Simple Job or Complex Engineering Discipline?

written by: Željko Rendulić, General manager at Duplico

Motivated by a recent visit to the ‘Green Energy’ fair, I felt the need to share observations that go beyond the glitter of impressive presentations and palpable enthusiasm. In conversations with exhibitors and visitors, it became clear that the complexity of battery energy storage systems (BESS) is often underestimated. A narrative of simplicity dominates: ‘You just need to request a change in energy consent, and everything is resolved, especially if there are no demands for an increase in connection power.’ A user, seduced by such simplicity, could easily make an investment decision without fully understanding its real implications. But is it really that easy?

Although the market is flooded with offers, and the regulatory path seems simple at first glance, the implementation of a battery system is anything but easy. It requires a multidisciplinary approach – from precise capacity calculations to in-depth knowledge of electrical engineering, automation, and information technologies, to continuous maintenance and, above all, compliance with safety standards and local grid rules. Therefore, it is important to remember: not everyone can sell a battery, as the implementation of a battery system is truly not a simple job. Here’s why.

1. Hidden Complexity Behind Energy Consent

Although obtaining energy consent is a necessary first step, it is just the tip of the iceberg. A series of key questions arise that are rarely mentioned at promotional booths:

Fire safety: What about the fire safety report?

Engineering calculations: Who is responsible for protection calculations, sizing of cable and conductor cross-sections, and ensuring selectivity in accordance with the HRN HD 60364 standard?

Power quality: How is electromagnetic compatibility managed, as well as the compensation and removal of higher harmonics, which are an inevitable consequence of installing battery inverters?

A battery system is not just a ‘box’ that connects to the grid. It is a complex electrochemical and electrical system whose implementation requires in-depth engineering knowledge and adherence to strict safety standards, such as HRN EN IEC 62619:2022. This standard defines everything from minimum distances and fire barriers to fire extinguishing systems, ventilation, and emergency plans.

2. Energy Potential: Comparison of a 500 kWh Battery and TNT

To illustrate the enormous energy potential hidden in batteries, let’s make a comparison. What is the energy equivalent in kilograms of TNT for a 500 kWh battery system?

Although there are several methods for calculation, one of the most commonly used is based on the total stored energy. While it does not take into account the efficiency of conversion to explosion, it provides a good idea of the order of magnitude.

Calculation method:

Conversion of battery capacity from kWh to Megajoules (MJ):
Energy (MJ) = Energy (kWh) x 3.6
Calculation of TNT equivalent:
TNT equivalent (kg) = Energy (MJ)/4.184 MJ/kg (where 4.184 MJ/kg is the approximate energy density of TNT)

Calculation for a 500 kWh system:
500 kWh x 3.6 = 1,800 MJ
1,800 MJ/4.184 MJ/kg ≈ 430 kg of TNT

More realistic estimates, which take into account that only part of the energy is released explosively during uncontrolled thermal runaway, suggest 50 to 100 kg of TNT equivalent. Even with such a conservative estimate, we are talking about a huge amount of energy concentrated in a small space, which requires the highest level of safety measures.

3. Importance of Continuous Maintenance

Once installed, a battery system is not a ‘install and forget’ solution. Continuous and professional maintenance is crucial for its longevity, safety, and optimal operation. The reasons are manifold:

Safety: Regular inspections identify and eliminate potential risks such as loose connections, insulation damage, or cooling system issues, which can lead to overheating and thermal runaway.

Performance: Monitoring the state of health (SOH) of battery cells ensures that the system delivers the declared capacity and power. Battery degradation is inevitable, but with proper management, it can be significantly slowed down.

Reliability: Software maintenance, including security patches and updates to management algorithms, ensures that the system operates efficiently and is resilient to external threats.

Warranty: Equipment manufacturers often condition the validity of the warranty on regular and certified maintenance.

Neglecting maintenance not only reduces the return on investment but directly jeopardizes the safety of people and property.

4. Operating Modes of Battery Systems

Battery systems can operate in multiple operational modes, depending on user goals, the energy profile of the facility, and market conditions. The most common models are:

Arbitrage model: The battery system charges during periods of lower energy prices (at night), and energy is used during the more expensive part of the day. This model is applied in facilities with a pronounced difference between lower and higher tariffs.

Charging excess from a photovoltaic power plant: The battery takes energy from the photovoltaic power plant when current production exceeds the internal consumption of the facility. It is used to increase self-consumption and reduce energy draw from the grid.

Peak shaving: The battery is activated only at times when consumption would exceed a defined power threshold. It is applied in operations with large short-term loads or where peak power is a significant cost.

Combination of multiple operating modes: An advanced energy management system (EMS) makes real-time decisions about charging, discharging, or idling the battery. The EMS processes data on consumption, production, tariffs, and grid constraints and optimizes system operation within defined technical parameters.

5. Specific Requirements of Microgrids

When a battery system becomes part of a microgrid (a local energy network that can operate independently of the main grid), the complexity exponentially increases. A microgrid requires a sophisticated EMS that balances production from various sources (solar, wind), consumption, and battery status in real-time. Ensuring voltage and frequency stability is an extremely demanding engineering task.

6. Software: The Brain of Cloud Operations

Particular attention should be paid to the software that manages the operation of the system. Often, these are advanced platforms based on artificial intelligence (AI) and machine learning, executed on cloud servers located in distant countries. This raises a number of serious questions:

Cybersecurity: Who protects the system from hacking attacks and unauthorized control over the energy infrastructure?

Latency: Can delays in communication with a remote server jeopardize the stability of the microgrid in critical milliseconds?

Reliability and dependency: What happens in the event of a service interruption from the cloud service provider or loss of internet connection?

Data sovereignty: Who owns sensitive data about energy production and consumption, and who has access to it?

Relying on critical infrastructure whose ‘brain’ is located outside national jurisdiction is a strategic risk that should not be overlooked.

7. Starting Point: Capacity Calculation and Return on Investment Analysis

Before any purchasing decision, the absolute starting point of any project must be a detailed calculation of the required capacity and a return on investment (ROI) analysis. Purchasing an oversized battery means unnecessarily locked capital, while an undersized battery will not meet expectations and energy needs.

For this purpose, specialized software tools have been developed that allow precise optimization of the battery system. Based on 15-minute consumption readings, such tools model system operation and find the optimal battery size that will ensure the fastest return on investment and maximum savings. The development of such software requires significant engagement from engineering teams with extensive experience in energy systems.

8. Specificities of the Croatian Market

Here we come to a key difference. Products coming from countries with different energy systems, billing models, and energy prices simply cannot function effectively in our grid environment without adaptation. Manufacturers offer hardware that meets general standards, but not necessarily the specific rules of grid operators (HOPS, HEP ODS). These rules are known exclusively by experienced designers and companies in Croatia that deal with this issue.

A battery is not the same as a solar power plant. Although photovoltaic systems have also become widely available, their interaction with the grid is simpler. A battery system is an active element of the grid that requires in-depth integration and programming in accordance with local rules. This is a job for experts.

Text created in collaboration with Duplico