J. A Hydrogen Storage Ravine

Hydrogen is going to become critical for low-carbon steelmaking and so we need to store it.

I see several good horses in the race for 99% renewable electricity.  Hydrogen as a fuel has a number of inherent disadvantages so that I have its use as a fuel in the "longshot" category, but if I were in the hydrogen technology business I'd still keep the R&D going.

First, hydrogen's negatives: hydrogen is quite a fussy fuel.  When you pour gasoline into your car's fuel tank it stays in the tank.  Hydrogen, on the other hand, often has to be compressed to 300 atmospheres. Compression has an energy cost. Also, two geology graduate students that I know went to the emergency room after a hydrogen tank in their lab started hissing and then the lab exploded just as they reached the lab door. Furthermore, obtaining hydrogen through electrolysis is relatively energy-inefficient - 40% to 60% of the available energy is lost. Most important, depressurization of hydrogen from a 300 atmosphere pressure can result in a stream of extremely cold hydrogen gas that can sometimes cause ice buildup issues.

Now the positives: Focusing concentrated solar heat on an industrial scale might soon cost perhaps 80% to 90% less than using photovoltaic panels to crank out electricity and then heating with that electricity. At these heating prices it's possible to economically split water into hydrogen gas and oxygen gas using a heat-driven chemical process, for example, the copper chloride cycle. Total energy efficiency will become a less meaningful measuring tool if solar heat in a desert setting becomes remarkably inexpensive.

Assuming a rock-bottom cost for production of hydrogen gas, I'd like to find out whether great quantities of hydrogen gas can economically be stored at normal air pressures within an enormous building or within an enormous abandoned mine or cavern.

J1. Huge buildings that only enclose air

I have two possible uses for an air enclosure building: first, a building can possibly store hydrogen gas, and second, a building can enclose a wide and tall stream of warm or hot air rising up a mountain slope.

The building needs to withstand hurricane-force wind gusts on its several sides. Also, in many climates the building needs to support several inches worth of frozen precipitation on its roof, and water must run off of the roof.

One of the best strategies for cost-efficiently deflecting the power of lateral wind gusts is a slanted wall. Whenever a building's roof extends all the way to the surrounding ground, almost all the power of a wind gust is deflected upward, over and past the building.

Constructing the building within a ravine uses the ravine as a natural part of the building's left and right walls. The building could equally be sited within an abandoned open pit mine. This would reduce total engineering costs of the building. There wouldn't be much interior detail in building this type of vast, enormous shed as it's mainly a roof to keep the weather outside, columns, roof support beams and guy wires to hold the structure together. I'd aim to construct a cost-effective enclosure to store, say, 10 million cubic feet of uncompressed hydrogen for day/night peak load coverage.

I'm especially looking for zero wind and zero precipitation indoors. Once zero pressure hydrogen storage containers are under shelter, we won't worry about indoor extreme winds, precipitation, ice buildup or heat expansion. Assuming that the hydrogen is never under pressure and always out of the weather, it's unlikely to suddenly leak out.

J2. Construction axioms for vast empty buildings

(these construction axioms will apply equally to the construction of any huge-scale mountain slope solar chimney)

If a building essentially contains nothing but air, it still has load-bearing pillars to vertically support the weight of the roof. The pillars are connected to each other with diagonal guy wires. These guy wires take up the strain with lateral wind gust overpressures. There aren't any bystanders inside to put lateral pressures on the load-bearing pillars.

Lateral wind gust pressures can be minimized by building a sloping roof all the way down to the ground on all sides. Sloping roofs shed wind gust overpressures against the side walls. Sloping roofs also shed precipitation. Cables sloping up from the ground outside the building can also help with wall overpressures.

We should create and store geothermally stored coldness below the building's center area when surplus electrical power is available. The lower the ground's temperature and the building's internal temperature, the more hydrogen can be stored within the same building volume. Insulation will help preserve the coldness.

Given support pillars in a triangular array, under-roof struts can branch out under the roof to form smaller and smaller triangular-shaped roof support areas.

J3. The hydrogen building's design and construction

My construction goals are maximizing the building's cubic footage per dollar and the building's survivability in extreme weather. I'm not designing a 100 story skyscraper that supports the combined weight of 10,000 people, only a hydrogen gas enclosure. The hydrogen gas inside the building is going to weigh slightly less than nothing. The building has no floors, walls or ceilings inside. The enormous building only needs to handle roof snow loads and lateral wind loads from any wind direction.

A 300 meter long building straddling a 30 meter deep by 60 meter wide V-shaped ravine encloses roughly 300,000 cubic meters (10 million cubic feet). Because the building will be in a ravine the building won't have high wind overpressures on its two long side walls from rare hurricane-force wind gusts. The two walls at the top and bottom of the ravine should also slope down to the ground to minimize wind loading. The building will be all roof and almost no wall except perhaps on the ravine's low side.

I could see a metal roof on the building with a 15 degree roof slant, enough of a slant to shed snow when the roof is above freezing but not enough of a slant to significantly increase lateral wind loads on the building.

The weight of the roof plus the weight of any snow load can be vertically supported from the ravine's bottom with parallel vertical columns of lightweight metal posts. To build this low-cost building, first install a hexagonal array of concrete or similar bases across the entire length and width of the ravine. The bases will optimally be spaced 10 meters horizontally apart from each other.

Posts similar to street light poles might come in standard 10 meter heights, plus a number of nonstandard lengths will be needed from the bases at the ravine's bottom to the top of the first level. All posts should be shipped with human footholds on their sides and with safety lines so that workers can easily and safely climb them. They should be fitted at their tops and at their bottoms with connecting bolts up and down, and with 12 holes top and bottomfor attaching diagonal guy wires. If the bases are all arranged in a hexagonal pattern, so are the post columns. The diagonal guy wires will criss-cross all of the building's interior, keeping all of the posts arrow-straight and transmitting lateral forces on the roof diagonally down to the ground.

It helps to lift every post into place with six pre-measured guy wires taped onto the post, with one end of each guy wire pre-attached to a hole at the top of the post. It remains to attach the bottom ends of all six guy wires to six neighboring posts. Tensioners on the guy wires can be used to equalize each guy wire's tension.

After completely hoisting the bottom layer of posts into place with a walking crane running above the ravine and attaching all guy wires to the bottom layer of posts, lift the second layer of posts into place, always bolting down and attaching the new guy wires attached to each new post. Following this method, four or five layers of the superstructure can be cost-efficiently assembled to a height of 40 meters.

Finally, raise rafter sections to connect the posts at their tops. Raise small roof pieces that bolt onto the rafters.

A creek would still flow through the bottom of the ravine. The bottom of the enclosed ravine would have plenty of room reserved for heavy stream flow during bad thunderstorms. Micro-swales and stream water poaching techniques, described later, might help to relieve peak storm flow.

Everywhere inside the ten million cubic foot building, huge thin rubber bags would be inflated with hydrogen gas production when the sun is shining and then the gas would be used for electricity generation during peak electricity demand hours. Leaving hydrogen in unpressurized thin rubber bags saves the energy of hydrogen compression.

Individual hydrogen containment bags can be sized to the empty areas between the girders. A 30 foot by 30 foot by 30 foot hydrogen bag in the shape of a cube would hold 27,000 cubic feet (760 cubic meters) and would fit between girders.

Each rubber bag will need a supportive lattice of cables on top because hydrogen weighs somewhat less than air. As a bag fills with hydrogen it will grow downward from its supportive top.

Colder gas takes up less volume per mole of gas than warmer gas. Keeping the building at a deliberately freezing temperature might help us to store 20% more hydrogen than we could store in a warm building. I remember from above that causing hydrogen gas to decompress can cause major coldness issues, but there's a coldness balance to be struck here. We can live with minor coldness issues. Any air inside the building needs to be dehumidified to prevent condensation.

As a building fills up with hydrogen, air will be exhaled from the building. As a building's hydrogen is burned in a fuel cell, air will be brought back into the building.

J4. An inert gas layer

I have a method for controlling hydrogen fires after bag punctures.

A layer of nearly pure carbon dioxide or nitrogen gas in inflatable ribs surrounding every hydrogen gas bag will add a level of gas handling safety. If tiny amounts of carbon dioxide gas leak into the hydrogen gas area, CO2 won't explode. If tiny amounts of carbon dioxide leak out into the outside air, that also won't explode. Any pressure change within the carbon dioxide layer is an indicator that the bag has sprung a leak and should be kept empty until replacement.

Small amounts of oxygen and nitrogen, gases with two atoms per molecule, can be gently separated from a volume of nearly pure CO2, a gas with three atoms per molecule, using a molecular sieve. Small numbers of oxygen molecules leaking into the CO2 will be too widely dispersed in the inert gas to maintain a fire. Optimally we lose nearly zero CO2 into the atmosphere from leaks, ever, and that's why the tiny CO2 losses aren't all that bad. Pure nitrogen gas will also work as our inert gas if the CO2 losses seem too bothersome.

Given both cheap solar hydrogen production and energy-efficient hydrogen storage, a city-sized hydrogen battery is possible. However, the competition will get rough pretty fast. Geothermal seasonal storage of heat at 200 degrees C has my inside track for electricity storage. Running in second place is a gravity-based method of electrical power storage.

For further reading: https://cleantechnica.com/2022/04/22/instant-long-duration-energy-storage-just-add-carbon-dioxide/ This battery compresses and decompresses carbon dioxide in a closed loop.