How CAES Works
Storing energy in compressed air has been around for decades, and has been used world-wide in many systems.
When power is abundant and demand is low, it’s drawn from the grid to compress air into a salt cavern hundreds of metres underground. When the power is needed, the air is let out from the cavern to regenerate the electricity.
Salt caverns have been used for many decades to store natural gas because not only are they naturally hermetic, but also salt undergoes plastic flow under pressure, so it seals any cracks that may occur. And what is safe for gas is safer for air.
There are salt basins globally, in which caverns can be made cheaply and easily.
Listen to Bill Gates on Energy Storage
1
Convert electricity to compressed air
Electricity from the grid or a renewable generator is used to pressurise the air.
2
Store compressed air underground
Air is stored at high pressure & ambient temperature underground.
3
Release & heat the compressed air
The compressed air is released & heated using energy from the heat store or by using gas.
4
Convert compressed air to electricity
The heated compressed air is expanded through a turbine to generate electricity.
Applications
Flexible Generation Plants
- Zero or low emissions
- 20MW to multi GW
- 4 hours to multi-day
- Balancing and ancillary services
- Enables renewables to power the grid
Optimising Wind and Solar
- Intermittency into dispatchable electricity
- Co-location with renewables also enables the generator to avoid grid access charges on its output energy, storage to avoid them on charging energy and storage to avoid capital costs of grid connections
- Increases revenues
- Eliminates curtailment
- Cuts grid connection costs
Grid Investment Deferral
- Relieves grid congestion at choke points
- Reduces local overloads at interconnectors
- Reduces overloads at wind farm landfalls
- Co-location with renewables benefits grids by greatly reducing reinforcement and adding real inertia 24/7
- Well placed for major generation and demand
Asset Repurposing
- Repurpose Fossil Plants into Storage
- Adds revenue streams
- Cuts emissions and costs
- Greater cavern revenues than gas storage
The Challenges of the Energy Transition – Podcast
The energy transition is essentially about replacing dispatchable (i.e. on-demand) power generation with intermittent, asynchronous renewables. It was recorded following Mark Howitt’s participation in a panel event on “Markets and policies for future flexibility needs”. In this podcast, Mark talks with Laura Sochat of Charles River Associates, a global energy consultancy, about what this entails, its consequences and what can be done about it to enable the energy transition to be affordable, reliable and resilient.
Listen to the Podcast
Advantages
Utility Scale
Up to 100’s+ MW, multi-GWh+, 4 hour to multi day duration.
Flexible System Design
Deployable multiple revenue streams allowing risk mitigation and adaptation to changing market conditions
Low Cost
Lowest installed cost/kWh available today for bulk energy storage, combined with high round trip efficiencies.
Green Energy On-demand
Environmentally friendly option with no hazardous chemicals.
Adiabatic Process
Emission-free option (no fossil fuel) operation & fossil fuel option with low carbon footprint.
Round trip AC/AC efficiency
Independently verified to achieve High efficiencies: Green CAES ™ 62%-70%; Hydrogen CAES ™ 50%->60%
Long Life
30+ Years without efficiency loss on mechanical and up to 100 years on cavern.
Proven Components
Mechanical components are in the standard product ranges of tier 1 OEM suppliers.
Unlimited Cycles
Proven rotating equipment means no limitations from cycling. Life of underground caverns >100 years and counting.
Excellent Reliability
Tier 1 OEM supplied mechanical equipment matched with system design according to well proven engineering principles.
Inertia Frequency & Voltage Support etc.
Many ancillary benefits provided by synchronous equipment.
Maximum Flexibility
Rate of charge, rate of discharge and volume of storage are all independent variables, so designs can be optimised for each location
Both unique and well proven
Storelectric’s CAES design brings known sub-system technologies, well proven at comparable scales, from other industries into CAES. This equipment has been optimised over decades in highly competitive situations, and made exceedingly reliable in difficult environments and extreme conditions
The main development work in this design lies in:
- Total system design and integration
- Interfaces between the sub-systems
- Control and safety systems relating to these
- This approach minimises development time, cost and risk, while maximising overall system efficiency and reliability.
- Currently our (pending) patents are all process IP which, for which further information can be provided on request.
- Hybrid solutions are being developed combining Green CAES ™ and CGGT CAES technologies.
Technology Choice
Currently there are only 2 technologies that have proven references of over 30years. These are Pumped Hydro Energy Storage (PHES) and Compressed Air Energy Storage (CAES). Other technologies are developing but are severely hampered by longevity issues, size and duration restrictions. As a project developer Storelectric Ltd is focused on investing in proven, scalable and competitive concepts. PHES while well proven is geographically constrained and very much more expensive than CAES with the added difficult of identifying suitable locations that have not otherwise been built upon or rejected. This leaves CAES which is proven, competitive, less geographically constrained and has the potential for scalability at both the distribution and transmission scales.
EXISTING CAES PLANTS
Huntorf, Lower Saxony, Germany
Compressed air energy storage (CAES) has been in operation since 1978 in Huntorf in Germany, and since 1992 in McIntosh, Alabama, USA. Both of these plants regenerate the electricity by feeding it into a gas-fired power station, roughly tripling the efficiency of the power station.
When compressing the air it heats up. When expanding it again, heat needs putting back into the air. Both Huntorf and McIntosh do not utilise the heat from the compression process, leading to only 42% overall efficiency in Huntorf and 54% in McIntosh (the difference being because McIntosh’s power station is Combined Cycle).
McIntosh, Alabama, USA
Huntorf and McIntosh have proved useful additions to their local grids, in operation daily. Storelectric has an alternative diabatic CAES technology, building on the success of these plants. This can be retro-fitted to CCGT power stations that are near appropriate geologies, which burns gas and has an efficiency expected to be above 60%.