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Sunday, December 30, 2018

Energy storage

Despite what you hear, we have already cracked the energy storage problem which was needed to make intermittent sources of renewable power such as wind and solar-electric a practical reality.  And it is not a single solution but a whole range of solutions.  Let's have a look at some of them.

1.  The clothes in your clothes cupboard and the dishes in the kitchen cupboard

Clean dishes and clean clothes are potentially energy storage devices.  All that is needed is a smart grid and smart meters.  I'm not talking about what many electrical companies have taken to call smart meters.  All these pitiful machines are designed to do is to eliminate meter readers and hence make more profit for the electrical distribution company. These so called smart meters send the power company information on how much power you have used.  That's all they do.

No, I am talking about a smart grid in which the price of electricity varies according to availability and a smart meter in each house that detects the current electrical price and controls to your smart appliance.  In the case of your clothes washer, you dial in the price you are willing to pay to wash your clothes and the machine comes on when the price falls to this level (because the sun is shining, the wind is blowing and electricity prices have fallen or because it is night and everyone has turned off the lights and gone to bed).  After a while, you will become pretty canny about not setting the dial so low that your clothes stay dirty but low enough to save you a nice bit of change.

One thing to consider, though, is that in the case of washing clothes or dishes, once the process starts, you don't want it to stop if the price of electricity increases.  Clothes and dishes won't get clean if the power keeps going on and off.  There are even better applications.

2.  Charging your car battery or heating your water.

Everything said above about washing your dishes and clothes applies but here it doesn't matter if the electricity goes on every time the power price has got down to what you dialed on your battery charger or water cylinder heater and goes off when the price rises above that level. Here though, we need another feature on our smart device

You need to be able to dial in "if the water isn't up to a certain temperature or the battery up to a certain level of charge when 5 in the morning rolls around, turn on the power regardless of price.  After all, you want to take a shower in the morning and have enough power in your electric car to get to work. You have gained charging or heating at a highly beneficial price through the night and just top up with more expensive power.

All the above is what is known as 'demand balancing' of the grid as opposed to the present supply balancing.  At present, the electric companies have multiple generating stations and they cut them in and out according to the momentary demand.  That will not change but now they have an additional tool.  By signaling when their base generation is in excess to demand, they can bring on more demand.  Then when demand rises, mainly in the morning as everyone gets ready for work and in the evening when everyone has all the lights on and is watching television, a whole bunch of electrical devices will not be demanding power.

This has a real 'up-side' for the power companies.  To build another power generation station which will only be used for peak shaving is bloody expensive.

Another up side is that they will pretty well always have a market for excess power.  Instead of letting water go over the spillway, they can run it through the generators and no need to feather their wind turbines.  Most of the time there will be a market for the excess.

3.  Pumped Storage
This is already done in many jurisdictions.  When you have excess power from a cheap source, you can use it to pump water up into a reservoir.  When power demand exceeds supply, you can run this water through a generator for 'peak shaving'.  Water power is probably the most useful source of power for peak shaving as it can respond instantly to increased  or decreased demand.  While you only get, say, 75% of the power out that you put in, this system is economically worth while.  It becomes even more so when you have wind and solar which will  often be generating far more power than is needed.  The more of this stored energy you have, the less coal you have to burn.

4.  Power walls
Tesla already produces a 6.4 and a 13.5 kWh battery pack that you can hang on your wall.  It uses lithium ion technology and a very good power management computer.  Even if you do not have solar panels or a wind generation, this could be worthwhile for you but only if we have smart grids and smart meters.  You could then charge your power wall when electricity is inexpensive and use it when power prices are high.  If you have your own renewable energy generation device, any power in excess of your instantaneous demand goes into your power wall.  This is a great advantage.

Many power companies give abysmal returns for power you send to the grid.  Unless you have an enlightened power company, you don't want to be sending them power but rather using it yourself.  A further possibility opens up here.

5.  Private peak shaving
  At some point the power company may need power for a peak demand and decide, OK, just now we will pay a fair return.  They could then draw on the power walls of the country until the peak passed.  The interval in a rugby game comes to mind when everyone puts on the jug for a nice cup of tea.  The owner of the power wall dials in the price he wants to get for sending power to the power company.  The power company can up the price until they have enough power to balance the system.  The power wall owner gets a nice little bonus any time this occurs.  Again, it all boils down to truly smart grids and smart meters.

6. Liquid metal batteries
Liquid metal batteries are not likely to be useful for home use although small units have been built.  These were invented by Donald Sadoway and his team of students at MIT.  They work at temperatures high enough to melt the metals that form the electrodes and the salt that forms the electrolyte.  The flow of current through the battery creates enough heat to keep the materials molten.  The trick is in a very well insulated container.

One of the metals is denser than the salt they use, the other less dense so they automatically form horizontal layers.  As the battery discharges metal migrates through the salt to the other layer and the reverse when the battery is being charged.

In terms of the cost per kWh stored, they are projected to be very cheap. They are also said to be very long lasting and very safe.  If I had one at home, I would still want it in an outbuilding.  They have had some start up problems but have gone through a re-design phase and apparently have solve these.  They say that they have also developed an alternate chemistry using even less expensive materials than with the initial batteries.  They are projected to be available by 2020.

There are over 90 elements in the periodic table and thousands of different salts.  Now that the basic system has been proven, we can expect an exploration of different chemistries to make liquid metal batteries with other chemistries. 

6. The Vanadium Battery
The vanadium battery is a very clever innovation.  It is known as a flow battery.  Instead of using two different elements, it uses a solution of Vanadium in  different oxidation states.  This way, if some of one solution leaks into the other one through the semi permeable membrane, all that happens is that the battery operates a little less efficiently.  And you can have tanks of any size of the solutions of Vanadium in the two different oxidation states.  Thus the storage capacity of the battery is only limited by the size of the tanks.  The Vanadium battery has huge storage capacity, very long life and a very fast response time to varying loads.

It is doubtful if it could be used in a car but one can imagine a train with the first car consisting of a giant battery of this type.  (or for that matter, a liquid metal battery).  If part of the rail line was electrified, the battery could be charged while the train was in motion over the electrified part of the track giving it enough power to bridge the gap between electrified portions of the track.  Large semi trailers might be similarly powered. However, at present these batteries are only used in static energy storage applications.

Again, there are over 90 elements in the periodic table, many of them with more than one oxidation state.  Now that the basic principle of a redox battery has been proven and brought to commercial application, we can expect further exploration of the elements of the periodic table.

7.  The Iron Battery
The Iron battery is another flow battery although I am puzzled about how it could work.  True, Iron exists in two different oxidation states, ferric and ferrous but the more oxidized ferric state is quite insoluble.  It seems to me that it would go one way and that would be it.  I am clearly wrong since this type of battery exists.  Apparently they use Iron chloride.

8. Ultra Capacitors
Ultra Capacitors don't hold huge amounts of power compared to batteries but their great advantage is that they can take up and deliver huge fluxes of energy as needed.  In many applications, this makes the delivery of stable power levels and frequencies feasible and by avoiding large fluxes of energy through batteries, greatly extends their life.  They are vital components of renewable energy systems.

9. Increased Efficiency 
This is not an energy storage system but is vital for the passage to renewable sourced of energy.  Think of lighting that in the USA uses about 10% of the power generated.  Florescent lights use about a tenths of the power of incandescent lighting and LEDs about one percent of the energy used for incandescent bulbs for the same amount of light.  Other effects such as the Halbach effect for electric motors can also make electric motors ligher and more powerful.  This is especially useful for transport applications.

Buildings use huge amounts of power and have huge surface areas to collect solar radiation.  The more we take advantage of their characteristics and use them to collect energy, the lower our electric demand will be and the easier it will be to meet it with renewable sourced of energy.

The key to energy storage is truly smart grids.  The sooner we have them, the sooner we will wean ourselves off fossil fuel.