Rough is this fesible math.
Heres the 1/2 hour spot market price sorted into price bins of sorts..
At USD $400/kwH for batterys, lets assume 3000 cycles to 80%, we can get 20,000kWh out of a 10kWh battery pack over its life. . Thats goign to cost me $NZD 0.10c per unit for the battery.
There is no savings to be made by using the battery to provide power until the unit cost of power is > average + 0.10c or in our case; 16.7c units. We should never charge the batterys if power is greater than average cost;
The average cost of 'peak priced power ) is 24.8c
There were 974 hours over the dataset that exceeded that ( 1489 days ).. or 2.7% of the time. 87% of the peaks that are greater than 16.7c are less than 2 hours wide. My household use does tend to use power in line with the peaks, and i use 1.4kWhr/hrs on average during the peak. ( i already ditch non essential loads ). 5kWh of storage probably will suffice, which will cost me about $2000USD ( $2800 NZD )
My potnetial savings over a year, are 236hours * 1.4kW ( 24.8 - 6.7c ) = $59.80!!!! Factor in the 'cost' of the battery.. its just $26.76 per year im ahead. If i factor in cost of money at say 4.9%,, ( 2800 * 4.95 ) = $138 / year. I'm down $110 a year for the hassle.
Conclusion: putting a battery in byitself to round off the peak power prices, has negetive economic benefit.
The next scenerio to consider is see what impact putting a sensible sized solar system in is along with the Batteries. Power generated locally is going to have an 9.8c advantage over anything that is imported as it wont' attract any distribution fees. I can also 'sell' surplus power back into the grid at the same rate as i buy it for ( the spot rate ).
I use about 1200kW per month on average. We only increase useage slighly during winter. The bulk of useage will fall outside of the peak solar production hours.