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Gravity Battery
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biffvernon



Joined: 24 Nov 2005
Posts: 18551
Location: Lincolnshire

PostPosted: Thu Feb 06, 2014 9:34 am    Post subject: Gravity Battery Reply with quote

So simple

http://gravitybattery.info/
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Little John



Joined: 08 Mar 2008
Posts: 5667
Location: UK

PostPosted: Thu Feb 06, 2014 11:33 am    Post subject: Re: Gravity Battery Reply with quote

biffvernon wrote:
So simple

http://gravitybattery.info/
I thought of this a few years back. But, someone pointed out to me how much potential electrical energy can be stored in a given weight at a given height and then compared this to how much energy is required by a fairly frugal household. The number didn't seem to stack up at very well at all. so, the problem is not that this would not work. It's that it would not work enough. Unless you are using a VERY BIG weight suspended at a VERY HIGH height or a hell of a lot of smaller ones suspended even higher.

I note that web page did not make any mention whatsoever of the actual amount of energy stored in those weights in the diagram.
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PS_RalphW



Joined: 24 Nov 2005
Posts: 5266
Location: Cambridge

PostPosted: Thu Feb 06, 2014 11:33 am    Post subject: Reply with quote

Err, this is a hydroelectric scheme without the hydro.

Have you seen the size of hydroelectric schemes?

How big a hole would you need to dig? How strong would those ropes
need to be?

Back of the envelope Energy = force times distance.

Force = mass times acceleration

Acceleration = gravity = 10 ms-2
distance = 10 metres
mass = 1000 kg
ten holes - total mass 10 tons = 10 cubic metres of water or 2 cubic metres of stone/sand/concrete
energy = 1000 x 1000 = 1e6 joules = 1e6 watt seconds
= 1000 KW seconds
= 0.28 KWh

Wow.
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Little John



Joined: 08 Mar 2008
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PostPosted: Thu Feb 06, 2014 12:27 pm    Post subject: Reply with quote

PS_RalphW wrote:
Err, this is a hydroelectric scheme without the hydro.

Have you seen the size of hydroelectric schemes?

How big a hole would you need to dig? How strong would those ropes
need to be?

Back of the envelope Energy = force times distance.

Force = mass times acceleration

Acceleration = gravity = 10 ms-2
distance = 10 metres
mass = 1000 kg
ten holes - total mass 10 tons = 10 cubic metres of water or 2 cubic metres of stone/sand/concrete
energy = 1000 x 1000 = 1e6 joules = 1e6 watt seconds
= 1000 KW seconds
= 0.28 KWh

Wow.
Exactly, it doesnt make any practical sense.

Would springs be a better store? Or, would it still be daft?
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PS_RalphW



Joined: 24 Nov 2005
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Location: Cambridge

PostPosted: Thu Feb 06, 2014 12:52 pm    Post subject: Reply with quote

Still daft.

Large flywheels can store useful amounts of energy in rational volumes, but they are high tech and need good maintenance.
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emordnilap



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PostPosted: Thu Feb 06, 2014 12:52 pm    Post subject: Reply with quote

The concept is intriguing if not really practical, if Ralph's figures are right. I thought of it at first as a bit like my deep well pump in reverse - not a lot of electricity for quite a lot of water pulled up 130ft.

So the 'battery' would have to be big - huge? - gigantic? - gargantuan? - but, apart from that, it should work: you simply scale up the deep-well-pump-in-reverse idea to imagine it.
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PS_RalphW



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PostPosted: Thu Feb 06, 2014 1:12 pm    Post subject: Reply with quote

That's before you take into account the energy conversion losses.

Electric to motor - 0.9
motor to electric - 0.9
Friction, Braking and acceleration 0.95 (?) = 77 % so that .28KWh becomes
0.215 Kwh.

A 12V 100Wh battery produces 1200 Wh = 0.12 Kwh

You would be better off with a couple of car batteries.
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adam2
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Joined: 02 Jul 2007
Posts: 6214
Location: North Somerset

PostPosted: Thu Feb 06, 2014 3:26 pm    Post subject: Reply with quote

PS_RalphW wrote:
That's before you take into account the energy conversion losses.

Electric to motor - 0.9
motor to electric - 0.9
Friction, Braking and acceleration 0.95 (?) = 77 % so that .28KWh becomes
0.215 Kwh.

A 12V 100Wh battery produces 1200 Wh = 0.12 Kwh

You would be better off with a couple of car batteries.


Yes, and the figures that you give are very optimistic for small motors and generators. 0.9 is reasonable for larger machines, but for a system such as as proposed to store much less than one KWH, that suggests charge and discharge rates of less than 100 watts. Motors and generators that small might be only 50% efficient.
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Tarrel



Joined: 29 Nov 2011
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Location: Ross-shire, Scotland

PostPosted: Thu Feb 06, 2014 8:04 pm    Post subject: Reply with quote

Actually, a typical car battery is 100Ah which, at 12v, is 1200Wh, or 1.2kWh. So the batteries make even more sense.

I think this discussion is a good illustration of how high our typical power demands are. As soon as soon as you start measuring energy needs in kWh, you immediately close off many possible practical ways of generating and storing energy. Small energy demands, in the Wh category,are much more realisable using small so.ar arrays, small wind turbines, modest batteries and even thinks like treadmills or bicycle-driven generators. Remember the TV programme about the household powered by a team of cyclists?
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Little John



Joined: 08 Mar 2008
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PostPosted: Fri Feb 07, 2014 12:26 am    Post subject: Reply with quote

This all reminds me of a calculation done by someone in terms of the number of human slaves required to be working flat out round the clock to produce the same amount of energy as is consumed by an average household on the back of hydrocarbons.

It was simply monumental.
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kenneal - lagger
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Location: Newbury, Berkshire

PostPosted: Fri Feb 07, 2014 4:16 am    Post subject: Reply with quote

Flow batteries look to be the best bet and are being worked on as we speak/type.
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emordnilap



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PostPosted: Fri Feb 07, 2014 11:19 am    Post subject: Reply with quote

stevecook172001 wrote:
This all reminds me of a calculation done by someone in terms of the number of human slaves required to be working flat out round the clock to produce the same amount of energy as is consumed by an average household on the back of hydrocarbons.

It was simply monumental.


They call it '22 billion energy slaves' - with most of that energy going to a minority of people.
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adam2
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Joined: 02 Jul 2007
Posts: 6214
Location: North Somerset

PostPosted: Fri Feb 07, 2014 1:35 pm    Post subject: Reply with quote

Only slightly off topic, I remembering answering an enquiry from an elderly engineer who recalled as a small boy staying in a large country house where "all fit males were expected to assist in the winding up of a large weight which gradually descended during the evening and powered the lights"

In later years the now qaulified engineer calculated how much power could have been produced, given reasonable estimates of the weight, height, and time to run down.
The result was at best enough to power a single small lamp for a few hours, certainly no question of lighting a large house.

So the enquiry was "did I imagine it, and if not how did it work"

The answer is left to the reader, it was in about 1930.
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Tarrel



Joined: 29 Nov 2011
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PostPosted: Fri Feb 07, 2014 1:44 pm    Post subject: Reply with quote

Probably imagined it. Either that or it was a bit of a wind-up.
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PS_RalphW



Joined: 24 Nov 2005
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PostPosted: Fri Feb 07, 2014 1:57 pm    Post subject: Reply with quote

When I was in India in a remote mountain village, they had at great expense and considerable effort installed a diesel powered mill to grind their grain, because otherwise the locals had to carry the grain thousands of feet down the mountain and the milled flour back up again, on their backs. No roads.

Unfortunately the locals couldn't afford the charges the miller asked, diesel being so expensive (even when heavily subsidised, 15 years ago) so they had a plan to build a water mill instead. No local stream to power it, so they were going to use their rainwater capture tank, up on the hillside, with a bucket and chain arrangement to drive the mill. However, of course they realised that they would quickly run out of water, so they decided to arrange the buckets to be filled up again, nearly full, so that most of the water would be carried back up the hill again to the top reservoir....
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