A lot of the discussion of my last post on energy issues was devoted to discussion of energy storage. Rather than get involved in that, I thought I’d collect my own thoughts on this. Broadly speaking, Here are some observations, labelled for convenience and partly derived from this study by the US Department of Energy
(a) Any reversible energetic process represents a potential storage technology. Reversibility entails that some energy is stored (as potential or chemical energy) when the process goes one way, and released when it goes the other. Of course, the Second Law of Thermodynamics implies that we will always add entropy (that is, lose useful energy) in this process
(b) Any technical or social change that shifts the time at which energy is finally used replicates the effects of storage
(c)Energy storage is in much the same position as renewable electricity generation was, say, 15 years ago.
(d) There are a lot of potential approaches, most of which have been developed in niches where particular characteristics are required. For example, car batteries need to store a lot of energy for given weight, household batteries need to store energy for a long time and so on. The needs of a renewable-dominated electricity system are very different and will require substantial modifications of these technologies
(e) With one big exception, there is currently no price incentive, in most jurisdictions to use storage technologies and therefore none are used
(f) The big exception is off-peak hot water. Coal and nuclear systems generate baseload supply when it is not needed for consumption. Price incentives are used to encourage people to store the resulting excess energy in the form of hot water
(g) There’s no technological obstacle, given the availability of smart meters, to changing the timing of hot water systems to reflect actual availability of excess electricity rather than reflecting the assumptions of a coal-based system
(h) All of this applies to electric cars. Even ignoring the possibility of feeding power back into the grid, the economics of electric cars would be drastically improved if they could be charged using low-cost power in times of excess supply (in the case of solar PV, around midday when lots of cars are sitting in parking lots)
(i) Something I just found out from the DoE study: Electric car batteries are considered unfit for services when they fall to 80 per cent of their original charge capacity (recall that energy density is critical for car batteries). But they still have a long potential life as static storage devices. This enhances both the economics of electric cars (since the battery has resale value) and of storage (since the opportunity cost is zero)
Here’s an older post, with a really simple example of how the argument works, once you get away from the fixation on replicating the characteristics of a coal-fired system.
John Quiggin 
It is currrently 12:37 in the afternoon on a cloudless Sunday. Solar power is providing about 22% or more of total electricity use in South Australia. And do you want to hear something funny? Because it’s Sunday and not too hot our peak grid demand today is expected to occur at about 1:00 am when all the off-peak hot water systems turn on. Our off peak systems are causing our peak today.
@Ronald Brak
An Adelaide relative tells me it was 35C at 2am one night last week though that spot may have been an urban heat island. PV loses performance after 6 pm when sunset is 8.30 pm. Providing cheap or free electricity for pensioner aircon is not unlike the UK’s heating fuel allowance. How will the electricity be generated?
@Hermit
We clearly need much more passive design. This means better insulated houses with special features to cool them in summer and warm them in winter. Brick veneer is such a bad idea. Double-brick is a better idea. To bring down costs there are modern system involving foam-filled blocks and variants on that theme.
A good idea too is the two-layer roof you get by roofing a house and then covering much of the roof in solar panels. The solar interception and air gap are excellent insulation. You still need in-roof inulation or sarking too. The extra solar power beyond your grid feed allowance, can charge batteries, charge an electric car, run air con, run some heating in winter and so on.
A rain tank built into the centre of the house acts as thermal ballast for the whole house. Higher ceilings help keep occupants cooler too. And so many other things you can do.
Hermit, one uses solar power to cool the house down during the day and avoid the 45 degree temperatures that kill people. And then the house is cooler in the evening than it would be because you’ve been running the air conditioner during the day. And if the temperature rises to 35 degrees that won’t kill people because it’s below human body temperature. But if people want to feel comfortable they can use long wires that are attached to their houses which are full of electricity. Currently electricity is put into the wires at night using a variety of methods including burning coal, burning natural gas, hydro power, and wind power.
And it’s now noon in Adelaide and solar power is providing about 23% of total electricity use.
@Ikonoclast
This is how the Germans think. If you are green deep inside who can quibble about more coal burning? Some of us think the aim should be to get rid of coal altogether.
@Ronald Brak sounds commendable but Adelaide is a mild 25C at the moment according to BoM. That happens to be about the best temperature and time of day for PV. That absolute output will drop somewhat and the relative percentage will fall when/if it goes back to 46C as happened three weeks ago in in the northern suburbs.
Hermit, during our latest heatwave solar power provided over 10% of peak electricity use in South Australia and apparently also did the same in Queensland and Western Australia:
http://reneweconomy.com.au/2014/rooftop-solar-provides-10-electricity-in-three-key-states-46081
If you want solar power to provide a greater portion of peak electricity use then this can be achieved by installing more rooftop solar. And in fact, this is what is being done right now. Once solar power capacity is doubled in South Australia it will be able to supply about 22% of peak electricity use and at times it would provide half of total electricity use.