Optimize performance with Usable and Recoverable energy

We have launched two new features that help you understand how much energy your system can deliver, how much energy can be recovered, and what actions you should take to recover this lost energy. Your key benefits:

• Get a clear overview of total usable and recoverable energy (MWh and %)

• Identify which AC and DC Combiners (or your own names for these levels) and strings have the highest amount of recoverable energy

• Receive specific recommendations, for example to fix imbalances, limiting cells or disconnected components

Usable and recoverable energy explained

Usable energy: how much energy can your BESS deliver right now?

Usable energy is expressed in percentage points (%) and megawatt-hours (MWh) and helps to answer the question, “How many MWh is my system currently capable of delivering?” It is influenced by multiple factors:

• Aging reduces energy capacity over time. This loss is irrecoverable and results from the unavoidable degradation of battery cells.

• Limiting cells may limit performance due to manufacturing differences, defects, or abnormal degradation. Identifying and addressing limiting cells can restore energy.

• Imbalances in the system occur when the state of charge (SoC) varies significantly across components. Since individual, highly imbalanced components can limit overall system performance, resolving imbalances can help recover energy.

• Non-operational components reduce usable energy. If strings (racks) or PCS are down, restoring them can immediately improve the usable energy.

Usable energy ultimately provides a status of how much energy your system is currently delivering and represents how much energy can be recovered.

Analogy:
Imagine your Usable Energy as the full size of a beer glass. If you fill this glass slowly and carefully, you can fill it completely, just like discharging at very low power allows you to extract all usable energy.

However, if you try to fill the glass as fast as possible, foam (akin to system inefficiencies) prevents it from being completely full. This is what the Penalty Risk Assessment metric shows - the portion of energy you can utilize when operating at maximum (nameplate) power.

From experience, to fully fill a beer glass to the brim, you slow down the filling speed (i.e., reduce charging or discharging power) toward the end. The same principle applies when maximizing usable energy in a battery system.

To learn more about the differences between usable energy, availability and State of Health, read this article.

Recoverable energy: how much energy is lost but still recoverable?

Recoverable energy identifies energy that can be restored by fixing issues like limiting cells, imbalances or offline components – helping you unlock additional performance without major hardware replacements.

We calculated recoverable energy based on soc imbalances, limiting cells, strings disconnected and PCS disconnected.

• For the soc imbalance, for each string we take the median of the soc spread of the day. This is the same number as in the State of Charge page under Performance.

• For limiting cells, it is detection based. If a limiting cell is detected, we use the energy loss that is caused by that limiting cell.

• Regarding strings disconnected, the nominal string capacity excluding aging is considered.

• Similar to strings disconnected, PCS disconnected considers the entire capacity of strings which are associated to the PCS into account, excluding aging.

How to optimize performance with usable and recoverable energy

Navigate to the Performance Manager, and click on Recoverable Energy. At the top of the page, you will find a date selector that shows you how the amount of usable and recoverable energy developed over time. After clicking on one specific day, the respective details will show up below.

The middle bar displays a summary for the respective day. Let's walk through the items one by one.

Energy overview

This part shows you an breakdown of the system's energy. On the left you will find the Nameplate Capacity (AC) at the point of interconnection. Below there is the Equipment Capacity as written in the data sheet. Both numbers will help you to put the donut chart on the right into perspective:

The total installed DC energy is split into the following segments:

• Usable Energy: Available immediately.

• Recoverable Energy: Requires action to restore, such as balancing or repairs.

• Missing Data: Missing Data implicates no data is available for that component in that time range. It should be investigated if there is an issue with the data ingestion or input sensors are missing.

• Energy Loss due to Aging: Represents energy loss due to degradation and cannot be recovered. For more insights about the storage degradation, head over to Health.

Energy at point of interconnection

This section provides you with an indication what amount of energy is required to charge the system and what amount can be used when discharging the system at the point of interconnection (AC). The starting point is always the Usable Energy in the middle. By adding the charging losses (based on Round Trip Efficiency if available, otherwise 5% each by default) you are provided with a higher energy amount for the AC Charge Energy and a lower amount for the AC Discharge Energy.

Recoverable Energy and Financial Loss per cycle

On the right hand side you will see a summary of the recoverable energy as well as how it changed over the course of the month.

Next to it the financial loss per cycle will give you an indication of the daily extra potential revenue this system can gain once the energy has been fully recovered. If available for your market, this is based on a derived index requested from Modo Energy (read more).

AC Combiner and DC Combiner overview

The AC Combiner level overview on the left hand side is sorted according to amount of recoverable energy, i.e. the Ac Combiner at the top is the one with the highest amount of recoverable energy, which is AC Combiner 1 in the example. Click on any one to view a breakdown on the right-hand side to see root causes.

Click on any root cause to get a more detailed breakdown of the problem and recommended steps of action.

How we detect root causes?

Limiting cell

TWAICE analyzes 24 hours windows of data for every string. For every 24 hours window, a cell is classified as "limiting cell" if the following conditions were met:

• The string was operated below 30% SOC

• One specific cell represents the min_voltage location at least 80% of the time

  • while operating below 30% SOC

  • with a string voltage spread > 10mV

• This string has a median SOC spread > 10%

To reduce noise and further stabilize the detection, we consecutively apply a post-processing:

• A limiting cell needs to be detected within four out of the last seven 24h-windows during which this string was operated below 30% SOC

Imbalance

For the root cause "imbalance", there are three different SoC spread thresholds available. These are by default following the settings from the TWAICE Performance Imbalance section:

• Imbalances:

  • Monitor (NMC <5%/ LFP <10%)

  • Inspect (NMC <10%/ LFP <20%)

  • Balance (NMC >10%/ LFP >20%)

Each root cause threshold has its own recommendation with more details on what to do about it and explanations.

String / PCS Disconnected - Missing Data

A disconnected state is means the component (string or PCS module) is electrically isolated and cannot charge or discharge, therefore not actively contributing to the system's energy throughput.

Missing data means the platform does not have the necessary datapoints to determine the component’s state or calculate KPIs for that time range.

Please check out this help article for details: What do “Disconnected,” “Idle,” and “Missing Data” mean in TWAICE platform?

Conclusion

Usable and Recoverable Energy help you optimize performance by understanding what actions to take to regain lost energy, as well as providing a status overview of how much energy your system can currently deliver.

We hope you find these new features useful, and please reach to us with any feedback or questions.