Storm Elliott: How extreme weather events massively impact carbon emissions from electricity grids

January 11, 2023


20 min read

During the Christmas period, storm Elliott hit the US with freezing temperatures. This had a large impact on some of the US power grids. This resulted in record high demand and many tonnes of extra CO2 emitted.

The storm

An extraordinary winter storm hit the USA and Canada around Christmas 2022. The storm was categorised as a bomb cyclone. From December 21 to December 26, states around the Great Lakes and on the East coast were hit by blizzard conditions and freezing temperatures. -50°C (-58°F) was the coldest recorded temperature in Montana. Around the Great Lakes and on the East coast, wind gusts reached over 110 km/h (68 mph). These winds created whiteout conditions and very low to no visibility in some areas. 

Traditionally, demand is lower during the Christmas holiday as there is less economic activity. Cleaner production technologies can be prioritised and the average carbon intensity often decreases during this time. In the regions affected by storm Elliott, this pattern was broken in 2022. The extreme weather conditions strained US power grids, from Texas to Maine. In many of these grids, power demand reached new highs. The grid operators engaged in rolling blackouts in an effort to protect the infrastructure and to deal with record power demand. It is estimated that more than 1.5 million households were temporarily without power.

The consequences of this sudden rise in electricity consumption are investigated in this blog post with a focus on the electricity production breakdown (what sources are used to cover the demand) and the carbon intensity of the electricity grid. This blog post will detail on the impact of the winter storm Elliott on the electricity sector in these five zones:

  • Electricity reliability council of Texas (US-TEX-ERCO): a new maximum was recorded for power demand highlighting the flexibility of the grid.
  • Midcontinent independent system operator (US-MIDW-MISO): this zone was the hardest hit by the storm and the security of supply was ensured by coal and gas power generation.
  • PJM Interconnection (US-MIDA-PJM): reserve capacity was key in ensuring the continuity of supply.
  • Southwest power pool (US-CENT-SWPP): the complementarity between wind and fossil production decreased the dependency on fossil fuels as demand increased.
  • Tennessee Valley authority (US-TEN-TVA): imports from neighbouring zones helped balance supply and demand. 
Figure 1: Location of the zones detailed below

Texas: Power demand reaches a historical maximum

In Texas, the grid operator is the Electric Reliability Council of Texas, hereafter ERCOT. The main impacts of the storm on the ERCOT grid were felt between December 23rd and December 28th as observed on Figure 2. The power consumption increased by 33% between the 22nd and the 23rd to reach 70 GW while the average power consumption in December 2022 was 45 GW. In comparison, during the cold snap in February 2021 consumption peaked at 60 GW. 

The incremental demand for power was mainly met by gas production. As shown on Figure 3, gas production increased significantly on December 23rd. On Christmas Eve,  gas production peaked at 40 GW, the highest value observed in 2022. Between December 23rd and December 25th, gas production was 76% higher than the average observed during the rest of 2022. This rapid production scale shows how  gas is used as a dispatchable power source in Texas and highlights how quickly gas production can ramp up.

On the other hand, during this period, wind production was 8 GW on average, 35% lower than the average observed in the rest of 2022. This created an additional strain on the power grid and increased demand for fossil generation.

Traditionally, demand is lower during the Christmas holiday as there is less economic activity, resulting in a lower carbon intensity as observed on Figure 4. The increase in  gas power production caused by the storm had a major impact on carbon intensity. During the Christmas holiday, carbon intensity was estimated at 476 gCO2eq/kWh. On Christmas day, the average carbon intensity was 505 gCO2eq/kWh, the highest in December 2022 and more than twice the carbon intensity on Christmas day 2021.

Figure 2: Power consumption in ERCOT in December (MW)

Figure 3: Power production in ERCOT in December (MW)

Figure 4: Average carbon intensity in ERCOT in December (gCO2eq/kWh)

Midwest region: Coal and gas power generation ensure continuous supply

The Midcontinent Independent System Operator (MISO) operates the grid stretching from the Great Lakes to Louisiana. The MISO grid was one of the most hit by storm Elliott. The harshest conditions were recorded around the Great Lakes and the Northern Plains. The impact on the electricity consumption can be noticed between December 19th and December 28th on Figure 5. During this period, total consumption was 21% higher than during the rest of December 2022 and peaked at 103 GW on December 23rd.

This increase in demand was met by increasing coal, gas and wind production as highlighted on Figure 6. Coal and  gas are the two main electricity sources in MISO representing respectively 34% and 33% of the average electricity production in 2022. During the storm, coal production peaked at 34 GW on December 23rd and gas production peaked at 35 GW on December 24th representing respectively a 48% increase and a 60% increase compared to the average over the rest of December. 

High wind speeds were recorded in the region resulting in a higher wind power production which represented 15% of the electricity production. The wind power production thus participated in removing part of the strain on the electricity grid.

With a greater electricity demand mainly met by additional generation from fossil-based power plants, the carbon intensity increased during the Christmas period in 2022 compared to the same period in 2021. From December 24th to December 26th, the average carbon intensity was 564 gCO2eq/kWh, representing an 18% increase compared to the same period in 2021. One can note on Figure 7 that the average carbon intensity was even higher between December 15th and December 21st with an average of 594 gCO2eq/kWh. While the electricity consumption was lower during these days (compared to the following days) the wind production was also much lower thus requiring coal and gas production to increase.

Figure 5: Power consumption in MISO in December (MW)

Figure 6: Power production in MISO in December 2022 (MW)

Figure 7: Average carbon intensity in MISO in December (gCO2eq/kWh)

North Eastern region: Reserve fossil fuel generators are activated to meet the unusually high demand

The PJM Interconnection is one of the main grid operators in the northeastern US. The PJM grid is pictured on Figure 1. The strain on the PJM grid was the highest from December 23rd to December 29th. On average, total consumption was 27% higher  compared to the same period in 2021. This is illustrated on Figure 8.

In PJM, gas represents the main power source with an average production of 38 GW in 2022. During the storm, gas production remained rather flat compared to the rest of the year. On the other hand, coal production increased by more than 50% during that period as shown on Figure 9. 

Figure 9 also shows an increase in oil production which is particularly highlighted on Figure 10. Oil represented 8% of the electricity production on Christmas Eve with a peak at 10 GW. This increase in oil production is particularly outstanding since it usually has a minor share in the PJM power mix (less than 0.5% on average). Oil and coal electricity production serve as the primary reserve capacity and are dispatched when demand increases rapidly. As part of their energy transition, PJM has accelerated the retirement of coal and oil capacity since 2010 in favour of less carbon intensive or more cost-effective power sources. These offline plants can however be started up again in the event of spiking demand to ensure supply security. 

As the power sources called to meet the higher demand were fossil fuels, the average carbon intensity increased significantly compared to the same period in 2021 which is observed on Figure 11. The average carbon intensity was estimated at 499 gCO2eq/kWh during this period compared to 397 gCO2eq/kWh during the same period in 2021, representing a 20% increase.

Figure 8: Power consumption in PJM in December (MW)

Figure 9: Power production in MISO in December 2022 (MW)

Figure 10: Oil power production in PJM in December 2022 (MW)

Figure 11: Average carbon intensity in PJM in December (gCO2eq/kWh)

Western region: High wind power generation contributes to releasing the strain on the grid

The Southwest Power pool (SPP) is responsible for the operations on the grid that stretches from the Northern Plains to Texas to the west of the MISO grid, as illustrated on Figure 1. The impact on the electricity consumption can be seen on Figure 12 from December 21st to December 28th. During this period, average total consumption was 37 GW and was 31% higher than during the same period in 2021.

Gas was the main power source used to balance the demand increase and gas power production was 22% higher during this period compared to the rest of 2022. Coal is the first power source in SWPP and increased by 14% during the same period compared to the rest of the year.  

Figure 13 also shows the complementarity between wind and fossil power sources. On December 22nd, the high wind production squeezed out demand for coal and gas. On the other hand, wind production became lower during the peak of the storm and gas ramped up to ensure continuity in supply. This can be observed towards the end of the year as wind production increased again. Gas was pushed out of the mix and gas production became lower than the daily average in December 2022.

The average carbon intensity in SWPP was 29% higher during this period compared to the same period in 2021 as highlighted on Figure 14. The maximum daily carbon intensity recorded was 622 gCO2eq/kWh on Christmas Eve, more than twice the intensity on the same day in 2021.

Figure 12: Power consumption in SWPP in December (MW)

Figure 13: Power production in SWPP  in December 2022 (MW)

Figure 14: Average carbon intensity in SWPP in December (gCO2eq/kWh)

Tennessee: Electricity imports mitigated the need for reserve fossil fuel generators

The Tennessee Valley Authority (TVA) is the grid operator in Tennessee.  The impacts of the winter storm on the TVA grid are illustrated on Figure 15. They are mainly seen from December 23rd to December 28th. During this period, the average electricity consumption was 27 GW, up from an average of 17 GW during the rest of December 2022. Consumption peaked on December 24th, at 31 GW. This was the maximum demand recorded for the balancing authority.

The main power source in TVA is gas, with an annual share of 31%. During the period of the winter storm, gas production was almost 50% higher than during the rest of the year. Production from other sources remained relatively stable during this period as noticed on Figure 16. Coal production even decreased compared to the rest of 2022. 

Interestingly, Figure 17 highlights how imports increased significantly to meet the higher demand. During this period, total imports averaged at 5 GW, more than double compared to the rest of the year. This emphasises the fact that TVA doesn’t have a lot of reserve capacity and relies on neighbouring balancing authorities in case of extreme pressure on its power grid. This is probably a result of TVA decommissioning older more emitting power plants as part of their commitment to limit their environmental impact.

During the period of the storm, the average carbon intensity in TVA was 359 gCO2eq/kWh. Compared to the rest of 2022, carbon intensity didn’t increase during this period. On the other hand, carbon intensity was much higher compared to the same period in 2021, up by almost 50% as shown on Figure 18. As mentioned above, consumption and carbon intensity are traditionally lower during the week between Christmas and New Year’s as there is less economic activity. This increase between 2022 compared to 2021 further highlights the pressure on the grid during storm Elliott.

Figure 15: Power consumption in TVA in December (MW)

Figure 16: Power production in TVA in December 2022 (MW)

Figure 17: Net imports in TVA  in December (MW)

Figure 18: Average carbon intensity in TVA  in December (gCO2eq/kWh)

Key takeaways

Winter storm Elliott was an extreme weather event and it greatly impacted different power grids. 

Overall, consumption increased significantly during the Christmas season and the incremental demand was mostly met by dispatchable fossil fuel-powered sources. As a result, carbon intensity was on average higher than what has been observed in 2021. It is interesting to point out the differences in the reactions to the event in the 5 zones detailed above. 

This extraordinary event highlights the sensitivity of power grids to weather conditions. The generation sources dispatched to match demand levels during these peaks are usually fossil. Any unusual incremental demand will therefore generate extra CO2 emissions. This was also observed in February 2021 in Texas. The cold snap resulted in higher-than-average demand which was mainly balanced by higher gas generation. This incremental fossil generation was responsible for higher emissions in this period. On the other hand, this can also be observed in the summer. During heatwaves, the demand for cooling is higher which leads to the increased output of fossil power plants and more carbon emissions.

As the storm faded, consumption levels dropped back down to seasonal averages and it seems like the strain on the different grids was released.

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Article written by
Mathilde Daugy
Data Analyst

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