I was tweeting an update on how much energy and CO₂ the PV array had generated/offset. To date it has, according to SunPower’s monitoring system, generated 4,151 kWh of electricity and “offset” 6,882 pounds (3,122kg) of CO₂. This is equivalent to burning about a ton of coal.
To find this number I did a little number crunching. Coal used for electricity in the US consists of about 70-75% carbon, however I used the more standard 80% carbon to make my numbers more conservative. Carbon bonds with 2 oxygen atoms when CO₂ is formed. Oxygen has a greater atomic mass than carbon (16 vs 12) making the CO₂ formed about 3.7 times the weight of just the carbon contained in the coal. The end result of this is that coal produces about 2.93 kg of CO₂ per kg of coal burned. So the 3,122kg of offset CO₂ is equivalent to 1066kg of coal (1.17 tons, 2350 pounds).
This is all great, but my friend Bryan asked how much CO₂ the panels had produced during manufacturing process and I didn’t have a number off-hand (I had heard a vague number in the past but didn’t remember anything firm). After a little looking, I found some reasonable looking numbers. I don’t claim these are perfect or thoroughly researched. Anyway, our array consists of 30 solar panels. These panels are each 1.248 m² so we have 37.44 m² of panels. According to that linked article, production of mono-crystaline panel such as ours range in CO₂ emissions in the 200-350kg/m² range. I used 250kg/m² in my numbers which means our 30 panels created 9360kg of CO₂. We’ve offset 3,122kg so far this year, so I expect we’ll offset the total production in less than 2 years, leaving over 23 years of the array’s expected lifetime to offset actual CO₂ emissions from coal burning power plants (even if you use the higher 350kg/m² the offset time only increases to around 2.5 years). 23 years of CO₂ offsets will be roughly equivalent to not burning more than 50 tons of coal. This is for one family. This is why I keep tweeting about the PV array. The more people that have them the more… well you can make your own conclusions.
References:
http://en.wikipedia.org/wiki/Coal#Carbon_intensity
