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Power to gas: Bridging renewable electricity to the transport sector
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Energy Processes.
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Globally, transport accounts for a significant part of the total energy utilization and is heavily dominated by fossil fuels. The main challenge is how the greenhouse gas emissions in road transport can be addressed. Moreover, the use of fossil fuels in road transport makes most countries or regions dependent on those with oil and/or gas assets. With that said, the question arises of what can be done to reduce the levels of greenhouse gas emissions and furthermore reduce dependency on oil? One angle is to study what source of energy is used.

Biomass is considered to be an important energy contributor in future transport and has been a reliable energy source for a long time. However, it is commonly known that biomass alone cannot sustain the energy needs in the transport sector by far.

This work presents an alternative where renewable electricity could play a significant role in road transport within a relatively short time period. Today the amount of electricity used in road transport is negligible but has a potential to contribute substantially. It is suggested that the electricity should be stored, or “packaged” in a chemical manner, as a way of conserving the electrical energy. One way of doing so is to chemically synthesize fuels. It has been investigated how a fossil free transport system could be designed, to reach high levels of self-sufficiency. According to the studies, renewable electricity could have the single most important role in such a system.   

Among the synthetic fuels, synthetic methane (also called synthetic biogas) is the main focus of the thesis. Hydrogen is obtained through water electrolysis, driven by electricity (preferable renewable), and reacted with carbon dioxide to produce synthetic methane. The concept of the mentioned process goes under the name Power to Gas. The electricity to fuel efficiency of such a process reaches about 50 %, but if utilizing excess heat produced during the electrolysis and the reaction, the total process efficiency can reach much higher levels.

The economics of the process is as important as the technology itself in terms of large scale implementation. The price of electricity and biogas are the most important influences on the economic viability. The minimum “spread” between purchase and selling price can be determined to obtain a general perception of the economic feasibility. In this case biogas must be sold about 2.6 times higher than purchased electricity per kWh.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , v, 50 p.
Trita-CHE-Report, ISSN 1654-1081 ; 2013:2
Keyword [en]
transport, renewable electricity, synthetic fuels, energy, power to gas
National Category
Chemical Engineering Energy Engineering
URN: urn:nbn:se:kth:diva-111457ISBN: 978-91-7501-597-2OAI: diva2:586467
2013-01-14, Biblioteket/Seminarierummet, Teknikringen 42, plan 6, Stockholm, 13:00 (English)

QC 20130111

Available from: 2013-01-11 Created: 2013-01-11 Last updated: 2013-01-11Bibliographically approved
List of papers
1. Strategies for a road transport system based on renewable resources: The case of an import-independent Sweden in 2025
Open this publication in new window or tab >>Strategies for a road transport system based on renewable resources: The case of an import-independent Sweden in 2025
2010 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 87, no 6, 1836-1845 p.Article in journal (Refereed) Published
Abstract [en]

When discussing how society can decrease greenhouse gas emissions, the transport sector is often seen as posing one of the most difficult problems. In addition, the transport sector faces problems related to security of supply. The aim of this paper is to present possible strategies for a road transport system based on renewable energy sources and to illustrate how such a system could be designed to avoid dependency on imports, using Sweden as an example. The demand-side strategies considered include measures for decreasing the demand for transport, as well as various technical and non-technical means of improving vehicle fuel economy. On the supply side, biofuels and synthetic fuels produced from renewable electricity are discussed. Calculations are performed to ascertain the possible impact of these measures on the future Swedish road transport sector. The results underline the importance of powerful demand-side measures and show that although biofuels can certainly contribute significantly to an import-independent road transport sector, they are far from enough even in a biomass-rich country like Sweden. Instead, according to this study, fuels based on renewable electricity will have to cover more than half of the road transport sector's energy demand.

Road transport; Import-independent; Biofuel; Synthetic fuel; Demand-side strategies
National Category
Chemical Engineering
urn:nbn:se:kth:diva-9252 (URN)10.1016/j.apenergy.2010.02.011 (DOI)000278306300005 ()2-s2.0-77951091042 (ScopusID)
QC 20100823. Uppdaterad från submitted till published (20100823). Tidigare titel: Strategies for a road transport system based on renewable resources: the case of a self-sufficient Sweden in 2025Available from: 2008-10-13 Created: 2008-10-13 Last updated: 2013-01-11Bibliographically approved
2. Biogas from renewable electricity: Increasing a climate neutral fuel supply
Open this publication in new window or tab >>Biogas from renewable electricity: Increasing a climate neutral fuel supply
2012 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 90, no 1, 11-16 p.Article in journal (Refereed) Published
Abstract [en]

If considering the increased utilisation of renewable electricity during the last decade, it is realistic to assume that a significant part of future power production will originate from renewable sources. These are normally intermittent and would cause a fluctuating electricity production. A common suggestion for stabilising intermittent power in the grid is to produce hydrogen through water electrolysis thus storing the energy for later. It could work as an excellent load management tool to control the intermittency, due to its flexibility. In turn, hydrogen could be used as a fuel in transport if compressed or liquefied. However, since hydrogen is highly energy demanding to compress, and moreover, has relatively low energy content per volume it would be more beneficial to store the hydrogen chemically attached to carbon forming synthetic methane (i.e. biogas). This paper presents how biogas production from a given amount of biomass could be increased by addition of renewable electricity. Commonly biogas is produced through digestion of organic material. Recently also biomass gasification is gaining more attention and is under development. However, in both cases, a significant amount of carbon dioxide is produced as by-product which is subject for separation and disposal. To increase the biogas yield, the separated carbon dioxide (which is considered as climate neutral) could, instead of being seen as waste, be used as a component to produce additional methane through the well-known Sabatier reaction. In such process the carbon could act as hydrogen carrier of hydrogen originating from water electrolysis driven by renewable sources. In this study a base case scenario, describing biogas plants of typical sizes and efficiencies, is presented for both digestion and gasification. It is assessed that, if implementing the Sabatier process on gasification, the methane production would be increased by about 110%. For the digestion, the increase, including process improvements, would be about 74%. Hence, this method results in greatly increased biogas potential without the addition of new raw material to the process. Additionally, such model would present a great way to meet the transport sector's increasing demand for renewable fuels, while simultaneously reducing net emissions of carbon dioxide.

Biogas, Renewable energy, Intermittent power, Synthetic fuels, Sabatier reaction
National Category
Energy Systems Chemical Engineering
urn:nbn:se:kth:diva-58804 (URN)10.1016/j.apenergy.2011.07.024 (DOI)000297426100003 ()2-s2.0-80055060615 (ScopusID)

QC 20120110

Available from: 2012-01-10 Created: 2012-01-09 Last updated: 2013-04-16Bibliographically approved
3. The competitiveness of synthetic natural gas as a propellant in the Swedish fuel market
Open this publication in new window or tab >>The competitiveness of synthetic natural gas as a propellant in the Swedish fuel market
2013 (English)In: Energy Policy, ISSN 0301-4215, Vol. 52, 810-818 p.Article in journal (Refereed) Published
Abstract [en]

The road transport sector today is almost exclusively dependent on fossil fuels. Consequently, it will need to face a radical change if it aims to switch from a fossil-based system to a renewable-based system. Even though there are many promising technologies under development, they must also be economically viable to be implemented. This paper studies the economic feasibility of synthesizing natural gas through methanation of carbon dioxide and hydrogen from water electrolysis. It is shown that the main influences for profitability are electricity prices, synthetic natural gas (SNG) selling prices and that the by-products from the process are sold. The base scenario generates a 16% annual return on investment assuming that SNG can be sold at the same price as petrol. A general number based on set conditions was that the SNG must be sold at a price about 2.6 times higher per kWh than when bought in form of electricity. The sensitivity analysis indicates that the running costs weigh more heavily than the yearly investment cost and off-peak production can therefore still be economically profitable with only a moderate reduction of electricity price. The calculations and prices are based on Swedish prerequisites but are applicable to other countries and regions.

Synthetic natural gas, Economiv feasibility, Sabatier reaction
National Category
Energy Engineering Chemical Process Engineering
urn:nbn:se:kth:diva-105565 (URN)10.1016/j.enpol.2012.10.049 (DOI)000313775100072 ()2-s2.0-84870695799 (ScopusID)

QC 20130205

Available from: 2012-11-22 Created: 2012-11-22 Last updated: 2013-02-22Bibliographically approved

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