Appendix 2: Compressed Air for Renewables Event
Date: Friday 12 th February 2010
Time: 14:00 - 17:00
Location: University of Edinburgh, School of Engineering
Event and audience
The event was coordinated by the Scottish CAES group with Scottish Renewables acting as secretariat for organisation of it. Attended by about 25, the audience at the event was mixed. There were some from academia, a few from industry, consultancy and students including one or two with PhD expertise.
Professor Ian G Bryden, Chair of Renewable Energy, University of Edinburgh.
Prof Bryden ran through slides on principles of energy storage and where CAES fits in the scheme of things. Parameters such as scale of stored energy and power output were explained. CAES requires the air to be cooled when compressing and re-heated when expanded. This can be costly/cumbersome. Engineers propose that a thermal (adiabatic) store could serve this purpose but this will not perform perfectly and offers a number of design difficulties.
A scheme is under development that can preclude the need for costly or cumbersome thermal storage when combined with Tidal Stream renewables technology. The design is at experimental stage and patent advice meant that details could not be described. An audience member surmised that the thermal properties of the sea were to be utilised.
The presentation gave a brief on Huntdorf CAES facility in Germany:
- Storage volume of 300,000 m 3 in a natural salt deposit
- Weight of the salt deposit is able to pressure confine the air reservoir at 70 atmospheres
- Electrically driven air compressors
- Delivers 300 Megawatts for 2 hours using the compressed air to drive a turbine
- Two major contribution to inefficiency: Energy is required to cool the air as it is put into storage.
- Energy required (usually from fuel) to expand the cool air taken from storage as it enters the turbine.
Prof. Seamus Garvey, University of Nottingham
The main content of the presentation set out the developments at University of Nottingham around Energy Bags. These are essentially undersea storage bags that will collect energy in the form of compressed air and use the pressure offered by undersea conditions to maintain compression. Greater depth offers greater pressure. They are called ICARES - or Integrated Compressed Air Renewable Energy Systems - and in future have potential that could see vast offshore energy farms being created off the coastline around the UK.
"Professor Seamus Garvey in the University's School of Mechanical, Materials and Manufacturing Engineering is looking at using a combination of wind, wave, tidal and solar power to compress and pump air into underwater bags anchored to the seabed. During periods of high demand, the air would be released through a turbine, converting it to electricity. "
"As methods of producing energy from renewable sources such as wind, solar and wave and tidal power become more advanced, the effective and efficient storage of that energy is fast becoming one of the key challenges facing the energy industry. As these types of renewables can only produce energy under favourable conditions, for example when the wind is blowing, storage capacity will help in ensuring supply can be matched to demand. "
Professor Garvey said: "At periods of peak demand in the day, the instantaneous value of electrical power can be several times greater than at periods of low demand. Energy storage can enable us to use off-peak energy to meet the demand in peak hours.
There followed a further presentation on Specialist compressor technology, but this, whilst interesting, was of no value to this project.
Discussion ensued on the subjects of the presentations and initially ran around issues of practicality of operation scale, commercial viability, and future markets.
The ICARES device sees its commercial value and viability from capturing energy all day to release to the grid at peak demand (and thus peak market price) times
Issues of relevance
In Scotland there are no salt mines to use as physical air compression caverns. The potential would be for using disused mines, of which there are many, for this purpose, but the geological soundness of this idea is unclear.
Storage possibilities in the UKL are shown in figure A2.1 below. This is from a foresighting report that looked at potential for natural gas storage. It can be seen that areas of potential lie in parts of England and Northern Ireland.
Fig. A2.1: Map showing the location of operational and proposed UK underground gas storage sites, including depleting oil and gasfield and mined Chalk facilities16
In figure A2.2 below the salt caverns available in the UK can be seen. As CAES is best designed when nearby a gas turbine power plant, the opportunities for this in Scotland are nil.
Fig. A2.2 Suitable geology for salt cavern development in the UK and Ireland
The first two presenters have design/experimental or pilot stage schemes.
The University of Edinburgh tidal device has no patent in place but this will be completed soon. The
The Tidal device of UoE will be based in Scotland probably somewhere with good tidal stream resource. The device is about 1 MW capacity and has discharge times measured in days.
They foresee a number of barriers at later stages including grid connection points and the balance between distance from the grid/best resources.
The ICARES devices have patent but are at experimental stage. They are modular in construction so as long as suitable storage locations are available, a number of energy bags can be put in place as required. The size is in MW capacity approximately and discharge times are in hours.
Barriers will be similar to the tidal devices and are centred on suitable location providing sea depths, grid connection and setting alongside energy generation devices.