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Comment by acidburnNSA | Hacker News Reader

With free fuel and falling supply chain costs this is all well and good. Worth noting is that the value of solar electricity goes down fairly sharply as a function of market penetration because of the intermittency. Once you start adding massive chemical electricity storage costs and environmental impacts get more gnarly.

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Right. So why add "massive" chemical etc?

People who install solar panels have a choice: ⓐ Restrict their power usage at night, ⓑ install batteries or blah, or ⓒ get power elsewhere. Or a combination.

Many people seem to think that option ⓐ does not exist. Ie. ⓑ+ⓒ has to be massive as you put it, because ⓐ cannot lighten the load.

Ooh, I really like your usage of ⓐ. How do you type those without looking them up on a Unicode chart and copy/pasting?

I use linux/X11, with a compose key and a large repertoire. If I type compose ( 4 ) (that's four keystrokes, in sequence) I get ④, compose ~ e gives me ẽ, which I'm sure some language uses but I've no idea which. http://rant.gulbrandsen.priv.no/xcompose describes my configuration (as it once was).

Again, I'll bring up what nobody seems to mention. With minute-by-minute pricing of electricity, intermittent supply problems can be greatly mitigated without batteries, peaker plants, etc.

On the consumer side, elastic electricity uses can be switched on/off through an app connected to the internet.

Elastic uses are things like charging car batteries, electric water heaters, A/C, refrigerator, etc.

Peaker plants are expensive to run and electricity from them is priced accordingly. If peaker plants are turning on, it's because no cheaper source of electricity was able to meet demand, and demand was inelastic enough to pay the higher prices.

Peaker plants are now more [1] expensive than solar+battery storage. And battery storage that without solar (ie, soaking up night time base-load) are even cheaper.

[1] https://electrek.co/2017/12/13/solar-batteries-to-take-10gw-...

My electric rates are fixed at the same price, 24/7. Trying to maintain this will be very expensive for the grid when faced with fluctuating supply.

Are there any utilities in the US that offer minute-by-minute pricing, or even hour-by-hour? If not, then we cannot conclude that demand is inelastic.

Agreed, I wanted this but the utility can't even do day by day metering.

Reflow batteries have low environmental impact, and are cheaper than lithium ion. The only real downside is that they are about 25% mode bulky for the same energy storage, but for many domestic installations this isn't a big problem.

Many solar plants are now pairing with large scale energy storage facilities too (eg, liquid salt, pump hydro, even some batteries).

I'm curious to know why other storage methods aren't taking off more. I would have assumed that the long-term costs of something like hauling something heavy up a hill (which could easily be a manmade earthworks in flat areas) would be quite a bit lower, on account of the equipment in question having a longer life span than batteries.

The keyword here is energy density. Batteries are really good when measured in electrical energy stored per volume. Your proposed mechanical potential energy store (lifting mass) cannot compete. The amount of stored energy is aurprisingly low in comparison. I did the math over a decade ago because I had the same idea and the numbers were underwhelming.

Yeah, but energy density isn't really significant. You may get less energy out of a m^3 of water pumped to a reservoir than you get out of a m^3 of battery, but even the smallest reservoir has a usable volume that probably surpasses the volume of all batteries ever built. You can just keep pumping.

No, you can't just keep pumping. To build a reservoir at the scale that you seem to imagine, you depend on locations that provide a suitable topography. Very few such places exist.

The energy density of gravity storage is terrible. But there's still a few plans for it:

https://www.wired.com/2016/05/forget-elons-batteries-fix-gri...

> 9,600 tons of rock- and concrete-filled railcars up a 2,000-foot hill.

> $55 million

> The Nevada project has a power capacity of 50 megawatts and can produce 12.5 megawatt-hours of energy.

Using the 4 cents/kWh figure upstream, that's ... $500 of electricity per round trip.

I'm still curious about that project. Energy density is a consideration, but it may not be the only one.

Yeah, as-is, there's no way it can pay for itself. But how much room does this have to grow, and at what cost? If most the cost is down to laying the track and making these custom railroad cars, then maybe there are some economies of scale that could come into play. And then I assume that most of the equipment involved could easily last for decades.

Up-front cost for battery installations may be cheap, but don't lithium ion batteries typically only last a few years? That means you won't be able to amortize the cost of equipment over a very big stretch of time at all.

This makes me wonder, why don't elevators generate electricity on the way down?

Elevators are counterbalanced -- when they are going down, there is a counterweight going up. So there's less energy than you might imagine being generated.

I know, but I can imagine that they would still generate some energy in a busy building. Then again, I don't really know how much energy they consume.

Moving the elevator down would only take potential energy out of the system when the elevator together with its load weighs more than the counterweight.

When it does, you might be able to use it to generate electricity. But I wouldn't be surprised if that isn't done simply because it wouldn't justify the added cost and complexity of building all that extra energy harvesting mechanism into the elevator.

Regenerative braking elevators exist: https://www.asme.org/engineering-topics/articles/elevators/w... has a good summary.

Having lived in a 17-story building with Thyssen-Krupp "green elevators", they're terrible! An elevator would break down and require days of maintenance every couple months, greatly increasing queueing times.

Or thermal mass storage for AC systems.

A lot of Hydroelectric plants on stable reservoirs can be used as large batteries.

During peak hours they'll increase the flow rate to turbines and during off hours they'll use surplus energy to pump water back into their reservoir.

See https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricit...

Biogenic methane emissions likely make these a non-option at scale.

http://journals.plos.org/plosone/article?id=10.1371/journal....

What kind of environmental impacts?

Also, what do we do with dead solar panels? Is there a recycling program, or research going into such a thing?

I'm so excited for this news and I feel like these are pretty minor cons though.

Giant batteries aren't great for the environment because they involve heavy mining.

And have a one to two decade lifespan, at best. After which you have to dispose of them.

They are fully recyclable and aren't dangerous to do so.

Lithium polymer batteries are highly recyclable, they primarily just have to be unwound, possibly reformed if something structurally changes in the cathode/anode, and the trace elements need to be washed off and processed.

Mea culpa. Thanks for the info!

Lithium is harvested from evaporation pools, not mined. If you're referring to cobalt content, there are several researchers working to remove the need for that element from the production process.

I'm guessing they meant battery production, which requires the mining of rare-earth elements: https://en.wikipedia.org/wiki/Rare-earth_element#Environment...

Batteries do not use rare-earth elements (as far as I am aware).

You may be thinking of cobalt, which is expensive and mostly mined in the Congo. Reducing the cobalt content of cathodes is a big priority for the industry:

https://cleantechnica.com/2018/06/09/cobalt-free-car-batteri...

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