IIRC, high temperatures are required to produce hydrogen. Nuclear reactors to have high temps, but it is used to produce electricity. One could use the energy to produce hydrogen instead, but it wouldn’t be ‘waste heat’.
DB2
Yes. The waste heat from today’s nuclear power plants is relatively low grade. For a power plant with once-through cooling, say on a lake, river, or ocean, the return temperature will be about 20 degrees F higher than the intake. There are often environmental regulations that limit how high the return water temperature can be.
The important point is that the waste heat from a nuclear plant is not useful for doing much work. Think of Carnot efficiency. You want the temperature difference between the heat source and the heat sink to be as high as possible, to get the maximum amount of work out of the system.
The abstract in the paper about the cement plant says they were using waste heat at 360 degrees C and higher! That is higher than the highest main steam temperature in most nuclear power plants. I doubt there are many nuclear plants with a waste heat stream higher than 35 degrees C or so.
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That is the concept behind a combined cycle power plant. Run a large jet engine (gas turbine) that is connected to an electrical generator. The discharge of the jet engine is at a high temperature, so that heat is then captured in a steam generator, and that steam is run through a steam turbine to produce even more power. It squeezes as much power out of the burned fuel as possible, and makes the power plant quite efficient, perhaps around 55% or 60% efficient, if conditions are optimal.
- Pete
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Would you care to entertain a hypothetical?
Say you can build X amount of carbon free generation capacity per year. Say electricity demand growth for existing uses is R. So, X - R = the amount of fossil fuel generation capacity that can be retired.
Add in demand for recharging EVs, C. Then the equation is X - R - C = amount of fossil fuel generation capacity that can be retired. Or, put simply, adding EVs to the mix would delay retirement of fossil fuel plants.
Steve
Even if adding EVs delays retirement of fossil fuel plants (and it does, at least to some extent, by the simple arithmetic), BUT by adding those EVs, you are reducing the other fossil fuel usage (gasoline and its refining). And you are reducing it by about 3 times as much due to the much higher efficiency (power-for-power)!
The way we measure stuff, including energy use, is mostly by money. And I know for a fact that $10 of gasoline would get me about 50 miles in my old nice 4-door ICE sedan. And I know for a fact that $10 of electricity gets me about 250 miles in my new nice 4-door EV sedan.
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I agree electric motors are more efficient than an ICE engine. But then you need to add in the losses at the power plant, and transmission losses. If it’s a coal fired plant, you have the energy used digging the coal, and transporting it by diesel powered train.
Fun with some numbers I came across:
Energy loss in power generation and transmission: about 66%
Of the current that makes it to the EV charger, anywhere from 10% to 25% is lost to the charging cycle.
So the 34% of the coal/gas energy that makes it to the charger, 25-30% of the coal’s energy makes it into the battery. Then another 5-10%, is lost pulling power from the battery to run the motor, so some 28.5-22.5% of the energy in the coal makes it to the EV’s wheels. assuming no power is being bled off to run lights, or a/c, or heat or other accessories.
Yes, it is more efficient than producing, transporting, refining, then burning gas in a car. One source I read claimed only about 5% of the energy in a barrel of oil in the ground actually makes it to the wheels of a car.
What I have not come across is the energy lost in producing and transporting the coal or gas to the power plant.
None of that is relevant. Ten bucks got me 50 miles in my ICE car, and now ten bucks gets me 250 miles in my EV. And they are very comparable cars, except the EV has better performance. Unless someone out there is giving away energy for below cost, those are indeed the real numbers.
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The “JCs” will solve that pricing disparity, when EVs become a significant factor in the US.
fwiw, I spent $26 gassing up the sled after a 264 mile trip, last Sunday.
Steve…who drives a car that fits his needs, not the biggest, most garish, thing around
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Yes, and that electricity can produce hydrogen by electrolysis.
A recent posting pointed out that electricity can be generated from the waste heat in sewage. That implies low pressure steam from a nuclear power plant can be used to generate still more electricity. It could also be used for hydroponics gardens to produce food.
You are producing a hell of a lot of CO2 and not likely to reach net zero.
Generally steam power plants are rated in their thermal efficiency…i.e. how much they keep. Older coal plants, maybe 33% and newer ones as high as 45%.
Transmission losses depends on the distance (and voltage used) but generally ~5%.
EV chargers are usually around 85% -90% efficient…only the slow 120v L1 charger would be less than that…you’ve got to run the car’s computers, etc for a much longer time to get a charge and the lower voltage is less efficient. You can measure the efficiency of an L2 charger by comparing the kwh the car says it gets with the number the charger says you are billed for. It’s about 88% in my tests years ago.
But keep in mind that the efficiency numbers for gas cars are usually quoted as their peak efficiency…maybe 20-25%. But they only run that efficient once warmed up and at moderate constant speeds on a highway with no stop and go. No one drives like that very much. This is why hybrids can get around 35%.
With a BEV they are “warmed up” immediately and the power plant where they got their power is pretty much always running at peak efficiency.
Both BEV and ICE cars suffer from the same lower efficiency as speed increases (basic aerodynamic drag)…but BEVs generally have a much lower coefficient of drag.
Mike
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Electrical engineers look at solar generation and battery storage as a system made of two components. As an engineer I have no problem with looking at the generation provided by the system. Without battery storage the system would not generate as much electricity daily/weekly/monthly/yearly.
I think we need to need to look at the growth of gas and renewables over 4 years (2020 to 2024).
Nat gas growth is 175,272 GWh
Renewables growth is 188,021 GWh
OK, but if you do that then wouldn’t you be double counting the electricity produced by solar and stored in a battery?
DB2
You can, but it is way too expensive to do it that way. The input cost of the electricity is far higher than the energy value of the hydrogen.
Initially waste heat will be used to partially reduce the amount of electricity needed for electrolysis. Presumably the process will get more efficient. In any case, it is going to be tested on small nuclear reactors soon.
We expect nuclear energy, especially in combination with high temperature electrolysis, to be able to produce zero-emission hydrogen competitively on a stand-alone basis. Additional value associated with the operational flexibility will further enhance the business case for this solution." Partners to study hydrogen production using Rolls-Royce SMR : New Nuclear - World Nuclear News
But I also posted links to Japan developing high-temperature nuclear reactors for hydrogen production. Japan is collaborating with Poland to build such a reactor there.
High-temperature reactors capable of supplying steam of up to 1000°C could replace fossil fuel as heat sources for chemical and petrochemical industries, leading to the decarbonisation of many production processes as well as enabling the economic production of hydrogen. Japan and Poland to begin work on high-temperature reactor design : New Nuclear - World Nuclear News
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For example, at idle the efficiency of an ICE is zero. For all their faults, EVs will always be more efficient than ICEs. For that reason (and others) I think it is good public policy to encourage EV adoption. Using energy more efficiently is a smart thing to do. Energy is so cheap that we waste enormous amounts of it. We should be looking for ways to use energy smarter.
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Re: hydrogen too expensive.
Yes, the best source of hydrogen is natural gas. Ammonia has been made that way since WWI.
Once again when measured vs fossil fuels green energy loses.
Methods that don’t require fuel like wind and solar might beat fossil fuels when fully developed. Energy storage cost remains an issue.
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To be fair, at “idle”, the efficiency of an EV is also essentially zero, if you measure efficiency in Wh/mi (as we do in the USA). My Tesla, for example, when I first start driving, and the A/C is blasting while cooling off the cabin, will often show well over 1000 Wh/mi initially. Then it tapers down as I drive further. Meanwhile, my overall average is 263 Wh/mi over the entire 32,000+ miles. Someone posted a photo (I can’t find it right now) of their display last week at the Mexico-USA border after sitting in their car in line for 2 hours with the A/C running. It said something like 14,000 Wh/mi.
There are two different concepts here. One is using waste heat to generate hydrogen. I suspected and @waterfell confirmed that the waste heat from nuclear power plants isn’t hot enough for industrial processes.
Looking at the original paper you posted, the costs came out to be about $0.08/KwH equivalent of hydrogen. That’s borderline (probably over the borderline) too high, and that’s starting from a free energy input.
The other concept is using heat from the nuclear reactor directly to make hydrogen. I agree that is 100% theoretically possible. But the problem is still that it requires multiple units of other energy to make one unit of hydrogen energy. If you are using the heat from your reactor directly to make hydrogen then you can’t use it to make electricity.
The back-of-the napkin calculation to show why this will never make economic sense is easy. Let’s say you want to make 1 kwh equivalent of hydrogen, and your electrolysis process is super-efficient at 80%. So 1 kwh/.8 = 1.25 kwh of electricity to make 1kwh equivalent of hydrogen. Now you take that 1 kwh of hydrogen use it in a fuel cell at 60% efficiency. That means it takes 2 kwh input to get 1 kwh output. That doesn’t scale. Because it requires energy to break and create chemical bonds, those numbers can’t change much (as long as the laws of physics hold).
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No it is not double counting. They are just counting the electricity being generated some which is stored for later use.