Oncor solicited a study that showed that a mass install of Tesla Powerwall devices would be an economic solution to this problem [1], at which point all the generators lost their minds and lobbied the PUCT to prevent Oncor from destroying their market [2] (because of their position as a Transmission & Distribution Service Provider in the market, it would require a change in law for Oncor to be able to implement the project).

[0] Work for a multinational in their energy & utilities consulting practice; above comment is my own.

[1] http://www.brattle.com/system/news/pdfs/000/000/749/original...

[2] https://www.texastribune.org/2014/12/15/state-law-could-shor...

It's interesting to see the stark contrast between the naysayers that don't have information to back their claims (such as comments sibling to yours), and the people who have looked at current tech and made realistic assessments like Oncor and Brattle.

A lot of people are willing to make confident, but very wrong, statements based on out of date information. It serves to protect entrenched interests and stop competition, but I have a feeling that disruption is far closer than anybody is publicly saying.

X is realistic and smart because it agrees with my opinion

You're amazing

Thanks. But it's not realistic and smart because of that, it's realistic and smart because it examines the facts at hand and makes plans instead of handwaving. This is an important distinction.

Some countries store energy by pumping water up a dam. Seems efficient.

Very. One of the first was in Scotland. Great to visit as you drive into the mountain and I think one of the Bond files had a scene filmed in it

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

Nope. It was filmed in Switzerland. https://en.wikipedia.org/wiki/Contra_Dam

Different films. "The World Is Not Enough" had scenes filmed at Cruachan, "GoldenEye" was at Contra.

Whoa! That sounds really cool so I looked it up. It's called "Pumped-storage hydroelectricity"

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

Yeah, and I believe that it's the only game in town for storing really large amounts of electricity.

Also interesting: https://www.quora.com/Can-electricity-be-stored

It's very efficient and it's a great solution overall; the only problem is there are only so many dams we can build, since each one requires drowning a valley.

Though you need less volume if it is only being used for overnight storage rather than long term rainfall storage. For example, to store enough energy to produce 1GW for 1 day (~10^5 seconds) with a head of 100m, use Pt=mgh to work out you need to store:

m = 10^9.10^5 / (10*100) = 10^11 kg of water. = 10^8 m^3

This is not a big reserviour, being 1/20th of the size of Warragamba dam's reserviour (in Sydney). One valley could provide 20GW for a day. Compare that with demand for where I live:

http://www.aemo.com.au/Electricity/Data/Price-and-Demand/Pri...

Peak demand for 7.5M people is 9GW, with an average closer to 7GW. One valley could provide overnight storage for over 20 million people, with first world demands (all of Australia). The limitation is transmission and generating/pumping capacity, rather than storage volume.

Note that's a winter peak you're looking at.

The highest summer peak appears to have been just above 13GW. http://www.wattclarity.com.au/2016/02/highest-electricity-de...

However your point still stands I believe.

But the summer peak is due to air conditioning during the day, when there's tons of "free" solar energy.

Solution: swimming pool on the roof.

http://www.fastcodesign.com/1672202/you-deserve-a-house-with...

The more sun, the more water in the pool. Win-win!

Seriously though has anyone crunched the numbers on rainwater storage for microgeneration in a domestic setting.

Could I efficiently use excess solar to pump water in to a house roof storage area and generate electric from that?

They crunch the numbers here: http://physics.ucsd.edu/do-the-math/2011/11/pump-up-the-stor...

The energy in one gallon of gasoline is equivalent to the potential energy stored in 13 tons of water one kilometer up

The Tesla Powerwall has 6.5 kwh = 23.4 M joules.

Gravity potential energy = mgh. Suppose pool is 10 meters up, then you need 239,000 kg of water = 63K gallons or 8400 cu ft. This is a huge pool: 29 ft. x 29 ft x 10 ft.

You could use the city water supply: borrow water through a turbine at night, and return it during the day :-)

Or have pool up very high, for example on a cliff overlooking the Mediterranean:

http://inhabitat.com/crazy-home-carved-into-a-coastal-cliff-...

The outflow from an Auckland homes storm water is not insignificant - an average roof would have something around 5 cubic metres of water come off it several times per year.

I remember a while ago on the show "Let's Get Inventing" (Saturday morning kids show with kids inventing stuff, think it was on TV2), they tried generating electricity from drainpipes, they couldn't get enough power to even power a servo squeezing the trigger on a spraybottle, they had to get a great big firehose from an firetruck to actually generate anything.

"Have you seen the swimming pool on the roof?"

;)

Flywheels are another option: https://en.wikipedia.org/wiki/Flywheel_energy_storage

Pumped storage is routinely used to store energy. It's not theoretical.

Has Flywheel storage every been seriously used in large-scale commercial applications? Someone mentions it on every energy-storage thread, and I'd like to know if the people suggesting it are just spinning our wheels.

FES is used in non-kill-zone habitable solutions like datacenters, bottoms of passenger trams/hybrid buses and electromagnetic aircraft catapults. The historical issue with FES is unscheduled, rapid disassembly, but carbon/kevlar composites have been shown to have greater integrity with least unsprung structural mass (because you want the most mass as close to the rim as possible to ensure highest moment of inertia.)

FES has 10x specific energy than supercapacitors or batteries with no memory and precise state of charge. Magnetic bearings and hard vacuums make them quite efficient.

The JET fusion reactor in Oxfordshire uses flywheels to provide very large pulses of electricity for short periods of time (a minute or two iirc). The reactor requires too much energy to run directly off the National Grid.

As I recall from a tour I went on of jet 30 years ago there are a large bank of flywheels which spin up over several minutes, these are then rapidly discharged to a bank of capacitors which are then used to power the experiment, I believe the duty cycle was 9 minutes. [1][2]

I believe some electric cars used capacitors to store regenerated electricity from breaking.

"More Ampères please Mister Woodbine." - Road to Welville

[1] - http://pia.sagepub.com/content/200/2/95.abstract

[2] - http://www.euro-fusionscipub.org/wp-content/uploads/2014/11/...

Sounds like they use it for high output rather than efficiency though. Still interesting that it has real world applications though. Shows that the technology has potential as well.

It's not even remotely on the same scale. There are three massive utility-level flywheel deployments according to Wikipedia that provide 15 minutes of output.

Edit: Seems the purpose is purely frequency regulation, rather than storage per se.

Better than nothing, but not that efficient. I took the tour of the somewhat mis-named Dinorwig Power Station (really a pumped storage facility) in Snowdonia, Wales. The figures they quoted there put it at about 75% efficiency. It's not really supposed to be for 24-hour power smoothing, more for rapid response to sudden demand; it's a lot faster to open a valve on a turbine than to stoke up a coal plant, and for some spikes (such as the example they quoted on the tour, when everyone puts the kettle on when Coronation Street finishes) you have a 30-second window or so. However, as demand has increased it's being used more and more, and the more it's used the more power we're wasting.

Interestingly, it does not use a dam. There's a natural lake at the bottom of a mountain and a man-made reservoir at the top, and the entire pumping facility is completely inside the mountain; it's not at all obvious that there's anything there at all from the outside. I think about that whenever people moan about the environmental impact, or flooding valleys.

Works great if you have the right geography.

I thought I read that some water districts run their pumps at reduced volume during peak hours and top them off before or after. It's a smaller volume but it's already a solved problem.

And it allows you to push some levers and dials as to whether it's cheaper this year to increase your water capacity or your power capacity. City planners love that kind of thing.

I grew up by one of these in NJ: https://en.wikipedia.org/wiki/Yards_Creek_Generating_Station

I remember parking at the lower reservoir and hiking to the upper one and being amazed at how big the water pipe is.

It's a problem, but the nature of the problem varies a lot from country to country. In the Netherlands, we don't have enough renewables yet for this to be an issue (~10%). Once you start getting to Germany's penetration, you start to see some issues with balancing the grid and meeting peak demand. There are more options than just storage, though.

Demand side response is already used in industry to regulate electricity demand and smooth peaks. Smart meter penetration will allow utilities to do this more and more in the residential sector too.

Supergrids are also starting to emerge and indeed, some large grid companies are pushing hard for international interconnects. (China wants a supergrid). Countries are building out more and more HVDC interconnects, both across borders and within countries. Once you have a network of utility scale renewable sources across multiple countries, meeting peak demand becomes more a matter of coordination between grids. Europe for example, is looking like a very interesting area for this right now with planned interconnects between North Africa and Southern Europe.

Since we're all citing employment, I work for a renewable energy company :)

Instead (or rather in addition) to storing power, we can also get better at coordinating demand.

There are already programs for industrial users to get electricity for much cheaper, if they can tolerate power cuts during peak demand. Those programs will become more and more rewarding to join and extend and automate as supply gets spikier.

That's great but then instead of increasing the effective capital cost of the generating plants, you're increasing the effective capital cost of the industrial facilities (by lengthening the time to pay off financing).

It'd be interesting to see a study comparing the two options.

The incentives create a market in which the energy consumer and producer can trade in their existing inefficiencies. The market will decide where it is best to make the compromise, whereas before there were just wasteful externalities.

If you have an industrial process that can cope with intermittent power supply, it may be only slightly more expensive to design or build so that interruption of power won't result in interruption of production. If the overall cost increase is less than the decrease of energy costs due to incentives, there is no downside.

The energy producers likewise price the incentives so that their loss of revenue is lower than their cost savings.

Unless of course the market is created and operated by Enron, then we're all fucked.

Yup. Having many distributed li-ion battery walls charging at night for peak assist during the day is one way to level out demand and make the energy infrastructure more resilient in a Google-servers-like way.

Is there a way to coordinate demand without asking thousands of people to give Alice the ability to shut off their appliances?

Sell electricity at spot prices, give consumers access to that spot price, and you'll see a lot of demand flatten simply through natural market forces.

Where I live, I pay five times more for electricity between peak hours of 2pm and 8pm than I do between off-peak hours of 10pm-8am. (The remaining hours are priced at a medium level.) This has changed my behaviour, in that I now tend to wait until bedtime before switching on the clothes dryer and dishwasher.

No, although the current system is pretty tame. The electric company can turn your electric water heater or air conditioner (depending on geography and utility) off for 15 minutes at a time, and in return you get a credit on your electric bill. Its opt in.

Actually, there already is, it's called OpenADR.

http://products.openadr.org/?posts_per_page=-1

See also Ecobee vs. Nest: http://controltrends.org/controltrends-news/news-and-informa...

Yes, industrial plants will turn off production (for instance at an aluminum smelting plant) in relation to the frequency of the grid. Grid frequency decreases slightly when demand starts outpacing "supply."

That frequency change used to be a natural reaction from the generators.

I wonder whether they create that signal artificially with electronics these days, or if it's still a natural consequence of the mechanics of the spinning generators they run in power stations?

I recall reading a while ago about using molten salt storage at large solar concentrators. Did this ever take off? The theory was you generate excess power during the day and you can use this excess to heat the salt solution which then release thermal energy during the night.

Does anyone know more about this? Is this able to meet baseload demand?

This one in Nevada came online not too long ago and is quite large -- apparently has 10 hours of storage and according to Wikipedia it generated 9.1GWh in February 2016 alone.

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

Solana Generating Station, a 280MW solar concentrating plant, currently, uses molten salt, which allows for six hours of energy storage.

https://en.wikipedia.org/wiki/Thermal_energy_storage#Molten_...

Thermodispatchable solar, even if the word does not exist, has been a recurring theme. But installations seem to be one-offs that are rarely followed by a direct successor project with the ever dropping price of photovoltaic.

In areas with cold weather, one of the most interesting (and underrated, due to only making fossil use more adaptable) developments is the installation of huge, insulated hot water tanks, to make the power generation and the great generation of combined cycle plants individually dispatchable.

Sorry for the late correction: in the last sentence I meant cogeneration plants, not combined cycle. (which would typically not be combined cycle, because the heat not captured for electricity is not wasted in cogeneration)

http://www.lightsail.com/ has been working on this for a while now

We have a lot of good technologies already, the problem is they just don't scale well.

I can envision older warehouses in an industrial district being converted in to vacuum flywheel storage sites where power fed in to the grid earlier is buffered and then released back to it.

Changing our culture is another possible approach. Power is used in the evenings because that's when most people get off work/home/etc and they tend to have /that/ time to do cooking and cleaning (thermal cooling / heating are more solvable with changes in materials and building shape than culture change).

Price electricity differently through the day according to its scarcity and people might eventually adjust their routines to reduce evening usage.

That seems backwards. The aggregate preferences and habits of humans should be seen as an incentivizing force for the creations of new technologies, not the other way around.

Yikes. Yes, of course technology is driven by human preferences. But, No, humans must occasionally accept that certain habits are not sustainable given current and near-future technologies.

I generally agree with your position but in this particular scenario the people with the greatest capacity to adjust their behavior are the people who will be affected the least financially by a hike in peak prices and thus less likely to change or more likely to invest in solar at home, while those with the least flexibility in work arrangements and spending, e.g. lower income earners working in the services sector, will be affected negatively the most and unable to work around it.

If the spot market was the status quo, and someone was suggesting a change to the current system of flat prices, one could make the same argument. (Ie already well off people are flexible enough to make use of the new system better.)

More variant pricing will better distribute usage. The unfortunate effects on the poor can be negated by a sales tax paid back to all citizens equally as a lump sum.

Well, in that case, pricing electricity differently through the day will encourage people to develop new technologies for cheaply generating and/or storing electricity for evening consumption peak.

That's like saying market economies are backwards. We need to match resources to people somehow, and markets are a very popular way to do that fairly and efficiently.

I'm not saying that markets should be unchecked but it's very strange to see such naked Marxism on this site.

I don't see any Marxism there. Marxism isn't just anti-market. It's a complex ideology.

It doesn't have to incentivize new technologies. It could just as easily incentivize new business models. Imagine a laundromat that sells "FREE DRYING" during the day. Heck, I bet you a lot more people will do laundry during the day time. Similarly, power companies can give incentives for more day time power usage. A lot of people already follow night time power usage today so its no reason to think it wouldn't work.

Variable pricing would create those exact incentives.

It's a two way street.

Aggregating the preferences via price will drive new technology and business models.

You are correct- there are energy storage solutions out there, I should have clarified my statement above. The issue is that they cant store power grid levels of power in an efficient, compact, and scalable manner. This is the rub. Maintaining a giant battery bank or other measures require maintenance and large capital expenditures.