Gravity Loss

Energy storage is needed to solve the variability of renewable energy. Main contenders are hydrogen and batteries. These can be built in regions that don’t have large lakes or mountains for leveling hydropower.

Which ones should we build? To get a feel for the question, we are comparing two existing systems.
Note that these are rough back of the envelope calculations!

The comparison

The world’s biggest battery energy storage at the time of writing is the Crimson Storage System in Southern California, delivered by Canadian Solar.

We compare it against NASA’s new liquid hydrogen tank at Kennedy space center in Florida.

Numbers

Label	Hydrogen tank	Battery farm
Energy content	6.5 GWh[1]	1.4 GWh
Power	N/A [2]	350 MW
Round Trip Efficiency	~30% [3]	88% [4]
Cost	$15 million[5]	N/A

[1] Energy content for hydrogen storage assumes 50% fuel cell conversion efficiency to electricity
[2] NASA uses this to fill rockets that burn the propellants, it is not converted to electricity.
[3] https://en.wikipedia.org/wiki/Hydrogen_economy
[4] Canadian Solar (90% at start, 87.5% at 20Y)
[5] This is just for the tank, doesn’t include the electrolyser equipment (and there are no fuel cells)

The hydrogen ball’s energy content is impressive, but the round trip efficiency for hydrogen is bad. Cost comparison is not available.

Other differences

Hydrogen

The technology is widely different. The hydrogen storage is a huge ball with a vacuum jacket. There is loose small glass ball insulation in the vacuum. The liquid hydrogen is kept at 22 K, while ambient air on the outside can be 300 K (+27 C). This is done with a helium cryocooler and it eliminates boil off (older systems had boil off).

One huge advantage of the hydrogen system is that because of the potential effects of the square-cube-law, there is proportionally less insulation needed if the tank gets bigger. Therefore it would make sense to create one big tank instead of two medium sized ones.

The technology has some commonalities with LNG storage, though LNG is much easier at 90 Kelvin and no embrittlement and less leakage issues.

Battery

The batteries at Crimson storage are provided by Canadian Solar. On the outside, regular looking shipping containers stand on short stilts in the desert. There seem to be mostly energy storage containers with probably a minority of different transformer containers in between.

The energy storage container looks simple. Inside, the battery modules are contained in racks, connected with thick wires. They can be serviced by people.
There don’t seem to be much scale advantages. More storage is gotten by adding more units.

Storage systems don’t take so much space compared to generation systems like wind or solar so it’s not such an important question.

Dangers

Hydrogen leaks are relatively harmless since it’s so light and rises up, even fires (outdoors) are not that dangerous compared to heavier fuels.
The battery systems are isolated into containers with a clear gap, meaning a fire in one container doesn’t cause a cascading failure into others.

Summary

Hydrogen might work for absolutely humongous, stadium-sized tanks, one per industrial or energy production area. It could be coupled with direct industrial usage of hydrogen (Fertilizer and steel, aluminum, nickel or chemical production), avoiding the fuel cell inefficiency (and cost). They could be constructed of relatively ordinary materials like aluminium, polystyrene and even plywood. Maybe some of the innovations from the LNG boom could be adapted. Because of the cost of electrolyzers and fuel cells, the power would be optimized to be low and it would make sense as a large longer term energy storage. Would seasonal energy storage be possible with very large hydrogen storage systems?

Large battery storage systems can be constructed in a modular fashion, and there are multiple levels of hierarchy. Some of the components can be interchangeable. The technology is developing rapidly. One could construct a facility from containers from multiple integrator contractors. A container could usem cells from multiple manufacturers. Current batteries are more suited for short term storage because of the cost and the way the technology is developed (for electronic devices and cars). Every city and solar or wind farm could have these.

Post note on tank size

Square cube law would favor larger tanks. On the other hand, if vacuum insulation is used, that means the tank is a pressure vessel and the force grows with area, and thus thicker material must be used for the same strength. Meaning the pressure vessels would have the same mass proportion no matter what the size. That takes away some of the advantages of the square-cube law for the whole tank. On the other hand, if tanks get larger, one could potentially get away with less insulation and not have to pull vacuum. Complicated questions.

What would a truly humongous tank be like? There’s already a good model, the famous Globe n or Avicii arena in Stockholm.

If we assume 1 m insulation thickness for both, Globen would have 4.7 times the effective tank radius and thus 100 times the volume of the NASA tank, with a whopping capacity of 650 GWh

This would mean two weeks’ output of the Olkiluoto 3 EPR 1.6 gigawatt nuclear power plant. Not enough to solve a small nation’s seasonal energy storage yet, but it would have a sizable effect.

In comparison, Germany’s natural gas storage capacity is 250,000 GWh or about 400 Hydrogen Globens.

Videos

Fossil fuels have been cheap. They have been used to produce electricity, reduce iron, make fertilizers and heat homes.
This has caused large carbon dioxide and methane emissions that can not continue. Fossil fuels will be phased out.

Electricity

Nuclear power plants, wind power and solar power will have to replace coal and natural gas electricity generation.
Wind and solar are variable. Adding some of those into an electricity generation mix can easily have a positive effect of reducing carbon emissions. Hydropower can also act as a leveler.
When you add more, trying to get rid of all the fossil fuels, the variability will cause more and more problems.
This can be also alleviated with making the demand flexible, where practicable.
At some point storing electricity will become necessary.

Batteries

Mobility

Electric cars are replacing oil fueled ones. Most current electric cars on the market today use lithium ion NMC (Nickel Manganese Cobalt) batteries. Cobalt and nickel are relatively expensive and form a large portion of the cost of such a battery.
However, some portion of the cars, with somewhat less range, use lithium LFP (lithium iron phosphor) batteries. These don’t involve any cobalt or nickel.
For large scale adoption of electric cars, it’s likely that the early expensive technologies will be ditched for scalable ones.
NMC batteries have also higher propensity for thermal runaway than LFP. For example Tesla encases NMC battery elements in small cylinders, and then glues them into one big pack with foam. This makes changing elements impossible.
LFP batteries can use large prismatic casings, making manufacturing potentially cheaper, and giving the possibility to remove one casing in maintenance.

Static batteries

Current static lithium ion battery plants usually tend to have a capacity of one to four hours at full power. For example a 100 MW power battery with 400 MWh energy capacity.
LFP technology might be still limited by the availability of lithium, even if the other materials were abundant.
Sodium ion batteries are one way around that, but the technology is still immature.
Also special graphite electrodes in lithium batteries can be a resource bottleneck – silicon electrodes in sodium ion batteries can work around that.
A sodium ion battery is heavier than a lithium ion, but it shouldn’t matter in the static setting – as the total cost and scalability should be way better. This is an area to watch.

Flow batteries

Flow battery technology is not yet widely deployed. The technology stores energy in liquid electrolyte or electrolytes, and has only small electrodes. This means if the electrolyte is cheap, one can have very large amount of storage with low power for very low cost.
State of the art is vanadium flow batteries, but vanadium is quite rare and expensive so it’s not very likely to scale.
Promising alternatives are either cheap bulk material electrolytes or cheap organic molecules. Research continues.
Again, energy density might not be good, what is more important is the total cost of the battery. Also round trip efficiency might not be as good as in lithium ion.
Flow batteries would be a better fit for longer term storage, days or weeks instead of hours.

Hydrogen as electricity storage

Hydrogen suffers from a few key problems. Electrolyzers use platinum and are expensive. Round trip efficiency from electricity to hydrogen and back is bad. Hydrogen as gas is extremely low density. Liquid hydrogen needs to be stored at 20 K, lowering round trip efficiency more and complicating matters like storage and transport greatly. Liquid density is still only one sixth of methane’s, which can be stored at 90 K. Hydrogen is also a small molecule that leaks out of very small holes and embrittles certain materials.

Heating

District heating

Dense cities in cold climates use district heating, either with steam or hot water. The heating generally happens in a few coal or natural gas power plants. This can be relatively efficient if the heat is seen as byproduct of electricity generation that would happen anyway.
Some cities in the middle of forests could perhaps be heated by wood or peat but it is not possible for large metropolises.

Nuclear district heating

Nuclear plants are built far away from cities, and piping the heat would lose some of the energy. It is nevertheless an alternative worth exploring.

Modern small modular reactors (SMR) could potentially be built closer to cities and could be used for district heating. Some SMR designs don’t have any electricity production capacity, only producing hot water that is the right temperature for district heating. These purpose designed reactors could be extremely simple, safe and low cost.
District heating works usually best if not too much of it is dependent on one power plant. This way, if one plant (or pipe) malfunctions, the city can still be kept warm. A regular nuclear power plant is often oversized for this purpose, easily filling more than a quarter of a large city’s district heat usage.

Heat pumps for district heating

Ground heat pumps could be used for creating district heat, but the problem is the high temperature. Heat pumps operate a lot more effectively if they can heat a large radiator (like floor heating) to 30 C than to heat a small radiator to 70 C.
Coal steam turbine plant waste heat is quite hot and the district heat grid can run at around 100 C temperature. All the buildings built over a century have small radiators as a consequence. Houses that predate district heating often had coal or wood furnaces, and also had small high temperature radiators. Hence there is a mismatch between existing urban buildings and heat pumps.

District cooling

Many office buildings and newer houses also heat the incoming air (and take most of the energy from outgoing air). This air can also be cooled. This cooling can be delivered by sending cool water through the district heating pipe network – called district cooling. The central power plant can make this cool water with the waste heat from electricity generation process with absorption cooling method. This can be very efficient compared to heat pump cooling.

House heating and cooling

Some cities have gas networks and the houses have natural gas burners. This is something hydrogen aims to replace without having to change the infrastructure. But hydrogen might leak out of the natural gas pipes. This is also a politically risky solution as the source of energy can not be switched like with district heating. There is a sole source for heating energy.
Ground heat pumps in cold climates and air heat pumps in warm climates could be a better solution.
Air heat pump efficiency lowers when outside temperatures get very cold. Ground heat pumps have much higher investment cost, but they are immune to changes in outside temperature.
Heat pumps can be used for cooling as well.

Industry

Nitrogen fertilizer making takes nitrogen (N2) from air and uses hydrogen to make ammonia (NH3). This can be turned into ammonium nitrate or ammonium sulfate. This is a good use case for hydrogen. Hydrogen is directly needed in the process, it is for example not converted back into electricity.
Places with cheap renewable electricity like Australia could create ammonia or the nitrate or sulfate and export it, as indirect electricity export. It is much easier to ship these products than hydrogen.

Iron reduction and steel making

Iron ore is an oxide of iron. It is reduced to iron pellets, currently using coal. Hydrogen can also be used and is being used in early facilities. Direct electrochemical reduction is also being researched. Hydrogen will probably be just an intermediate model.
Steel making from iron pellets and additives already happens with electricity in arc furnaces. Hydrogen has no role.
The iron reduction and steel arc furnace can happen in the same plant, in which case it is called a combinate. But iron pellets can also be shipped overseas to a steel factory.

Industry refactoring

Iron and steel production in the past was placed where coal and iron ore were properly available. Coal can not play a role in the future. It is likely that many current heavy industrial areas will not exist in the future and new ones will be created elsewhere.

This will have a trickle down effect. Currently, iron mines are not opened in places from where the ore is not cheap to transport to reduction with coal. So iron mines could move. If an area has cheap electricity, it might make sense to create an iron ore mine, a reducer and steel factory there.
Then, large users of steel like shipbuilding or car manufacturing might want to locate close to the steel factory. Then, contractors that make ship or car components. And so on.

This could have large effects on some nations as their industrial areas of strength can not compete anymore. They might try to prop them up with subsidies, or lobbying for coal emission exemptions. But the writing could be on the wall and investors would be wary.

This is the great industry refactoring that can happen.

Post scriptum: The path not taken

There is one alternative that would lessen the industry refactoring somewhat, but not completely: build a lot of nuclear power. Nuclear power decouples electricity generation from physical location as one doesn’t need wind or sun for it. However, it’s unlikely for electricity price to go as extremely low for periods that is possible with renewals, the position which fertilizer production, iron reduction or steel making would exploit. It would be a way how existing players with a lot of heavy industry but lack of renewable energy resources could attempt to stay in the race.

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Sources:

I have not added precise numbers or sources to the text. This is a blog post without advertisement provided to you free of charge. 🙂

Some great but not exhaustive material:

https://en.wikipedia.org/wiki/Direct_reduced_iron

https://en.wikipedia.org/wiki/Iron_ore

https://en.wikipedia.org/wiki/Lithium_iron_phosphate_battery

Histories and documentaries of aircraft tend to just plainly list aircraft performance. The next generation of aircraft is just better than the previous one, but it’s rarely explained how this is possible.
This is especially curious regarding aircraft like the F-4 and F-15, both manufactured by the same company, McDonnell Douglas.

Eagle

Well, to not bury the lede, the biggest difference is simply the engine. F-4 used two GE J79 engines, while F-15 uses two Pratt & Whitney F100. The J79 engine had a thrust to weight of 3.1 while the F100 has 4.5. This is a mind boggling difference. With afterburner the numbers are 4.6 and 7.3. This means the F100 without afterburner is as good as the J79 with afterburner. This affects the whole airplane, resulting in an empty dry thrust to weight 0.8 for the Phantom and 1.0 for the Eagle, or 1.2 and 1.7 with afterburner.

There is a lot of discussion around the big wing of the F-15 and how it enables maneuverability, which certainly is great. But that maneuverability is much more useful with the high thrust to weight ratio of the plane, which is possible only thanks to the much higher high thrust to weight ratio engine. The F-4 with a bigger wing would not have been nearly as useful. The F-15 also has great aerodynamic design (NASA did a lot of base research), good flying qualities, radar, ergonomics and electronics etc. But the engine really makes the plane.

So the most interesting question should be, what made the engine so much better? Certainly it’s a turbofan compared to the previous generation’s turbojet, and there’s materials advantages, but let’s discuss that further down.

Raptor

What about the jump from the F-15 to the F-22? The Pratt & Whitney F119 engine in the Raptor has an astounding dry thrust to weight ratio of 6.6, and 8.8 with afterburner. Again, large strides from the F100:s 4.5 and 7.3. The F-22 needs internal weapons bays to maintain stealth, that should hurt weight, yet the whole airplane has empty T/W 1.2 dry and 1.6 with afterburner. The plane can accelerate vertically without afterburner, much better than the F-15 that can only maintain speed. This is one of the reasons why the Raptor can supercruise, ie fly supersonically without afterburner. Afterburner doesn’t bring as big a gain as in the F-15 but it’s still impressive.

The F-22 of course has stealth, thrust vectoring, all computerized flight controls, synthetic array radar in the wings etc. Even the F-15 has not been won in air combat and has hundreds of kills. The F-22 then is so good it’s nott really even deployed anywhere so that adversaries can’t test their sensors against it, and it has never been exported.

Engines

So, the most interesting question is, how did the engines get so much better? The United States Government has run multiple long very high budget programs to research and mature new engine technology: IEDP, IHPTET, VAATE, ITEP, ADVENT etc. The results have been shared to engine manufacturers, and the manufacturers have been contracted to create demonstrator engines.

So, the reason, at some level, is government committing large sums of money over a long term into engine research and development. The technical aspect to fighter engine development would warrant its own research topic.

The work has continued, and the next fighter engine after F119, the Pratt & Whitney F135 in the Lockheed Martin F-35 Lightning II has a 7.5 dry and 11.5 afterburner thrust to weight ratio. Later programs have been AETD and AETP.

As comparison, the Eurojet EJ200 in the Eurofighter has T/W 6.1 dry and 9.2 with afterburner, relatively close to F-119.

All data is sourced from Wikipedia.

Based on the fly through video published in spring 2022

Body

Inner body panels arrive pre-cut to rough shape at 0:20

They are shown to be stamped to a 3d shape, and the extra is cut off at 0:23

The front and rear castings are cast from molten aluminum alloy at 0:52

It is not shown but the inner body panels and the castings are welded together, also some roof beams

Outer body panels are welded on at 1:14

Doors and rear and front hoods are attached at 1:34

Painting

The body is dipped into various liquids, sprayed and painted at 1:42

Skateboard

The skateboard is attached from below at 2:06

The skateboard includes the battery, motors and suspension

Before this the doors and hoods are removed

Doors are furnished at 2:15

Hood furnishing is not shown, neither is door and hood attachment

Interior finishing is not shown

Final checks at 2:20

At this point the car is finished with ready hoods and doors already attached and interior.

The VTOL variant, F-35B, has the lift fan behind the cockpit. This means weapons bays or the inlet ducts can not be on the centerline, behind the cockpit – instead they are on the sides. This applies to all the variants*. This makes the airplane fatter, more draggy and slower. This is also exacerbated by the fact that the carrier version is length limited. Since it’s a stealth airplane, it needs internal weapons bays. Since it’s multi-role, the bays are large, to be able to fit bombs.

A from-scratch designed airplane with the same engine and other systems as the F-35, but no shared structure, designed for air superiority, would probably have a smaller centerline weapons bay and would be longer and thinner. And yes, it would be faster. Manufacturing the structures would be more expensive (because of no sharing) and it would not be able to carry bombs (or at least not as many) stealthily.

Disclaimer: not an expert on the subject. I just haven’t seen this reasoning mentioned in the complaints about F-35.

*: In the non-lift fan variants, there’s a fuel tank in the lift fan space.

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