Delivering net-zero carbon heat: What’s best for homeowners and the energy system?

Proposed sustainable transition pathways for moving away from natural gas in domestic heating focus on two main energy vectors: electricity and hydrogen. Electrification would be implemented using vapour-compression heat pumps, while hydrogen could substitute natural gas in boilers or be used in thermally–driven absorption heat pumps. Researchers on the IDLES Programme at Imperial College London have developed a consistent thermodynamic and economic methodology to assess the competitiveness of these options. In a new paper published in Energy Conversion and Management, the three technologies, along with the option of district heating, are for the first time compared for different weather/ambient conditions and fuel-price scenarios, first from a homeowner’s and then from a whole-energy system perspective. Here, the authors explain the research and its findings.

Andreas V. Olympios1, Marko Aunedi2, Matthias Mersch1,3, Aniruddh Krishnaswamy1, Corinne Stollery1, Antonio M. Pantaleo1,4, Paul Sapin1, Goran Strbac2, Christos N. Markides1*.

What is the motivation behind this research?

Many economies around the world have committed to net-zero carbon emissions by 2050. Despite recent advancements in renewable energy generation, when it comes to heating, there are still many challenges and a lack of a clear strategy. Currently, domestic heating is dominated by fossil fuel technologies. The main technologies that are being proposed to replace fossil-fuel-based systems are electric heat pumps and hydrogen boilers, which are locally carbon-neutral technologies.

Why is this work valuable?

The paper provides insights into the potential of currently proposed domestic heating options and into the key technoeconomic factors that influence their competitiveness in the context of heating decarbonisation. A comparison from both homeowners’ and a whole-energy system perspectives was conducted and provides evidence to support both technology advancement and energy policy.

What is new in this paper compared to previous work?

Although the concepts of electrification and hydrogen in the context of heat decarbonisation have been explored in the past, a comprehensive technoeconomic comparison of domestic electrical- and hydrogen-driven heating technologies that captures how their performance and cost depend on their design and operation, has not been presented in the literature thus far. Furthermore, to the best of the authors’ knowledge, the potential of absorption heat pumps has never been explored using comprehensive design and costing methods in the context of heating decarbonisation.

In the paper, comprehensive thermodynamic and component-costing models of a domestic electric heat pump, an absorption heat pump driven by heat from a hydrogen boiler, and of a standalone hydrogen boiler were developed. Using an average UK household as a case study, the technologies were sized and costed using a framework of consistent modelling approaches and assumptions. Along with the option of district heating (DH), the competitiveness of the different options was first assessed for various electricity, hydrogen and DH prices from a homeowner’s perspective. Then, the developed models were used to provide inputs to a whole-energy system model of the UK, which was used to investigate the effects of the uptake of these technologies on the energy system transition cost and technology mix.

Schematic diagram of investigated electric and hydrogen-driven domestic heating options. A wide uptake of each of these options would require drastic and different changes to the country’s energy system technology mix.

Collaboration between IDLES Projects 1 and 2

This work is part of the EPSRC-funded IDLES Programme and involved a collaboration between the programme’s Projects 1 and 2. The comparison of heating technologies from both a homeowner’s and from a whole-energy-system perspective required expertise at various levels (technology, system, policy) and IDLES was the best grouping to provide this unique contribution. Project 1 involves the central, whole-energy-system modelling framework, which was used to investigate the effects of the uptake of different heating technologies on the energy system transition cost and technology mix. Project 2 involves the development of comprehensive thermodynamic and costing models of heating technologies and their comparison from a homeowner’s perspective.

What are the key findings?

From a homeowner’s perspective, electric heat pumps were found to be the most competitive technology in most electricity and hydrogen price scenarios. For an electricity price for domestic consumers close to 0.20 £/kWh, absorption heat pumps and hydrogen boilers become competitive for hydrogen prices below about 0.10 £/kWh. Therefore, if electricity prices in the UK do not significantly drop in the future, the competitiveness of hydrogen technologies will depend on the ability to produce hydrogen cost-effectively. In the case that DH is an additional option for homeowners, this was shown to be the best option if heat can be supplied at a price lower than 0.10 £/kWh.

From the whole-energy system’s perspective, it was shown that the total system cost per household (which accounts for upstream generation and storage, as well as technology investment, installation and maintenance) associated with electric heat pumps is in the range 790-880 £/year for different system scenarios, meaning that electric heat pumps are the lowest-cost decarbonisation pathway. Assuming hydrogen is produced by electrolysis, the total system cost associated with hydrogen boilers or absorption heat pumps will be significantly higher, at 1410-1880 £/year. However, if hydrogen can be produced cost effectively (e.g., by ATR with CCS), the system cost drops to 1150 £/year, reducing the gap between the two technologies. Furthermore, it was shown that when considering total system transition costs, hydrogen-driven absorption heat pumps are a competitive alternative to hydrogen boilers in all hydrogen-pathway scenarios.

Comparison of electric heat pump, hydrogen-driven absorption heat pump and standalone hydrogen boiler for different electricity and hydrogen household prices based on annual total (investment, operational and maintenance) cost. Horizontal and vertical lines represent the estimated retail prices of carbon-neutral hydrogen from different sources and the current electricity price in the UK, respectively.
Total system transition cost to decarbonise the UK domestic heating sector by 2035 when heat is delivered through: (i) electric heat pumps (EHPs); (ii) hydrogen-driven absorption heat pumps (AHPs); or (iii) standalone hydrogen boilers (HBs), for six investigated scenarios. More details about the scenarios can be found in the paper.

Click here to read the paper in full.

 1 Clean Energy Processes (CEP) Laboratory and Centre for Process Systems Engineering (CPSE), Department of Chemical Engineering, Imperial College London, London SW7 2AZ, UK

2 Department of Electrical and Electronic Engineering, Imperial College London, London SW7 2AZ, UK

3 Centre for Environmental Policy, Imperial College London, London SW7 2AZ, UK

4 Department of Agro-environmental Sciences, University of Bari, 70121 Bari, Italy

* Corresponding author. Tel.: +44 (0)20 759 41601. E-mail: c.markides@imperial.ac.uk

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