Energy storage-aware demand charge minimization
Systems and methods for power management include determining a demand threshold by solving an optimization problem that minimizes peak demand charges and maximizes a usable lifetime for a power storage system. Power is provided to a load from an electrical grid when the load is below the demand threshold and from a combination of the electrical grid and the power storage system when the load is above the demand threshold.
1. A computer-implemented method for power management, comprising:
determining a demand threshold by solving an optimization problem that minimizes peak demand charges and maximizes a usable lifetime for a power storage system; and
providing power to a load from an electrical grid when the load is below the demand threshold and from a combination of the electrical grid and the power storage system when the load is above the demand threshold.
2. The method of claim 1 , wherein the optimization problem comprises a peak demand charge term, an average state of charge term, and an accumulated discharged energy term.
3. The method of claim 2 , wherein the optimization problem is defined as:
min
∑
i
=
1
T
α
[
AvgSoC
i
]
+
β
[
AADE
i
]
+
γ
[
D
C
rate
any
·
P
max
grid
any
+
D
C
rate
peak
·
P
max
grid
peak
+
D
C
rate
partial
·
P
max
grid
partial
]
where α, β, and γ are weighting parameters that that are set in accordance with a particular optimization method, T represents the number of days in a given month, while i represents a particular day of the month, AvgSoC i represents the i th average state of charge, AADE i represents the i th annual average discharged energy, DC rate refers to the demand cost at various periods of the day, Pmax grid refers to the maximum value of the demanded power from the grid at various periods of the day, “any” refers to any time of day, “peak” refers to peak demand periods during the day, and “partial” refers to partial peak periods of the day.
4. The method of claim 1 , wherein the optimization problem is solved in a combined manner that optimizes the peak demand charges and maximizes the usable lifetime at the same time.
5. The method of claim 1 , wherein the optimization problem is solved in a cascaded manner that optimizes the peak demand charges first and then optimizes the usable lifetime in view of a fixed peak demand charge value.
6. The method of claim 1 , wherein determining the demand threshold is performed periodically, with provision of power being based on a latest demand threshold.
7. The method of claim 6 , wherein the demand threshold is determined monthly.
8. The method of claim 1 , wherein determining the demand threshold comprises calculating per-day demand thresholds for a plurality of recorded earlier days and selecting a representative demand threshold value.
9. The method of claim 1 , wherein the optimization problem is solved subject to a constraint on annual average discharged energy and demand charges.
10. A computer-implemented method for power management, comprising:
determining a monthly demand threshold by solving an optimization problem, having a peak demand charge term, an average state of charge term, and an accumulated discharged energy term, that minimizes peak demand charges and maximizes a usable lifetime for a battery system; and
providing power to a load from an electrical grid when the load is below the monthly demand threshold and from a combination of the electrical grid and the battery system when the load is above the monthly demand threshold.
11. A power access system, comprising:
a monthly demand module configured to determine a demand threshold by solving an optimization problem that minimizes peak demand charges and maximizes a usable lifetime for a power storage system; and
a grid access controller configured to provide power to a load from an electrical grid when the load is below the demand threshold and from a combination of the electrical grid and the power storage system when the load is above the demand threshold.
12. The power access system of claim 11 , wherein the optimization problem comprises a peak demand charge term, an average state of charge term, and an accumulated discharged energy term.
13. The power access system of claim 12 , wherein the power storage system is battery-based.
14. The power access system of claim 11 , wherein monthly demand module is configured to solve the optimization problem in a combined manner that optimizes the peak demand charges and maximizes the usable lifetime at the same time.
15. The power access system of claim 11 , wherein monthly demand module is configured to solve the optimization problem in a cascaded manner that optimizes the peak demand charges first and then optimizes the usable lifetime in view of a fixed peak demand charge value.
16. The power access system of claim 11 , wherein monthly demand module is configured to determine the demand threshold periodically, with provision of power being based on a latest demand threshold.
17. The power access system of claim 16 , wherein the demand threshold is determined monthly.
18. The power access system of claim 11 , wherein the monthly demand threshold is configured to calculate per-day demand thresholds for a plurality of recorded earlier days and to select a representative demand threshold value.
19. The power access system of claim 11 , wherein the optimization problem is solved subject to a constraint on annual average discharged energy and demand charges.
20. The power access system of claim 11 , wherein the optimization problem is defined as:
min
∑
i
=
1
T
α
[
AvgSoC
i
]
+
β
[
AADE
i
]
+
γ
[
D
C
rate
any
·
P
max
grid
any
+
D
C
rate
peak
·
P
max
grid
peak
+
D
C
rate
partial
·
P
max
grid
partial
]
where α, β, and γ are weighting parameters that that are set in accordance with a particular optimization method, T represents the number of days in a given month, while i represents a particular day of the month, AvgSoC i represents the i th average state of charge, AADE i represents the i th annual average discharged energy, DC rate refers to the demand cost at various periods of the day, Pmax grid refers to the maximum value of the demanded power from the grid at various periods of the day, “any” refers to any time of day, “peak” refers to peak demand periods during the day, and “partial” refers to partial peak periods of the day.