| dc.description.abstract | To reduce greenhouse gas emissions, federal and provincial initiatives have pushed for increased renewable energy penetration on Canadian electric grids. However, renewable power sources such as wind and solar power require “balancing” to provide reliable and affordable energy. Within the context of renewable energy and the electric grid, balancing refers to services and activities which help match instantaneous electrical supply and demand. This balancing is necessary at different power and time
scales to be able to meet demand from second to second and from day to day. Furthermore, the economics of renewable energy relies on these power sources not being curtailed frequently. Grid-scale (100+ MW) energy storage is an ideal low-carbon solution for balancing renewable energies, and compressed air energy storage (CAES) is a preferred option for this because it is a low-cost, low-impact, low-risk and mature technology. CAES uses conventional air turbine technology in tandem
with underground caverns to compress and store air during periods of low electric demand. The stored air is then heated and used to generate electricity during periods of high demand. The air is typically heated by burning natural gas but at much more efficient rates than natural gas turbine power. Alternatively, a newer thermal energy storage technology can be used to store the heat of compression and then use it to heat the expanding air. Several CAES projects are in different stages of planning and
development around the world, including a demonstration-scale CAES facility in Goderich, Ontario. However, CAES deployment in Canada faces a number of barriers, including a lack of awareness about the technology, its potential, and facility siting requirements.
To support the development of low-carbon energy, through removing barriers to energy storage deployment, two supporting studies were conducted: a CAES siting study and a life cycle assessment (LCA) of CAES. The siting study examined the first-order technical feasibility and potential application of CAES as a bulk energy management system for balancing renewable energy with electricity demand across Canada. This evaluation required a new methodology to be developed which could identify potential opportunities for CAES in Canada. To determine these opportunities, a multi-criteria analysis (MCA) framework was established and implemented in a geographical information system (GIS) software. The LCA study compares the global warming potential (GWP) impacts of balancing renewable energy with CAES to a single-cycle combustion turbine (SCGT) fulfilling the same role. The LCA only considers the operational phase of these facilities and examines the impacts of realistic operating conditions on the carbon intensity of energy produced from these technologies.
The MCA uses a robust linear weighted additive model with simple linear piece-wise scoring systems for the criteria. This study used six criteria, salt formation (i) depth and (ii) thickness, (iii) renewable energy potential, (iv) energy demand, (v) proximity to existing natural gas infrastructure, and (vi) proximity to existing electrical infrastructure, grouped into three categories, namely, geology, energy potential, and existing infrastructure. Studies with a more focused area of interest are encouraged to include additional criteria and detail, such as caprock considerations, proximity to environmentally and socially sensitive areas, and economic assessment. The weighting for the criteria in this analysis was determined by an informal survey of experts on CAES from industry and academia.
There are three major geologic basins in Canada which contain salt strata for storage: the Western Canadian Sedimentary Basin which underlies much of the prairies, the Michigan basin which underlies part of southwestern Ontario, and the Maritimes Basin complex which underlies a section of the Gulf of St. Lawrence and extends under New Brunswick and Nova Scotia. Generally speaking, all three of these formations are suitable for salt cavern storage but with unique challenges. The salt beds in Ontario are not very thick and could require multiple caverns and careful consideration of non-salt roof rocks GHG Reduction through CAES in Canada for cavern stability and tightness. In Saskatchewan and Alberta, the salt layers are quite deep, and some are impure enough to create extra challenges. The Maritimes Basin has been subjected to high tectonic stresses, and folding and faulting have resulted. These structural complexities make mapping and use of the rock salt more challenging. This issue is worsened by the lack of information available on the basin’s salt formations.
The availability of existing natural gas and electrical infrastructure were not determined to be a significant limiting factor in this first-order analysis. However, further investigation into capacity-constrained transmission lines will be an important determining factor in regional CAES siting.
Municipalities such as Sarnia and Windsor in southwestern Ontario are ideal for their salt presence, nearby wind and solar energy potentials, available infrastructure, and high energy demand stemming from a large industrial sector. Saskatchewan and Alberta rely on coal and fossil fuels for a significant portion of their energy demand, but they both have access to large salt formations and strong solar energy potential. The salt formations in western Canada also happen to underlie many areas of heavy industrial development which uses huge amounts of energy. Areas of interest for Western Canada include Yorkton, Saskatoon, North Battleford, Bonnyville, and, potentially, Edmonton and Fort
McMurray. Nova Scotia and New Brunswick are also dependent on coal power for much of their energy; however, these provinces have access to thick salt domes and strong coastal winds. Wind energy supported by CAES may be able to replace coal power in the Canadian Maritimes. Furthermore, the east coast has access to exceptional tidal power which will require support from energy storage once it has been developed. Areas of opportunity for CAES in Nova Scotia and New Brunswick include Moncton, Amherst, Port Hawkesbury, and Dartmouth.
Location score is highly dependent on the depth and thickness of available salt formations. This emphasises the need for high-quality geologic data, a more comprehensive list of geologic criteria, and the need for further studies into alternative storage mediums such as porous aquifers. According to survey respondents, the proximity of a site to existing electrical transmission infrastructure is also an important consideration. This accentuates the need to address the assumptions made in the evaluation of this criterion, namely that a CAES facility could connect to the electric grid at any point and that transmission congestion is not an issue.
Although there is elements of uncertainty in the MCA conducted in this study, spatially distributed multi-criteria analysis proves to be a viable but data-intensive methodology. A discrete analysis, in which only a few key alternatives are selected and compared, is likely to be a simpler and less resource-intensive investigation in most cases. This can be particularly true at different scales where a higher quality of data is needed to produce reliable results. The MCA results determined in this study illustrate the key areas that should be considered for a more in-depth discrete analysis. Such a study could focus on including a more comprehensive list of criteria and their scoring systems.
Given that CAES has been demonstrated to be technically feasible across Canada, it is important to evaluate the environmental and economic differences between CAES and gas turbines for renewable energy integration. Standard LCA modelling methodology evaluates energy generation technologies function at optimal efficiency, referred to as design point operation or design load. Results from this study are in close agreement with other studies regarding CAES and SCGT design point impacts. Under these ideal conditions, SCGT energy has greater impacts than CAES by a factor of 2.2. However, these technologies have different partial loading efficiencies and minimum operating loads which play an important role during highly variable operation characteristic of balancing intermittent power sources.
To evaluate the impact of these operating differences between CAES and SCGTs, an operations model was created using scaled down 2016 data from Ontario’s electricity grid. Both technologies are operated to try to provide the power required to meet a net flexible energy demand which represents the difference between Ontario’s demand and the summation of all of the inflexible power produced in Ontario, including hydro, nuclear, and renewables. This demand reflects the role typically filled by gas turbines on Ontario’s grid. This modelling found that SCGTs’ minimum load of 40% results in a significant portion of wasted energy from excess power production.
The realistic operating scenario created and the partial loading efficiency curves are integrated into the LCA which evaluates the average impact per unit of energy for these technologies under these conditions. It was found that the GWP impact per kWh increases by 19% for SCGTs and 3% for fuel-fired CAES. These operating considerations increase the ratio of impacts from SCGTs and CAES to 2.5.
These differences in GWP impacts are important when considering which technology should be used for balancing renewable energy. However, this modelling is also important to predict the impact that carbon pricing will have on the economics of these technologies. Two recent studies indicate that CAES and SCGTs are relatively cost competitive today. However, given that the Canadian federal government is mandating 10 $/tonne CO2e carbon pricing by 2018 and is generally expected to increase over time. Based on the GHG emissions calculated in this study, at 50 $/tonne CO2e the levelised cost of energy for SCGTs will increase by 4.0 ₵/kWh compared to just 1.6 ₵/kWh for CAES. This indicates that SCGTs are sensitive to carbon pricing and should not be installed for renewable energy integration. Instead, CAES is an ideal form of energy storage for large-scale renewables integration. | en |
