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Dinorwig, the UK's biggest pumped hydro scheme at 1,750 MW manages about 75% efficiency. (For every 100kWh you put in, you get only 75kWh back)

There is no reason why liquid should have higher efficiency than a gas. The biggest losses with pumped air is the stuff gets hot when it is compressed, which represents waste energy. And that's not the end of it, because when it expands in the generation phase it gets much colder which lowers the efficiency so you have to heat it before it goes into the turbines - which costs more energy.

The PHES system can be modified to take advantage of this problem - there is an explanation on the Isentropics site - which raises the overall efficiency to around 90 to 95%

The melting point of Granite is about 1200C. Plenty hot enough. Its specific heat is about 800 J/kg/degree C so if it is raised through 1000 degrees, a kg would store 800,000 Joules or about a quarter of a kWh. a tonne of it would hold 250 kWh, four tons a MWh and so on. To store what Dinorwig stores - about 11GWh, would require 11,000 tons of it. This is roughly a 20 metre cube. Yes its a lot, but far, far less than a whole mountain and two lakes etc, god knows how many miles of concrete lined tunnels and massive underground installations.

And you can put lots of smaller ones wherever convenient to get the same storage capacity.

Batteries ARE an expensive way of storing energy but in this instance it is an island with limited journey.
So in this instance the 2 birds 1 stone philosophy i can see the sense in it.
Wish i could find the article. But it was Norway who have very strong EV sales anyway due to the generous tax breaks.
EVs currently make up nearly a quarter of all car sales. Up 70% on last year.
This was a community initiative which saved them having to import electricity from the grid saving the community collectively.
They charged for free on the condition that they would feed back when required.

Wouldnt work in the UK, we would get our charge and then unplug.
Screw everyone else, i am alright Jack.

Dinorwig is 1960's technology and I have read now that hydro can be a more efficient with expected 80% minimum round trip and possibly approaching 90%.

There are two problems with compressing a gas compared to pumping a fluid, the first is seals which will be a compromise between leakage and additional friction or other losses, the second is that it does compress and so you will never exhaust all the compressed gas from the pump, assuming some sort of reciprocal action. I can't see how it would be possible to produce a linear high pressure pump but neither have I looked into it yet.

In its simplest form water could be bucketed upwards with very little loss (possibly the most efficient way for large vertical heights?), I can't see the advantage of bottom pumping - I believe they are even looking at bucketing rubble as a means of achieving gravitational storage using its higher density over water to reduce volume.

Anyway, grid storage is a secondary problem to generation and much to my disgust it looks like we are going the nuclear route yet again, it would be safer to use ultra compact nuclear generators in cars than large nuclear reactors on the grid imho.

Erratum!

In my previous post, the 11,000 tons should have read 44,000 tons, and the 20 metre cube would then be a 35 metre cube.

The large oil tanks at Stanlow are much bigger than this. Some are about 80 metres in diameter.

How about starting a new thread as this is getting pretty far from EVs?
Some pretty specialised processes getting discussed now.
May even get other participants who have no interest in "battery cars" but alternative/renewable energy.

I think, diggingdeeper, that on a large scale gas and water are pumped with turbines not reciprocating pumps so sealing is not an issue.

Isentropics' explanatory video uses reciprocating pumps, but the general principle applies to a turbine variant as well.

On a smaller scale I doubt whether sealing is a big problem any more than it is in a car engine, or a steam engine. This sort of technology has been well and truly sorted out by now surely.

The storage of large quantities of gas has been done in old salt mines. Apparently salt 'self-seals' so high pressures can be used. Obviously Cheshire would be good for this.

I have sent an email to those running the site asking for a new Forum on 'Renewable Energy'

Got a reply saying

"New Forums take time, you may find dedicated solar panel forums have more information sharing similar issues, its only a quick google."

I'm not sure if that means yes or no.

The problem with dedicated solar forums is that they tend to be filled with enthusiasts to whom any discussion of problems is seen as a personal attack on them. I think (hope) it might be more conducted more dispassionately here.

Just thought I'd update this thread.

Three recent developments have occurred.

Ways have been found to fast charge batteries which may reduce charging down to between 5 or ten minutes.

A practical method of producing the allusive stable aluminium batteries has been developed, these could hold twice the charge of lithium and be considerably cheaper.

A method of producing mass sheets of graphene cheaply has been developed which has got the potential to produce better performing batteries.

Battery 'breakthroughs' come thick and fast. Alas, they seldom make it to production. The problem is that improvements in one area - say fast charging - seem to come at the expense of another area like energy density or safety. It is a multi-dimensional problem which is nowhere near being solved.

A 'perfect' battery is not the only problem however.

A little old lady can put a MegaWatt hour of energy into her car in complete safety in the form of diesel in about a minute. To do that with electricity would require power levels of 60 MegaWatts. That is 60,000 volts at a thousand amps! You wouldn't allow a little old lady or anyone else anywhere near that sort of power.

Moreover, if you consider this going on at a motorway services with perhaps two dozen cars simultaneously, the required power level would be almost 1.5 GigaWatts - the entire output of a medium sized power station! For a single motorway filling station!

Contrast this with a hydrogen filling station with the hydrogen produced by wind and solar. The hydrogen can be stored easily and large amounts of energy transferred to cars in perfect safety, quickly and easily. The hydrogen can be produced from fossil fuels in the short term, so that an easy changeover to all renewable sourced hydrogen can be carried out. Also, we will not have to rebuild the national grid and build loads of power stations. The infrastructure for supplying hydrogen cars is not much more expensive than that for petrol or diesel.

A hydrogen powered road transport system is a lot more practical than battery cars!

Glad to see you are warming to hydrogen.

Local charging capacity has a few solutions:-

Cassette batteries.

Local storage (which ties up nicely with local power generation like solar etc).

Wireless on-the-go charging (yeah, I'm sceptical on this one as well).

Another thought slightly related is the car-train concept being furthered to a physical coupling which not only saves the amount of energy required but could also redistribute charges.

I don't think battery swapping is practical. How many batteries would a filling station have to store? Where would you charge them? Could you get car manufacturers to agree on a standard, or would there be dozens of different types?

Most of all, however it is done, transferring the energy requirements of the road transport system onto the National Grid would involve rebuilding it, as well as a lot of power stations. It certainly couldn't cope as it stands!

A big bit of news in January was a relatively simple process to turn Carbon Dioxide from air into Methanol.

That would be a fantastic solution to portable energy storage.

Its been done many times before but the catalyst normally gets eroded away however the new process has achieved a stable re-usable catalyst.

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