# Carbon intensity of US grid dropped by 30%

17 Jul 2018

A new method for computing the carbon intensity of the US electricity sector could make it simpler to assess emissions trends over different timescales and by region. Electricity generation results in over a quarter of all US greenhouse gas emissions, and deep decarbonization of the sector is closely linked to meeting climate targets.

Overall, the group based at Carnegie Mellon University, US, found that between 2001 and 2017 the average annual carbon dioxide emissions intensity of electricity production in the US decreased by 30%. The primary drivers for the change were an increase in generation from natural gas and wind accompanied by a reduction in coal-fired power.

Thanks to the switch from coal to gas, all US regions showed at least some decline in carbon intensity over the period. But markets can disrupt this pattern. In the first half of 2017, for example, the US natural gas price climbed from under $2 per GJ to over$3 per GJ, leading to an increase in coal generation. Where renewables are available, energy providers have more options.

The calculations point to large increases in wind generation across three of the eight North American Electric Reliability Council regions that cover the US lower-48 states, and at state level. By looking at generation levels month-by-month across multiple years, it’s clear that a rise in wind power has the potential to flatten summer peaks in natural gas demand.

One idea under discussion is the use of high-voltage direct current (HVDC) transmission to move renewable power from region to region more efficiently. Analyses such as this study could identify seasonal peaks in the generation of low-carbon power at different sites across the country. Correlating these results could reveal where HVDC links would be most effective.

“Negative seasonal correlations between two regions would mean that additional low-carbon power generated in each region could be shared, lowering the carbon dioxide intensity across regions,” explain the scientists in Environmental Research Letters (ERL).

Making information readily available and quick to navigate is key to tracking progress and gaining insight into changes in the energy mix.

“The goal is to have a method that is easily reproducible, temporally relevant and usable by different decision-makers,” writes the team.

Quarterly emissions updates, open data, and analysis code are freely available at the Power Sector Carbon Index website.