Combined heat and power plants in decarbonized energy systems: Techno-economics of carbon capture and flexibility services at the plant, city and regional levels
Doctoral thesis, 2022

Our present energy system is the main driver of climate change. Variable renewable electricity generation and carbon dioxide removal (CDR) are key technologies in the transformation to a sustainable energy system, but their broad implementation implies challenges related to energy system flexibility and energy requirements of CDR technologies. The aim of this thesis is to investigate the potential and incentives for combined heat and power (CHP) plants in Sweden to contribute with CDR and flexibility services in the energy system. A techno-economic assessment scheme that considers variability in boundary conditions, such as electricity prices, and includes the CHP plant, city, and regional energy system levels is developed and applied. System optimization modeling and process-level case studies are performed to investigate how CHP plant flexibility measures are utilized and valued, and to estimate the cost and potential of CDR from Swedish CHP plants.

The results indicate a large potential for Swedish CHP plants to contribute to CDR, with at least 10 MtCO2/year being available for capture and storage. The realizability of this potential is challenged by the cost of carbon capture which increases notably for CHP plants that are small and have few full load hours. CHP plants can cost-effectively contribute with flexibility provision in the studied electricity system, although the impact on the total system is limited, as the installed capacity of CHP plants is small relative to the magnitude of net load variability. From a plant perspective, the plant revenue can increase if the operation is scheduled to follow electricity price variability, but this requires a significant level of price volatility and access to large-scale thermal energy storage for maximum benefit. The fuel price has a strong impact on the competitiveness of biomass-fired CHP plants on a regional level, that compete with power-to-heat technologies in the district heating sector. In contrast, in cities, there are stronger incentives for CHP plants as heat producers regardless of how the surrounding energy system and market prices develop, due to a limited availability of other technology options and a limited grid connection capacity to drive power-to-heat.

Negative emissions



District heating

Energy system modeling

Combined heat and power

Techno-economic assessment

On campus: Sal KC, Kemigården 4, Göteborg. Online: zoom-link below (password: CHPflex)
Opponent: Professor Niall Mac Dowell, Imperial College London, UK


Johanna Beiron

Chalmers, Space, Earth and Environment, Energy Technology

Kraftvärmeverk för framtidens energisystem
Kraftvärmeverk har sedan 1950-talet varit en viktig del av Sveriges energisystem, genom att samproducera el och fjärrvärme för uppvärmning av bostäder. I omställningen av energisystemet mot minskad klimatpåverkan finns fler funktioner som med fördel skulle kunna samordnas, t.ex. koldioxidinfångning och flexibilitetstjänster. Avhandlingen undersöker kraftvärmeverkens potential att bidra med dessa tjänster.

Sveriges kraftvärmeverk förbränner avfall och rester från skogsindustrin som genererar biogena koldioxidutsläpp. Genom att fånga in och permanent lagra denna koldioxid kan så kallade negativa utsläpp skapas, dvs, kraftvärmeverken skulle bidra till att sänka mängden koldioxid i atmosfären. Avhandlingen visar att samordning med el/värmeproduktion möjliggör infångning av 11-17 MtonCO2/år till en maximal kostnad av 100 €/ton (exkl. transport och lagring), vilket motsvarar ca 25-40% av Sveriges fossila koldioxidutsläpp.

I elsystemet förväntas andelen väderberoende elproduktion (vind- och solkraft) öka kraftigt. Flexibilitetstjänster behövs då i ökad utsträckning för att balansera tillgång och efterfrågan på el, t.ex. kraftvärmeverk som producerar el när det inte blåser. Resultaten visar att kraftvärmeverk kan bidra med flexibilitet i elsystemet på ett kostnadseffektivt sätt, men kraftvärmeverkens inverkan på det totala systemet blir liten då fjärrvärmebehovet är litet i förhållande till elsystemets storlek. Enskilda anläggningar kan däremot tjäna på flexibel drift genom att anpassa sin produktion efter elprisvariationer.

Combined heat and power plants for the future energy system
Combined heat and power (CHP) plants have since the 1950s been an important part of the Swedish energy system, by coproducing electricity and district heating for heating of buildings. In the transition to an energy system with reduced climate impact, there are additional functions that could be advantageous to coordinate, e.g., the capture and storage of carbon dioxide (CO2) and flexibility services. The thesis investigates the potential for CHP plants to contribute with these services.

Swedish CHP plants combust waste and residues from the forest industry, which generates biogenic CO2 emissions. By capturing and permanently storing the CO2, so called negative emissions can be achieved, i.e., the CHP plants would contribute to a lowering of the amount of CO2 in the atmosphere. The thesis shows that coordination with electricity/heat production enables the capture of 11-17 MtCO2/year to a maximum cost of 100 €/tCO2 (excl. transport and storage), which corresponds to 25-40% of Sweden's fossil CO2 emissions. 

The share of weather-dependent electricity generation (wind and solar power) is increasing strongly in the electricity system. Flexibility services are needed to balance the supply and demand for electricity, e.g., CHP plants that produce electricity when there is no wind. The results indicate that CHP plants can cost-effectively contribute to electricity system flexibility, although the impact of CHP plant operation on the total system is limited, since the district heating demand is small in relation to the electricity system. Individual plants might, however, benefit from flexible operation by scheduling the production to match electricity price variations.

Flexible Combined heat and power plants for power systems with volatile electricity prices

Swedish Energy Agency (S44910), 2017-10-01 -- 2020-11-01.

Subject Categories

Energy Engineering

Energy Systems

Areas of Advance




Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5177



On campus: Sal KC, Kemigården 4, Göteborg. Online: zoom-link below (password: CHPflex)


Opponent: Professor Niall Mac Dowell, Imperial College London, UK

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