Energy storage in enterprises – key parameters from 100 kW

Electricity energy storage systems are becoming a permanent element of both daily life and businesses for an increasing number of Poles. In 2024, energy storage systems with a total capacity of 1317 kW were installed in domestic installations (20 kW or smaller), and in commercial installations with a total capacity of 2792 kW. According to forecasts by EUPD Research and the Polish Energy Storage Association (PSME), in the years 2026–2028, Poland will experience a real boom in the use of energy storage technology, and its market, depending on the forecast source, will grow during this period with a dynamics from 34% to 293% year-on-year.

The largest increase in the cumulative capacity of energy storage systems in our country will occur in the next two years. Due to the growing popularity and interest of the business sector in LFP technology energy storage, this article will advise you on what to pay special attention to when choosing the optimal solution for your company.

System Efficiency

In enterprise energy storage systems, PCS efficiency determines real savings. Higher efficiency means lower ESS lifecycle costs.

The two most important components of energy storage systems (ESS) are: (1) the energy storage, consisting primarily of battery cells where energy is accumulated with a specific capacity expressed in Wh (watt-hours), and (2) the PCS (bidirectional inverter), which determines the charging and discharging power of the energy storage, expressed in W (watts). The efficiency of the entire all-in-one ESS depends mainly on the latter. This is a key parameter determining the profitability of using this technology in an enterprise.

For example, an energy storage system with an efficiency of 88% (the standard on the Polish market) will allow you to use 88 kWh of electricity out of 100 kWh used for charging/discharging. If we compare an ESS with such efficiency to the S3-EStore solution from Kehua (one of the largest manufacturers of inverters and UPS systems in the world), where this parameter is 90.2%, we can easily calculate that for every 100 kWh used for charging and discharging the energy storage, we will save 2.2 kWh. Considering that the lifecycle of this model, according to the manufacturer's information, will be at least 1,300,000 kWh, thanks to higher efficiency, we will save a total of 28,600 kWh.

Converting this result into PLN and assuming the price of electricity (active energy plus energy distribution) at PLN 0.9/kWh net, we will achieve savings of PLN 25,740.00 net over the minimum product lifespan (excluding inflation/electricity price increases).

Battery Cell Technology

Enterprise energy storage systems based on modern LFP cells (≥304 Ah) ensure longer lifespan and stable parameters.

Most of the most popular all-in-one energy storage systems use prismatic battery cells made with LFP (lithium iron phosphate) technology. However, the energy accumulation density, expressed in Wh/kg (watt-hours per kilogram), is fundamental, which can often be indirectly assessed by the capacity of a single cell. This value can also indicate the battery's manufacturing technology.

Older energy storage systems used cells with a capacity of up to 245 Ah and a density below 160 Wh/kg; until recently, the standard was a capacity of 280 Ah and a density of about 165 Wh/kg, while the latest solutions have a capacity of at least 304 Ah and a density above 175 Wh/kg. For the buyer of an energy storage system, the most important information is that the newer the battery cell technology, the longer their lifespan. For example, the lifecycle of two-hour energy storage systems with 280 Ah batteries, with a depth of discharge up to 80% and a temperature of 25°C, is most often specified by manufacturers at 6000 charge and discharge cycles, while with 314 Ah batteries – 7000–8000 cycles, even with a greater depth of discharge of 90%.

Therefore, an ESS with cells with an energy density above 175 Wh/kg can serve its owner up to 50% longer compared to a solution with 280 Ah batteries. There is no point in comparing with older technologies – they are completely outclassed.

Cooling System

For enterprise energy storage systems, liquid cooling maintains a uniform temperature of the packs and extends battery life.

According to the information above, battery cell manufacturers make the number of charge and discharge cycles over the product's lifespan dependent on temperature. To achieve the longest battery durability, the temperature of their immediate surroundings should be maintained at 25°C. Any deviation upwards or downwards causes a change in the rate of capacity degradation. It is very important to maintain the most uniform temperature of all batteries to ensure their even degradation, which is extremely problematic with air cooling.

Therefore, liquid cooling is used in most technologically advanced energy storage systems, which maintains a uniform temperature and humidity across all battery packs, positively and significantly affecting the lifespan of the cells.

Warranty

For enterprise energy storage systems, two warranties count: product and capacity – check the terms and production date.

Two types of warranties are granted for energy storage systems: (1) product warranty and (2) capacity warranty over the lifecycle. The first is more general, as it concerns the operation of individual ESS components and usually ranges from 3 to 5 years, with the option of extension up to 10 years. However, the production date is crucial, as the warranty period is most often calculated from it. The guaranteed usable capacity over the lifecycle is much more varied, both in terms of the value expressed in kWh and the criteria that the energy storage system user must meet. Therefore, I recommend conducting a thorough analysis of the warranty conditions of the considered ESS model.

Manufacturer

When choosing enterprise energy storage systems, verify the manufacturer's credibility (Tier 1, history, production capacity).

Above, I wrote that product and battery capacity warranties can be issued for up to 10 years, but the fundamental issue determining whether we can use such warranties will be whether the manufacturer of the purchased ESS will exist until the end of that period. "Manufacturers" (in quotes, as many companies self-proclaim this label, and in practice, such entities should be called assemblers or even OEM sellers) have been springing up worldwide like mushrooms after rain in recent years. Therefore, it is increasingly difficult to distinguish the wheat from the chaff in the energy storage market, and a wrong choice can mean that we have obtained a warranty only "on paper."

To protect ourselves from purchasing products of dubious origin, we can, for example, trace the company's history, information about production facilities, or order a report from a business intelligence agency. In this context, Bloomberg New Energy Finance also comes to our aid, which, among other things, creates a ranking of the most financially reliable energy storage manufacturers. Those with the highest stability are included in the Tier 1 ranking.

The information about who produced the battery cells used in the ESS is also significant. Among the largest manufacturers in the world are CATL, LG Energy Solution, Panasonic, BYD, EVE Energy, which have the most modern production lines. They are the ultimate guarantors of the number of cycles and the total usable capacity over the battery's lifespan.

Certification

Enterprise energy storage systems must comply with Polish standards and NC RfG – check the PTPiREE list instead of relying on declarations.

An energy storage system that we intend to use in a facility connected to the power grid must have full certification for the Polish market. Unfortunately, documents confirming compliance with the obligations arising from European Union directives, including the CE declaration of conformity, are not sufficient for this purpose. The energy company, before issuing connection conditions, will require the ESS buyer to present documents confirming compliance with the requirements of Polish industry standards and the NC RfG regulation.

A publicly available list of devices meeting the criteria of Distribution System Operators (DSOs) is maintained by the Polish Society of Transmission and Distribution of Electric Energy (PTPiREE). With all my sympathy for the specialists from the Far East, I would advise my compatriots to exercise caution regarding their assurances of full certification, as I myself received such promises from many "manufacturers" of energy storage systems at industry trade fairs in Nadarzyn and ENEX in Kielce, and in many cases, it turned out that full certification was lacking.

What's more interesting, according to the words or emails of the sellers, the missing documents were supposed to be issued "any moment now," but in most cases, I did not receive them by the time of writing this article.

Safety

For enterprise energy storage systems, IP, fire protection, extinguishing system, and anomaly monitoring at the cell level are crucial.

The applied safety systems and the protection degrees of individual system components are also very important aspects. When choosing an energy storage system, we should check whether the device is intended for outdoor or indoor installation, which is indicated by the IP protection rating. Due to the need for intensive air exchange and imprecise fire regulations, installing an ESS inside a building can be problematic at best.

A separate article could be written about safety systems – in this publication, I will limit myself to what I consider the most important, which include: operational monitoring with alert dispatch in case of anomaly detection at the level of each ESS component; sealed battery cell enclosures; explosion protection; extinguishing system (e.g., aerosol).

Emergency Power Supply

Enterprise energy storage systems with islanding functionality require STS and adequate capacity – this is the condition for real backup.

All-in-one energy storage systems in most cases do not provide emergency power supply functionality without additional accessories. To switch the ESS to islanding operation (independent of the power grid), we will need at least a Static Transfer Switch (STS), which automatically switches power sources in case of voltage loss in the main source. An energy storage system equipped with an STS, due to its significantly shorter switching time compared to a generator set, can successfully replace or supplement a company's emergency power supply system.

However, we must remember that the usable capacity of the energy storage will be the decisive parameter – it will answer the question of how long the ESS will maintain power without support from another source. Additionally, I would like to emphasize that STS and similar devices require separate certification.

Energy Management System

Effective enterprise energy storage systems need EMS (not to be confused with BMS) to generate financial benefits and meet EU requirements.

Most manufacturers state that the devices they sell have a built-in EMS (Energy Management System), but unfortunately, it usually turns out to be just a simple application for controlling the energy storage system with a specific charging or discharging power. There are also cases where a manufacturer's representative confirms that their solution uses an energy management system, but it turns out to be a BMS (Battery Management System).

This is also a very important system whose role is to manage energy within the energy storage (e.g., the state of charge of individual battery cells or the voltage at the connections). BMS is implemented in all LFP cell energy storage systems known to me, but it does not allow controlling the ESS in a way that generates financial benefits for its owner. EMS is used for this purpose. Manufacturers of storage systems and software providers from outside the European Union with their own energy management system often cannot use it within the EU due to legal restrictions.

The transposition of NIS2/CER and the requirements of TSO/DSO raise the bar significantly (tests, audits, local access, SLA, event logging, vulnerability management), RED-cyber and CRA add design obligations, and Regulation 2019/1020 requires an "economic operator" in the EU. Therefore, the owner of an energy storage system will face a choice mainly between local EMS providers, including software provided by Technius EMS, the company I represent.

Selection

Summarizing the criteria simplifies the selection of an energy storage system for an enterprise – efficiency, cells, cooling, warranties, certification, and EMS.

After analyzing all the above criteria based on several product data sheets for energy storage systems with a capacity of 100–500 kW, our choice fell on the S³-EStore, manufactured by Kehua Tech, because:

1. According to information provided by the manufacturer, the efficiency of the S³-EStore is 90.2%, making it the king of efficiency among energy storage systems.
2. The latest model uses prismatic battery cells with a capacity of 314 Ah, manufactured by EVE Energy Co., Ltd. (one of the largest and most technologically advanced battery manufacturers in the world).
3. The liquid cooling system with a control system for battery pack parameters contributes to more stable and efficient system operation and slower, uniform cell degradation.
4. The product warranty for Kehua's S³-EStore is 5.5 years from the production date as standard, with the option to extend the warranty to 10 years at a reasonable price. The usable capacity warranty over the minimum device lifespan is 1.3 GWh or 8000 cycles.
5. Xiamen Kehua Digital Energy Tech Co., Ltd. is a world-renowned manufacturer of PCS, UPS, and photovoltaic inverters, among others, with over 37 years of history, employing over 2000 engineers.
6. Kehua has full certification for its solutions, and the S³-EStore is listed as a device meeting DSO criteria maintained by PTPiREE.
7. The S³-EStore is equipped with a 2-stage fire protection system with an aerosol extinguishing system, 3-stage explosion protection, and an advanced BMS system with ground fault detection and leak detection. Furthermore, tens of thousands of S³-EStore units have been installed worldwide, and according to the manufacturer, there have been no fire hazard situations – all safety measures and preventive actions have worked correctly.
8. Thanks to the use of an on/off-grid switching cabinet of 200–1000 kVA, manufactured by Kehua, and the possibility of connecting up to 5 S³-EStore units, an energy storage system with an emergency power supply function from 100 kW to 500 kW can be built.
9. Kehua's extensive Modbus protocol allowed us to successfully integrate our Technius EMS energy management system and achieve savings in energy and power costs from the first day of our software installation.

I will discuss the significance of the parameters described in this article in the practical use of energy storage systems in more detail during my lecture, which I will give on November 28 at Hotel Uroczysko in Cedzyna as part of the ESS/EMS Conference, dedicated, among other things, to the practical aspects of using energy storage in business, including a discussion of implemented investments in all-in-one energy storage systems for business energy consumers.

Representatives of enterprises and auditing, sales, and installation companies who are interested are encouraged to contact me at the following email address: konferencja@pcde.pl.