Seal (no flow boundary)

Seal (no flow boundary)

Parameter RangeGas Turbine

Polytropic Efficiency 0.7 to 0.92

Compressor Polytropic Efficiency 0.7 to 0.90

Motor/Generator ~0.95Compression Ratio 1:3 per stage

~ ¹.⁵ ⁻ ² ᵏᵐ

Well

Total 303 TWh

78 TWh

50 GW

Total 53 GW

~ 5 cm

Energy Storage Potential (TWh)Windfarm StatusAgreement for Lease

LeaseIn OperationSearch Area

0.0 - 0.5>0.5 - 2>2 - 4>4 - 8>8 - 14

Julien Mouli-Castillo*, Dr Mark Wilkinson*, Dr Dimitri Mignard**, Dr habil Christopher McDermott*, Prof R. Stuart Haszeldine*, Prof Zoe Shipton****UoE School of Geosciences, **UoE School of Engineering, ***University of Strathclydejulien.moulicastillo@ed.ac.uk

Unlocking Renewable Energy With Compressed Air Energy Storage in Porous Rocks

2. The Need for Electricity StorageRenewable energy generation is constantly increasing in the UK¹ which posses a significant challenge: how to meet a predictable and continuous demand with a challenging to predict and discontinuous generation ?

Using energy storage is one way of addressing this challenge by storing excess energy during periods of low demand, and returning it during periods of high demand (Fig. 1).

1. Research GoalEstimate the potential of Compressed Air Energy Storage in Porous Rock for UK offshore saline aquifers. Project Start : 09/2014

3. Porous Rock Compressed Air Energy Storage (PM-CAES)The concept of PM-CAES is to use cheap electricity supply to compress ambient atmospheric air at high pressures in subsurface porous rocks (Fig. 2 (Injection)). When electricity is needed once more the air is recovered from the store and expanded through a turbine which runs a generator (Fig. 2 (Production)). To prevent damage in the turbine and to increase efficiency the air needs to be heated. Currently the only viable way of heating the air is by burning natural gas.Porous rock formations of the UK represent vast volumes of potential storage. Preliminary calculations have shown that up to 21 bn m³ of air could be stored in that way, allowing PM-CAES to be used for seasonal energy storage.

4. Modelling Porous RockPorous rock offers a vast storage potential in terms of volume. To be able to achieve the research aim a workflow addressing the key elements of the PM-CAES system had to be developped, including a porous rock model in which to model pressure variations during a storage cycle.

A homogenous cylindrical model was chosen to address the range and diversity of the UK offshore geology, whilts having a limited simulation time in order to be run multiple times with different parameter combinations.

5. Modelling the well and Power PlantThe next step was to model the pressure changes induced by the well, and the related power consumption of the compressor and power output from the turbine. Analytical models4,5 where used and polytropic efficiencies where used to account for efficiency losses. The models where implemented in Python 2.7. Parameter ranges tested for the plant model are shown in Table 1.

7. Key Findings

7. References1. DECC. (2013). UK Renewable Energy Roadmap. Carbon (Vol. 5). Retrieved from http://www.decc.gov.uk/en/content/cms/meeting_energy/renewable_ener/re_roadmap/re_roadmap.aspx2. Kushnir, R., Ullmann, A., & Dayan, A. (2012). Thermodynamic and hydrodynamic response of compressed air energy storage reservoirs: a review. Reviews in Chemical Engineering, 28(2-3), 123–148. Crotogino, F., Mohmeyer, K.-U., & 3Scharf, R. (2001). Huntorf CAES�: More than 20 Years of Successful Operation, (April), 1–7.3. Images: http://voices.nationalgeographic.com/2013/05/13/behind-the-lens-above-the-ground-with-photographer-dave-showalter/ and http://www.apexcaes.com/caes and http://www.nhbr.com/May-1-2015/Renewable-Energy-Fund-RIP and http://www.kocurekindustries.com/sandstone-cores

4. Çengel, Y. a. (2004). Thermodynamics: An Engineering Approach. McGraw-Hill.5. Smith, R. V. (1950). Determining friction factors for measuring productivity of gas wells. Petroleum Transactions, 189, 73–82.6. http://www.co2stored.co.uk/home/index accessed 19/10/2016.7. https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/548015/Electricity_since_1920.xls accessed 19/10/2016

Figure 1: Typical diurnal base, intermediate and peak loads. The concept behind the use of energy storage to enable energy transfer to meet peak demand is highlighted by the green arrow.²

Figure 3. 2D cross section through the cylindrical model showing the pressure variation in the porous rock when air is extracted from the reservoir.

Figure 4. Map of the UK showing potential storage formations and UK offshore windfarms.

Table 1. Plant model parameters.

Figure 2. Schematic representation of the operations of a PM-CAES plant.

Preliminary results indicate a storage capacity of c. 50 GW for 2 months using c. 6000 wells. c. 94% of UK peak demand7

PM-CAES has the potential to c. 72-83 TWh of energy. c. 25% of UK annual demand7

6. Preliminary ResultsOnce the modelling of the system was performed, correlations could be established between geological parameters and storage potential. These correlations where used to estimate the storage potential of geological formation taken from the CO2 Stored database6. The map shows formations offering storage potential. The darker the color the greater the storage potential.