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NRP's Joint Synthesis on 'Electricity Storage via Adiabatic Air Compression' now online

Please find the National Research Programmes (NRP) joint synthesis on 'Electricity Storage via Adiabatic Air Compression' here: in English, in German and in French.

Summary: The phasing out of nuclear power plants and the expansion of solar and wind energy mean that electricity production is becoming more volatile. New storage systems are needed to ensure that electricity is available as and when it is required.

A promising technology for this purpose is adiabatic compressed air storage. It uses excess electricity from solar and wind energy systems to compress ambient air and store it in an underground cavity. When it is required, the compressed air is expanded again, driving a turbine and generating electricity once more. As the heat which was generated during compression is used for this process, the efficiency level stands at 65% to 75%, which is similar to that achieved by pumped-storage systems. The environmental compatibility of compressed air energy storage (CAES), in terms of the potential for emitting greenhouse gases and the damage inflicted on ecosystems, is also comparable to that of pumped-storage systems.

CAES systems are technically feasible. Important components such as turbomachinery and heat accumulators are either already available on the market or have been tested in a pilot plant. The process for constructing cavities is also well-developed due to the experience gained in tunnel and cavern construction.

Adiabatic CAES therefore represents an efficient, environmentally friendly and technically feasible storage solution. Due to the high capital costs and the unclear economic and legal framework conditions, however, it is uncertain whether they can be economically viable. This also complicates the financing of a demonstration plant.


White Paper Power-to-X Completed!

On July 8, 2019 the White Paper Power to X was officially introduced to the public.

In a joint research project of five Swiss competence centers for energy research, scientists of the Paul Scherrer Institute (PSI), the Swiss Federal Laboratories for Materials Science and Technology (Empa), ETH Zurich, the Zurich University for Applied Sciences (ZHAW), the University of Applied Sciences Rapperswil (HSR), the University of Geneva, and the University of Lucerne have prepared a white paper on "Power-to-X" for consideration by the Swiss Federal Energy Research Commission. The goal of the white paper is to gather together the most important insights available on Power-to-X technologies. Among other things, the study sheds light on contributions that could be made to Switzerland's energy strategy by different technologies based on conversion and storage of various forms of energy. The experts presented the findings of this study on July 8, 2019 at ETH Zürich.

The white paper is currently in revision. Please contact us for further information.

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SCCER CREST Annual Conference 2020

Early 2021 - Basel, Switzerland (to be confirmed)


The Swiss Competence Center for Heat and Electricity Storage

The SCCER HaE is dedicated to energy storage research and the first three years were completed successfully and the second funding period till 2020 has begun. It is about time now to report some highlights from the different fields of research of the SCCER. The energy turnaround, replacing fossil and nuclear by renewable sources, is facilitated if energy storage solutions become available in line with the progress of the transition towards renewable energy sources. During Phase I (2014-2016) of the SCCER Heat and Electricity Storage a variety of storage technologies were investigated. Among the different research projects, the following examples show extraordinary potential to become relevant within the scope of ES 2050 and therefore selected as highlights of Phase I of the SCCER HaE.

1 / 6
HYDROGEN PRODUCTION VIA REDOX FLOW BATTERY
Type of storage centralized
Stored energy mechanical
Most economic cycle period hrs/days
Efficiency estimated: 70%
Status Demonstrator

 

 

2 / 6
ADVANCED ADIABATIC COMPRESSED AIR STORAGE
Type of storage centralized
Stored energy mechanical
Most economic cycle period hrs/days
Efficiency estimated: 70%
Status Demonstrator

 

 

3 / 6
DEMONSTRATORS
Type of storage centralized
Stored energy chemical
Most economic cycle period days/weeks
Efficiency estimated: 40%
Status Demonstrator

 

 

4 / 6
SODIUM ION BATTERY
Type of storage decentralized
Stored energy chemical
Most economic cycle period hrs
Efficiency estimated: 90%
Status Proof of principle

 

 

5 / 6
CO- ELECTROLYSIS
Type of storage centralized
Stored energy chemical
Most economic cycle period days/weeks
Efficiency estimated: 60%
Status Proof of principle

 

 

6 / 6
ASSESSMENT OF ENERGY STORAGE IN SWITZERLAND
A ranking for storage options, depending on cycle time is given.
At a system size of 1 MW, for short (< 1 min)
term storage battery systems are most economic and associates with the
least greenhouse gas emissions, while for medium term storage (day),
battery is still advantageous in terms of cost,
but not in terms of green-house gas emissions, Batteries fall
behind pumped hydro and adiabatic air storage.

 

 


REDOX FLOW BATTERY (RFB)

Like in fuel cells, the redox flow cell is supplied with fuel (electrolyte) form external. Like an accumulator the process is fully reversible in one device. Since the electrolytes are in liquid phase, storing them is straight forward (plastic containers can do the job). However, the down side of RFB is a low energy density and the relatively low energy efficiency of (80-85%) compared to other batteries. This limits the use of RFB to niche applications so far, but makes them interesting for research. During phase I of the SCCER Hae, an idea was formulated: If the redox couple were Cerium III/IV combined with Vanadium II/III as electrolytes, a parallel catalytic reaction can produce hydrogen and oxygen, thus the cell can do electrolysis once the electrolyte is fully charged. This is interesting for processes which require a continuous stream of hydrogen, like biogas upgrading at waste water treatment plants. More details are available in the SCCER HaE Annual Activity Report 2016, p. 37-38 .

ADVANCED ADIABATIC COMPRESSED AIR ENERGY STORAGE (AA-CAES)

The growing share of fluctuating renewable energy sources like wind and solar requires short- and long-term energy storage to guarantee the power supply. Pumped hydro storage is at present the main option for large-scale storage. Electricity Storage systems based on pumped hydro are available since little more than 100 years and the massive capacity build up started in the 1970’s. Therefore the best locations for such installations are already explored. One promising alternative to pumped hydro storage is advanced adiabatic compressed air energy storage (AA-CAES) with an estimated round-trip efficiency of more than 70%. In Phase I, a demonstration plant was commissioned. The close collaboration of three research groups and the industrial partner enabled the fast progress, supported by project funding from the CTI SCCER- and the NRP 70 programme. More details are available in the SCCER HaE Annual Activity Report 2016, p. 5-9.

DEMONSTRATORS

Many concepts for energy storage exist on paper, on material level and lab scale devices. The assessment of the concepts in terms of their suitability for everyday use can be done only on demonstrators of power and capacities of about 1/100 to 1/10 below the real application. Two of such demonstrators are described in separate highlights (AA-CAES and RFB with Hydrogen production and the hydrogen filling station). Within the SCCER, three more demonstrator projects can be reported. Already at the beginning of Phase I the 25 KW power to gas plant at the HSR in Rapperswil was put into operation and two years of experience with this plant was gathered. The energy system integration platform (ESI), an installation with increased complexity was commissioned in phase I of the SCCER. Here, the interplay of different conversion type storage systems is explored on a 100kW scale. More details are available in the SCCER HaE Annual Activity Report 2016, p. 63-66.

 

SODIUM ION BATTERY

Batteries are the most energy efficient way to store electricity since no transition between energy carriers take place. Therefore it is the first storage option when it comes to store surplus electricity. For stationary use, weight and volume constraints on batteries are less demanding than for mobile applications, therefore a reduced lower power density is acceptable if there is a cost advantage associated. Due to the abundance of sodium in the Earth’s crust, sodium ion (Na-ion) batteries could be a more economical alternative to lithium-ion (Li-ion) batteries. In phase I of the SCCER, it was possible to work out the special needs of the Na –ion battery chemistry and a first full cell based on abundant low cost materials was tested. More details are available in the SCCER HaE Annual Activity Report 2016, p. 24-26 .

CO2 REDUCTION

In terms of grid scale storage options, the question remains how to deal with surplus electricity (once all the available high efficiency storage options are loaded). Can one afford to allow for curtailment shall the energy stored in a chemical compound at a lower efficiency but for long time scales. The later becomes an interesting option if seasonal or transportation aspects are considered. Also organic chemistry, not relying on fossil feedstock, becomes an option if the conversion process of CO2 and H2O to CH4 or other low molecular hydrocarbons (e.g. methanol or formic acid) is mastered in an efficient manner., Thereby a coupling of the sectors transportation and chemistry with electricity is possible, as well as long term energy storage. The proof of principle for a direct electrochemical conversion was presented during phase one, including economic considerations for identifying the best product (formic acid and methanol, was found to be economically most interesting together with CO). More details are available in the SCCER HaE Annual Activity Report 2016, p. 53-57 .

ASSESSMENT FOR ENERGY STORAGE IN SWITZERLAND

Besides of all the technical solutions for energy storage, whether they are state of the art or exist only in concepts, the economic, regulatory legal and environmental aspects are key for future implementation of storage in the energy grid. In phase I the system assessment group (a collaboration of three institutes) developed the tools necessary to conduct studies on economic and environmental scenario around energy storage technology. A comprehensive study on different storage options in terms of their costs and greenhouse gas emissions are the highlight of phase I. A ranking for storage options, depending on cycle time is given. At a system size of 1 MW, for short (<1 min) term storage battery systems are most economic and associates with the least greenhouse gas emissions, while for medium term storage (day), battery is still advantageous in terms of cost, but not in terms of greenhouse gas emissions, Batteries fall behind pumped hydro and adiabatic air storage Also a closer look behind the economics of power to gas revealed that only methane or even hydrogen production is economically not viable. Only if additional services can be sold, the business case is positive. More details are available in the SCCER HaE Annual Activity Report 2016, p. 59-62 .