Battery Energy Cost Calculator
Calculate usable energy, charging energy, annual delivered energy, and cycling cost from battery capacity, efficiency, cycles, and energy rate.
- Usable energy per cycle
- kWh
- Charge energy per cycle
- kWh
- Annual delivered energy
- kWh/year
- Annual input energy
- kWh/year
- Annual energy cost
- $/year
- Cost per delivered kWh
- $/kWh
Calculation details
- Calculation basis
- Review boundary
Recent results
Formulas
- \(E_{\mathrm{usable}} = E_{\mathrm{capacity}} \times \frac{\mathrm{DOD}_{\%}}{100}\)
- \(E_{\mathrm{charge}} = \frac{E_{\mathrm{usable}}}{\eta_{\mathrm{round\ trip}}/100}\)
- \(E_{\mathrm{delivered,annual}} = E_{\mathrm{usable}} \times N_{\mathrm{cycles}}\)
- \(C_{\mathrm{annual}} = E_{\mathrm{charge}} \times N_{\mathrm{cycles}} \times r_{\mathrm{energy}}\)
- \(C_{\mathrm{delivered}} = \frac{C_{\mathrm{annual}}}{E_{\mathrm{delivered,annual}}}\)
A battery energy cost calculator estimates the energy purchased to charge a storage system and the cost of the energy it delivers over a year. The primary result is Cost per delivered kWh: the charging-energy cost assigned to each kilowatt-hour available from the battery after the entered depth of discharge and round-trip efficiency are applied.
This calculation is commonly used during early battery-storage load and operating-cost review. It helps compare a battery’s expected cycling expense against utility time-of-use rates, avoided peak-period purchases, generator operating cost, or the economics of an energy-management strategy.
The calculation does not size a battery inverter, branch circuit, feeder, overcurrent protective device, conductor, raceway, or service. Those electrical design decisions depend on the actual listed energy-storage equipment, inverter output, nameplate current, installation instructions, conductor ampacity, terminal ratings, voltage drop, available fault current, and AHJ requirements.
Battery Energy Inputs
| Input | Electrical meaning | Unit |
|---|---|---|
| Battery capacity | Nameplate battery energy capacity before applying an operating discharge limit | kWh |
| Depth of discharge | Portion of nameplate capacity intended for use during one discharge cycle | % |
| Round-trip efficiency | Ratio of energy delivered from storage to energy required to recharge it | % |
| Cycles per year | Expected full-equivalent discharge-and-recharge cycles each year | cycles |
| Electricity rate | Utility energy charge used to value charging energy | $/kWh |
Battery capacity is entered in kilowatt-hours, not ampere-hours. A battery labeled in Ah requires its nominal voltage and manufacturer-specific operating information before its usable energy can be established in kWh. The calculator begins with the stated kWh capacity because the resulting cost is expressed per kWh delivered.
Depth of discharge establishes the usable portion of the nameplate energy. A 10 kWh battery operated at 80% depth of discharge has 8 kWh available per cycle under this calculation. The remaining capacity is not treated as deliverable energy.
Round-trip efficiency accounts for storage losses between charging and discharge. If a system has 90% round-trip efficiency, it must receive more than 1 kWh of charging energy for every 1 kWh delivered from the battery.
Cycles per year converts a per-cycle energy calculation into annual energy throughput. It should reflect the actual anticipated operating schedule, including whether the system cycles daily, only during seasonal peak periods, or only during outages and demand-response events.
Electricity rate is the charging rate used for the estimate. Where a utility tariff has time-of-use periods, the entered value should represent the energy rate during the periods when the battery will actually charge. Demand charges, fixed customer charges, export compensation, taxes, and rider charges are outside this calculation.
Storage Energy Calculation
The calculator applies the following sequence:
\(\displaystyle \text{Usable energy per cycle} = \text{Battery capacity} \times \frac{\text{Depth of discharge}}{100}\)
\(\displaystyle \text{Charge energy per cycle} = \frac{\text{Usable energy per cycle}}{\text{Round-trip efficiency}/100}\)
\(\displaystyle \text{Annual delivered energy} = \text{Usable energy per cycle} \times \text{Cycles per year}\)
\(\displaystyle \text{Annual input energy} = \text{Charge energy per cycle} \times \text{Cycles per year}\)
\(\displaystyle \text{Annual energy cost} = \text{Annual input energy} \times \text{Electricity rate}\)
\(\displaystyle \text{Cost per delivered kWh} = \frac{\text{Annual energy cost}}{\text{Annual delivered energy}}\)
The final cost per delivered kWh can also be expressed directly as:
\(\displaystyle \text{Cost per delivered kWh} = \frac{\text{Electricity rate}}{\text{Round-trip efficiency}/100}\)
Battery capacity, depth of discharge, and cycles per year affect annual delivered energy and annual energy cost. With all other inputs unchanged, they do not change the charging-energy cost per delivered kWh. Round-trip efficiency and electricity rate do.
Calculation Example
Enter the following values:
| Field | Entered value |
|---|---|
| Battery capacity | 10 kWh |
| Depth of discharge | 80% |
| Round-trip efficiency | 90% |
| Cycles per year | 365 cycles |
| Electricity rate | $0.16/kWh |
The calculator produces:
| Result | Calculation | Result |
|---|---|---|
| Usable energy per cycle | 10 times 0.80 | 8 kWh |
| Charge energy per cycle | 8 div 0.90 | 8.8889 kWh |
| Annual delivered energy | 8 times 365 | 2,920 kWh/year |
| Annual input energy | 8.8889 times 365 | 3,244.4444 kWh/year |
| Annual energy cost | 3,244.4444 times $0.16 | $519.1111/year |
| Cost per delivered kWh | $519.1111 div 2,920 | $0.1778/kWh |
The battery delivers 2,920 kWh per year, but it requires 3,244.4444 kWh of purchased charging energy. The 324.4444 kWh difference represents the round-trip energy loss implied by the 90% efficiency input.
Electrical Design Boundary
Battery energy cost is not the same as battery installation cost, battery replacement cost, or lifecycle cost per kWh. The calculation includes only purchased energy used to charge the battery, based on the entered electricity rate and round-trip efficiency.
The following must be established separately from the listed equipment and installation conditions:
- Battery chemistry, usable operating window, degradation rate, calendar aging, and warranty throughput limits
- BMS operating limits, inverter conversion behavior, parasitic or standby consumption, thermal-management loads, and temperature effects
- Charging source capacity, branch-circuit loading, feeder loading, demand effects, and service-load review
- AC and DC conductor size, AWG or kcmil selection, ampacity, adjustment factor, correction factor, insulation temperature rating, and terminal rating
- Overcurrent protection, disconnecting means, grounding and bonding, available fault current, and equipment listing requirements
- Raceway fill, conduit routing, conductor pulling conditions, voltage-drop review, working space, and equipment clearances
- Utility tariff structures, demand charges, export rules, taxes, maintenance expense, financing, and replacement cost
- Applicable electrical code requirements, manufacturer installation instructions, utility interconnection rules, and AHJ approval
Use the calculated annual energy and charging-energy cost for operating-cost screening. Use the actual listed energy-storage system nameplate data and the governing installation requirements for electrical design and code compliance.
For a broader cost review, compare the result with the Electricity Cost Calculator, then review storage sizing with the Battery Capacity Calculator and Battery Runtime Calculator.
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FAQs
What does the cost represent?
It estimates the energy cost of charging and cycling the battery at the rate you enter.
Does it include battery replacement?
No. This page estimates cycling energy cost only and does not include replacement, maintenance, or financing.