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Author Topic: How do we store solar and wind energy?  (Read 1280 times)

Offline thedoc

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How do we store solar and wind energy?
« on: 23/02/2016 17:28:50 »
How do we store solar and wind energy?
Asked by Signe Klange

                                        Visit the webpage for the podcast in which this question is answered.
 ...or Listen to the Answer or [download as MP3]
« Last Edit: 23/02/2016 17:28:50 by _system »


 

Offline alancalverd

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Re: How do we store solar and wind energy?
« Reply #1 on: 23/02/2016 22:53:46 »
I've always advocated using spare electricity to electrolyse water. The existing gas grid can store and distribute hydrogen either by itself or mixed with methane (old fashioned town gas was 50% hydrogen) and already has sufficient capacity and distribution reach to supply about half of all industrial and domestic power requirements, with existing storage capacity for  several weeks' supply. Why invent anything else? 
 

Offline Space Flow

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Re: How do we store solar and wind energy?
« Reply #2 on: 24/02/2016 05:57:27 »
How do we store solar and wind energy?
Asked by Signe Klange
Why invent anything else?

My favorite has always been to use gravitational potential as a storage system. 
This is more of a local storage system and is not necessarily connected to and distributed by the grid, although there is no reason why it couldn't be. 
And it is not a new invention. 

The system consists of two water tanks separated by enough height to allow an on demand hydro generator enough head to supply all the requirement that a household can demand. Obviously the water capacity of the system has to be enough to maintain that output for a minimum of 24 hours. 
It uses solar energy and any other energy input you want to couple to it, to pump water from the bottom to the top.
It then uses this gravity battery to run the hydro generator. 
It can be a stand alone Off-Grid system, or hooked into the Grid to sell power back once the top storage tank is at capacity.   
In Off-Grid mode such a situation would just overflow the top tank back in to the bottom tank. 
In a Grid-connect system this overflow is run through the hydro unit into the Grid.  $$$$$ 

The normal problem with local storage of excess power is the batteries. They are expensive and need regular replacing. 
Done properly this Gravitational potential battery, has minimum maintenance and no replacement costs.

« Last Edit: 24/02/2016 06:00:57 by Space Flow »
 

Offline alancalverd

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Re: How do we store solar and wind energy?
« Reply #3 on: 24/02/2016 09:10:24 »
The problem with gravitational storage is its very low energy density.

The energy stored in 0.5 ton of water at 4 meters height (that's about the mass of your coldwater tank in the loft) is mgh = 500 x 9.81 x 4 = 19,620 joules. Enough to heat your 1 liter kettle by about 4.5 degrees.

Your 100 Ah car battery stores Vit =  12 x 100 x 3600 = 4,320,000 joules in a lot less space and weight - say 10 kg

1kg of methane or hydrogen will release about 45,000,000 joules on combustion.

Go for gas!
« Last Edit: 24/02/2016 09:14:08 by alancalverd »
 

Offline chris

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Re: How do we store solar and wind energy?
« Reply #4 on: 24/02/2016 12:06:46 »
But what about the energy cost in storage of the gas; high pressure needed, embodied energy in infrastructure etc...?
 

Offline alancalverd

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Re: How do we store solar and wind energy?
« Reply #5 on: 24/02/2016 13:36:13 »
We already have a gas grid - it feeds factories, hospitals, your cooker and boiler, and about 60% of the UK electricity generating industry!

It used to transmit town gas, now methane. Town gas was stored at low pressure, methane is now imported and stored as liquid.

The entire infrastructure already exists and is in everyday use.
 

Offline Ethos_

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Re: How do we store solar and wind energy?
« Reply #6 on: 26/02/2016 02:11:33 »
I agree with alan regarding the storage of energy in the form of hydrogen gas. Not only can it be mixed with methane for use in home and industrial heating purposes, it can be used in the hydrogen cell and become an efficient form of electrical energy for use in transportation as well.
 

Offline chiralSPO

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Re: How do we store solar and wind energy?
« Reply #7 on: 26/02/2016 18:07:24 »
How do we store solar and wind energy?
Asked by Signe Klange
Why invent anything else?

My favorite has always been to use gravitational potential as a storage system. 
This is more of a local storage system and is not necessarily connected to and distributed by the grid, although there is no reason why it couldn't be. 
And it is not a new invention. 

The system consists of two water tanks separated by enough height to allow an on demand hydro generator enough head to supply all the requirement that a household can demand. Obviously the water capacity of the system has to be enough to maintain that output for a minimum of 24 hours. 
It uses solar energy and any other energy input you want to couple to it, to pump water from the bottom to the top.
It then uses this gravity battery to run the hydro generator. 
It can be a stand alone Off-Grid system, or hooked into the Grid to sell power back once the top storage tank is at capacity.   
In Off-Grid mode such a situation would just overflow the top tank back in to the bottom tank. 
In a Grid-connect system this overflow is run through the hydro unit into the Grid.  $$$$$ 

The normal problem with local storage of excess power is the batteries. They are expensive and need regular replacing. 
Done properly this Gravitational potential battery, has minimum maintenance and no replacement costs.

The average american household draws about 27 kwh per day. If you wanted to store that gravitationally, it would require pumping about 100000 liters (100 m3) of water to a height of 100 meters.

Even accounting for 50% round-trip efficiency of electrolysis, converting 15 liters of water into hydrogen would store the equivalent amount of useful energy.

Imagine every household having a 100 m high tower with a 10m3 capacity, plus the pumps and dynamos required for conversion: $$$$ indeed!
 

Offline Space Flow

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Re: How do we store solar and wind energy?
« Reply #8 on: 26/02/2016 19:44:06 »
Imagine every household having a 100 m high tower with a 10m3 capacity, plus the pumps and dynamos required for conversion: $$$$ indeed!
Perhaps it does sound like a bit of an ask when you put it that way and for the average house in America it would not be feasible. For the average house in America putting excess power into the existing grid is probably the best available option at the moment.   
I live in Australia and at the moment we pay an average of about 25 cents a kilowatt hour. The current offering for putting your own generated power into the grid is about 6 cents per kilowatt hour and there is talk of that coming down. I have a roof full of solar panels and the Only way to see any value out of them is to use the power they generate myself. Grid storage is a joke. 
Alan's idea sounds fine but it would require new technology.   
New metering and a pressure system to override the supply pressure so gas can be stored that way. There would also major safety concerns with such a generation and pumping system in a private home. Research, development, installation and maintenance costs are at this stage unknown as I have not heard of a feasibility study on such a thing. 

I live out of the city and don't have piped gas anyway. 
What I do have is over 100000 litres of water storage already and the cost of that storage is not as expensive as you might think. 
I also have 68 metres of fall. This is not an unusual situation in hilly country. I agree you would not consider such a system if you had to do it with towers. 
But for an initial set up cost that is not really outrageous you end up with a power storage system that done properly should last for several generations with minimal maintenance. And you can always have the option of further hibridising if you want to sell excess into the electric or gas grid.

So what is the best way to store solar and wind power? 
It really depends on country and more importantly situation..
 

Offline alancalverd

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Re: How do we store solar and wind energy?
« Reply #9 on: 27/02/2016 00:08:53 »
Alan's idea sounds fine but it would require new technology.   
New metering and a pressure system to override the supply pressure so gas can be stored that way. There would also major safety concerns with such a generation and pumping system in a private home. Research, development, installation and maintenance costs are at this stage unknown as I have not heard of a feasibility study on such a thing. 
No need for a feasibility study. Nobody needs to generate gas at home, nor is it remotely sensible to do so when surplus electricity is produced in bulk from otherwise pointless windmills. The entire UK, and AFAIK most of Europe, and all US cities, have had a piped gas supply to homes and workplaces since around 1820. Investors are still building gas-fired power stations, and consumers complain if their new homes are not on the gas grid. The entire economy of Russia seems to depend on exporting gas to the rest of the world. I think 200 years' experience is enough to prove that it works.

If anyone wants to use small-scale storage from off-grid electricity, I'd advocate generating Brown's Gas by simply electrolysing water with alternating current, inside an ordinary steel gas bottle fitted with an ordinary gas regulator. This will give you all the delivery pressure you could possibly want, without pumping. The stoichiometric mix of hydrogen and oxygen can be burned in an unventilated space, unlike methane or pure hydrogen, which should make for a very efficient miniature central heating boiler. And you can condense the exhaust for drinking or recycling.
« Last Edit: 27/02/2016 00:19:13 by alancalverd »
 

Offline chiralSPO

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Re: How do we store solar and wind energy?
« Reply #10 on: 27/02/2016 02:24:06 »

If anyone wants to use small-scale storage from off-grid electricity, I'd advocate generating Brown's Gas by simply electrolysing water with alternating current, inside an ordinary steel gas bottle fitted with an ordinary gas regulator. This will give you all the delivery pressure you could possibly want, without pumping. The stoichiometric mix of hydrogen and oxygen can be burned in an unventilated space, unlike methane or pure hydrogen, which should make for a very efficient miniature central heating boiler. And you can condense the exhaust for drinking or recycling.

I don't think storing Brown's gas would be sensible (certainly not pressurized), as it could explode. I have detonated small quantities of Brown's gas as part of a demo for school children (50 mL of atmospheric-pressure brown's gas gives quite a bang!!) Then, if you can't store it, and just convert it to heat as it's produced, why not just drive an electric heater with the excess energy and avoid conversions altogether?

I think rechargeable zinc-air batteries could do nicely for storing significant amounts of energy in a home. With an energy density of 38 MJ/L (40 khw/gal), as well as significant power density, and no risk of fire, explosion or toxicity, zinc makes an ideal stationary energy carrier (it's a bit heavy for use in a mobile setting, only storing about 5.3 MJ/kg).

Zinc air batteries are also a fairly mature technology, and the rechargeable versions are advancing quickly.
 

Offline alancalverd

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Re: How do we store solar and wind energy?
« Reply #11 on: 28/02/2016 18:23:48 »
Then, if you can't store it, and just convert it to heat as it's produced, why not just drive an electric heater with the excess energy and avoid conversions altogether?
The problem, particularly for the UK, is that the hottest and coldest days are those with no wind, so we absolutely need to store energy from windmills if they are going to replace more than 10% of our electricity supply.
 

Offline chiralSPO

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Re: How do we store solar and wind energy?
« Reply #12 on: 28/02/2016 18:36:59 »
Then, if you can't store it, and just convert it to heat as it's produced, why not just drive an electric heater with the excess energy and avoid conversions altogether?
The problem, particularly for the UK, is that the hottest and coldest days are those with no wind, so we absolutely need to store energy from windmills if they are going to replace more than 10% of our electricity supply.

Oh, I quite agree that storage is necessary. I was just pointing out that Brown's gas is not suitable for storage, and that if it is to be converted immediately to heat by combustion, why not just cut out the dangerous intermediate and go directly to heat?
 

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Re: How do we store solar and wind energy?
« Reply #12 on: 28/02/2016 18:36:59 »

 

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