A 100% renewable electricity calculator for the United States

In 2020, I wrote an article outlining the flaws in studies that claim 100% renewable energy is unaffordable. I talked about those studies overestimating storage needs and opting for insufficient renewable energy storage. I advocated for increased use of power-to-gas technology to achieve an affordable 100% renewable electricity grid. However, the lack of accurate input data made a deeper analysis of the input data used impossible. I had to rely on a few scenarios provided by the researchers to find an affordable path to 100% renewable electricity.

In the meantime, other studies have been published. The new releases are more transparent about the input data used: everyone now has access to 39 years of solar and wind data to analyze the US power grid and find their own scenarios for a 100% renewable power grid.

To make the data more accessible to everyone, I suggest using an ordinary spreadsheet. This way, anyone can easily analyze US solar and wind data, adjust the amount of storage, solar, and wind power to optimize the costs of a renewable energy grid. In addition, the spreadsheet then automatically calculates the percentage of demand that is covered by solar and wind power, the amount of reduction, the backup capacity required, and the amount of power-to-gas (carbon-neutral synthetic gas made from hydrogen and carbon dioxide captured directly from the air) that would be needed to achieve a 100% renewable electricity grid. The tool then divides the total costs by the total covered demand to calculate the cost per kilowatt-hour (usable). To make this tool more flexible, the user can change the cost of wind, solar, grid extension, storage, gas supply and backup plants, as well as the storage efficiency and storage power (hours needed to completely unload the storage device). This way, the spreadsheet tool can be easily updated whenever new solar, wind and storage cost data is released. The spreadsheet tool also contains default cost data sources as well as solar, wind and demand data sources (“sources and figures” table).

Spreadsheet tool download

The spreadsheet tool can be downloaded from here.

Using the spreadsheet tool

Fields highlighted in blue can be edited manually by the user. Based on an assumed capacity factor of 20% solar and 35% wind, the tool automatically calculates how much solar and wind power will be generated at any given time, and how much demand covered directly by solar and wind power. The demand data does not reflect changes in demand over time, it is simply one year’s demand data, copied and pasted 36 times. Depending on the storage amount and storage discharge hours, any excess will be assumed to charge the battery (the emulator will consider charging inefficiency and charging power). This means that a 100 GWh, 2 hour storage device takes 2 hours to fully charge. If the charging efficiency is 80%, it takes two hours of 62.5 GW of solar/wind power to charge the storage device.

Advanced users can also change the efficiency of the storage device as well as the cost of backup power plants, solar, wind, storage, and grid investments.

Results

The results are calculated automatically. The tool calculates both the percentage of grid electricity supplied by solar, wind and storage energy, as well as the cost of solar and wind energy (including reduced electricity), storage and emergency power plants. Backup power plant capacity will be automatically calculated based on the maximum gap between solar/wind/storage power and grid demand. Additionally, the tool will add the cost required to switch to 100% renewable energy. This is defined as the cost of solar and wind energy (including reduced electricity), storage, emergency power plants and power-to-gas technology. Efficiency is defined as the percentage of solar and wind energy that is actually used (not reduced or lost due to storage inefficiency).

Accuracy of the spreadsheet tool

To test the accuracy of the spreadsheet against professional software, I used input data provided by Tong et al, “Geophysical constraints on the reliability of solar and wind energy in the world” (https://doi.org/10.1038/s41467-021-26355-z).

This study provides 39 years of solar and wind data for the United States and calculates a variety of scenarios: different amounts of solar and wind power (overcapacity up to 3 times demand) as well as storage (no storage, 3 hours storage, 12 hours storage). This test shows the limits of the calculation of a spreadsheet: the tool returns slightly different results from the results provided by the professional software. One possible cause is the inherent inaccuracy of the spreadsheet calculation (each number is limited to 15 digits). Moreover, the tool does not take into account the self-discharge of the storage. However, for all scenarios, the error was never greater than one-tenth of one percent.

At the end of the line

Calculations show that a 100% renewable electricity grid is affordable. At current costs, that’s just over 8 cents per kilowatt hour. The results also show that achieving 100% renewable energy using battery storage is significantly more expensive than using power-to-gas technology.

By Georg Nitsche

Georg Nitsche holds a master’s degree in history. He is interested in lobbying and propaganda, as well as the history and future of renewable energy. Contact the author: [email protected]


 

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