Energy arbitrage by load shifting
First Claim
1. A computer-assisted method of electrical energy load shifting utilizing an electrical energy storage device connected to receive electrical energy from an electrical power grid, comprising the steps of:
- establishing a budget of unreserved cycles of discharging and charging the electrical energy storage device for load shifting purposes within a given time period;
establishing a schedule for load shifting within sub-parts of said time period, based upon said budget and input data regarding multiple rate levels applicable to electrical energy available from the electrical power grid during the sub-parts of said time period; and
executing load shifting cycles within one or more of said sub-parts of said time period, in accordance with said schedule, by discharging electrical energy stored in said electrical energy storage device in a first interval for which a first rate is applicable to energy available from the grid, and charging said electrical energy storage device with electrical energy obtained from the grid during a second interval for which a second rate lower than said first rate is applicable to energy obtained from the grid;
wherein said budget is computed by a data processor based at least in part on of at least one;
an input indicating a cycle life of the electrical energy storage device;
an input indicating a time life of said electrical energy storage device; and
an input reflecting a number of cycles reserved for purposes other than load shifting;
wherein the step of establishing a schedule for load shifting comprises splitting the time period into rate periods, and calculating values of P−
(O/E) for days within each rate period, where P is a peak rate applicable to energy obtained from the grid during a first time interval of any given day, O is an off-peak rate applicable to energy obtained from the grid during a second time interval of the given day, and E is a measure of the efficiency of the electrical energy transfer during a cycle of discharging and charging the electrical energy storage device;
wherein a rate schedule applicable to the rate periods has energy usage level-based tiers, said method further comprising calculating the values P−
(O/E) for days within each rate period so as to account for increased rates applicable to electrical energy usage above a tier boundary representing a maximum energy usage within a rate period before crossing into the next tier, wherein said calculating comprises;
recording an expected energy usage for each rate period apart from any load shifting;
calculating an additional amount of energy that will be used by a load shifting cycle;
calculating for each rate period the number of cycles Y of load shifting that can be executed before crossing into the next tier;
sub-dividing the rate periods into days corresponding to number of cycles Y, and days remaining; and
calculating the quantity P−
(O/E) for days remaining with values for the next highest tier.
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Accused Products
Abstract
Methods and systems are provided for realizing energy cost savings through load shifting utilizing a battery bank that may serve as a battery back-up on a premises for providing power in the event of a grid power outage or curtailment. A budget of unreserved cycles of battery charging and discharging is determined, taking into account the rated battery life in terms of both time (e.g., years) and number of cycles. That cycle budget is allocated to days of the year identified as days on which the greatest savings can be realized through load shifting. These days are identified by taking into account the peak and off-peak usage rates applicable on those days, any rate tiers that may be entered as a result of the additional energy expended to load shift, and the round trip efficiency of the charge/discharge cycles. Load shifting is executed in accordance with an established schedule of the identified days, by discharging the batteries during peak usage hours and charging the batteries during off-peak periods. In the event the budget of unreserved cycles exceeds the number of profitable days for load shifting, the depth of discharge on each cycle may be increased to realize greater savings on the scheduled days, at the tolerable cost of losing cycles not expected to be used in any event.
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Citations
16 Claims
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1. A computer-assisted method of electrical energy load shifting utilizing an electrical energy storage device connected to receive electrical energy from an electrical power grid, comprising the steps of:
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establishing a budget of unreserved cycles of discharging and charging the electrical energy storage device for load shifting purposes within a given time period; establishing a schedule for load shifting within sub-parts of said time period, based upon said budget and input data regarding multiple rate levels applicable to electrical energy available from the electrical power grid during the sub-parts of said time period; and executing load shifting cycles within one or more of said sub-parts of said time period, in accordance with said schedule, by discharging electrical energy stored in said electrical energy storage device in a first interval for which a first rate is applicable to energy available from the grid, and charging said electrical energy storage device with electrical energy obtained from the grid during a second interval for which a second rate lower than said first rate is applicable to energy obtained from the grid; wherein said budget is computed by a data processor based at least in part on of at least one; an input indicating a cycle life of the electrical energy storage device; an input indicating a time life of said electrical energy storage device; and an input reflecting a number of cycles reserved for purposes other than load shifting; wherein the step of establishing a schedule for load shifting comprises splitting the time period into rate periods, and calculating values of P−
(O/E) for days within each rate period, where P is a peak rate applicable to energy obtained from the grid during a first time interval of any given day, O is an off-peak rate applicable to energy obtained from the grid during a second time interval of the given day, and E is a measure of the efficiency of the electrical energy transfer during a cycle of discharging and charging the electrical energy storage device;wherein a rate schedule applicable to the rate periods has energy usage level-based tiers, said method further comprising calculating the values P−
(O/E) for days within each rate period so as to account for increased rates applicable to electrical energy usage above a tier boundary representing a maximum energy usage within a rate period before crossing into the next tier, wherein said calculating comprises;recording an expected energy usage for each rate period apart from any load shifting; calculating an additional amount of energy that will be used by a load shifting cycle; calculating for each rate period the number of cycles Y of load shifting that can be executed before crossing into the next tier; sub-dividing the rate periods into days corresponding to number of cycles Y, and days remaining; and calculating the quantity P−
(O/E) for days remaining with values for the next highest tier. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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Specification