Sigenergy debuts large-scale Bulgarian energy storage project assembled from 240 kWh battery stacks

Sorting stationary battery energy storage systems (BESS) by size starts with the smallest, stack systems, progresses to cabinets, and culminates in containerized units.

A large container can offer up to 5 MWh of energy storage capacity and cabinets several hundred kilowatt-hours while stacks are chiefly used by homes and small businesses.

While multiple BESS can be combined, smaller types have rarely been used to offer the capacity of systems the next size up – until now.

Chinese company Sigenergy has launched the SigenStack stackable system, based on the smallest size of stationary BESS.

The Shanghai-based manufacturer has installed 90 SigenStacks at a solar project in Malko Tarnovo, Bulgaria, near the Turkish border. Each unit features a 110 kW hybrid inverter, battery managment system, and five battery stacks. Each stack offers 12 kWh of energy storage capacity and there are four in each SigenStack unit, for a 10 MW/20 MWh total system capacity at the Bulgarian site.

Sigenergy, founded three years ago, says a maximum 100 parallel SigenStacks can be combined.

Galina Peycheva-Miteva, head of family-run company Trakia-MT, owns the 11 MW solar park where the Sigenergy system has been installed and ordered the innovative set-up despite only prototypes having been used at that stage.

Sigenergy’s Sigenstor home BESS product, by contrast, is popular in Germany.

Ten-day assembly

The grid-scale BESS was installed by five workers, using a forklift truck, in just 10 days, helped by Sigenergy sending Trakia a mock-up of the system for installation planning. Commissioning the system, expected to last two days, “took only 20 minutes,” said Peycheva-Miteva.

Roy Zhang, Sigenergy’s head of global sales and solutions, said the direct-current (DC)-coupled system offers solar-power-storage round-trip efficiency two percentage points higher than that of alternating-current (AC)-coupled systems, as are used in containerized batteries. The DC system also eliminates the need for an AC combiner and a regular photovoltaic inverter, reducing the number of components versus container systems. The Sigenstack also requires no external data logger as one is integrated into the inverter, which also includes the energy management system (EMS).

With all components made by the same manufacturer, commissioning is a cinch, courtesy of automatic networking. Containerized batteries often feature devices from different manufacturers, Zhang said.

The sales executive, pointing to the regular maintenance needed for air conditioning systems, smoke detectors, air inlets, and battery modules in containerized systems, described the Sigenstack as “maintenance free.”

Better availability

Each Sigenstack stack contains temperature sensors and a small fan. A built-in smoke detector, fire extinguisher, and decompression valve are designed to contain any fire to one stack in the event of thermal runaway. Unit shell and insulation pads prevent stacks catching fire from the outside.

All stacks not directly affected by a blaze could continue to be used following a fire check by the company, Zhang said, and stacks can easily be replaced in the event of failure. That adds up to 99% system availability annually, compared to 11 months per year for containerized systems, according to Zhang.

With ever-larger containerized battery systems testing the limits of what can be transported in one go, separately-shipped energy storage modules require more cabling and site rework, Zhang said, including the use of cranes for installation, necessitating clearance from surrounding buildings.

Stacked systems are simpler to transport and install, even if they have a larger footprint once in place: The Bulgarian system occupies around 400 m².

The fact stacked systems could be installed near buildings makes them apt for commercial clients with limited space and Zhang said inverter noise is barely audible just a few meters away, even if it would be too loud directly below a window.

AI-powered trading

The large-scale BESS in Malko Tarnovo will trade electricity on the energy market. When grid electricity prices are low or negative, “we will stop the solar system and charge electricity from the grid,” said Peycheva-Miteva.

The inverter-integrated EMS will optimize BESS operation based on electricity prices, weather forecasts and the expected electricity load of commercial clients.

The Sigenstack can also offer grid balancing services, thanks to a 100 ms response time to grid requests. Zhang said a Sigenstack could be divided such that part of it offers grid services, and the balance energy trading.

The stackable BESS innovation could offer large-scale energy storage in commercial areas and would offer smaller installation companies a foothold in the large-scale business.

As a retrofitted option, or a standalone BESS built simply to back the grid, the returns would be smaller and investors would have to weigh the claimed year-round availability advantages, and variable distribution, versus a larger installed footprint and a price tag more expense than containerized alternatives.

From pv magazine Deutschland.

Energy storage case study: Bulgarian commercial and industrial project sets new deployment benchmark

On June 26, pv magazine will be offering a webinar, in English, on the Malko Tarnovo battery project. Jade Martyn, Africa sales director at Sigenergy, will present the project and we will discuss the possibilities for industrial and commercial storage with him and other guests.  More information and free registration for the event can be found here.