Proposed integrated PSR assessment and enhancement framework.
5. Threats to PSR
5.1. CC, Extreme Events and PSR
Studies reveal that the increase in occurrence, extent, and intensity of extreme weather events are caused by CC
[9,10,11,12][9][10][11][12]. CC is also responsible for rising global temperatures, variations in rainfall patterns, increased frequency and strength of drought days, cloudiness, higher winds, sea-level rise
[9,10,12[9][10][12][58][59][60][61][62],
75,76,77,78,79], cold waves, heavy snow, and lightning strikes on or near overhead conductors
[80][63]. Each of these effects of CC can affect the PS in different ways, at different degrees, either on their own or in combination, as is normally the case. The degree of damage on the PS depends on the significance of the weather or climatic conditions, and the condition of the components. Prior works have focused on the impact of extreme weather events (as another effect of the impact of CC) on power systems along with their mitigation strategies. This extensive directional study supports the fact that LPHI events are among the principal causes of cascading outages and severe impacts following a disruption. However, CC is here to stay, and world trends indicate the possible increase in CC
[79][62]. This calls for consideration of climate adaptation and mitigation. PS operation (contrasted to planning) has constantly been strongly related to weather conditions and vulnerable to extreme weather events that may in some cases be a large, if not the largest, contingency event. It is important to clarify that the “CC impacts” relate only to how this interdependency and vulnerability are likely to change over the years. The critical issue arising from CC is that these natural hazards are projected to intensify and become more frequent and increasingly unpredictable. It was thus significant to consider CC in the system resilience studies.
The impacts of CC on generation, transmission and distribution (T&D), and demand are reviewed in
[80,81][63][64]. Rising global temperatures affect solar photovoltaic (SPV) modules, hydropower generation, T&D, and the demand landscape. Higher ambient temperatures reduce the generation efficiency of SPV modules
[10]. The conversion efficiency of the photovoltaic (PV) modules is negatively affected by elevated temperatures, which reduce their optimal output. Elevated temperatures also affect generation output of hydropower plants due to increased evaporation in water bodies
[10,81][10][64]. Rising temperatures further affect the T&D system in terms of transmission efficiency and capacity. Physical characteristics of different PS components, including transformers and overhead lines (OHL), have a linear relationship with allowable maximum operating temperature. Increasing global temperatures accelerate T&D losses and line sag
[79][62], lower existing capability, and derate T&D equipment to survive the elevated temperatures
[10].
There is continuous research to curb the effects of CC on critical infrastructures. A framework for risk measurement and enhancing the resilience of critical infrastructures centred upon the ideologies of elasticity, variety, and industrialised ecology, incorporating both short-term and long-term influences of climate consequence has been proposed
[79][62]. Risk assessment is considered one of the critical activities to be undertaken in the prediction stage as a positive step toward climate risk resilience. CC mitigation and adaptation might have a positive impact, and possibly lessen the slope or rate of degradation, when LPHI events finally strike.
5.2. CC, Electricity and PSR
Many studies in CC assess the impact on demand profile. Generally, CC will increase average annual electricity demand
[82[65][66][67][68][69][70][71][72][73][74][75][76],
83,84,85,86,87,88,89,90,91,92,93], and it has been demonstrated that in the wake of extreme temperatures, electricity utilisation escalates more with heating demands than with cooling demands in Portugal
[82][65]. This was explained by the adoption of other smaller cooling technologies. In contrast, the authors of
[83,84][66][67] proved that the escalated need for cooling would lead to increased electricity utilisation in China, which is explained by China’s climatic warming trend, which was also observed for Northern and Southern Europe
[86][69], due to the knowledge that CC will shift the distribution of seasonal electricity consumption
[85,88][68][71]. At minimum temperatures, temperature rises cause a decrease in electric space heating and, to a certain degree, a decrease in the utilisation of indoor appliances, the use of which escalates during cooler weather
[87][70]. The impacts of space cooling through air conditioners and the use of other appliances prevail at higher temperatures. Whereas climate warming decreases electricity demand for heating in winter and increases the demand for cooling in summer, it conclusively increases demand
[85,89][68][72]. Fluctuations in population, tariffs, and CC were explored in
[88][71], where each one of the electricity demand determinants was allowed to vary, while the rest of the factors remained unchanged. The results implied that the effects of the weather variables on the overall path of electricity demand were comparatively moderate, but positive over the full projection time. Generally, studies in
[78,85,89,90,91,92,93][61][68][72][73][74][75][76] have demonstrated an increase in electricity demand during summer and spring times due to CC. This was described by an increase in the number of buildings with air conditioners (ACs), and the extra cooling load on those air conditioners. This was attributed to the different heating and cooling techniques in different regions, such as in China
[92,93][75][76].
5.3. Adaptation Measures against CC and Its Impacts
Adaptation works on coping principles. CC adaptation has been defined as a means to cope with CC impacts
[95][77]. Adaptability studies target the enhancement of strategic resilient elements to assist in mitigating the impact of future climatic events
[96][78]. These studies further boost sturdiness, resourcefulness, and recuperation before an imminent disaster. Improvement in resilience for the energy sector can be on both the large-scale and household level.
Forms of climate adaptation strategies can be classified into: (1) structural, which was further subdivided into technological-, engineering-, and eco-system-based, (2) capacity building, which was further classified into educational, informational, or behavioural adaptation, and (3) institutional, which was further categorised into economic tools, laws and regulations, and governance
[9]. Adaptation approaches for a single classic event, or several events, fall into either one, or a combination of two or more, of all the forms. The authors in
[97][79] demonstrate the relationship between resilience and CC adaptation. It was perceived that principles of resilience were inherent in CC adaptation approaches and that different forms of adaptation approaches build resilience.
CC adaptation measures were classified as: (1) hardening (structural), which might comprise undergrounding power delivery structures, upgrading, rerouting, elevating structures or having redundant structures, and (2) effective operating procedures
[96,97][78][79]. The structural adaptation measures aim at lessening the exposure of the PS to impacts of CC, while effective operating procedures aim at minimising the restoration time, which improves the recovery features of resilience. Microgrids (MGs) and distributed energy resources (DERs) were considered as means of reinforcing PSR against the impacts of CC in
[96][78], which were performed to enhance operational capability. Geothermal energy was used as a climate adaptation strategy where a double relationship was observed
[98][80]. One point of view is that there was maladaptation, which takes place if geothermal resources were not properly or sustainably implemented, and conversely, that there was adaptation, which was achieved through sustainable water heating, electricity generation, sustainable livelihoods, and eradication of effects of drought in hydropower. Renewable energy technologies (RETs) such as biogas, improved cookstoves, micro hydro and solar power were also recommended as a way of rural adaptation to CC, as these reduce not only traditional biomass use but also carbon dioxide emissions
[99][81]. Policy and regulatory instruments in solar energy were recognised as adaptation methods in PS, which can be applied either at an enterprise, regional, national, or international level
[95][77].
6. PSR Enhancement Strategies
Two purposes served by grid resilience enhancement strategies are: (1) reducing the magnitude of the immediate impact caused by a severe weather event, and (2) reinstating the grid functionality to its pre-event state as quickly as possible after a severe weather event. Many researchers categorised grid enhancement into (structural) physical hardiness and (non-structural) operational capability
[3,14,16,62,104,105][3][14][16][42][82][83]. Structural improvement is used to reduce the magnitude of the impact, and non-structural enhancement is applied to reduce the restoration time or increase grid functionality
[21]. Thus, embracing both measures (“Hybrid enhancement”) might guarantee both impact and restoration time reduction. On the contrary, the resilience enhancement approaches can be grouped into planning and operational methods, which can either be short or long term
[18]. It was argued that underlying enhancement principles can be categorised into system executions; regional methods; community methods; national methods; methods highlighting the role of the valuation; methods emphasising the notion of security and plea for risk supervision studies; and sectoral methods
[60][38]. Prior studies have evaluated both structural
[3,20,48,105,106,107,108][3][20][30][83][84][85][86] and non-structural or operational
[14,16,22,28,50,55,109,110,111,112,113][14][16][22][24][25][87][88][89][90][91][92] PSR enhancement techniques separately.