Power consumption calculation in the company: step by step

Do you know exactly what your company's energy bill represents? Understanding consumption in kWh is the first step to identifying waste, optimizing contracts, and even negotiating better market conditions. 

In this guide, you will learn how to calculate your company's energy consumption, understand the impact of tariffs, and discover errors that may be costing you dearly.

What are kWh and kW in businesses?

Before diving into the calculations, it is worth clarifying two fundamental quantities: power and energy. The kilowatt (kW) indicates power, meaning the instantaneous capacity of energy use by machines, motors, or systems. Imagine a 15 kW compressor running at full load — this value reveals the peak energy it demands at that moment. This number is key to calculating contracted demand and avoiding costs from unexpected peak surges, especially when dealing with captive consumers versus free consumers. 

On the other hand, the kilowatt-hour (kWh) measures energy consumed over time. In other words, how much electricity was used during the month by each piece of equipment, sector, or shift. If that same 15 kW compressor operates for one hour, it consumes exactly 15 kWh of energy. It is the kWh that appears as consumption on your bill and serves as the basis for calculating monthly costs and process efficiency, as well as setting reduction targets and supporting strategic decisions regarding energy efficiency.

In practice, do not confuse power (kW) with energy (kWh). The former is used to size loads and demands, while the latter records the accumulated consumption that will be billed. 

On the corporate energy bill, both appear: kWh is broken down by periods (peak, off-peak, intermediate) and kW is associated with demand contracts and potential peak charges for medium/high voltage consumers. 

What is the difference between kWh (consumption) and kW (demand) on the bill?​

kWh reflects the total amount of energy used in the month, while kW shows the highest power value demanded and, in the case of Group A, is contracted and audited to avoid penalties. 

In Group A bills, both consumption and demand are detailed according to tariff periods and utility rules.​

Knowing how to interpret these figures is essential to avoid compromising operations with excesses and to keep the company competitive in energy planning.

How to calculate kWh consumption? Step by step

Calculating energy consumption starts with surveying the equipment and understanding how and how much they operate on a daily basis. Check out a practical guide:

1. Survey power (W/kW) and usage time per equipment​

List all relevant equipment in your process. Define the rated power (W or kW), operating hours per day, days of use per month, and whenever possible, the load factor (average percentage of actual use) and efficiency for each.

This data can be checked on rating plates, technical manuals, spot measurements, or management systems (BMS).

2. Applying the consumption formula

The calculation is straightforward. For power in watts (W), use:

kWh/month = [Power (W) x Hours/day x Days/month x Load factor] / 1000

If the power is already in kilowatts (kW):

kWh/month = Power (kW) x Hours/day x Days/month x Load factor

Example: An 11 kW pump used 10 hours a day, for 26 days/month, with a load factor of 0.6:

kWh/month = 11 x 10 x 26 x 0.6 = 1,716 kWh/month

3. Consolidate by sector/shift and total facility

For an effective diagnosis, group the calculated consumption by sector, shift, or production line. Generate specific indicators, such as kWh per shift, unit produced, square meter, or workstation. This allows you to identify where the main bottlenecks and consumption peaks are located.

4. Estimate the monthly cost

Converting estimated consumption into cost requires attention to local tariffs, taxes, and tariff flags. The basic formula is:

Cost ≈ (Peak kWh x Peak tariff) + (Off-peak kWh x Off-peak tariff) + Charges + Contracted demand + Taxes

Important: tariff flags apply proportional additions for every 100 kWh consumed, according to ANEEL's signaling for the month.

7 common mistakes in energy consumption calculation​

1. Confusing kW (power) and kWh (energy): this mistake distorts cost allocation among cost centers and can generate undue charges;

2. Ignoring peak hours when estimating total expenses: results in underestimating the real cost and can lead to surprises on the bill, especially under differentiated tariff structures;

3. Failing to consider the impact of reactive energy and power factor: these factors can lead to fines and unforeseen increases on the bill, raising operational costs;

4. Always using rated power without applying the load factor: usually causes overestimation or underestimation of monthly consumption;

5. Not grouping consumption by shift or sector: prevents the identification of specific bottlenecks and savings opportunities, harming decision-making;

6. Estimating costs without considering the division between TUSD, TE, and tariff flags: can leave important gaps and distortions in expense projections;

7. Reducing contracted demand without analyzing seasonal peaks: increases the risk of excess charges, fines, and instability in energy supply.

How to calculate the kWh of a specific company equipment?​

The method is direct: simply multiply the rated power (in kW) by the usage time (hours per day and days per month) and the load factor. For example, for a three-phase motor that works 8 hours/day for 22 days a month with a load factor of 0.7:

kWh/month = 15 x 8 x 22 x 0.7 = 1,848 kWh

If part of this operation occurs during peak hours, proportionally divide the blocks and apply the corresponding tariffs.

#SerenaEnergiaTip: always segmenting the calculation by tariff schedule brings more precision to cost management and supports strategies for tariff migration or contracting energy in the Free Energy Market.

What changes between Group A and Group B for calculation and billing?​

Group A companies deal with tariffs separated by time of day, measured vs. contracted demand, and extra costs for excess usage. In Group B, the calculation is simpler, focusing on kWh and allowing the choice of the White tariff, which is more advantageous for those who can concentrate operations outside peak hours.

How to consider peak and off-peak in consumption and cost?​

Map the schedules defined by the energy distributor and segment the consumption calculation according to the periods. By shifting high-consumption activities to off-peak hours (such as forklift recharging, chillers, or flexible production), your company reduces the risk of additional charges and optimizes the use of tariffs.

Do reactive energy and power factor impact consumption or just billing?

Reactive energy, measured in kvarh, is not converted into useful kWh, but it can increase costs if the power factor drops below the regulatory limit. To avoid fines, monitor and correct the power factor using automatic capacitors or filters. Good management prevents current increases, technical losses, and frees up capacity for growth without investing in infrastructure.

How to use this data to reduce costs?

Performing a detailed calculation of your company's energy consumption is only the first step. To turn knowledge into concrete results, it is essential to apply this information to the business routine and use the indicators to guide smarter decisions.

Main practical actions to improve results:

• Identify peaks and optimize operations at the right times;

• Readjust contracted demand according to the production profile;

• Plan energy efficiency actions by sector and shift;

• Evaluate opportunities in the Free Energy Market and incentivized energies.

Turning data into strategy with the support of Serena Energia

Understanding and monitoring your company's energy consumption is the first step to achieving greater efficiency and competitiveness. By analyzing peaks, detailing usage profiles, and truly understanding your business demands, you build the necessary foundation to make more assertive decisions — including when to migrate to the Free Energy Market.

If your company seeks flexibility, contractual freedom, or better cost predictability, Serena Energia enables direct purchasing in the Free Market through a 100% digital and secure contracting process. 

Simulate your electricity bill discount with Serena!

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