for domestic energy needs Developing countries don’t have the resources to build nuclear reactors, and we might not want to export the nuclear technology anyway, but we can export the actual energy this way.
sametmax 9y ago
Because we have convenient gas station network and a lot of combustion engines already. That also have the benefit of a huge range and instant top up. A tech to transition would be a good thing.
empath75 9y ago
If this actually works and global warming gets bad enough, we could build a bunch of nuclear plants for this, if nothing else.
ynniv 9y ago
Rechargeable batteries aren’t currently as mass or volume efficient as these chemical forms. https://en.m.wikipedia.org/wiki/Energy_density#/media/File%3AEnergy_density.svg https://en.m.wikipedia.org/wiki/Energy_density#/media/File%3...
TheCoelacanth 9y ago
If you apply this idea, fossil fuels are no longer a source of energy, they are now a way of storing and transporting energy. You could have a bunch of solar panels in Arizona where there is a lot of sun and cheap land and then ship the fuel somewhere else where solar is less efficient.
- fyi1183 9y ago
  They are also no longer fossil fuels, just chemically equivalent or at least similar hydrocarbons. I wonder if language will eventually change to reflect that.

by eloff 9y ago

a3n 9y ago

The CO2 is already there, now. Might as well use it.

jcranberry 9y ago
I think the worry is that it might cost more energy to process the CO2 than it actually produces. In which case the energy would be more of a byproduct of removing the CO2 from the atmosphere, I guess?
- notabee 9y ago
  No, the worry is that without negative emissions, there's no realistic way to head off worst case climate change. The IPCC scenarios that have us averting disaster already assume that we're going to develop carbon sequestration technology that is beyond what we can currently do. There will inevitably be some inefficiency in the conversion, but even a fairly inefficient process that is still carbon negative is desirable.
  - mkempe 9y ago
    And what will you do when the current interglacial ends? the last one --the Eemian-- was much warmer, and it did end. Or do you believe that this particular interglacial will, somehow, never end?
    - kmonsen 9y ago
      It seems like we have the technology to warm up the planet within reach already
      - mkempe 9y ago
        You believe that you can control the cycles of the changes in orbit and axis of our planet, as well as the cycles of solar activity? Or do you have evidence for other primary cyclical causes of ice ages, interglacials, and glaciations?
- jtbayly 9y ago
  Might? I’m pretty sure that’s not a question. If they were claiming it would generate more energy than it took, this article would have been about a perpetual motion machine.

allthenews 9y ago

The advantage of fossil fuels in this case is energy storage density, and potentially longer engine life than that afforded by modern batteries.

derekp7 9y ago

The renewable power source for the electricity isn't close enough to where it is needed (hydro-electric), or not stable enough (wind, solar). And the fuel produced can be used for applications other than power generation. And used as a storage medium to even out the bumps in solar/wind. For that last category, this process needs to be more effective than battery storage.

ttul 9y ago
And if there is a price on carbon pollution that is high enough, that would help make the case.
- ebbv 9y ago
  It wouldn’t help because at best this is carbon neutral. But in reality it’s unlikely to be anywhere close to carbon neutral, in which case a tax on carbon makes this much more costly than battery storage.
  - usrusr 9y ago
    And if it was carbon-neutral, it would also be energy neutral, at best (realistically: much worse). But there is a time-shift opportunity in there, capture the CO2 when renewable output is lower than demand, recycle the CO2 into fuel when renewable energy is abundant. Retrofitting existing gas peaker plants into giant flow batteries would be the holy grail of grid scale energy storage.
    - ebbv 9y ago
      Except we know that existing fossil fuel burning plants are about 30% efficient. No battery is that bad. This is a really weak idea that only sounds good if you don’t think about the details at all. (And remember that 30% is only on the recovery side, you’d have to factor in any inefficiencies on the storage side before getting a final efficiency number to compare against other means such as batteries.)

kragen 9y ago

Basically this is a reasonable idea for transport fuels. Sunlight gives you 1000 W/m², or 160 W/m² at 16% photovoltaic efficiency. A Boeing 777 has a surface area on top of something under 1000 m², and so if you cover it with solar panels, you get 160 kW when the sun is shining directly on it. But its engines produce somewhere between 700 and 1100 kN at a cruising speed of 900 kph, or 250 m/s, which if you work it out means it would need 175–275 MW if the engines are 100% efficient, a bit over 1000 times what it can gather from the sun. (A bit less since it's not running the engines at full power when it's cruising, but a lot more when you take into account that the engines are quite inefficient.) There are ways you can design the plane to use less power, and Solar Impulse 2 demonstrated that it is in fact possible to fly on solar power alone, but Solar Impulse 2 also took 23 days to go around the world, has a maximum speed of 140 km/h, and has a maximum passenger capacity of 1, rather than a few hundred. Design compromises like these are necessary to lower the power intensity of flight to a solar-feasible level. So, it's likely that liquid-fueled aircraft (the 777 burns kerosene) will continue to have substantial advantages over solar aircraft for the foreseeable future. The obvious solution is to use some 10⁸ m² of area on the ground — something like a 10 km by 10 km square for each 777 in flight — to generate electricity to produce the liquid fuels for the liquid-fueled aircraft. That sounds like a ridiculous thing to do, building a city-sized solar plant for a single airplane, and today it would be — the photovoltaic modules would cost US$5 billion and installing them would cost another US$5 billion, for a total of US$10 billion. The entire Boeing 777 development cost was only US$5 billion, and each plane sells for US$300M or so. So the cost of the power plant would be something like 30× as high as the cost of the airplanes themselves. From an exponential point of view, though, that's only 5 doublings. If the price-performance of photovoltaic modules improves by a factor of 2 five times, the power plant falls to the cost of the plane. If PV modules continue dropping in price by 30% per year, as they have been for the last four years or so, that crossover happens in 2028; if they continue dropping in price by 20% per year, as they have been over a somewhat longer period, it happens in 2033. It's only in a scenario where PV modules effectively stop dropping in price where this remains a ridiculous idea. The same logic applies, but in a weaker form and a nearer crossover, for other challenging transport fuel uses such as ships and trucking.

entee 9y ago

ebbv 9y ago

Your suspicion is correct. This is a film flam. At best this is an extremely inefficient way to store energy.

skybrian 9y ago

This is for soaking up renewable energy that either isn't connected to the grid yet, or is being generated at the wrong time. Since there's no fuel cost for wind or solar, you might as well do something with it. Anyone willing to buy electricity at inconvenient places or times will help make renewable energy generation more profitable, so more will be built. There are lots of potential competitors, though: other kinds of energy storage (such as charging a battery), industrial users that can run in the off hours, or maybe generating Bitcoin. It's probably too soon to say whether this technology will win. Buying electricity at a low price and selling it at a different time or place at a higher price is basically a form of arbitrage. Hopefully energy storage will become more efficient at getting electricity to customers when they need it, so they can outbid things like Bitcoin mining.

eloff 9y ago
That makes sense, I was struggling to grasp how it could be economical.
Gravityloss 9y ago
Demand elasticity. We are still really far from reasonable deployment. Talking to a friend who worked for a power utility here, it's a very foreign concept. Some room for disruption there.
Gravityloss 9y ago
For this you would need to store the CO2. For each ton of coal burned you generate about 3 tons of CO2. At atmospheric pressure thats 1500 cubic meters. A small 200 MW power plant could burn 80 tonnes per hour. Thats 120 000 cubic meters. That is a building 12 m high and 100 m square. I guess everything is possible given the right subsidies...
- ajnin 9y ago
  You wouldn't store the CO2 gaseous at atmospheric pressure, you'd use the energy to compress it, presumably liquefying it. Liquid CO2 has a density of around 1100kg/m3, according to a quick Google search, so your example power plant would need only about 200m^3 to store the CO2 produced in one hour, or a cube of about 6m wide. Or 120m wide per year. Still seems like a lot, and I don't know how much energy is needed to compress and cool all that CO2 but it's dubious the surplus renewable energy would suffice to compress all the CO2 produced by fossile-burning power plants.

myrryr 9y ago

Time... It is all about when you want to use the electricity.

philwelch 9y ago

This could be useful for developing countries, if the following supply chain became feasible: 1. Rich country builds nuclear reactors to generate power 2. Rich country uses nuclear power to synthesize hydrocarbons for export 3. Developing country imports hydrocarbons for domestic energy needs Developing countries don’t have the resources to build nuclear reactors, and we might not want to export the nuclear technology anyway, but we can export the actual energy this way.

sametmax 9y ago

Because we have convenient gas station network and a lot of combustion engines already. That also have the benefit of a huge range and instant top up. A tech to transition would be a good thing.

empath75 9y ago

If this actually works and global warming gets bad enough, we could build a bunch of nuclear plants for this, if nothing else.

ynniv 9y ago

Rechargeable batteries aren’t currently as mass or volume efficient as these chemical forms. https://en.m.wikipedia.org/wiki/Energy_density#/media/File%3AEnergy_density.svg https://en.m.wikipedia.org/wiki/Energy_density#/media/File%3...

TheCoelacanth 9y ago

If you apply this idea, fossil fuels are no longer a source of energy, they are now a way of storing and transporting energy. You could have a bunch of solar panels in Arizona where there is a lot of sun and cheap land and then ship the fuel somewhere else where solar is less efficient.

fyi1183 9y ago
They are also no longer fossil fuels, just chemically equivalent or at least similar hydrocarbons. I wonder if language will eventually change to reflect that.