Three Energy Forms, One Roof

BY ROBERTA PRANDI

MAN Energy Solutions Switzerland Ltd. and ABB Switzerland are collaborating on a new three-way energy storage system. The pair signed a cooperation agreement to develop, produce and commercialize the Electro-Thermal Energy Storage system (ETES), which is designed to storage massive quantities of electricity, heat and cold for customer distribution.

“ETES is the only storage system able to store electricity, heat and cold at the same time and also distribute them to consumers, which makes it unique,” said MAN Energy Solutions Schweiz AG‘s Managing Director Hans Gut.

Turbomachinery technology and thermodynamic cycles are at the core of the system. As dictated by the agreement, MAN will supply the complete system for the ETES, including an HOFIM compressor, an oil-free barrel type compressor with integrated high-speed induction motor, and active magnetic bearings.

ABB will provide its expertise on the electrical side, with the power transmission from the grid into the system and the reverse process. MAN will manage the commercialization of the system.

The ETES is location independent and able to fit a variety of applications. For example, the system could provide heat for the food-processing industry or laundry facilities, and cold for data centers or air conditioning for multi-level buildings, according to MAN.

Patrik Meli, MAN Energy Solutions’ vice president, head of compressor engineering, said MAN and ABB wanted a system that went beyond basic energy storage.

“This is not just a storage system, but an energy management system,” he said. “We realized early enough that having a system only able to store electricity would have hardly been commercially viable – at least not in those areas where the price of electricity is on the low side. Thus we decided to stop thinking only in terms of electricity-in and electricity-out and expand the concept to heat and cold as well.”

Technical Project Manager Emmanuel Jacquemoud said the ETES can store energy from any source, but it is optimized for renewable sources as it can balance their fluctuating nature. The system is based on the thermal storage of energy and works with two basic processes: charging and discharging.

“Charging is a typical heat-pump process, in which surplus electricity is taken from the grid to power the oil-free HOFIM compressor and is there turned into thermal energy by compressing CO₂ to its supercritical liquid state (typically about 212/248°F [100/120°C] and 2030.5 psi [140 bar]),” Jacquemoud said. “The CO₂ is then fed into a high performing heat exchanger and heats the storage medium – water – which is then stored in tanks.”

After the heat transfer ends, the CO₂, which is still at high pressure, passes into an expander to lower the pressure, which liquefies and cools the substance. This cold energy is then transferred through another heat exchanger to the cold storage side, where water is frozen to 32°F (0°C) and stored in a tank in the form of ice.

Jacquemoud said the hot water on the heat side can be maintained for several days, although the typical charge/discharge cycle for the system runs once or twice a day.

“The discharging process actually works the same way, with thermal energy brought back into the system, this time not into the compressor but into an electrically-driven liquid pump,” Jacquemoud said. “The gaseous CO₂ is brought through another heat exchanger and condensed thanks to the cold from the ice tank. The liquid pump then increases the CO₂ pressure and feeds it into the heat exchanger to be heated up again by the hot water in the hot-side tanks. This thermal energy can be fed into a power turbine to generate again electricity for the grid supply.

“To complete the loop, the heated CO₂ is condensed into its liquid form at low temperature and low pressure, so that it is ready for another cycle,” he said.

The ideal size for the ETES system is about 5 to 15 MW electrical power, Jacquemoud said. The system has a five times higher energy density compared to a conventional steam turbine. The system is also modular and flexible, allowing for adjustments to fit the customer’s needs. For example, a customer could request an ETES system with larger tanks, he said.

The ETES is optimized for three energy outputs, but can be used in data centers, which require two outputs for electricity and cold, Jacquemoud said. The ETES creates an interesting opportunity for data centers, especially when most of them are popping up in urban areas, Meli said.

“Data centers are currently responsible for 3% of the global CO₂ emissions and, being located into the cities, they are under a lot of pressure to reduce their emissions and become CO₂ neutral,” he said. “In the application case of data centers, ETES makes it possible for the customer to get rid of engine-powered gen-sets but to keep batteries to guarantee the fast reaction times – in the order of milliseconds – for a reliable, uninterrupted power supply.

“In the case of data centers, the system can be made more profitable by adopting the three-way energy storage and deliver heat to external customers,” Meli said. “In industrial or urban areas, these customers could be utilities for district heating, process industries, food processing or large industrial laundries.

Asia and Europe are the primary markets for ETES. MAN Energy Solutions expects to sell the first ETES application within 24 months, with MAN associates already discussing the first project.