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Batteries

A 100 Percent Renewable Electricity Calculator for the United States

In 2020, I wrote an article describing the flaws in studies that claim that 100 percent renewable energy is unaffordable. I talked about these studies overestimating storage requirements and opting for inadequate renewable energy storage. I argued in favor of using more power-to-gas technology to achieve an affordable 100 percent renewable electricity grid. However, the lack of precise input data made it impossible to make a more thorough analysis of the input data used. I had to rely on a few scenarios that were provided by the researchers to find an affordable path to 100 percent renewable electricity.

In the meantime, more studies have been published. The new publications are more transparent with regards to the input data used: Everyone now has access to 39 years of solar and wind data to analyse the US electricity grid and find their own scenarios for a 100 percent renewable electricity grid.

To make the data more accessible for everyone, I propose using an ordinary spreadsheet tool. That way, anyone can easily analyze the US solar and wind data, adjust the amount of storage, solar power, and wind power to optimize the costs of a renewable energy grid. In addition, the spreadsheet tool then automatically calculates the percentage of demand that is covered by solar and wind power, the amount of curtailment, the required backup capacity, and the amount of power-to-gas (synthetic, carbon-neutral gas made from hydrogen and direct-air-capture carbon dioxide) that would be required to achieve a 100 percent renewable electricity grid. The tool then divides total costs by total covered demand to calculate the cost per (usable) kilowatt-hour. To make this tool more flexible, the user can alter the cost of wind, solar, grid expansion, storage, power-to-gas, and backup power plants as well as the storage efficiency and the storage power (hours it takes to fully discharge the storage device). That way, the spreadsheet tool can be easily updated whenever new data about solar, wind, and storage cost is published. The spreadsheet tool also contains the sources for the default cost data as well as the sources for the solar, wind, and demand data (table “sources and figures”).

Downloading the spreadsheet tool

The spreadsheet tool can be downloaded from here.

Using the spreadsheet tool

 

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

Advanced users can also modify the storage device efficiency as well as the 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 provided by solar, wind, and storage as well as the cost for solar and wind (including curtailed electricity), storage, and backup power plants. The backup power plant capacity will be automatically calculated based on the maximum gap between the energy provided by solar/wind/storage and the grid demand. In addition, the tool will add the required cost to go to 100 percent renewables. This is defined as the cost of solar and wind (including curtailed electricity), storage, backup power plants, and power-to-gas tech. The efficiency is defined as the percentage of solar and wind power that gets actually used (not curtailed or lost due to storage inefficiency).

Spreadsheet tool accuracy

To test the spreadsheet tool’s accuracy compared to professional software, I used input data that was provided by Tong et al, “Geophysical constraints on the reliability of solar and wind power worldwide” (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: Various amounts of solar and wind power (overcapacity up to 3× demand) as well as storage (no storage, 3 hours storage, 12 hours storage). This test shows the limitations of spreadsheet software calculation: The tool returns results that are slightly different from the results that are provided by the professional software. A possible cause is the inherent inaccuracy of spreadsheet tool calculation (each number is limited to 15 digits). In addition, the tool does not account for storage self-discharge. However, for all scenarios, the error was never greater than one tenth of one percent.

Bottom line

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

By Georg Nitsche

Georg Nitsche has a master’s degree in history. He’s interested in lobbyism and propaganda, as well as in the history and future of renewable energy. Contact the author: georg.nitsche@mailfence.com

 
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