It’s About Time: How Hourly Data is Crucial for Telling the Full Story of Electricity Decarbonization

Stories of Grid Decarbonization: Journey Through Different Stages

Hourly data tells us the true stories of grid decarbonization. When looking at hourly CFE % across the year, we see significant variations in the availability of clean power. To do this, we use heatmaps, with one block for each hour in the year. 

Every grid tells its own unique story. To summarize, we have grouped these unique stories into four groups, taking specific representative examples to tell the story of the different phases of the decarbonization of power systems. Check out the Annex for full details on the statistical spread of hourly CFE across all regions analyzed.

Story 1 – Fossil Dominant (<20% Annual CFE)

• Region Characteristics: Fossil-dominant regions, like Australia’s Northern Territory, are essentially fossil-fueled around the clock. The highest CFE penetration reached just 2% in 2023.  
• Similar Regions: 16% of grid zones were in this category, including zones like Singapore (SG), United States-Florida SEC (US-FLA-SEC), and Eastern India (IN-EA).
• Priorities: The priority in these regions should be adding new CFE at all times of the year, for example, through bulk solar and wind additions, while preparing for better integration with storage systems from the early stages. 

Story 2 – Getting Going (20-40% Annual CFE)

• Region Characteristics: The heatmap reveals large fluctuations between 13% and 55% during the year, showing progress in integrating clean energy while still relying on fossil fuels, especially during off-peak renewable periods.
  
• Similar Regions: 25% of grid regions were in this category. This includes United States Florida Power & Light (US-FLA-FPL), Japan Hokkaido (JP-HKD) and Australia Victoria (AU-VIC) where renewable energy penetration is growing but remains inconsistent across the year.
• Priorities: The priority should be to increase clean energy penetration while improving grid flexibility and storage to balance out the peaks and troughs in clean energy availability. 

Story 3 – Mid-Transition (40-80% Annual CFE)

• Region Characteristics: These regions have significant contributions from one or more CFE technologies. Due to the variability of renewables, these regions are almost totally carbon-free at certain times of the year while remaining fossil-reliant at others. Below we deep-dive into an example of a wind, solar, and nuclear-heavy region in this category. 
• Similar Regions: 37% of grid regions were in this category. These regions include Spain (ES), United States New York Independent System Operator (US-NY-NYIS) and Germany (DE). 
• Priorities: To reduce reliance on fossil fuels, these regions should invest in short and long-duration energy storage, flexibility, and grid management technologies to ensure that clean energy can meet demand even during low-output periods.

Wind-Heavy

• Region Characteristics: For regions like GB (Great Britain), wind power accounted for 31% of the total power consumption in 2023, playing a crucial role in providing clean energy, with CFE percentages ranging from 28% to 94%. The heatmap illustrates a strong but still highly variable clean energy supply with reliance on fossil fuels during periods of low wind output, more flexibility of supply and demand will be key. 

Solar-Heavy

• Region Characteristics: In the United States California Independent System Operator, solar energy accounted for 17% of generation in 2023 and is peaking during the middle of the day in the summer months. Fossil fuels are still relied upon quite heavily during the evenings and fall months when solar output is lower, as the heatmap shows CFE ranging from 22% to 88%.

Nuclear-Heavy

• Region Characteristics: In the US MIDA PJM (Mid-Atlantic region), the electricity grid is transitioning toward decarbonization, with 34% of its total energy coming from nuclear power. The relative stability of nuclear energy provides a baseline of clean electricity, but the grid still relies on fossil fuels, particularly during high-demand hours and seasons with lower nuclear generation.

Story 4 – End-Game: Where We All Want to Be (>80% Annual CFE)

• Region Characteristics: Regions like East Norway (NO-NO1) are at the forefront of electricity decarbonization, with carbon-free electricity levels always over 90%. There is very little variability in carbon-free electricity percentage throughout the year, thanks to Norway’s abundant hydropower resources. 
• Similar Regions: 23% of grid regions were in this category. This includes France (FR), Iceland (IS), and Finland (FI),  which benefit from stable clean energy resources such as hydro, wind, and nuclear energy. In terms of overall electricity generation, these regions remain in the minority.
  
• Priorities: The final challenge for these regions is to eliminate the last traces of fossil fuel use and ensure that 100% clean energy is available at all times, even during periods of low renewable output and as electricity demand continues to grow. 

We hope this data helps underline the importance of time, when analyzing grid decarbonization. We need to think in hours, not months or years as we track and account for grid decarbonization efforts. 

P.S. Below are the Annexes with lots more data on all the regions we analyzed. 

Annex 1 – Overview of Regional CFE Performance

The boxplots (showing the mean, interquartile range and min/max values) below gives a comparative overview of the carbon-free electricity percentage for different non-U.S. zones, sorted by mean CFE:

Non-US Zones:

US Zones:

Annex 2 – Summary Visualization

• This .gif image gives the CFE heatmaps for all zones analyzed.