1. Assuming the alternative is combined cycle nat gas at 400 grams carbon dioxide per kwh; with 17 TWh per year of electricity, that’s 6.8 million tons carbon dioxide avoided per year by Diablo Canyon. Those numbers are slight underestimates, so 7 million tons of avoided carbon dioxide is a good ballpark estimate, times 50 years is 350 million tons.
2. http://energyalmanac.ca.gov/electricity/electric_generation_capacity.html To utility-scale solar production, I added my estimate of 3.4 TWh from 2.29 GW of rooftop solar panels (US DOE Energy Information Agency) assuming a 17 percent capacity factor http://www.energy.ca.gov/2013publications/CEC-400-2013-005/CEC-400-2013-005-D.pdf.
3. http://energyalmanac.ca.gov/electricity/electric_generation_capacity.html My estimate of 3.4 TWh from 2.29 GW of rooftop solar panels (US DOE Energy Information Agency) assumes a 17 percent capacity factor http://www.energy.ca.gov/2013publications/CEC-400-2013-005/CEC-400-2013-005-D.pdf.
4. Last year Diablo Canyon generated 17 TWh of electricity while California’s wind turbines generated a total of 12.997 TWh. Utility-scale PV generated 4.639 TWh, but that doesn’t include rooftop PV, and I specify rooftop solar panels. Without finding any hard data on specifically rooftop PV generation in California, I had to estimate it from capacity and capacity factor data. EIA gives a figure of 2.29 GW of rooftop solar in California at the end of 2014, while this California state government source gives a figure of 2.4 GW of distributed solar as of July 29, 2015. This state report on distributed rooftop solar from 2013 puts average capacity factor at about 17 percent, by eyeball from figure 3. So 2.4 GW of rooftop solar with a capacity factor of 17 percent gives total annual generation from California’s current rooftop solar panels of 3.57 TWh. The 12.997 TWh of wind generation plus 3.57 TWh of rooftop solar generation is 16.567 TWh combined, a bit shy of Diablo Canyon’s last-year generation of 17 TWh. (Diablo Canyon averages about 17.5 TWh per year.)