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Comment by TheDong | Hacker News Reader

Why would they be ubiquitous at the household level, not centralized as a "electric grid backup battery", like Australia's "big battery" https://victorianbigbattery.com.au/ ?

For hot water heaters, it's obvious that the water would arrive cold if it were boiled in a central location, but electricity can be transmit so efficiently that storing excess load will be much more efficient in centralized locations rather than at individual houses.

My guess is that this will be roughly as common as household generators, since both this and a generator are hedges against the electric grid failing more than anything else.

The equivalent water analogy would be everyone having their own household water cistern in case the water system failed, which I also think is vanishingly rare.

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I think you would see both, but not quite ubiquitous like GP claimed unless in a region with trouble keeping their grid up. Utilities will do the cost-rational thing and deploy those batteries where beneficial, and households will adopt them as well because there is always the chance that an outage can happen between the big battery and your house. Or, if the entire system falls over for some reason, you can still be an island unto yourself with solar + batteries

re: hot water heaters - it should be noted that hot water and steam delivery systems exist and are quite effective(commonly derived from cogeneration sources) e.g.

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

LV circuits households connect to often don’t have a lot of spare capacity to absorb excess solar export in the day.

Voltage management is also a challenge with large amounts of solar export to the grid.

Solar systems are typically capped in the rate they can export to the grid for this reason.

Having a decent household battery to absorb solar output during the day and provide power at night could be a win-win both for households and power distributors.

For me I pay 20c (AUD) per kWH at night for electricity while selling electricity for 10c per kWH during the day. Using the electricity I generate at night instead potentially saves me 10c/KWH. At the right price I’d love one of these.

One reason is that overall power consumption needs, timing and priority are going to vary a lot household to household. For one household a power outage might be no problem, for another which depends on life support equipment, a power outage might be life threatening.

If you have centralized batteries, then the decisions about (a) how big they are (b) who they cut off if the battery is running out and (c) how the batteries impact the pricing of power are all made at the community level, which has value as a way to optimize the way an entire community draws from the power grid, but it lacks precision in how it helps individual households.

If you have localized batteries then people can choose (a) if they need batteries at all, (b) how many batteries they need and (c) how they want to use the batteries to offset their grid usage (some people might want to rely on batteries mainly for emergencies, others to aggressively charge and discharge based on different price levels throughout the day). It might be less efficient in aggregate but it is much more accurate in terms of delivering the benefits to the people that need them.

> Why would they be ubiquitous at the household level, not centralized as a "electric grid backup battery", like Australia's "big battery"?

Let's assume the existing electrical grid to be a somewhat fixed system that gets augmented from time to time here and there but does not get changed in fundamental parameters like voltage. Then there's a certain grid capacity for transmitting power (watts) from central nodes (existing or former big power stations) to that large number of end nodes (homes) or in the opposite direction.

Let's also assume that the combined capacity of all the power lines which connect the homes to the grid massively exceeds the capacity of those (big) lines that connect the "central nodes" to the grid.

This means, that there exists a certain level in the hierarchy of the electrical grid (between central nodes and end nodes) where the lines do indeed match the capacity of all homes.

I'd think, these are the locations where you would build/connect centralized big batteries to the grid.

Because you could then take up all solar power from homes and at the same time you'd have some centralisation which would make building the facilities less expensive because of economy of scale.

Batteries also allow you to offset your solar use. You can fill the battery during the day and use the energy at night. That’s the most common use. Having one during a power outage is handy but shifting use is the primary use case.

Yep, and power prices are only set to increase as well - it makes for a great combination with solar.

8.7kWh is not a great amount, but if the price was right it could make a lot of sense. Two of those units ... now I'm interested!

8.7kWh at a somewhat high EU price yields somewhere between $2 and $3 a day. If this thing is about $6k, it should pay for itself within a year (if you have excess solar energy production, most contracts around here either don't pay anything for this, or trade at some 90%-ish discount).

Did I miss anything? I thought it would be 6 years at ~$1k saved per year, so I'm kind of waiting for prices to come down a fair bit more myself - also in the knowledge that batteries are rapidly improving now thanks to all the new players.

Regardless of the time to get ahead: Battery would make a great difference if your goal is to eliminate grid reliance and also to power an EV by solar only.

Whilst in summer a 6.6/5 system can produce 40kWh in a day, during winter months in Australia there really isn't too much sun - and what we get tends to be patchy. So being able to feed it into the battery would be great for avoiding grid use overall, and not to let bursts of sunshine go to waste.

>also in the knowledge that batteries are rapidly improving now thanks to all the new players

What is improving - energy density, price, need for rare materials?

What electricity price did you calculate with? I used the $0.2/kWh from my invoice, but quite a few EU countries are soaring towards $0.4 right now.

You're sidestepping a lot of infrastructure difficulties by putting it at the household level. Your giant battery has to be put somewhere!

This is why I'm also pretty happy about solar, because you sidestep a lot of the NIMBY stuff that comes with building huge solar farms.

It's not at all ideal, though I don't know how inefficient it is (this model means that upgrades can happen gradually as well, instead of being multi-decade projects). But hey, you try building anything in most modern city bureaucracies filled with people who care about their real estate values.

Home roof is a great place to put solar panels because it's virtually free space. Battery is different story.

I mean the pics of this make batteries look pretty small. Like smaller than a storage shed.

Sure it's only storing 8 hours, but the use cases described here are not bad. Imagine if we had 8 hours of battery storage across the world per household!

Still it takes a bit space for non-rural Japanese houses. I agree it's good to have it for backup if free space is available.

Australia has widespread usage of both. States are rolling out batteries to smooth supply disruptions while individuals are buying them to get the most out of their solar. Solar is so widespread in Australia that the rate to sell the power mid day is almost nothing. So you’d rather hold it and use it after sunset.

Because transmission and distribution is expensive, can go down, and offsets the savings.

>The equivalent water analogy would be everyone having their own household water cistern in case the water system failed, which I also think is vanishingly rare.

I had a lot of power failures living in Canada, always due to the above-ground power delivery. I'm guessing this would also count for large parts of the US and the developing world. In Europe, I would bet on centralized solutions because the underground power lines rarely fail. But anywhere with above-ground power delivery, having a battery per household makes a lot of sense.

>Why would they be ubiquitous at the household level, not centralized as a "electric grid backup battery", like Australia's "big battery" https://victorianbigbattery.com.au/

For the US, there is little chance that such a centralized backup system would ever be built. The US doesn't really build big infrastructure things like this. They prefer everyone to have their own little version, at higher cost and less efficiency.

Not true.

https://www.kcra.com/article/pge-tesla-megapack-battery-cali...

So about half the size of the battery in question. That is to say, Australia built a centralized battery almost twice the size. Their population is 25m. California’s is 40m.

My point stands: this won’t catch on in the US.

There's a commercial incentive to build electric storage, if the price is right; you can buy when prices are low and sell when prices are high. Depending on the market regulations, prices are likely to get high during an outage, so there's your motivation for construction. Of course, siting is important too; if the big backup battery is right next to the big power plant, that helps for power plant outages, but doesn't help for wiring faults. And a battery facility that's not sized to power the grid island it finds itself in likely can't provide any power, unless the grid island has sufficient load shedding mechanisms, I'd guess.

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