Christian Rolli

With the steady increase of global temperature renewable energy sources become more and more important to reduce greenhouse gas emissions. Compared to fossil resources renewables are subjected to higher fluctuations. Therewith the demand for large-scale energy storage is growing.

Energy System Transitions (IPCC)

According to the IPCC 2018 report renewable energies as solar and wind are well in progress to contribute a significant mount to reach the 1.5°C-consistent pathways. Since the IPCC AR5 report of 2014 the amount of solar and wind energies had a huge increase. One of the main factors was the decrease in costs for solar panels and solar batteries. Therewith small-scale energy and commercial projects like rooftop solar stations became affordable. [1]

Energy Storage (IPCC)

With a growing amount of renewable energies, the demand for large scale energy storage systems due to higher fluctuations in electricity production is increasing fast. With only 1.7GW (in 2016) the grid-connected battery capacities are on a small-scale level and due to high costs and environmental impact of the production they will not be able to solve that problem unless new technologies improve those issues. Almost a factor 100 higher is the capacity of pumped hydro stations with 150 GW (in 2016). But that’s still not enough to compensate the large seasonal fluctuations occurring with rise of renewables. Therefore, research in new energy storage systems is inevitable together with optimizing the existing technologies. The installation of smart-grid systems and an intelligent distribution is essential to connect those different approaches. Especially thermal and chemical systems could provide a feasible way for seasonal storage. But so far most of those projects haven’t reached large scales. [1]

Power-To-Gas and Power-to-Liquid

Power-to-Gas and Power-to-Liquid are chemical processes in which fuel gas like hydrogen and ethane respectively liquid fuel like ethanol or diesel are produced by using electrical energy. There are many different projects competing for more efficient and economic ways to use this kind of storage and one of them is Sunfire.

Sunfire

Sunfire is a German company stationed in Dresden which is specialised in the production of synthetic produced gases and liquid fuels using renewable electricity, carbon dioxide and steam. In 2015 the company was able to process the first litres of their synthetic fuel and is meanwhile in 2020 cooperating with other companies and scales their processes up to industrial level. [2]

Figure 1: The orange box symbolizes the Sunfire – SynLink co-electrolyser [9]

To produce Syngas there are normally two seperate steps of reactions:

With SynLink Sunfire managed to combine the two chemical steps to only one in a Co-Electrolyzer. Through this and other improvements like using steam instead of liquid water a high efficiency level of more than 80% became possible. [3]

The company also developed a commercial power generator which allows to reverse the process using gas like ethane to produce electricity. As it is in a modular design a decentralized electricity production becomes possible. The generators reach an electric efficiency of over 50% and together with use of the thermal energy occurs a total system efficiency of 85%. So, a combined system of a SynLink co-electrolyser and their power generators can work as a battery-system with a total efficiency of 68%. [4]

Figure 2: A singular module of the Sunfire commercial power generator [10]

The bridge between two energy sectors

I think solutions like this Power-to-Gas-to-Power will play an essential role in extending smart grids by connecting the electrical and the fuel energy sectors. If we completely exit fossil fuels the huge existing gas grid would be out of use and could be filled with syngas. There are already large-scale reservoirs for natural gas which could be used and extended as seasonal energy storage, filled during the sun intensive summer months where solar systems reach their power peak and used to provide energy during the colder winter months with higher energy demand.

Especially for countries without the ability to build large hydro-power reservoirs like Switzerland this could be an important storage technology. But even in Switzerland where we don’t have any underground reservoirs to store the gas it could be an attractive solution to increase our existing energy storage systems due to nature conservation conflicts to build new large hydraulic reservoir power stations. The storage capacity of the swiss gas grid itself is about 14.4 GWh which is quite low. Because of that the company Gaznat SA owns a share of a French reservoir called Etrez near the borders which is secured by political contract. The swiss share of this reservoir account to 1.51 TWh [5]. This equals 2.62% of the swiss annual electricity demand (in 2018) [6] or the amount of energy that is produced by the nuclear power plant Gösgen during the period of two months. Additional to this there are places in Switzerland that would be suitable to build another reservoir. For example, a project in the Grimsel area that didn’t got realized so far planned up to four compartments with a gas storage capacity of each 28 million cubic metres [7]. Calculating with a 9.97kWh/m3 energy density of ethane the energy capacity would be 1.12 TWh and in a similar range as the share from the French one. Together those two larger reservoirs could increase the swiss energy storage volume by 29.7% compared to the existing capacity of hydraulic reservoirs (8.85TWh) [8] is a significant amount.

Considering all those facts I think it is essential to invest in solutions like this along with renewable energies to still guarantee a stable electric grid and to be able to use energy over production to produce fuels or other carbon-based chemicals for industries instead of just wasting it.

References:

[1] IPCC, 2018: Global Warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty [Masson-Delmotte, V., P. Zhai, H.-O. Pörtner, D. Roberts, J. Skea, P.R. Shukla, A. Pirani, W. Moufouma-Okia, C. Péan, R. Pidcock, S. Connors, J.B.R. Matthews, Y. Chen, X. Zhou, M.I. Gomis, E. Lonnoy, T. Maycock, M. Tignor, and T. Waterfield (eds.)].

[2] https://www.sunfire.de/de/ (visited: 06.04.2020)

[3] https://www.sunfire.de/files/sunfire/images/content/Produkte_Technologie/factsheets/ Sunfire-SynLink_FactSheet.pdf (visited: 06.04.2020)

[4] https://www.sunfire.de/files/sunfire/images/content/Produkte_Technologie/factsheets/Factsheet%20Commercial%20Generator.pdf (visited: 06.04.2020)

[5] https://www.iet.hsr.ch/fileadmin/user_upload/iet.hsr.ch/Power-to- Gas/Kurzberichte/17_Speicherkapazitaet_Erdgas_Schweiz.pdf (visited: 06.04.2020)

[6] https://www.bfe.admin.ch/bfe/de/home/versorgung/statistik-und-geodaten/energiestatistiken/gesamtenergiestatistik.exturl.html/aHR0cHM6Ly9wdWJkYi5iZmUuYWRtaW4uY2gvZGUvcHVibGljYX/Rpb24vZG93bmxvYWQvOTc3NA==.html (visited: 06.04.2020)

[7] https://www.tagesanzeiger.ch/schweiz/standard/gasspeicher-im-grimselfels-soll-die-schweiz-unabhaengiger-machen-/story/15440504 (visited: 06.04.2020)

[8] https://www.bfe.admin.ch/bfe/de/home/versorgung/statistik-und- geodaten/energiestatistiken/elektrizitaetsstatistik.exturl.html/aHR0cHM6Ly9wdWJkYi5iZmUuYWRtaW4uY2gvZGUvcHVibGljYX/Rpb24vZG93bmxvYWQvOTk5NA==.html (visited: 06.04.2020)

Graphics:

[9] Figure 1: https://www.sunfire.de/de/anwendungen/synthesegas (visited: 06.04.2020)

[10] Figure 2 : https://www.sunfire.de/de/produkte-und-technologie/sunfire-powerplus (visited: 06.04.2020)