What the BESS model does
The BESS (Battery Energy Storage System) model simulates how a battery or energy storage system is used over time.
It shows:
How much energy flows into and out of the battery
How fast the battery is charging and discharging
How battery usage affects your contracted power limits
This helps you understand whether your battery is sized and configured correctly for your site and use case.
BESS setup parameters
To set up a BESS correctly, you’ll need to configure the following parameters.
Installation Date (optional)
What it is: The date the battery is installed and starts operating.
Why it matters:
If the battery is installed mid-year, this allows the simulation to only account for usage from that moment onwards.
If left empty, the model assumes the battery is available for the entire simulation period.
Max Discharge Power
What it is: The maximum power the battery can deliver to your site (in kW).
How it’s used:
Limits the maximum discharge rate in the simulation.
The model will never let the battery discharge faster than this value.
Max Charge Power
What it is: The maximum power the battery can absorb from the grid or PV system (in kW).
How it’s used:
Limits the maximum charging rate.
The battery won’t charge faster than this set limit, even if more power is available.
Maximum Storage Capacity
What it is: The total amount of energy the battery can store (in kWh).
How it’s used:
Defines the upper limit of how much energy the battery can hold.
All state of charge (SoC) values in the report will range from 0 to this maximum.
Initial Charged Capacity (%)
What it is: The battery’s state of charge at the start of the simulation, expressed as a percentage.
Example:
50% means the battery is half-charged at the beginning of the simulation (e.g. upon delivery or commissioning).
Why it matters:
Affects the initial behavior of the battery in the first hours/days of the simulation.
Buffer Percentage
What it is: The portion of the battery capacity that is reserved and not used by the normal control strategy. It is used when contracted limits are at risk.
Why it’s used:
To keep a buffer for emergencies or specific operational constraints.
Our Energy Management System (EMS) will still aim for optimal control, but it will respect this buffer.
Example:
With a 20% buffer on a 500 kWh battery, only 80% (400 kWh) is used for normal operation.
Budgets and prices – BESS
You can configure a surcharge per kWh to reflect the cost of using the battery over its lifetime (based on purchase price and warranty cycles).
Surcharge
What it is:
A cost per kWh charged or discharged that represents the battery’s depreciation per cycle.Formula:
First, calculate the purchase cost per kWh of capacity:
Purchase price per kWh capacity = Purchase price / Capacity (kWh)Then, divide that amount by the warranty cycle count:
Surcharge per kWh = (Purchase price / Capacity) / Warranty cycles
Example:
Purchase price: €100,000
Capacity: 500 kWh
Warranty: 5,000 cycles
Step 1 – Cost per kWh of capacity:
€100,000 / 500 kWh = €200 per kWh (capacity)
Step 2 – Surcharge per kWh over the warranty life:
€200 / 5,000 cycles = €0.04 per kWh
So in this example, you can configure a €0.04 surcharge per kWh charged or discharged.
Report explanation
Once the simulation is run, the BESS report will show several key results.
Chart 1 – Stored energy (state of charge)
Displays the amount of energy stored in the battery (kWh) over time.
The values range from 0 to the Maximum Storage Capacity (e.g. 0–1000 kWh).
This helps you see:
How often the battery is fully charged or empty
How the state of charge changes during the day, week, or year
Chart 2 – Charge and discharge power
Shows the charge and discharge rate of the battery (in kW).
The chart uses:
Positive values to represent discharging (power delivered to your site/grid)
Negative values to represent charging (power absorbed from grid or PV)
This helps you understand:
When the battery is charging vs. discharging
Whether power peaks are being reduced as intended
Maximum Storage Capacity (result)
Indicates the maximum stored energy (kWh) reached during the selected period.
This is a result value, not just the configured capacity:
It shows how “full” the battery actually got in the simulation timeframe.
Useful to see if your battery is underused or frequently fully charged.
Highest Charge/Discharge Rate
Shows the peak charging or discharging power (kW) reached in the simulation.
Helps answer questions like:
“Did we ever reach the battery’s Max Charge Power or Max Discharge Power limit?”
“Are our power peaks within the battery’s design specifications?”
Number of Full Cycles
The Number of Full Cycles is a key indicator of how intensively the battery is being used over a given period.
What is a full cycle?
A full cycle is defined as:
One full charge from 0% to 100%, and
One full discharge from 100% back to 0%.
In practice, batteries rarely charge and discharge in perfect full cycles, so the model calculates equivalent full cycles based on total energy throughput.
How the number of full cycles is calculated
The simulation sums:
The total energy charged into the battery
The total energy discharged from the battery
These values are added together to get the total energy throughput.
The total energy throughput is then divided by the energy of one full cycle, defined as:
One full cycle = Battery capacity (kWh) charged + Battery capacity (kWh) discharged
For a battery with a 400 kWh capacity:
One full cycle = 400 kWh (charge) + 400 kWh (discharge)
So one full cycle = 800 kWh total energy throughput.
If the model records, for example, 8,000 kWh total throughput over a period, that corresponds to:
8,000 kWh / 800 kWh per cycle = 10 full cycles
Why full cycles matter
Helps estimate battery degradation over time.
Allows you to check usage against the manufacturer’s warranty (e.g. 5,000 cycles).
Supports better planning for:
Replacement timing
Financial calculations (e.g. cost per kWh including battery wear)
By monitoring the Number of Full Cycles, you can see if your battery is being used as expected and whether your current configuration is sustainable in the long term.