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Frank Hovis

Mechanical Batteries

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Is there any work being done on these? Large scale for grid surpluses and small scale for homes.

The only one I can think of is in North Wales where water is pumped up a tunnel to a reservoir in times of surplus.

I was thinking along the lines of massive clock weights being raised with slow controllable energy release.

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I think there has been. Many years ago I read about experiments with giant spinning shafts being used to store kinetic energy. No idea if it ever went into service.

My instinct says surplus power would be best used to produce synthetic fuel which can then be stored without losses.

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Ah, like hydrogen cells. Yes, I can see that.

It's the chemical batteries that seem to get all the publicity and they seem very hard to materially improve.

This point was hugely underlined by James May in his excellent "Cars of the People" series where he drove his own modern electric car and compared it to one from a hundred years ago (when petrol engines were competing against electric and steam, and it was close).

They had pretty much the same range.

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No, not Hydrogen. It's a pita and leaks out of everything. I'm thinking of things like the Fischer Tropsch process and various others to take in a feedstock and produce liquid fuel.

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Many years ago I heard of vehicles using gyroscopes to store energy. Gentle/controlled braking or going downhill would capture energy in spinning faster, which would then help power it accelerating or uphill. Particularly useful for vehicles with lots of start/stop, like milk floats or city buses.

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Compressed gas has also been used as an energy storage medium.

In a lab or in reality?

I don't think there has previously been the big necessity. Whilst demand was erratic (kettles going on at half time in EastEnders / footie matches) the supply side was predictable. Now that's up and down with sunshine and wind it must be incredibly hard to manage.

PVs on a house means that when the sun shines you can supply half a dozen houses; a big black cloud comes over and that supply drops to not enough for one so you get a demand surge.

So you either get oversupply and waste, undersupply and power cuts, or you have a wide scale storage solution of some kind.

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Construction of pumped storage plants in the UK was abandoned with the abandonment of the nuclear programme. A number of pumped storage plants had been planned to go along with the construction of Hinkley Point C and Sizewell C during the 90s, but when these plants were cancelled, the pumped storage was cancelled too.

Flywheel technology is used on moderate scale - e.g. London underground have installed flywheel storage systems which store a minute or two of power. This allows for more effective capture of braking energy which the trains discharge into the track, but unless that energy can be used by an accelerating train nearby, or stored, it must be discharged into large heaters. The use of flywheels allows this system to provide energy savings, even if the acceleration and braking of trains isn't precisely synchronised.

There is also growing interest in flywheel UPS technology for datacentres and critical industrial/commercial plant. Battery UPSs require expensive batteries which have a short life time and require regular maintenance. Moreover, the discharge rate of batteries is limited, so that batteries must be substantially oversized - typically 5 minutes is the minimum feasible capacity, but for this type of equipment, a generator capable of starting and taking full load within 10 seconds is standard, meaning that the batteries need to have a capacity about 30x what is actually needed. Flywheels have the advantage of having much higher discharge rates, so can be more precisely sized giving a lower capital cost. They also tend to be more reliable, longer lived and maintenance free.

For grid scale use, there has been some interest in compressed air energy storage. Air would be compressed into a depleted gas field, or artificial cave (usually a salt cavern, which is washed out with water), and could be released through a turbine to recover the energy. Most plans would actually burn gas in the compressed air, and use that heated exhaust to drive the turbine, as you improve the efficiency of energy recovery if you heat the air before extracting the energy with the turbine. Effectively, this design takes a regular gas turbine which consists of a compressor, combustor and a turbine, and inserts a storage component between the compressor and combustor.

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Why not put your spare enegy in a cupboard, with all the tinned pies and beans. I will use it in the future!

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Guest eight

Why not put your spare enegy in a cupboard, with all the tinned pies and beans. I will use it in the future!

Funnily enough I am just starting to think about this domestically and the it seems the logical thing is to turn it all into hot water.

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Many years ago I heard of vehicles using gyroscopes to store energy. Gentle/controlled braking or going downhill would capture energy in spinning faster, which would then help power it accelerating or uphill. Particularly useful for vehicles with lots of start/stop, like milk floats or city buses.

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

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Funnily enough I am just starting to think about this domestically and the it seems the logical thing is to turn it all into hot water.

There was a thread on domestic wall-mounted batteries but they were thought not quite to be there yet.

Instead of charging / discharging daily as you would expect they were designed for ?30 discharges a year. So more emergency backup than evening supplement.

The view was that the daily use will be achieved in one or two years so worth a watch.

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The trouble with physical energy storage is that we don't really appreciate the energy density in the energy storage that we've got.

So, consider a set of 'home' type devices.

  • Say, 10m3 of water storage with a height between reservoirs of 10m - that will store about 1MJ before round trip losses. 10 tons of water - doable, but large.
  • Or a 10kg 1m diameter flywheel running at 10,000rpm - stores about 1MJ before running and round-trip losses. Doable, but you'd need to run it in a vacuum to stop friction losses, that requires special bearings, etc.
  • Or you could use a 50AH deep cycle battery. That will store about 1MJ assuming 50% depth of discharge. You can buy one today for less than £100.
  • Or you could go carbon and use about 20g of methane.
  • Or, at a push, you could just buy it from your electricity company - 1MJ of electricity costs about 4p.

Then, you can use this 1MJ of energy to heat up the water in your 100l hot water tank by 2 degrees.

We have such amazing access to huge levels of energy that we don't really understand what we've got.

This isn't to say that mechanical storage isn't possible - but it does require massive scales (hydro schemes) or really fancy engineering (flywheel types) to get anything useful at all. Even the massive hydro storage schemes in the UK aren't really used to store energy for use at a later time (sort of) - they're mainly used for load management (because they have a very fast time to spin-up, so they can be used to compensate for additional load during e.g. the Coronation Street advert breaks) - you could do this load management with conventional power stations but the increase in fuel consumption would be substantial over the hydro type schemes.

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^

Which is why I think that excess power should be used to produce liquid hydrocarbon that can then be used in generators etc.

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^

Which is why I think that excess power should be used to produce liquid hydrocarbon that can then be used in generators etc.

I'd agree with that. We've even (kind of) got the distribution network sorted.

And definitely not hydrogen. A dangerous pain of a gas to work with. I think people don't realise that an important reason that so many (car) companies are pushing hydrogen is that they can hold IP in it and make money on that - while all the patents in normal carbon type fuels (manufactured for storage rather than fossil) are either out of patent or owned by someone else.

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Hydrogen is God's first element. :blink:

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Funnily enough I am just starting to think about this domestically and the it seems the logical thing is to turn it all into hot water.

I do this with my PV panels. A device called an immerson channels any unused electricity generated to the immersion heater. Once the tank is hot, then it sends any excess to the grid. We get a tank of hot water daily about 8 months of the year as a result (a tank of hot water costs us about 60p so the device will have paid for itself in about 3.5 years). I did briefly consider solar thermal but apparently payback is >10 years and it would be much longer given we have the immerson now.

I've considered battery storage - but I don't think the ROI or reliability is there yet.

Oddly enough I live fairly close to a massive pumped storage facility in North Wales.

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In a lab or in reality?

I don't think there has previously been the big necessity. Whilst demand was erratic (kettles going on at half time in EastEnders / footie matches) the supply side was predictable. Now that's up and down with sunshine and wind it must be incredibly hard to manage.

PVs on a house means that when the sun shines you can supply half a dozen houses; a big black cloud comes over and that supply drops to not enough for one so you get a demand surge.

So you either get oversupply and waste, undersupply and power cuts, or you have a wide scale storage solution of some kind.

Both Germany and the USA have utility scale compressed air storage utilising salt caverns.

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

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^

Which is why I think that excess power should be used to produce liquid hydrocarbon that can then be used in generators etc.

Ammonia production.

As well as fertilizer Ammonia can be used in diesel engines with minor modifications and is much much cleaner burning

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Is there any work being done on these? Large scale for grid surpluses and small scale for homes.

The only one I can think of is in North Wales where water is pumped up a tunnel to a reservoir in times of surplus.

I was thinking along the lines of massive clock weights being raised with slow controllable energy release.

Gravity Lights Very small scale for homes, charged similar to a Lantern Clock

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Don't gyroscope cars turn over in corners, lie gyroscopes? :blink:

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