I'm looking to offset the carbon footprint of my wedding.

I'd like to do it by helping out some local community solar projects.

I've calculated that the weddings footprint will be about 23,000 KG of CO2, and that this would be offset by about 37,000 kWh of solar generation (if 1kg of CO2 = 1.64 kWh).

But over what period do I measure those kWH to calculate how much of a contribution to community solar is meaningful? Over 1 year? Over 5 years? And how do I estimate what would be generated over that time period - I know peak will be far from actual, and how many sunny days do you estimate?

What's an appropriate way to calculate the appropriate contribution?


There isn't an easy answer on offsetting time: in theory, the sooner the better, because every year that passes with higher greenhouse gas levels. increases the heat content of the Earth.

If you wanted it just to come out net zero addition of greenhouse gases to the atmosphere, over the PV's whole lifetime, then reckon on 20 years if it's monocrystalline. Maybe 15 years if it's thin film. We don't have a lot of experience of the latest thin-film tech, so lifetimes are a bit uncertain, but 15-20 years won't be too far from the end result.

As for average production, there are sites like PVGIS to help you calculate that; here in Britain, and in Germany, average capacity factors are 9-10%, so you might reckon on say 800 full-load hours equivalent, per year. So if a system was 1kW peak, that would be 800 kWh each year. Accumulated over 20 years, that's 16,000 kWh. You might want to reduce that by 10-15% to account for the greenhouse-gas footprint of manufacture of the PV system itself: specifics would vary, depending on the system.

  • Brilliant. That's exactly what I wanted. Thanks! – ChristopherJ Oct 17 '13 at 5:28

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