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Comment by fbdab103 | Hacker News Reader

I am waiting for the day when there is an affordable (<$5k? <$10k as an absolute maximum) residential system that can run on home solar and produce ethanol/hydrogen/ammonia/whatever combustible fuel from excess electricity. Round trip efficiency can be horrible, so long as the system is low maintenance and can be configured to run exclusively off of spare generation.

Is anything like that on the horizon? Or do all of these liquid fuel synthesis options require industrial pressures/volumes/input electricity so as to forever be out of reach from residential synthesis?

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You can effectively accomplish the same thing from an environmental perspective by running your house as efficiently as possible. If you already have home solar, you are reducing the amount of carbon put into the air by power plants. Since CO2 molecules are indistinguishable from each other, that carbon reduction could just as well have come from burning renewable synthetic fuel made at home. If you have a big solar setup and sell excess back to the grid, that carbon reduction will be larger than if you used the same energy to inefficiently synthesize fuel.

You can't operate a car / tractor / hot air balloon with just an efficient house.

Also, you can't run your house on an efficient house + solar over the 2-6 months the sun isn't in the right place (in the sky) for very long or when your panels are covered in snow for a week.

An efficient house gets you to the table and is a multiplier, but long term energy storage is also really important for lots of people.

Hydrogen, though, that stuff's tough. I think 99% of Hydrogen advocates don't understand just how nasty the stuff is.

Interestingly, our solar panels seem to shed the snow pretty fast, in fact faster than the plain roof. I guess the black cells warm up in the sunlight and the snow just slides off them after a couple of days. Pre-solar, we used to have to rake the roof to prevent ice dams from building up, but no longer.

It's probably more efficient to centralize storing weeks worth of energy.

Many people in rural New England have or wish they had secondary power generation because you need that local energy more often when there are external events that likely also break the grid (big snow storm).

The chain of events is "once in a gazillion century storm wipes power to huge region; millions of households are stuck without power, power company can't go out and fix all the broken things for weeks/months, many people have their houses wrecked by frozen pipes / die from running poorly improvised heat systems"

The round trip energy storage with batteries is pretty good but not terribly cheap at scale. The round trip into hydrogen, theoretically, seems pretty good but the actual "nuance" in the equation is basically a bunch of dragons waiting to eat you and everyone who ever loved you. Anyone selling a "power into hydrogen" thing is probably actually selling a "turn natural gas into hydrogen and sell that hydrogen to hippies" thing.

Maybe if you can figure out how to stick a carbon or two or three onto those hydrogens you'd be in business, but it's hard to get those carbons.

Anyhow, this is a hard problem. People have gotten used to hydrocarbons which are basically magic given their stability and energy density.

> Maybe if you can figure out how to stick a carbon or two or three onto those hydrogens you'd be in business, but it's hard to get those carbons.

Or maybe you stick three hydrogen atoms to one nitrogen atom and have ammonia.

It's pretty obvious that the single most important reason why the vast majority of machines/engines runs on hydro _carbons_ instead of hydro nitrogens, is that hydrocarbons have been humanity's most important energy source for centuries.

So it makes sense, everything is geared towards them.

But for the future, ammonia appears to be a much better choice, because nitrogen is readily available and the only thing that's missing is matured tech that runs on ammonia. Fuel cells, engines, ...

IIRC there are already container ships being built that run on ammonia.

If the concern is gaurenteeing that power is always available, the answer is a backup generator. It won't consume fossil fuels unless it's actively in use (very rarely). The carbon taken out of the atmosphere by having an efficient house with solar and grid connection during the rest of the year will more than offset the generator.

I contend that the unsexy combination of solar, a bidirectional grid connection, and an emergency diesel generator is more efficient and environmentally friendly than any existing system involving hydrogen or batteries.

Hydrogen storage is not particularly cheap either. I would be surprised if a house-scale system can beat batteries in terms of cost.

That depends on how far away the center is and whether you trust the people between here and there.

Part of my thinking was for fully off-grid homes. Are we approaching a point where they could capture the excess for long-term storage? Batteries are not the answer.

Perhaps. But then that means the power lines need to be maintained, even when not in use. I'm not sure what the amount is, but it's probably not insignificant.

I live in New Mexico with a 6.7kW array. My house is heated with air source heat pumps. In the summer, we generate 3x the electricity we need. In the winter, we generate 1/3x of the electricity we need. Last year we generated 91% of all our electricity, the year before 93%.

We would need a gigantic store for heating our house, because for 4-5 months a year, we are generating less electricity than we need. Something on the order of 15MW of storage.

We could certainly our home's thermal efficiency, though this would be complex. We could also add more panels, but then we'd be overproducing by even more during the summer.

15MWh of storage seems very high? I appreciate I don't know your raw numbers of production and consumption, but don't you still produce some power during the winter? ie; you would only need to cover your shortfall.

For context, I live in the cloudy-ish south of Australia, and have similar problems with our solar power in winter. However, we still produce reasonable amounts of power through the day, and our total winter shortfall is only about 500 kwh, once offset against the daily production.

So for us, 500kwh -> 2080.8 MJ -> 462.4 litres of storage required (assuming 4.5 MJ / litre and ignoring round trip losses), which seems an entirely reasonable for local storage, safety aspects not withstanding.

Our problem is not the shortfall in the winter generative capacity (sure, it drops a bit, but is still not far from 1MW/month). The problem is the increased load required for heating. I figure we need about 3MW/month for heat, for maybe 4-5 months, but you're right, the storage would only need to be 8-10MW, not 15MW since we'd still generate about 1MW anyway.

This is all correct with the caveat around how you want your "features" to be defined and how you want your "bugs" to be defined. Most notably, that's around the grid.

Implicit in your assumption is that the grid is reliable, always on, not subject to geopolitical or climate risks, etc. "Inefficiently" converting solar power into otherwise portable fuel might be a feature rather than a bug for those living in conditions where the central grid is often unreliable. Before the past few years, I'd say that would generally be countries in the global south, but we've seen a lot more grid instability even in the US as of late.

It’s just a matter of cost. Cost savings will come from improved efficiency and manufacturing innovation. You can make a lot of electrofuels in a distributed way:

Hydrogen (Water + Electricity): There are many containerized electrolysers

Ammonia (Air + Electricity): https://www.nitricity.co/

Methane (Air + Electricity): https://terraformindustries.com/

Looks promising!

10k is an absolutely wishful thinking - 10k is just the low end of a bog standard geothermal pump.

Also what's the purpose of the ethanol (the rest are not useful, esp. hydrogen which has to be stored somewhere, ammonia is rather dangerous)? I can imagine making vodka alike - but beyond that, using internal combustion engine to burn it means an extremely very low efficiency to conserve enegy. The energy density is there but the efficiency is not.

Heh. Yeah, I was thinking that any kind of home synthesis operation was unlikely to offer a financial payback. Hence the low aspirational cost, but you are right that figure is laughably low.

Ethanol - easier to synthesize than gasoline (which is a complicated mixture of hydrocarbons). It has ~2/3 energy density of gasoline, which I do not think is horrible. I believe it is also less volatile and easier to store long-term.

Couldn't it just burn off excess hydrogen? It would just be H20 byproduct.

A composter costs very little and can product a decent amount of methane.

Animals like goats and pigs can produce a lot of dung that will turbocharge that quite a bit.

A little searching yields stuff like: https://www.motherearthnews.com/sustainable-living/renewable...

The low tech route is far cheaper and easier at small scale if you want to make combustible fuel.

This is currently the Lavo hydrogen electrolysis product for home use [1]

However the storage tanks are quite small. I would prefer if they made the hydrogen production and storage separate, so you could save up hydrogen in the summer to use in the winter.

[1] https://www.lavo.com.au/

Hydrogen storage is not something that you really want to do at home, especially in "saving up" quantities. It is quite happy to explode, you need tremendous pressures and low temperatures for efficient storage, and also hard to contain (many "normal" materials are permeable to hydrogen). [1]

[1] https://en.wikipedia.org/wiki/Hydrogen_safety

There are ways of storing hydrogen in metal hydrides at room temperature and pressure. This makes a LOT of sense for people who may want to have an option of buying stored energy - such as those who live in apartments without access to the terraces where solar panels can be deployed.

If these metal hydride storage is used similar to how changeable batteries are used, it is conceivable that you could drive up to a place like a fuel station just to change out your metal hydride storage in a matter of a couple of minutes and perhaps even get additional supplementary units packed at the back of the vehicle if they intend to go on a long journey.

https://www.frontiersin.org/articles/10.3389/fenrg.2021.6161...

There has also been recent advances in using Boron Nitride for storage - a perfectly safe chemical.

https://www.geelongmanufacturingcouncil.com.au/2022/07/innov...

There is a case for portable storage, sure.

Hydrogen at scale is going to look more like a means to export sunlight energy from equatorial climes (Australia, Sahel, etc) to Europe, the northern US, Canada as required.

Efficiencies dictate the most likely roll out is large central generation of electricity and dispersal via the existing electrical grid system.

In a similar view individual per apartment solar panels make little sense, panels should be built into entire buildings .. across roofs and across any required parking structures, etc.

Is the watts/kg for this electicity ->hydrogen+metal hydride storage solution better than an electicity -> lithium-ion battery solution ?

> Hydrogen storage is not something that you really want to do at home, especially in "saving up" quantities. It is quite happy to explode, you need tremendous pressures and low temperatures for efficient storage, and also hard to contain ..

Agree, hydrogen storage is not something you do as easily as say piling up some fire wood.

On the other hand, it's totally possible to do at home and it is being done. Hydrogen can be stored in regular gas cylinders. See the realized projects from Home Power Solutions [1].

If these cylinders are located outside, explosions should be rather unlikely due to ventilation.

[1] https://www.homepowersolutions.de/en/picea-plus/

This [1] comment mentions https://homepowersolutions.de/

There's also a recent HN topic [2] about it, but without any comments yet.

[1] https://news.ycombinator.com/item?id=34298804

[2] https://news.ycombinator.com/item?id=34302276

In my opinion you are mistaken , affordability does not mean home appliance.

Hydro is pretty cheap , does not mean it’s fit for home.

Here the best scenario is similar to Singapore - Australia or UK - Morocco remote solar grid.

This innovation is very interesting compared to Water- Hydrogene electrolysis that is a bit expensive and needs metals that are going to become difficult to source in the coming decades.

Gallium is quiet abundant from my understanding.

There are also things like MAGFLY that stores electricity (from e.g. solar panels) as kinetic energy in flywheels:

- https://www.flywheel.dk/

- https://wattsuppower.com/flywheel/

> combustible fuel from excess electricity. Round trip efficiency can be horrible

If that's really all you want, you can get a 9 year old to put together some kitchen waste and art supplies to achieve this.

That's how I did it at that age.

I did use a battery though, so you might want to check the wiring and add a voltage divider, but those are also easy to build even without understanding.

And I have no idea if you even can, let alone should, just pour gaseous hydrogen into, for example, a gas heater's fuel input pipe.

But actually making hydrogen is utterly trivial.

Low maintenance, safe, compact, and high enough output is a different story.

For the second, you probably want a methanol, methane or ammonia output and they all require high temperatures or exotic materials.

Just use the grid, they can move energy through time a lot more efficiently than you can ever hope to do. https://www.moderndescartes.com/essays/factobattery/

Even the grid's may benefit from green hydrogen, without any major overhaul: https://www.ge.com/gas-power/future-of-energy/hydrogen-fuele...

Also conceptually related (small-scale): https://news.ycombinator.com/item?id=32694644

Why not just a 20kWh battery for energy time shifting. Or are you looking to sell the hydrogen?

The commenter's goal is presumably season-shifting, which is two orders of magnitude off from feasible battery capacity. In most areas in the US, a full-roof solar system will produce enough energy in aggregate to power the home's use year-round, but there's no way to get all those summertime watt-hours into the lines in winter when the panels are dark.

But indeed, no, this just doesn't work. Best available efficiency for round-trip electrolytic fuel production / electricity generation is 40% or so, meaning that those roof panels wouldn't be enough anyway. (Also there's the problem of having every home store a winter's worth of pressurized hydrogen or whatever on-premises. Yikes.) It's not worth it.

Home solar is attractive because unlike most infrastructure it scales down really well and is actually feasible to do at the level of an individual user. But, like most infrastructure, seasonal power management is a grid-wide problem and needs to be solved at the utility level. There are plenty of tricks available there that homeowners don't have access to.

No interest in storing a season's worth of energy which would be infeasible without a ludicrously over provisioned system. More -what could you do with spare capacity that is not trash-tier net metering? Generating liters of fuel weekly would be enough to power my ICE car (I rarely drive). Or being able to generate and store a ~week of liquid backup energy.

Such a system would be unlikely to ever payback for itself. Not deluding myself on that one.

Depending on where you live, simply electrifying your home and driving an EV should be enough to get you within a few percent of your peak summer output. You won't be wasting that much. Buy the heat pump water heater, the induction range, etc... Pick the low hanging fruit, then worry about using that last bit of juice in June.

FWIW: net metering seems like "trash tier" precisely because that summer PV excess really is mostly wasted (this is true for big panel farms too). The utilities were taking a huge haircut on the old 1:1 billing that California just rolled back. It wasn't sustainable.

If you drive say 300 miles a week that’s 100kWh for a typical electric car. Another 150 for domestic use and that’s 35kwh a day. You have a system that generates more than that if you have excess to pump into liquid storage, but why do you want a weeks worth of backup energy? Why not 3 days? Or 2 weeks?

This will last less than a day.

What to do in the winter? If the answer is "use the grid", then we just kick the can to someone else, who will probably use fossil fuels to provide the energy. The basic problem remains - solar/wind are intermittent and fluctuating.

Compressed air has a higher round trip efficiency than storage, and pumped hydro is twice as efficient as compressed air.

However until zero kWh is generated from fossil fuels in summer, solar/wind and battery is a massive gain, even if gas is still used for 2 months a year.

But gas is used also in the summer. And energy is not only electricity - heating is currently done mostly by natural gas, and is often absent from those calculations.

Efficiency is irrelevant. The only thing that matter is cost and feasibility. The cost of energy from solar is ~$0.02/kwh and sometimes even $0.00/kwh (when the grid curtails production). Even with 30% efficiency each kwh retrieved from storage will cost a record-low of $0.06/kwh (3-10 times lower than the consumer price).

The biggest factor here is the capex and ease-of-use of the equipment. Not the energy input cost.

If you do and you're my neighbor please wait with switching it on until I can move away.

I think the closest to what you need would be some sort of pico hydro with pumped storage.

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