Late last year, Tom Blees, I and a few other people from the International Award Committee of the Global Energy Prize answered reader’s energy questions on The Guardian’s Facebook page. The questions and answers were reproduced on BNC here. Now we’re at it again, this time for the website Eco-Business.com (tagline: Asia Pacific’s sustainable business community). My section is hosted here (Part I), and Tom’s here (part III).
Part II, which I don’t reprint, answered by Iceland’s Thorsteinn Sigfusson, covered the relationship between large-hydro and climate change, and why solar conversion isn’t used more extensively.
I’ve reproduced my and Tom’s answers below.
Barry Brook’s Q&A
Sunil Sood: What are the “Real Energy Payback Periods” for Solar PV and Wind Energy Systems? Taking in to account the energy consumed during manufacture of components, balance of systems, transportation, installation, servicing and variations in availability of energy and usage patterns, actual life expectancy (not theoretical). Are we consuming more of ‘Dirty Coal’ to produce these so-called ‘Clean’ energies?
Calculating true energy paybacks are tough. Every energy system has initial investments of energy in the construction of the plant. It then must produce energy for a number of years until it reaches the end of its effective lifetime. Along the way, additional energy costs are incurred in the operation and maintenance of the facility, including any self-use of energy. The energy payback period is the time it takes a facility to “pay back” or produce an amount of energy equivalent to that invested in its start-up. A full accounting of energy payback includes not only the materials and energy that are input into the extraction (mining) and manufacturing processes, but also some pro-rata calculation for inputs into the factory that constructed the power generation facility, some estimate for human (worker) inputs, etc. As you can imagine, it can be difficult to fully integrate all possible inputs.
However, there are reasonable ballpark estimates for a range of technologies, including wind, solar PV, solar thermal and nuclear. Material inputs tells one part of the story, and some attempts are a standardized comparison are given here and here for a few technologies (wind, solar thermal, Gen III nuclear). As a short-cut for estimate of total energy-returned-on-energy-invested (ERoEI), we can use studies that have looked at the life-cycle emissions of alternative technologies, and then calibrate these against the emissions intensity of the background economy used to produce the technology. This gives us an approximate ERoEI. Based on a range of studies, the estimates range from 180 to 11 for Gen III nuclear, 30 for wind, 11 for solar thermal and 6 for solar PV. That is, your PV panels would repay their inputs 6 times over during their lifespan, and if they lasted on your roof for 25 years then the payback time is about 4 years. If a nuclear plant had a ERoEI of 50 and operated for 40 years, its energy payback time would be 10 months.