Energy Storage

Energy storage and power generation are two separate issues that appear to be getting muddled by politicians and journalists. For example hydro power is essentially energy from the sun and therefore renewable.  The solar energy lifts water into the sky, eventually residing in dams where it now has potential energy which can be converted to electricity in dynamos.  It can then be pumped back into the dam.  If hydro is used here there is simply an energy loss.  Other energy sources, producing energy in a different time frame need to be used and it is this energy that is then stored.  If you pump it up using coal fired power then it is coal energy being stored.

So let’s look at energy storage options. Previous blogs have substantially looked at power generation options.

Non Renewable

Modern metals based batteries store chemical energy. If those metals are not able to be recovered economically then we need to continually mine more. One measure of storage effectiveness has been devised by Stanford University and that is the Energy Stored on Investment index or ESOI. For lithium batteries produced in recent times that number is around 10. For Zinc Bromide and Vanadium batteries it is about 3 and for lead acid batteries it is about 2.  These numbers are always a bit rubbery as technology improves or base products become scarce.  It is also difficult to keep up with what exactly constitutes a particular sort of battery at any point of time.

The Li ion battery seems a clear winner here and these numbers suggest that if this battery is used at greater than 10% of its available energy storage then you are on to a winner in regard to ESOI (but not necessarily on cost or environment). These batteries have a limited lifetime (and limited number of cycles). If they are required to be used less than 10 percent of the time then a direct energy source (eg gas) is more effective (not necessarily on cost or environment).

Li ion batteries use a number of different metallic elements including lithium and cobalt. Lithium salts make up about 10% of the weight while cobalt is slightly more. The actual lithium metal ions is about 2%.  Again these figures are fairly rubbery, depending on the battery and its uses. At recent production rates many tonnes of both lithium and cobalt are being mined.  Lithium has mostly come from high altitude salt lakes in the Atacama desert (Chile, Bolivia, Peru and Argentina) and in Tibet. Here the highly mineralised brine is slowly evaporated (solar energy) and then separating out the lithium salts.  This is generally a benign, low energy production method.  Locals, particularly in Tibet may disagree.

If we ramp up lithium production to go from phone batteries to cars and grid storage systems we need many times the amount of lithium we are currently using. Australia is producing hard rock lithium (basically spodumene) for the Chinese market.  Elon Musk is looking at Shale lithium in Nevada for Tesla batteries.  Both of these will require a much larger energy intensity to produce the lithium metal (or salt).  To produce lithium from spodumene the ore needs to be heated to over 1050 deg C, generally done in a gas or coal fired furnace and then dissolved in concentrated acid baths at 200 degrees C.   The ESOI of batteries made from this lithium will drop substantially, possibly becoming negative if ore quality is low!

Similarly cobalt is produced as a by-product of nickel and copper mining and can be produced economically at the current rate required. If production needs to be ramped up we get a problem.  This extra cobalt will likely come from “conflict minerals’ sources in the Congo using very dangerous practices.

So comparing batteries gas suggest that the latter is the best option by ESOI if usage is low (for example to cover for emergencies). In fact if usage is very low (once or twice a year for a day or so) then diesel generators may be the most efficient and least polluting option.

In my opinion we should keep batteries for smart phones, cars and isolated communities and not in major grid storage systems.

Renewable storage

Renewable storage must be our ultimate goal. Options to date include pumped hydro (ESOI about 200), compressed air (ESOI about 240) and molten materials (including salt and silica).

To make them renewable all of these need to store energy that has been created renewably. Pumped hydro cannot store hydro energy efficiently (if you use hydro to pump water back up the hill you are losing energy).

Pumped hydro is a great storage facility where it is practical to build substantial dams and fresh water is plentiful. There are still various environmental, health and cost issues (eg in digging tunnels and deviating water).

It is most likely a very effective and renewable system in the Snowy mountains if it is storing wind or solar generated energy. In NSW the vast majority of electricity is created in coal fired power plants and if this is stored it becomes an increased use of coal instead!

In places like South Australia pumped hydro is problematical. There are few locations where a substantial dam would be tolerated and there is little fresh water available.  A pumped hydro facility at Cultana on the Eyre Peninsula would require a large body of fresh water that is protected from evaporation.  Sea water could be used but has a large environmental and engineering failure risk.  It is probably unlikely that a substantial and effective system could be built in any short timeframe.  The location also only allows a small scale solution.

Compressed air Energy Systems (CAES) are a different story. Although largely untested, they could be a long term energy storage system.  Air is compressed in a large container in an underground cavern and then used to run a generator when needed.  Three utility station size plants are currently operating in the US and Germany with build costs at around US$50 million per 100MWh system.  Another 6 systems are being currently planned or built in Germany, Us and UK.  I am not aware of any in Australia but small scale systems have operated for many years.

Thermal Energy Storage Systems (TESS) use molten materials to store heat and use that to run generators ( or simply use the heat) are another potential utility sized system that are substantially renewable. Molten salt has been used as a storage medium in solar power facilities for quite a while.  Recently the University of South Australia researchers were awarded the Eureka prize for inventing a “phase change” system using salt to store electrical energy.

Another South Australian Company working with TESS working with molten silica is 1414 Degrees. The technology is currently being tested for a 10 and a 200 MWh system.  It looks like a very promising system and can hopefully fit SA needs in the very near future.

 

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