Battery Load Profile Calculator

What the Battery Load Profile Calculator Measures

The Battery Load Profile Calculator combines two ideas that are often separated in battery planning: energy and timing. Energy tells you how many watt-hours the loads consume over a day. Timing shows when those loads overlap, which changes the highest running power the battery and inverter may need to supply.

The page uses a 24-hour repeating schedule. Each enabled row has running watts, quantity, a start time, scheduled duration and duty cycle. Duty cycle affects energy because a refrigerator, pump or thermostatically controlled load may be active only part of its scheduled window. Peak concurrent running power, however, uses the full entered running watts whenever scheduled windows overlap. That conservative distinction is intentional.

Battery Load Profile Calculator: Energy, Power and Load Shape

The Battery Load Profile Calculator treats watts as an instantaneous rate of energy use and watt-hours as energy accumulated over time. A 100W load running for three hours consumes 300Wh. If two 100W loads operate at the same time, their concurrent running power is 200W; if they run at different times, the daily energy can be identical while the peak power is lower.

This distinction is useful for battery systems because energy capacity and power capability solve different problems. Battery watt-hours or amp-hours help answer how long the system can support the loads. Inverter continuous rating, BMS discharge current, cable ampacity, fuse sizing and voltage drop must also accommodate the highest current and power that can occur. One number cannot replace the other.

Load shape describes how demand changes across time. A flat profile has similar demand through the day. A peaky profile has short periods of much higher demand. The U.S. Department of Energy discusses both load magnitude and load shape when evaluating interval electricity data, including hourly and 15-minute measurements. For a real site, measured interval data is generally more informative than estimates from appliance nameplates alone.

How the Battery Load Profile Calculator Works

The Battery Load Profile Calculator calculates daily energy for each enabled load with a direct watt-hour equation. It then repeats the schedule across a 24-hour day in 15-minute increments to identify the largest combination of enabled running loads. The entered start time and duration are constrained to quarter-hour increments so the concurrency estimate follows the same time grid.

The load-energy formula assumes the entered watts represent normal running power. Duty cycle is entered as a percentage from 1% to 100%. For a 120W refrigerator scheduled for 24 hours at a 35% duty cycle, the daily energy estimate is 120 × 24 × 0.35 = 1,008Wh. The peak calculation still treats that refrigerator as a possible 120W load during the scheduled window because its compressor may be running when another load starts.

Battery Load Profile Calculator: 5 Smart, Essential Checks

Use these five checks after the Battery Load Profile Calculator produces a result. They are the five promised checks from the SEO title and help prevent a mathematically neat capacity estimate from becoming an undersized or unsafe real system.

1. Check the daily energy inputs. Verify running watts and realistic hours of operation. Nameplate maximum power can overstate some loads, while standby consumption can be easy to miss. Where practical, compare the estimate with measured energy from a suitable meter.
2. Check concurrency, not just watt-hours. Loads that overlap can raise inverter and battery discharge requirements even if daily energy remains unchanged. Shift flexible loads in time when that is operationally acceptable, but do not assume users will always follow an ideal schedule.
3. Check surge and starting current. Pumps, refrigerators, compressors, motors and some electronic power supplies can draw substantially more than their running watts for a short period. The Battery Load Profile Calculator does not add a universal surge multiplier because actual surge magnitude and duration are equipment-specific.
4. Check usable capacity and efficiency at the intended conditions. Battery temperature, age, discharge rate, BMS cutoffs and inverter efficiency can change usable energy. Enter realistic planning values, then confirm the selected battery's published limits and the inverter's performance.
5. Check the whole electrical path. Battery capacity alone is not approval for the design. Confirm continuous and peak BMS current, inverter rating, DC cable ampacity, voltage drop, fuses or breakers, disconnects, terminals, charger limits and installation requirements before commissioning.

Battery Load Profile Calculator Examples

Example 1: Refrigerator, lighting, router, laptop, pump and fan

The default Battery Load Profile Calculator example uses six loads. The refrigerator contributes 1,008Wh/day from 120W × 24h × 35%. Lighting contributes 300Wh, the router 288Wh, the laptop about 182Wh, the water pump 125Wh and the fan 216Wh. Together they total about 2,119Wh per day, or 2.12kWh.

The pump is scheduled from 06:00 to 07:00, while the refrigerator and router are also scheduled all day. During that window their entered running powers can overlap, producing a 632W running peak. The average power across the full day is much lower: about 2,119Wh ÷ 24h = 88.3W. This is a clear example of why average power is not a substitute for peak power.

With one day of autonomy, 15% reserve, 90% combined efficiency and 80% usable DoD, the default example requires roughly 3.38kWh of nominal battery energy. At 48V that is about 70.5Ah. At 12V the same energy requirement would translate to roughly four times as many amp-hours, which is why amp-hours should always be interpreted together with nominal voltage.

Example 2: Moving a flexible load can reduce the running peak

Suppose a 900W appliance runs for one hour in the evening while a 700W appliance runs during the same hour. Together they create a 1,600W running peak and consume 1,600Wh if both operate continuously for that hour. If the 900W appliance is shifted to a non-overlapping hour, daily energy remains 1,600Wh but the peak drops to 900W. The Battery Load Profile Calculator makes this timing effect visible.

Example 3: Duty cycle changes energy more than possible running peak

Consider a 200W freezer scheduled for 24 hours with a 30% duty cycle. The Battery Load Profile Calculator estimates 1,440Wh/day for that load because 200 × 24 × 0.30 = 1,440Wh. During any moment when the compressor is actually running, however, it can still contribute its full 200W running power to the concurrent peak. Starting surge may be higher still and must be checked separately.

Example 4: Two autonomy days double the energy requirement

If the entered daily load is 3,000Wh and all other assumptions stay the same, selecting two days of autonomy doubles the pre-loss storage requirement from 3,000Wh to 6,000Wh before reserve, efficiency and DoD adjustments. The Battery Load Profile Calculator repeats the 24-hour energy profile for the selected number of days; it does not assume charging occurs between those days.

Battery Load Profile Calculator: Concurrency, Duty Cycle and Timing

Duty cycle is different. It describes how much of a scheduled period a cycling load is expected to be active. A 40% duty cycle over ten hours means the energy calculation assumes roughly four equivalent full-power hours. It does not mean the appliance always draws 40% of its rated running power. For that reason, the Battery Load Profile Calculator applies duty cycle to energy but not to possible running concurrency.

Sizing Battery Capacity From the Battery Load Profile Calculator

For example, a 4,000Wh/day load with two days of autonomy represents 8,000Wh before reserve and losses. Add a 10% reserve and the target becomes 8,800Wh delivered from storage. At 92% efficiency and 85% usable DoD, nominal battery energy is about 11,253Wh. At 51.2V, that is about 220Ah. The Battery Load Profile Calculator performs the same sequence with your entries.

Peak current also falls as system voltage rises for the same power. A simplified 1,200W battery-side requirement is about 100A at 12V before losses, 50A at 24V and 25A at 48V. Real equipment must still be checked against actual operating voltage, efficiency, surge, BMS limits and conductor design. Use the site's Load Current Calculator for a separate current-focused check.

Battery Load Profile Calculator Data, Limits and References

For broader context, the U.S. Department of Energy guidance on utility-rate evaluation explains electric load in terms of both magnitude and shape. DOE's end-use load profile project describes hourly and sub-hourly usage patterns for planning. These are useful references for understanding why time-resolved data matters.

The NREL REopt load-profile tutorial discusses using actual interval data when available. For storage system design and procurement, see DOE's lithium-ion battery storage technical specifications and battery energy storage system evaluation method. Those resources are broader than this calculator and do not validate a specific installation.