So looking at the amount of CO₂ created by producing solar panels is one thing, but there’s also the idea that the amount of actual energy used to create the panels somehow larger than the panels will be able to pay off.  In reality, this thought is actually very similar to the CO₂ question addressed in my previous post; since CO₂ is just a byproduct of energy production (be it a gasoline engine or a coal fired power plant) you can figure out how much energy it takes to produce a given array.  

Coal power plants produce roughly 2kWh per kg of coal burned.  Thus, we can quickly figure (using the highest 350kg CO₂/m² number described in the CO₂ offset post), that our panels used the equivalent of 4,472 kg of coal to make (37.44 m² of PV Panels * 350kg CO₂/m² to make them / 2.93kg CO₂ created per kg of coal burnt) or the equivalent of 8.94MWH of electricity.  Our set of panels should produce close to 7MWH/year so they should be net positive in December if this fall is similar to last year’s.  This would be 16 mos. after installation.

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

http://www.fueleconomy.gov/feg/co2.shtml

http://www.lowtechmagazine.com/2008/03/the-ugly-side-o.html