Plug-in distributed energy resource

1. A distributed energy resource (DER) comprising:

a plug configured to couple to an AC circuit and receive or deliver AC power from or to the AC circuit;

an energy storage circuit;

one or more controllers;

a program memory storing executable instructions that when executed by the one or more controllers cause the DER to:

determine an amperage difference between a first threshold value and the amperage of an AC power transmitted to a load device plugged into the DER,

determine whether to set the DER to a charge state or a discharge state,

if the DER is set to a charge state, charge the energy storage circuit with AC power received from the AC circuit only if the amperage difference is above a charge threshold value, and

if the DER is set to a discharge state, deliver AC power to the AC circuit by discharging the energy storage circuit.

2. The DER of claim 1 further comprising:

a receptacle configured to receive a plug of a load device and transmit AC power to the load device.

3. The DER of claim 1 wherein the program memory further stores executable instructions that when executed by the one or more controllers cause the DER to:

if the amperage difference is equal to or less than the charge threshold value and the DER is set to a charge state, not charge the energy storage circuit.

4. The DER of claim 1 further comprising an overcurrent protector configured to disconnect the load device from AC power if the amperage of the AC power transmitted to the load device is greater than or equal to the first threshold value.

5. The DER of claim 1 wherein the energy storage circuit includes:

one or more rechargeable batteries, and

a bidirectional DC/AC converter configured to convert AC power received from the AC circuit into DC power and apply the DC power to the rechargeable batteries when the DER is in a charge state, or convert DC power from the rechargeable batteries into AC power and deliver AC power to the AC circuit when the DER is in a discharge state.

6. The DER of claim 1 wherein the program memory further stores executable instructions that when executed by the one or more controllers cause the DER to determine whether to set the DER to a reactive power source state, and

wherein the energy storage circuit is configured to source or sink reactive power to the AC circuit when the DER is set to a reactive power source state.

7. The DER of claim 1 wherein the program memory further stores executable instructions that when executed by the one or more controllers cause the DER to:

receive a command to set the DER to a charge state, and

receive a command to set the DER to a discharge state.

8. The DER of claim 1 wherein the executable instructions that when executed by the one or more controllers cause the DER to determine whether to set the DER to a charge state or a discharge state include instructions to:

set the DER to a charge state during a first period of time when AC power is priced at a first amount of money,

set the DER to a discharge state during a second period of time when AC power is priced at second amount of money, wherein the second amount of money is greater than the first amount of money.

9. The DER of claim 1 :

wherein the AC circuit is coupled to a distributed renewable energy source; and

wherein the executable instructions that when executed by the one or more controllers cause the DER to determine whether to set the DER to a charge state or a discharge state include instructions to:

set the DER to a charge state during a first period of time when the distributed renewable energy source is generating power above a second threshold level,

set the DER to a discharge state during a second period of time when the distributed renewable energy source is not generating power above the second threshold level.

10. A method for operating a distributed energy resource (DER) having a plug, a receptacle, and an energy storage circuit, the method comprising:

receiving AC power from an AC circuit via the plug of the DER;

determining an amperage difference between a first threshold value and the amperage of an AC power transmitted to a load device plugged into the DER;

determining whether to set the DER to a charge state or a discharge state;

if the DER is set to a charge state, charging the energy storage circuit with AC power received from the AC circuit only if the amperage difference is above a charge threshold value; and

if the DER is set to a discharge state, delivering AC power to the AC circuit by discharging the energy storage circuit.

11. The method of claim 10 further comprising:

transmitting AC power to a load device coupled to the DER via the receptacle of the DER.

12. The method of claim 10 further comprising:

if the amperage difference is equal to or below the charge threshold value and the DER is set to a charge state, not charging the energy storage circuit.

13. The method of claim 10 wherein charging the energy storage circuit with AC power includes charging the energy storage circuit with AC power at an amperage substantially equal to the amperage difference.

14. The method of claim 10 further comprising:

if the amperage of the AC power transmitted to the load device is equal to or greater than the first threshold, ceasing to deliver AC power to the AC circuit.

15. The method of claim 10 further comprising:

determining whether to set the DER to a reactive power source state; and

if the DER is set to a reactive power source state, sourcing or sinking reactive power to the AC circuit.

16. The method of claim 10 wherein determining whether to set the DER to a charge stage or a discharge state includes receiving a command to set the DER to one of a charge state or a discharge state.

17. The method of claim 10 wherein determining whether to set the DER to a charge stage or a discharge state includes:

setting the DER to a charge state during a first period of time when AC power is priced at a first amount of money,

setting the DER to a discharge state during a second period of time when AC power is priced a second amount of money, wherein the second amount of money is greater than the first amount of money.

18. The method of claim 10 wherein the AC circuit is coupled to a distributed renewable energy source; and

determining whether to set the DER to a charge stage or a discharge state includes:

setting the DER to a charge state during a first period of time when the distributed renewable energy source is generating power above a second threshold level,

setting the DER to a discharge state during a second period of time when the distributed renewable energy source is not generating power above the second threshold level.

19. The method of claim 10 further comprising:

coupling the DER to the AC circuit by inserting the plug of the DER into a receptacle coupled to the AC circuit; and

coupling the DER to the load device by inserting a plug of the load device into the DER receptacle.

20. A distributed energy resource (DER) comprising:

a plug configured to couple to an AC circuit and receive or deliver AC power from or to the AC circuit;

a bidirectional DC/AC converter;

one or more controllers;

a program memory storing executable instructions that when executed by the one or more controllers cause the DER to:

determine whether to set the DER to a reactive power source state; and

if the DER is set to a reactive power source state, use the DC/AC converter to source or sink reactive power to the AC circuit.