Severe Space Weather Events–Understanding Societal and Economic Impacts (2009)(science.nasa.gov)
science.nasa.gov
Severe Space Weather Events–Understanding Societal and Economic Impacts (2009)
http://science.nasa.gov/science-news/science-at-nasa/2009/21jan_severespaceweather/
See also the OECD's report: http://www.oecd.org/governance/risk/46891645.pdf
The remarkable thing is that it would cost in the low billions to safe the United States' EHV transformers, which are the most difficult components to replace, but I suppose we simply don't invest in infrastructure anymore.