High-Temperature Heat Pumps - HTHP Symposium
High Temperature Heat Pump Symposium 2024, held in Copenhagen. Picture credit: Organizer of HTHP Symposium 2024

MAN’s Transcritical CO2 High-Temperature Heat Pumps Could Help Balance Power Grid Fluctuations, According to Study

Researchers found that a MAN CO2 high-temperature heat pump could reduce its electricity consumption by 7MW in just 30 seconds

A MAN Energy Solutions’ transcritical CO2 (R744) high-temperature heat pump (HTHP) has shown the ability to reduce its power consumption by up to 7MWel in 30 seconds, which could make it capable of balancing power grid fluctuations, according to a new study.

The study, “Grid Stability of a 30MW Transcritical CO2 Heat Pump From Experiment and Simulation,” was authored by Emmanuel Jacquemoud and Leonhard Wolscht and presented at the High-Temperature Heat Pump Symposium 2024 held in Copenhagen. The study sourced data from a MAN high-temperature heat pump tested in a laboratory.

The study identified two elements that made it possible for the MAN COHTHP to reduce its power consumption so drastically.

First, the heat pump employs a transcritical CO2 cycle that avoids phase changes in the high-pressure heat exchanger, which can cause operational challenges, such as choking or abrupt pressure drop changes, which can potentially destabilize the system. The transcritical CO2 cycle leverages CO2’s high density to facilitate the turbomachine’s rapid response. This is achieved by minimizing the mass that needs to be moved in the high-pressure section, thus reducing the system’s rotational inertia.

In addition, MAN has developed a high-speed oil-free integrated motor compressor that operates on magnetic bearings and uses a medium voltage variable-frequency drive for speed control, eliminating the need for mechanical gears. The design includes a levitated shaft, allowing quick power transitions without physical wear on the turbomachine, which enables it to adjust power output swiftly without diminishing its service life.

In rapidly reducing its power consumption, the MAN COHTHP is able to feed energy back into the power grid, acting as a frequency reserve in the event excess power is needed. Historically, these services were supplied by gas and steam turbines. However, as these fossil fuel-fired sources fade from the energy landscape, the study notes that the responsibility for maintaining grid stability will increasingly shift to electricity consumers, such as operators of high-temperature heat pumps.

As a primary reserve power balance, the facility operating the HTHP independently monitors the electricity grid’s frequency and responds immediately to any frequency deviations exceeding 0.05Hz by adjusting its output accordingly. The facility must prove it can achieve its maximum power adjustment within a 30-second timeframe to be eligible for this role. However, this adjustment in operation is temporary and typically does not exceed 15 minutes.

The business case

The study also presented a business case for heat pump operators with a hypothetical 12MWel heat pump with a heating capacity of more than 30MW (8,530TR). Designing the system to consume up to 16MW of electricity allows the operator to act as a primary reserve and provide up to 4MW of electricity to the grid on demand. The study notes that the facility could operate the heat pump continuously at 16MW of power consumption, thus enabling it to act as a primary reserve around the clock.

Under what the study calls an “optimistic scenario,” one where the power fed into the grid by the operator is purchased 100% of the time, and and there are 200 days of grid balancing operations per year, revenues could range from €500,000 to €655,200 ($540,612 to $708,418) annually. The operational cost for running a 12MW plant over 200 days is estimated to be approximately €5.7 million ($6.16 million), assuming an electricity cost of €100/MWh ($108/MWh). Hence, oversizing the heat pump to consume more power can potentially reduce the heat pump operator’s annual electricity costs by nearly 10%.

“There are additional grid services markets accessible for sophisticated heat pump technologies, such as intra-day trading, day-ahead market balancing energy markets, [which are] easily accessible for such kinds of dynamic technology,” the study said. “This may allow increased profitability of the presented theoretical or future business cases.”

“There are additional grid services markets accessible for sophisticated heat pump technologies, such as intra-day trading, day-ahead market balancing energy markets, [which are] easily accessible for such kinds of dynamic technology. This may allow increased profitability of the presented theoretical or future business cases.”

Research study from MAN Energy Solutions

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