Before proceeding with this discussion of EROEI, I thought it would be worth defining what this target for a renewable transition actually looks like:
First, it's important to recognize that there are a variety of possible targets. Some include: a general transition target (either total transition to renewables, or transition to some arbitrary %), a peak-oil mitigation target, a peak fossil-fuel mitigation target, and a climate change mitigation target. All have differences and similarities. Clearly, its one can define a "target" that is plainly achievable, as can one define a "target" that simply can't be done (e.g. 100% transition in 5 years). As such, the definition of "transition target" represents an easily manipulable variable in any discussion of renewables transition. If two people or organizations don't recognize the same target, they'll be constantly talking past each other in discussing renewables and the practicality of transition. While I certainly don't think that I'll be able to convince all parties to adopt a unified transition target in this blog post, I do plan to argue for a threshold target that, in my opinion, represents a minimum rate of transition to keep the "viridian vision" of a renewable future possible: a peak oil mitigation target.
So, it seems clear that a renewable energy transition will need to, at a minimum, replace the decline in oil production with renewable energy generation. I'll elaborate on why I draw this line in the sand below, but in brief the viridian vision (by which I mean a general continuation of our current neo-liberal, capitalist/market-socialist civilizational structure into the distant future by leveraging technological advances and a transition to a renewable energy base and "green" economic foundation) requires that we maintain generally the same level of present energy consumption into the foreseeable future.
Why this focus on the "viridian vision"? I think my personal biases are clear: I'm very skeptical about the practicality of viridian vision--to be more plain, I don't think it's realistic, and further I think it's the modern opiate of the masses when it comes to confronting current energy issues. That said, I think anyone who refuses to recognize that both 1) the viridian may be possible, and that 2) it may be fundamentally impossible is taking a faith-based and irrational position. I don't want anyone to accuse me of hiding the ball as this series progresses--my own studies to date suggest that the renewables transition necessary to fuel the viridian vision is most likely not realistic, and my purpose in this series is to build an argument to this effect. I'm not trying to be pessimistic. Rather, I'm trying to prevent a waste of effort, focus, and our limited (and dwindling) supply of surplus energy on an epochal folly. For lack of a better analogy, it's a bit like our childhood fantasies: at some point, the little league baseball player needs to give up on the dream of becoming a star professional athlete and focus on a more realistic plan for the future. Sure, for any given kid it's a possibility to become the next big star, but it would be folly to advise all of them to pursue that dream at all expense.
It's also important to point out the obvious, that there are significant differences between the energy produced by renewable technologies (that, for our purposes, produce electricity) and the energy lost by declining oil production. In general terms, in order to use the electric energy produced by renewables to replace oil, there will be an additional energy cost required to transition the energy-consuming infrastructure to utilize electricity rather than oil. This will increase the overall amount of energy required to affect this transition. For the time being, I'll ignore this additional cost--the result is that my estimates will be more conservative than an estimate that would account for these additional transition demands.
One key argument in favor of the viridian vision is that we can mitigate peak oil with increases in efficiency and energy conservation. These arguments generally don't, however, address how we're going to meet the energy demands of 1) a growing population, and 2) a huge third-world population that wants to live at Western standards of energy consumption. The more optimistic population estimates show the Earth's population peaking at 8.3 billion, and more pessimistic estimates show population peaks between 9 and 13 billion. It's important to point out that may population estimates reason that population will stabilize--and then decline--because of the effect of bringing the standard of living of the world's poor closer to Western standards. Will the energy pressures presented by population growth and efforts to improve living standards roughly balance out any improvements in efficiency and conservation? I think so. In fact, I think that this is overly optimistic, and that demographic pressures will more than eat up any energy savings from efficiency and conservation. For this reason, I think that we must increase renewable generation capacity at the same rate that oil production declines--we can't count on efficiency and conservation to make up any of this decline.
Additionally, any renewables transition that attempts to mitigate peak oil must cope with the disparity between effective ramp-up rates and effective oil decline rates. It's nothing more than a simple issue of math: if you use a post-peak decline rate of 5% for oil decline, then that works out to about 4.4 million barrels per day of decline per year, gradually decreasing over time. Conversely, because the current renewable generation base is so small (excluding hydropower, which can't be easily ramped up), even a 100% per year increase in renewable generation comes nowhere close to mitigating this 4.4 million barrel per day decline in the early years. At some point, a 100% annual increase in renewable generation overtakes the declining annual oil production decline figure, but there is a significant gap, especially if we are currently at or very near peak oil. For this reason, we can't necessarily look at the rate of increase of renewables generation over a 20 or 30 year window, because this long-term view alone may overlook a very significant energy gap. It's possible that this gap can be filled with fossil alternatives that are not yet at peak--specifically coal and gas--but that's probably the best we can expect from such fossil alternatives given that they are already experiencing significant EROEI declines (and cost increases) and that their climate consequences may be incompatible with the viridian vision...
All of these values--renewable generation, population growth, conservation, efficiency--are arbitrary decisions. There are simply too many variables to produce a single, agreed set of assumptions on which to base a target estimate. Here, my goal is simply to make my assumptions (and their rationale) clear so that others can question them and change them if they wish. Ultimately, I'll continue with this Renewables Hump series using this peak oil mitigation transition target outlined below. If others have alternative targets, it should be relatively simple to apply the remainder of this series to those different targets...
In looking at these figures, I'm choosing to ignore hydropower, which has a current generation capacity of approximately 800 GW. My rationale is that hydropower is largely location constrained, and is not scalable in the way that other renewables (especially wind and solar) are. For example, only about 10 GW of hydropower were added in 2008. Compare this to a rough doubling in wind generation capacity.
The world consumes roughly 500 Quads per year (Quadrillion BTUs) from all energy sources. Of this roughly 186 Quads come from oil consumption. If you accept a post-peak decline rate of 5% per year, then that represents a decline of 9.3 Quads per year. 9.3 Quads equates to roughly 102.3 GW-years, or 896,000 GWh. To round that off, let's call it 100 GW-years, or 900,000 GW-hours. That's how much new renewable generation must be added each year going forward. That's the transition target. How does that compare with current renewable generation rates?
The current global installed (nameplate) solar capacity is about 15 GW, including about 5.5 GW added in 2008. That works out to roughly 1 GW-year of solar generation capacity added in 2008. One EIA study estimates that, under an "aggressive" growth scenario, total all sources of solar power could displace a total of 22 Quads of fossil fuel consumption by 2050 (that's the total from present to 2050, to an annual rate). Clearly this rate of transition is woefully insufficient to mitigate peak oil.
At the end of 2008, global (nameplate) wind generation capacity was 121 GW. That works out to roughly 42 GW-years of total global wind generation, of which 35 GW, or about 12 GW-years of wind generation was added in 2008. Combining solar and wind, we added about 13 GW-years of renewable generation capacity in 2008. That's a bit over 10% of the rate at which we'll need to add new renewable capacity each year just to compensate for a 5% global oil production decline rate (not to mention future natural gas decline, coal decline, etc.). There are two take-aways from this: 1) the current rate at which we are increasing renewable energy generation is an order of magnitude lower than that necessary to mitigate peak oil, and 2) the amount of energy invested in renewable energy projects at present does not pose the kind of energy drain that will be presented by investment sufficient to mitigate peak oil.
On this last point, mitigating a decline of 4.4 million barrels of oil per day each year with new renewable generation capacity will impose a significant up-front energy cost. If the energy payback time is 1 year for the mitigating renewable source, and this represents a 90% increase in current renewable energy investment, then we need to invest the equivalent of an additional 3.96 million barrels of oil each day to facilitate the transition. That's like adding another half of China to global demand, and that 1-year payback time assumes an EROEI of 40:1 on a 40-year generating life. If the energy payback time is 2 years (or a 20:1 EROEI) then you can add another full China to global demand. If it's 10 years (an EROEi of 4:1), then go ahead and add 5 Chinas. You can see where this is going--getting an accurate measure of EROEI, and properly understanding the mechanics of scalability, are critical before we can determine if it's possible to mitigate peak oil with renewables...