Energy storage

1. A method of controlling storage of electrical energy, the method comprising:

detecting one of a candidate charging occasion and a candidate discharging occasion with respect to pricing data and energy losses, the pricing data indicative of future prices of electrical energy over time and the energy losses caused by charging and discharging an energy storage device and the electrical energy being supplied from an external electrical supply network, by selecting a next occurrence of a locally minimum price in the pricing data as the candidate charging occasion or a next occurrence of a locally maximum price in the pricing data as the candidate discharging occasion;

validating, by circuitry of an energy management system, the one of the candidate charging occasion and the candidate discharging occasion when a price difference between the one of the candidate charging occasion and the candidate discharging occasion and another later price in the pricing data compensates for the energy losses;

charging, by the circuitry when the candidate charging occasion is validated, the energy storage device with the electrical energy at the candidate charging occasion; and

discharging, by the circuitry when the candidate discharging occasion is validated, the energy storage device at the candidate discharging occasion, wherein

the validating further includes confirming whether

P D >P C /Eff , where

Eff is an efficiency of the charging and the discharging of the energy storage device and Eff is equal to a ratio of energy retrieved during the discharging to energy input during the charging, and one of

P D is a price at the candidate discharge occasion and P C is a price paid at a most recent charging of the energy storage device, or

P C is a price at the candidate charging occasion and P D is a price received at a most recent discharging of the energy storage device.

2. The method according to claim 1 , wherein the validating the one of the candidate charging occasion and the candidate discharging occasion comprises detecting whether the pricing data relating to the candidate charging occasion and the candidate discharging occasion represents the respective lowest or highest price before the later price which validates that candidate occasion, and if not, replacing the candidate charging or discharging occasion by the respective lowest or highest price before the later price which validates that candidate occasion.

3. The method according to claim 1 , wherein the pricing data used by the detecting and validating represents a time average of the pricing data over a predetermined time period.

4. The method according to claim 1 , wherein the validating integrates the cost of electricity consumption against time over a charging cycle to detect the price associated with a charging occasion.

5. The method according to claim 1 , wherein the validating applies a time-varying energy loss relating to a charged energy storage device in dependence upon an elapsed time since the last charging occasion.

6. The method according to claim 1 , further comprising determining whether a first of the occasions should he a charging occasion or a discharging occasion in dependence upon a present charging state of the energy storage device.

7. The method according to claim 6 , wherein the determining comprises comparing a measure of the present charging state with a threshold amount.

8. The method according to claim 7 , further comprising varying the threshold in dependence upon the pricing data.

9. An energy storage controller for controlling storage of electrical energy, the energy storage controller comprising:

circuitry configured to

detect one of a candidate charging occasion and a candidate discharging occasion with respect to pricing data and energy losses, the pricing data indicative of future prices of electrical energy over time and the energy losses caused by charging and discharging an energy storage device and the electrical energy being supplied from an external electrical supply network, by selecting a next occurrence of a locally minimum price in the pricing data as the candidate charging occasion or a next occurrence of a locally maximum price in the pricing data as the candidate discharging occasion;

validate the one of the candidate charging occasion and the candidate discharging occasion when a price difference between the one of the candidate charging occasion and the candidate discharging occasion and another later price in the pricing data compensates for the energy losses;

charge, when the candidate charging occasion is validated the energy storage device with the electrical energy at the validated candidate charging occasion; and

discharge, when the candidate discharging occasion is validated, the energy storage device at the candidate discharging occasion, wherein

to validate the one of the candidate charging occasion and the candidate discharging occasion, the circuitry is further configured to confirm whether

P D >P C /Eff , where

Eff is an efficiency of the charging and the discharging of the energy storage device and Eff is equal to a ratio of energy retrieved during the discharging to energy input during the charging, and one of

P D is a price at the candidate discharge occasion and P C is a price paid at a most recent charging of the energy storage device, or

P C is a price at the candidate charging occasion and P D is a price received at a most recent discharging of the energy storage device.

10. An energy storage apparatus, comprising:

the energy storage controller according to claim 9 ;

the energy storage device comprising one or more batteries; and

an inverter for producing an output voltage higher than the battery voltage.

11. An energy storage apparatus, comprising:

the energy storage controller according to claim 9 ; and

the energy storage device comprising:

one or more batteries;

a movable mass having a motor for driving the movable mass; and

a generator for generating electrical power from motion of the movable mass.

12. A non-transitory computer readable medium storing computer-executable instructions which, when executed by circuitry of a computer, cause the computer to perform a method comprising:

detecting one of a candidate charging occasion and a candidate discharging occasion with respect to pricing data and energy losses, the pricing data indicative of future prices of electrical energy over time and the energy losses caused by charging and discharging an energy storage device and electrical energy being supplied from an external electrical supply network, by selecting a next occurrence of a locally minimum price in the pricing data as the candidate charging occasion or a next occurrence of a locally maximum price in the pricing data as the candidate discharging occasion;

validating the one of the candidate charging occasion and the candidate discharging occasion when a price difference between the one of the candidate charging occasion and the candidate discharging occasion and another later price in the pricing data compensates for the energy losses;

charging, when the candidate charging occasion is validated, the energy storage device with the electrical energy at the candidate charging occasion; and

discharging, when the candidate discharging occasion is validated, the energy storage device at the candidate discharging occasion, wherein

the validating further includes confirming whether

P D >P C /Eff , where

Eff is an efficiency of the charging and the discharging of the energy storage device and Eff is equal to a ratio of energy retrieved during the discharging to energy input during the charging, and one of

P D is a price at the candidate discharge occasion and P C is a price paid at a most recent charging of the storage device, or

P C is a price at the candidate charging occasion and P D is a price received at a most recent discharging of the energy storage device.

13. The energy storage controller according to claim 9 , wherein the circuitry is configured to validate the one of the candidate charging occasion and the candidate discharging occasion by detecting whether the pricing data relating to the candidate charging occasion and the candidate discharging occasion represents the respective lowest or highest price before the later price which validates that candidate occasion, and if not, replacing the candidate charging or discharging occasion by the respective lowest or highest price before the later price validates that candidate occasion.

14. The energy storage controller according to claim 9 , wherein the pricing data used represents a time average of the pricing data over a predetermined time period.

15. The energy storage controller according to claim 9 , wherein the circuitry validates by integrating the cost of electricity consumption against time over a charging cycle to detect the price associated with a charging occasion.

16. The energy storage controller according to claim 9 , wherein the circuitry validates by applying a time-varying energy loss relating to charged energy storage device in dependence upon an elapsed time since the last charging occasion.

17. The method according to claim 1 , wherein the energy losses include lost energy released as heat during the charging or the discharging of the energy storage device.

18. The energy storage controller according to claim 9 , wherein the energy losses include lost energy released as heat during the charging or the discharging of the energy storage device.