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So why were you bringing up batteries and the seasonal supply of natural gas?

 

Not exactly but that's not a bad way to think of it from an energy perspective. Another way is to realize liquid water is going to result in two gasses - hydrogen and oxygen.

In the fuel cell..

Nope. The two gasses join and the heat of condensation is not recovered as electricity. It's just water vapor and the heat of condensation has to be carried away by a cooling loop.

Well, you can apply this loss (HHV-LHV) either place. It's customary to apply it to the electrolytes.

I thought that was what I said.

 

To point out that battery storage won't work and we will have to do something else - like dispatchable load.

 

Yet no one was claiming battery storage was the only solution. Right now Li-ion is just a cheap solution, but that will change when energy storage and vehicles start completing for supply. Which is why development of other solutions hasn't stopped. They all pros and cons.

Dispatchable load does too. The pro is that you don't need to build storage sites with their efficiency losses. A con is that you need to overbuild the renewable generation which may not be feasible for some grids. Then some storage may still be needed. Another con is that plant operators using the excessive would want to run there plant as much as possible to make the most return on the investment. Without a regulatory structure to prevent it, these plants could just become part of the regular load on the grid.

 

Old grid sized systems would pump water back uphill behind a dam and it’s still more efficient than hydrogen

 

Pumped hydro is only around 50% efficient - better than hydrogen returned to the grid, but not by much. The advantage is that it's pretty cheap for the amount of energy it can store. We have a "small" one where I live that is (IIRC) 330MW for 4 hours. 1.32GWh for a "small" pumped hydro plant - slightly larger than the world's largest battery storage system. The world's largest pumped hydro system is 20 times as large as the largest battery system and even that is designed for diurnal storage, not seasonal.

 

That's what you said but you used LHV and HHV values for hydrogen (not water) to to come up with your theoretical maximum of 84%. Do you have a link to a published work that states that theoretical maximum efficiency of an electrolyzer is 84%?

 

I was simplifying but if you want a more detailed explanation, read this, written by my friend and coworker.

https://www.nrel.gov/docs/fy10osti/47302.pdf

 

Where do you get that figure from? This site is claiming 70% to 85%, https://www.eesi.org/papers/view/energy-storage-2019, and this review paper is 70% to 80%, Pumped hydro energy storage system: A technological review - ScienceDirect

Your proposal doesn't address seasonal storage either. It doesn't even address diurnal storage needs.

Electrical use in the continental US, and most places with four seasons, peaks in the summer for air conditioning, and in the winter for heating(other heating fuels still need pumps and fans to operate). Right now we build generation capacity to meet those peaks, and I have seen no suggestion that we don't do the same when switching to renewable generation. Seasonal storage simply isn't going to be needed. Diurnal will be as renewable production won't always line up with time of use.

The first time I've seen seasonal storage brought up was in regards to monsoon season, which isn't something seen in the US; Hawaii and southern Florida have a rainy season. A true monsoon has more and heavier rain. Enough that production of solar and wind will drop, and overbuilding for the monsoon means lots of unneeded production for the rest of the year. Hydrogen might work there for storage because the cost to store enough can be less than other methods.

 

I was at the control room of my local utility and that's what they told me..

It addresses everything including thermal and transportation, including 10 minute, diurnal and season needs.

 

If other posts here you said converting hydrogen back into electricity for the grid is inefficient and shouldn't be. How are you addressing grid storage then?

 

It's complicated but you don't need a lot of grid storage if you have a lot of dispatchable load. What you do need can be addressed by hydro, V2G, geographic diversity and small amounts of stored hydrogen returned to the grid (once a year or less - emergencies only).

 

Thanks Lee Jay.

What I took from that is that the overall system (electrolyzer+fuel cell) efficiency can top out at 83.x% unless there is some heat recovery system at play. Thanks for opening my eyes to LHV and HHV. I had not given that any consideration until you brought it up.

 

You're welcome.

Like I said it's customary to apply that loss to the electrolyzer side of the equation. But I guess not *everyone* does that.

 

84% is theoretical for a PEM or alkaline type fuel cells with no way to use the waste heat. The most efficient that we know of is a steam type fuel cell, where waste heat can be used to create the steam. Here we can get to around 95% theoretical, but ... its not just the cost of the electricity its the cost of equipment, and in most practical purposes this will be between 70%-80% efficient.

If electricity costs a Nickle/kwh then a kg of hydrogen (33.5 kwh) will cost $2,4 for the 48 kwh of electricity in a 70% efficient electrolysis or about $0.73 more than a 100% efficient electrolyzer. With natural gas prices a combined cycle generator provides a utility with electricity for about $0.02/kwh and I would expect excess wind or solar to be at this cost or lower or about $0.29 more per kg in a 70% efficient electrolyzer versus 100%. Now you have to pay for the electrolyzer (90% efficient will cost a lot more than 80%) and utilization will be low, which means cost of the electrolyzer is going override the difference in price for electricity in deciding efficiency. Co locate the buffer in a combined cycle plant and its likely you can modify the equipment to burn hydrogen instead of methane and not only store for reliability and seasonal storage but also substitute some natural gas use for buffered lower price fuel stock.

There was talk about this making sense for light transportation and not grid reliability and storage. To me this does not make much sense. In that case you need to produce hydrogen to demand not based on excess electricity supply. You need 3x the excess electricity for a light fuel cell vehicle versus a comparable bev or phev. The thing that was going to make people pay for this was fueling convenience but hydrogen convenience is much worse than plug-in convivence today and is likely to be for the foreseeable future given the very high cost of fuel and infrastructure.

 

It's no big surprise that nuclear physicists and economists or anyone else that has a vested interest in currently available energy, might not be thrilled with a technology that might compete with those interests.

Having current data in the public domain might also not be in the interest of several groups herein unnamed.
Not that it matters to me, that stuff is way above my pay grade.
from the wikipedia page footnotes

NASA Glenn Research and Technology
Nuclear Fusion Reactions in Deuterated Metals

 

For the BILLIONTH time, H2 light vehicles should be PLUG-INS! 80% of your miles and 99% of your driving legs would be based on battery-stored electricity derived from a grid source. H2 would be used on road trips out of town where slow "fast" charging is inconvenient and painful. It would also be used on off-hightway vehicles (construction, mining, etc.), ships and airplanes.

 

Makes good sense. A PHEV using a hydrogen fuel cell as a range extender would be more practical.

You don't need a 500 mile BEV to be practical. I just read a news report that said a 100 mile range, $4400 4 person EV made by a GM subsidiary was the best selling EV for a recent quarter. ( GM's electric car outselling Tesla Model 3 in China | Fox Business )

Dan

 

I've done 99% of my driving legs and 78% of my driving miles on electricity in my Prius Prime, with it's EPA-rated 25 mile range. Most people don't need a lot of range on a daily basis if they can charge at home. However, I've driven that same car over 600 miles between charging stations when out on the open road on a vacation, and I've driven it over 300 miles without stopping the car.

 

The issue is in packaging all the equipment. The battery goes under the floor. While a bigger battery allows a less powerful fuel cell, the auxiliary equipment might still make it bulky. The main concern though is the hydrogen tanks. Because of the high pressures, they have to be cylinder shape, which means they'll take more space than their volume would imply, and they are bulky to begin with; tanks for 5kg of hydrogen are around 40 gallons.

If the designers don't want to lose cargo or passenger space, the amount of hydrogen carried will likely be reduced. This is what Honda did with the Clarity PHEV. They put in a small gas tank, with a range of about 270 miles without grid electricity. So more stops on a long trip to actually fill the tank.. Let's say the small fuel cell and large battery mean overall better efficiency than current FCEVs, so 85mpge on hydrogen. With 5kg tanks that's 425 miles, but the PHEV might only carry 3kg for 255 miles. In the thread here about the Clarity PHEV, several felt the 270 miles is too short, and stopping more often would be a hassle.

I posted a picture of that car in another thread. It might be as big as a Spark, and I've seen those listed for $10k. Compared to China, people generally drive more miles. 120 mile range is probably the minimum for a BEV here. The problem now is convincing enough people that is more than enough for their regular use so that some company is willing to bring a cheap BEV with that range to market.