[mchusma]

Incentivizing usage during peak times makes total sense, but if price swings are this wild, how are grid scale batteries not highly economical? My rough ballpark math was that you need roughly 20 kilowatts of battery storage to make this issue basically nonexistent, and that would cost about 10 billion dollars, which doesn't seem that much for this.

[jeeeb]

Grid scale batteries and household batteries are being widely deployed.

Australia is the third largest market in the world for grid scale batteries, and has the highest per-capita capacity in the world; https://www.pv-magazine.com/2025/10/21/australia-becomes-wor...

Not to mention more than 200k new household batteries installed in 2025 (out of roughly 10 million households).

[michaelt]

I think it's less a question of batteries being economical, and more a question of the relative economics of batteries vs solar panels.

After all, if the highest demand is between 16:30 and 19:00 you could use batteries to store power at 12:00 and sell it at 18:00 - or in famously sunny Australia you could build enough solar panels that solar output at 18:00 matches power demand.

If batteries have a solid 9% return on investment, but solar panels have an even better 12% return on investment, panels will outpace batteries even though the batteries are a decent investment.

(Also, from a politican's perspective, making batteries highly economical is how you get batteries built. And an awful lot of pro-environment policies involve raising taxes, banning things and creating new chores; it's nice to have some green policy announcements that actually benefit voters in the short term.)

[perilunar]

> you could build enough solar panels that solar output at 18:00 matches power demand

No you could not. For half the year the sun has set by 18:00.

[sevenseacat]

I mean in the dead of winter, yes. For six months of the year? Definitely not.

[perilunar]

Definitely so. Unless you are on the equator, the sun is up for less than 12 hours a day from the autumnal equinox to the spring equinox. The sun will set before 18:00 local solar time. So apart from funkiness with time zones and summer time (which extends a couple of weeks past the autumnal equinox in Aus), yes, roughly half the year.

[tialaramex]

You're not crazy in the broad sweep of your idea, but actually because the sun isn't a point of light you're also not strictly correct, for example in Singapore the day is always more than 12 hours long.

[perilunar]

Singapore is close to the equator (1°17′N) — the days are roughly 12 hours long all year. No, it's not exact. They vary from +3 to +12 minutes. It's close enough (<2% error).

It's not entirely due to the apparent size of the sun — refraction due to the atmosphere has a slightly greater effect.

(Singapore is also in the 'wrong' timezone. The sun sets around 7 pm every day, giving it effectively permanent daylight saving time.)

But regardless, Australia is not near the equator. The timezones are mostly ok. In most of the country (for most of the population anyway) the sun sets before 18:00 for roughly half the year. No amount of solar is going to power the evening peak demand without storage.

[danmaz74]

You won't get 12% return if your panels generate electricity which is only paid between 18 and 19, because there is already overcapacity between 16:30 and 18.

[marcosdumay]

If you build enough solar that the output at 18:00 matches the demand, it will not have the same ROI as if you are using batteries.

[throwaway2037]

    > If batteries have a solid 9% return on investment, but solar panels have an even better 12% return on investment, panels will outpace batteries even though the batteries are a decent investment.

Sorry, normally I hate this follow-up on HN, but can you share a source? I tried to Google for sources, but there is a pretty wild range of ROI in different countries/regions. My point: Ideally, can you provide personal/anecdotal experience, or something that is specific to a country or region?

EDIT

I forgot to say: I like your idea of intraday arbitrage using batteries! It is a very cool idea. Surely, this could be well modeled to know your expected ROI before investment/build-out.

[josephcooney]

One of my co-workers (I'm Australian) has 500 kilowatt-hours of storage at home...which is wild. Much more common is the 10-20 kilowatt-hours of domestic storage for a house.

[protocolture]

My dad buys lead acids written off from storm damage to solar systems (The whole system gets replaced under insurance even if the batteries are just a bit worn) and then sells them to preppers in the middle of nowhere. For a while he had above 300KW/h of storage, basically completely off grid with few shutdowns. It was kind of nuts. His house did burn down, but it was arson.

[jondwillis]

What is their fire suppression setup like??? Granted I guess they could be doing pumped hydro storage lol

[defrost]

If they're in a rural / industrial area setting it could quite literally be a fire break around the battery area (bare dirt and no overhanging trees).

Fire control in Australia is first and foremost about limiting spread - the bush in Australia goes off if it catches hard.

"Mini" pumped hydro is a thing here (in places): https://www.abc.net.au/news/2024-12-01/australian-first-mini...

[sire-vc]

'Is a thing' - obviously, stalled due to red tape. As an immigrant to Australia I am repeatedly amazed at how long anything involving the the government takes.

[josephcooney]

Yeah, he is in a rural area. The batteries are off in a metal shed away from everything else.

[dzhiurgis]

That's ~8 used EV batteries. Each cost less than 10k, maybe 6-8k AUD.

If you know your way around high voltage DC, got a tractor and appropriate emulator - not exactly difficult or super expensive to pull off.

Granted it's pretty uncommon setup as grid batteries themselves are pretty cheap too and used EV battery is simply too large for home user, too much hassle, liability, etc to save like $2-3k.

[BLKNSLVR]

More details please, do they have a website that explains their setup?

Are they a hoarder of old car batteries and the like?

[josephcooney]

I think they bought a whole bunch of batteries of some kind from China. I don't ask too many questions...which is I think how they like it.

[fnordian_slip]

Does he have a saltwater aquarium, or any other hobby that can make use of it? If not, I can highly recommend that he get into it, if he's into that kind of overkill :)

[Walf]

They are, but they still take time to build, and loans to finance.

Here are two of SA's (which has the most renewable generation): https://en.wikipedia.org/wiki/Hornsdale_Power_Reserve https://web.archive.org/web/20220523164905/https://www.elect...

[jofzar]

> but if price swings are this wild, how are grid scale batteries not highly economical

They are super economical in Australia and the government even offers discounts and interest free loan of 15k to buy them.

[ghiculescu]

They are super economical… which is why there’s a subsidy required for people to buy them?

[stubish]

The more households that buy them, the less peak power generation is needed and less large scale battery deployments. If the ROI of a household battery was just 4%, you are better off economically paying higher power bills and sticking that money in an index fund. But if subsidies increase that ROI, more people buy batteries. The money the government contributes hopefully ends up less than they would need to spend on large scale battery deployments or on legacy power generation to power peak usage times. It also has the side effect of getting more citizens (literally) invested in sustainable power usage, and people get more interested in insulating their homes, buying more efficient appliances, moving away from gas etc.

[chii]

> which is why there’s a subsidy required for people to buy them?

the gov't also offers interest free (but inflation indexed) loans to tertiary education.

Just because there's a subsidy, doesn't mean the tax payer is paying a price for inefficiency. The policy itself needs to be individually examined to determine whether it's an efficient use of funds, not simply that it's a subsidy (time frame needs to be taken into account too).

[ghiculescu]

Yes, and nobody would describe Australian tertiary education as "super economical".

[embedding-shape]

Is it so out of the ordinary that a government tries to help people save money or what's the question? Sounds like you've only had the American experience in life unfortunately.

[AnthonyMouse]

If something actually saves money then it doesn't require a subsidy because people would be doing it regardless.

Meanwhile the government doesn't have any of its own money, so it can't really give you something that was yours to begin with, all it can do is take it from you and then give it back with strings attached. How is that helping you? Instead of subsidizing something you can make up your own mind about whether you want, they should just lower your taxes by the amount of the subsidy and let you use your money for that or something else at your choice.

[embedding-shape]

> If something actually saves money then it doesn't require a subsidy because people would be doing it regardless.

Spoken as someone who never been poor. There is definitely a ton of stuff people with money can do to save more money, that is completely out of reach for the people who would actually benefit from those savings the most. Subsidies is quite literally about reaching these folks that others tend to forget about.

> all it can do is take it from you and then give it back with strings attached. How is that helping you?

Compared to "take it from you and not give it back to you", it's definitely helping people who have less money. Not sure how this needs explaining.

[AnthonyMouse]

> Spoken as someone who never been poor. There is definitely a ton of stuff people with money can do to save more money, that is completely out of reach for the people who would actually benefit from those savings the most. Subsidies is quite literally about reaching these folks that others tend to forget about.

Except that there is no additional money, its just your own money but now there are strings.

On top of that, that still isn't necessary for things that save a non-trivial amount of money, because that's what loans are for. If it has a $100/mo loan payment and saves $150/mo on the electric bill then you take out a loan or buy it on an installment plan and don't need to have any accumulated capital in order to do it.

> Compared to "take it from you and not give it back to you", it's definitely helping people who have less money. Not sure how this needs explaining.

Why would anybody want that either, instead of just not taking it from you to begin with?

[abecedarius]

To target the "poor people need more money" problem, the most direct answer is give them money. If someone's answer is a variety of politically-allocated narrow subsidies, you should wonder what interest they're really aiming to satisfy.

When you get money, you can choose to spend it on what's worth the most to you. Thus "strings attached" on the opposite.

[budsniffer952]

That's a strange definition of "subsidy".

[throw0101a]

> If something actually saves money then it doesn't require a subsidy because people would be doing it regardless.

…assuming people are good at math.

And given that most people probably don't have a bunch of cash just sitting there doing nothing, they will have to take out a loan and most folks probably don't like going into debt even though 'the math says' it's a good ROI.

The idea that 'ROI good, therefore people will do it' is the 'spherical cow' of economics. In reality there are all sorts of other motivations for human economic actions:

* https://en.wikipedia.org/wiki/Behavioral_economics

* https://en.wikipedia.org/wiki/Homo_economicus

[mothballed]

To be clear, this doesn't change the price floor for ROI calculations. A non "approved" contractor or DIY job non-subsidized is well cheaper than a piddly few percent interest rate arbitrage to a pre-approved list. This does nothing beyond let some rich contractors regressively allocate money from taxpayers to themselves by artificially appearing a bit less of a premium to the alternatives.

It looks more like to me some installers saw their industry was becoming commoditized and the government got together with them to figure out how to grift taxpayers into making the more connected ones command a premium while simultaneously being better positioned to eat the lunch of the small middle class "guy and a truck" who does cash jobs for cheap but has no resources to become "accredited" on a subsidization list.

[BeeOnRope]

It can work when the marginal cost of new capacity is high, compared to existing capacity.

E.g., if the marginal cost of supporting 1 kW of new capacity may be X, while the current averaged cost of 1 kW provided to existing customers may be Y, with Y < X.

The customer will calculate their ROI on a battery purchase based on the cost Y of kW to them, which may be poor (4%), while on the government level of the ROI may is closer to that implied by the cost X (say 10%). However, the government cannot easily pass on the "marginal cost" to customers as there is no specific kWh which is that marginal one across all customers.

In this case a subsidy directly picks out customers who can reduce their demand by buying a battery (e.g., a subsidy which raises the ROI to somewhere between 4% and 10%).

[master-lincoln]

Think about people who could not afford the initial investment. It's beneficial for society here if the government redistributes wealth for the benefit of all.

[AnthonyMouse]

> Think about people who could not afford the initial investment.

This is what loans and installment plans are for, the payments for which come out of the savings on the utility bill.

> It's beneficial for society here if the government redistributes wealth for the benefit of all.

Which has nothing to do with batteries. If you want to do that then provide them with a refundable tax credit that allows for a negative tax rate in cases where that's deemed desirable.

And even that doesn't apply to the majority of people who are currently paying a non-negative amount of tax. Why attach strings to the money going to a middle class homeowner who should have just been allowed to keep that portion of their own salary?

[EliRivers]

"If something actually saves money then it doesn't require a subsidy because people would be doing it regardless."

Yet people frequently don't. This assertion and reality disagree.

[rswail]

Because the individualized incentives do not take into account the community benefits.

The money saved is distributed across the community, for both those that directly benefit and those that can't (eg renters, apartments etc). The general benefit is of greater value than the individual savings.

Your attitude that somehow taxation is theft is a very silly Ayn Randian Objectivism outgrowth that has never been true, even in the most "free" US states.

[AnthonyMouse]

> Because the individualized incentives do not take into account the community benefits.

Only if the utility company is pricing things incorrectly.

If the price of electricity is ~free during the day and expensive in the evening then the individualized incentives for installing a battery line right up.

> Your attitude that somehow taxation is theft is a very silly Ayn Randian Objectivism outgrowth that has never been true, even in the most "free" US states.

Whether it's theft or not doesn't change the arithmetic. When you're paying them the money they're paying you, it was your money to begin with.

[TheOtherHobbes]

Think of it as a giant corporate tax break, but for the little people.

[AnthonyMouse]

> Think of it as a giant corporate tax break

So the thing everyone correctly maligns because it's generally some form of corruption or inefficiency?

[Panzer04]

Yes, the government subsidies for home batteries specifically are a very poorly targeted handout. Unfortunately splashy policies like this are classic vote buying measures, even if economically they don't make much sense

- home batteries cost more

- homeowners buying batteries are already pretty well off on average

- a large portion of the population (renters) is excluded from the policy.

- prices are falling anyway so the subsidy is just a waste of tax dollars, arguably

- grid scale batteries are more cost effective and benefit everyone via cheap prices broadly, instead of specific homeowners.

Etc. but pork barreling be pork barreling.

[vitro]

I know people who would purchase solar panels and batteries, but they do not have enough capital to do so.

[aianus]

In Australia? The houses are like 30x-100x more expensive than a battery, how would this be possible?

[liamkinne]

The government loan changes the calculus. Allows for short term thinking and a long term benefit.

[TheOtherHobbes]

Yes. People can't always afford super economical things when the initial cost is high and the pay-off takes a while, but is easily worth it in the end.

[xbmcuser]

Yeah this is why a lot of people were thinking that the Australian opposition asking for spending $40-50 billions for nuclear that would come online in 20-30 years and to keep using coal and gas till then were being stupid.

[thedays]

It wasn’t $40-50 billion. It was estimated to cost $116-$600 billion to build 7 nuclear reactors https://smartenergy.org.au/nuclear-fallout-116-600-billion-t...

I think the likely cost would have been hundreds of billions considering Australia does not have a nuclear energy generation industry. It currently has a very small nuclear workforce as it only has a small nuclear medical reactor on the outskirts of Sydney.

[xbmcuser]

I am talking about the $30 billion that the opposition was making up. My point was that even those made up numbers for nuclear were still more expensive than installing solar and batteries.

[ZeroGravitas]

It's not stupid if they are paid off by the people selling the coal and gas.

It's just a treasonous level of corruption.

Voters opting to be extorted like this would have been stupid.

[rswail]

They are, and they are being rapidly rolled out and the "post sunset" spikes are rapidly being flattened by both grid storage and "behind the meter" home batteries.

[christina97]

One issue with grid scale batteries is that the solar is predominantly generated in the suburbs, but the grid wasn’t built for a huge “generator” in the suburbs. It requires retrofitting the grid for this huge excess. It would be better to instead store it in the suburbs in household batteries (which they are also building out like crazy).

[thatsit]

Well, i can only be cheaper to shift demand to high production hours then building a battery. Especially as you don’t only need an inverter for the battery but also the charger or MPPT to suck up the peak solar power which is only lasts for about 3 hours. So you can save building a lot of excess batteries

[numpad0]

Maybe they just don't work? Otherwise someone's leaving tons of money on the table. Which implies nobody is.

[3stacks]

They've already burned at least $15bn on that disastrous Snowy Hydro "battery" project... Could've just rolled out consumer batteries on a large scale instead.

[simondotau]

At current battery project prices, matching Snowy 2.0’s roughly 350 GWh of energy storage capacity with Tesla Megapacks would cost around AUD $218 billion [0] and require Tesla’s entire global Megapack production capacity redirected to a single client for five years.

$15 billion is far more than Snowy 2.0 should have cost. But it remains substantially cheaper than any lithium-ion battery build for bulk storage. Storage on this scale is essential in a post-coal electricity grid, and batteries are not (yet) plausible substitutes for bulk storage.

[0] This assumes linear scaling. In reality, placing an order like this would grossly distort supply and demand on many levels. Thus the cost would ultimately be superlinear.

[ZeroGravitas]

Snowy 2.0 has major limitations on what it can supply, the headline number is very misleading.

And the comparison shouldn't be to batteries alone, but solar/wind and batteries. The former can be used directly and fill the batteries repeatedly on a timeline that is predictable.

It provides no extra value for the electricity to be stored long term if for the same money you can generate and store it short term.

Article on the various restrictions on Snowy 2.0:

https://theconversation.com/snowy-2-0-cost-blowouts-might-be...

[simondotau]

Your reply — and especially the attached article — misunderstand the reality of operating a grid at scale.

Responding to you:

Solar and wind are just as relevant to pumped hydro, which is really just a different kind of battery. The real question is how much short-duration storage is needed from chemical batteries and how much long-duration storage is needed from pumped hydro. Chemical batteries are essential for grid stabilisation, frequency control, and intra-hour balancing. They're necessary, but not sufficient.

Pumped hydro provides something that no economically realistic combination of batteries, solar, and wind can yet deliver at scale: enough stored energy to contribute towards grid stability through consecutive overcast, low-wind days. The main alternative is to build and maintain gas-fired peaking plants for occasional backup, which is both costly and keeps us dependent on fossil fuels.

Responding to the article:

While there are credible doubts about the value of Snowy 2.0, the article does not establish its headline claim that batteries are a cheaper system-level alternative. Most critically, it doesn't acknowledge the role of pumped hydro as an insurance asset. The point of insurance isn't to be cost effective in normal times, it's to be cost effective against the risk-adjusted consequences of grid destabilisation.

It is true that under normal conditions, Snowy Hydro would have little incentive to discharge fully because doing so could depress market prices. That is why capacity contracts, underwriting arrangements and reliability options exist. We know that strategic storage has substantial social value that its owner cannot fully capture through energy arbitrage. This is a common problem for reliability assets: their success can destroy the scarcity rents needed to finance them. Hence contracts.

[ZeroGravitas]

We want to eliminate fossil fuels and lower costs as quickly as possible.

Vague claims that some alternative like nuclear or Snowy 2.0 will somehow make that last 1% of fossil easier to eliminate are both dubious and irrelevant if their construction uses money that could have easily eliminated 1% of fossil fuel every year for decades.

And once we get close to that last few percent of fossil gas in the electric system it would be better for costs and climate to focus on electrifying industry and homes with cheap electricity anyway.

[angry_octet]

Yes Snowy 2.0 just won't have enough water for many of the years in out future.

[fragmede]

Yeah the battery storage story has to acknowledge the fact that global production capacity simply isn't actually high enough to deliver that many batteries so we need alternative solutions to the problem as well.

[asdefghyk]

From Australlian ABC news...

The cost of the Snowy 2.0 pumped-hydro project is estimated to range from \(\$12\) billion to as high as \(\$42\) billion depending on the scope of costs included (such as direct construction, interest, and broader transmission). Originally announced in 2017 with a $2 billion price tag, the project has faced massive scale and logistical blowouts. The cost of the Snowy 2.0 pumped-hydro project is estimated to range from $12 billion to as high as $42 billion depending on the scope of costs included (such as direct construction, interest, and broader transmission).

That said , hydro systems have a LONG LIFESPAN - 100 YEARS ?

Batteries need to be replaced every X years.

So the ecomiomics of the comparisoan would need to be calculated ...

[robin_reala]

Dinorwig[1] was opened in 1984, and is looking at a £1B refurbishment shortly for “at least another 25 years” lifespan.[2]

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

[2] https://www.waterpowermagazine.com/analysis/re-planting-the-...

[angry_octet]

All the complexity has been in geotechnical issues, pockets of mud, sinkholes, then ultra hard rock, then loose shale, damage in blasting operations, needing to pump liquid nitrogen into the rock to deal with subterranean water flow, soluble limestone etc etc.

One of the scariest industrial deaths you can imagine: cutting into a pocket of shale and the TBM and crew just vanishing into the maw of the Midgard serpent and the whole tunnel filling.

https://www.abc.net.au/news/2024-05-22/tunnel-boring-machine...

[stephen_g]

That was exactly the point of the project though - it was designed by the conservative side of politics in our country to try and crowd out investment in batteries and other renewables while taking enough time to build to keep coal plants operating longer in the meantime.

It didn't work at all for that though - we had a lot of private investment in large-scale batteries anyway, because the cost came down quickly just as most people (apart from the conservatives) expected. Then the other side of Government got in and put a subsidy scheme to get hundreds of thousands of home batteries installed, which has been multiple times better bang-for-buck than the Snowy 2.0 scheme, as well as taking far shorter a time. At the same time coal plants are shutting down as expected because they are increasingly unreliable given their old ages.

Snowy 2.0 be an expensive stranded asset basically, it will work and be somewhat useful but extremely uneconomical so basically relying on the cost being written off - if it had to recoup any investment then it couldn't run because it'd never be able to sell the power for high enough.

[Scoundreller]

You can do similar math with building above ground oil storage tank capacity aaaaaand giving everyone free gas cans.

And you can get out every drop. And it’s always ready to go. Do need to cycle your inventory.

Fire departments probably wouldn’t be happy about it.

[pjc50]

Affordability is always relative. Australia can't afford that much battery storage, it has to spend $368bn on nuclear submarines. /s

(did you mean 20kwh per user, or 20GW overall?)

[angry_octet]

The submarines will be in port so much of the time, we may as well hook up their nukes to power the grid.