CO2 savings via a PV solar system

[Codyroo]

Hi all,

We had a 3.7 kW system installed on our house last August and it has been working well (knock on wood). On our Sunnyboy 4000US inverter, it displays the amount of CO2 saved by running our system.

I have to go back and revisit the inverter manual, but I believe it said it was the kilowatts generated multiplied by 1.7 (default value), this would mostly jive with what we've seen (5600 kilowatts generated * 1.7 = 9500 lbs of CO2....well except our display says 95000 lbs of CO2. I'm guessing an input error of 17 instead of 1.7).

Anyhow, does anyone know how they came up with the value of kilowatts * 1.7 as a CO2 calculation? Does this assume an average of the entire US for kilowatt vs CO2 generated by our power plants?

[KK6PD]

As of yesterday, my year to date total value, since going on line Aug/04, with my 7.5 kW system I have generated 58,783 kWh of Solar Power!

Iguess that means 999311 CO2 savings!!!

GO SOLAR!!!

PAT KK6PD

[Tadashi]

It all depends on the source of your power and efficiency of the plant.

If my calculations are correct you should multiply 0.698043165 by the number of kWh to get the total kg of carbon saved from coal power. That is an avg value as coal from different locations burned in different plants produce different amounts of power. This value comes pretty close to the SMA value my Solar system gives me. I am not sure what the conversion is for kW vs kWh. So I am not sure how they get 1.7.

[miscrms]

Originally Posted by Tadashi

It all depends on the source of your power and efficiency of the plant.

If my calculations are correct you should multiply 0.698043165 by the number of kWh to get the total kg of carbon saved from coal power. That is an avg value as coal from different locations burned in different plants produce different amounts of power. This value comes pretty close to the SMA value my Solar system gives me. I am not sure what the conversion is for kW vs kWh. So I am not sure how they get 1.7.

0.698 kg = 1.54 lbs Not quite 1.7, but not far off. 1.54 seems to be the number Energy Star uses for their CFL program calculations. Below is an example from Aspen where two power companies come in at 1.265 and 1.795. Here in AZ we run about 1 lb/kWh due to large nuclear contribution, & some hydro.

http://aspenglobalwarming.com/pdf/01Elec&Notes.pdf

So, as you said it does vary quite a bit depending on sources. You'd really want to at least get your state average, if not a number from your actual power company.

Rob

[burritos]

Ok you math wizards, anyone know how much energy is needed to manufacture a 100 watt solar panel?(in other words, the energy to dig up the silicon, to refine it to polysilicon, process the panel, etc...)

[Tadashi]

oops did did not notice you were working in imperial measurements. So I guess the 1.7 is not too far off. Maybe they estimate the worse case scenario power plant. Also they are a German company so many that is the avg for power plants in Europe.

Again, not all manufacturers are created equal. Each has a different process and uses different material. I do recall reading a study that came to the conclusion that over the 25-yr life span of a panel, it does create more energy than it takes to make the panel. For some reason the figure of $4.5 to $5 a watt come to mind for the cost to make the panels. My house system costs $6.75 a watt including installation. This is without any rebates. I am not sure if the gov't provides any subsidies prior to the sale.

[Codyroo]

Originally Posted by miscrms

0.698 kg = 1.54 lbs Not quite 1.7, but not far off. 1.54 seems to be the number Energy Star uses for their CFL program calculations. Below is an example from Aspen where two power companies come in at 1.265 and 1.795. Here in AZ we run about 1 lb/kWh due to large nuclear contribution, & some hydro.

http://aspenglobalwarming.com/pdf/01Elec&Notes.pdf

So, as you said it does vary quite a bit depending on sources. You'd really want to at least get your state average, if not a number from your actual power company.

Rob

Thanks for the link. That gave me enough information to do a google search on CA

Carbon Footprint Calculator Assumptions

seems Pacifc Gas and Electric generates 0.524 lbs of CO2 per kilowatthour (kwh). Thus, in our area, we've saved about 3000 lbs of CO2 vs the 96,000 lbs the inverter is reading. Hmmmm, only a factor of 32 off....

[icarus]

Originally Posted by burritos

Ok you math wizards, anyone know how much energy is needed to manufacture a 100 watt solar panel?(in other words, the energy to dig up the silicon, to refine it to polysilicon, process the panel, etc...)

Amortized for over the live of the panel vs the life of a coal or gas fired plant,,,,way less. Silicon, while not cheap to refine is abundant. Panels have a life span warranted for ~20 have a life expectancy of 40+ years.

Icarus

PS I don't know the detailed answer to your question however.

[tripp]

It really depends on the the panel. The recent panels are using less and less silicon because of the supply constraints. So compared to older panels the EROI is probably considerably better. Also, mono vs polycrystalline vs amorphous/thin film way be important in the calculation.

[tripp]

I remember hearing once that the EROI is around 2 years. I can't verify that or remember the source (mighta been darrel). Again, could be considerably less now given panel mfg methods.