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Comment by cduzz | Hacker News Reader

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.

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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.

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.

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.

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.

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.

> 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.

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