The roads to our alternative energy future

A while back I tried to figure out whether we can keep running things the way we’re running them: do we need to transition off of fossil fuels, how fast, and would we be able to provide today’s level of energy supply using alternatives?  I didn’t include many of the details in that post, so I’d like to consider a few additional questions and look at this topic in greater depth.


  • How fast do we need to transition off of fossil fuels?
  • What industrial capacity is available today for different alternative energy technologies and what is likely to be available in the future?
  • What might we do if we can’t replace fossil fuels with alternatives fast enough, and what might the consequences be?

I finally got around to re-doing these calculations (so I could present them in a talk last week), and wanted to go through the numbers.

How fast do we need to transition?

In his excellent talk on climate change and energy, Saul Griffith analyzes how fast climate change might require a transition off of fossil fuels.  While there is good reason to think that 350 ppm of CO2 should be our global target, we passed that point in the late 1980s and have shown no signs of turning back.  Ultimately the goal is to avoid exceeding 2C of warming, as it marks the rough threshold at which many climate feedbacks are likely to kick in, including permafrost melt and loss of the Amazon.  Griffith observes that 400 ppm should be a target since it gives us a reasonable shot of staying below 2C, but we’re only 2-3 years away from 400 ppm (we’ll be at about 393 ppm by the end of the year) so it seems that is unlikely to happen.  Griffith does his calculations assuming a target of 450 ppm, which by various projections only gives us a 1/3 to 1/2 chance of staying below 2C of warming.  (As a point of reference, the “agreement” at the Copenhagen climate conference would have taken us to 770 ppm, which equates to roughly 5C of warming.)

Given a target of 450 ppm, Griffith calculates we need to transition in about 20 years.  I think about it as follows: we’re increasing CO2 by about 2.5 ppm / year at the moment (a little less when the economy isn’t growing quickly – this is a whole other subject I’d like to explore).  Any real-world deployment of alternatives would necessarily face some ramp-up and would be producing much more towards the end of the transition, and thus we’d probably keep fossil fuel generation going until near the end of the transition period.  As a result, there’d be little drop-off in emissions until near the end, and so we should aim to transition over a period of about 20 years to avoid overshooting 450 ppm.  As for transitioning faster, we can look to the Hirsch report, which argued that a 20 year energy crash program is about as fast as it can be done.  So 20 years it is.

Industrial capacity

I had done some quick calculations last time around, but I wanted to delve into more detail on industrial production numbers.  Specifically, what does the alternative energy industry say?  I figure that each industry is its own best advocate, so it’s likely that their numbers will be on the optimistic end of the spectrum.

First, how much would we need to build to provide 15 TW globally using mostly alternatives in 20 years?  Griffith calculates that we’d need to build 2 TW each of Solar PV, Solar Thermal, Wind, and Geothermal, 3 TW of Nuclear, and 0.5 TW of Algae fuel (we’d also keep some existing fossil fuel and other production capacity).  While I could quibble with the particulars, it’s a fairly balanced profile and is a reasonable starting point for a calculation.

Let’s start with Solar PV, with this blurb that says we’ll be at 28 GW / year of (nameplate) production by 2012.  Let’s round that up to 30 GW / year and use a capacity factor of 15% (considering the 200 W / m2 that’s available in most temperate zones).  That yields about 4.5 GW / year of production.  Let’s allow for a steady 20% yearly increase in production over the next two decades.  Combined production over 20 years will thus produce about 745 GW of PV capacity.

I’m going to assume that Solar Thermal can easily meet its 2 TW production slice, since there’s not much to it (mirrors, motors, pumps, generators).

How about Wind?  The Global Wind Energy Council expects 2500 GW of wind nameplate capacity by the 2030s.  Using a standard 30% capacity factor gives us 750 GW of Wind capacity in 20 years.

Geothermal is a bit complicated, as there really aren’t that many easy places to tap geothermal energy.  The International Geothermal Association expects a 9 GW nameplate capacity increase over 5 years.  Assuming the same growth trend, this yields 94.5 GW of capacity.  Including a 65% capacity factor, this yields about 61 GW of new geothermal capacity in 20 years.

Biofuels are also complicated.  While there are numerous current-day biofuels, including ethanol from corn and sugarcane, Griffith rightly considers better options such as algae-based oil.  Biofuels digest estimates a production capacity of 1.6 billion gallons / year by 2014.  That’s about half of one day’s global production of crude oil, per year.  Given the 15% production growth rate, this yields 26 billion gallons / year of capacity in 20 years, which is about 1.7 million barrels of oil per day (about 2% of today’s oil production).  Assuming the same energy density as gasoline, this yields about 105 GW of capacity in 20 years.

Finally, nuclear.  There are no good sources for expected production capacity, so to be optimistic (side note: I don’t actually think we should build any more nuclear, but that’s another issue) let’s use the peak rate of construction ever achieved, 30 GW / year of nameplate capacity construction (MacKay looks at a 60 year construction horizon, which is far too long).  This would yield about 600 GW of capacity in 20 years, assuming no loss thanks to nuclear’s high capacity factor.

In total this yields about 4.2 TW of new capacity to add to an existing 2 TW of fossil fuels, 1 TW of nuclear, and 0.5 of hydro, yielding 7.7 TW – about half of the target.  That is, even assuming optimistic rates of production of alternative energy sources, we’d be about 50% short of our energy target in 20 years.

A few scenarios

Doing the analysis above reminded me that a wholesale transition to alternatives seems unlikely to deliver energy at current levels of consumption/production.  I’d like to briefly consider a few possible trajectories / scenarios here, which I’ll explore in more depth another time.

  • Business-as-usual: we’ll just keep on going with fossil fuels until we can no longer do so; that is we’ll follow the oil depletion curve down and try to substitute with coal, tar sands, and other dirty fuels.  We may not build new coal plants in the United States, but we probably won’t decommission them as fast as we should to deal with climate issues, and China, India, and other countries will continue using coal at breakneck rates.  This scenario might, in the short term, maximize global economic output (though it will likely still be decreasing on a long-term basis given the economic impact of oil depletion).  It will however cause us to overshoot 450 ppm of CO2, taking us to perhaps 500 or 550 ppm, which is probably past the point of no return in terms of warming – natural feedbacks are likely to take over.  (I think we probably are unlikely to go much further than that, since we’ll start running out of cheap coal at that point.)
  • Unmanaged descent: we’ll keep using fossil fuels, but the economic contraction due to oil depletion will hit hard enough that we’ll end up using less energy overall.  In this way, we’ll haphazardly decrease our energy use at the expense of global human hardship.  In this scenario, we’d probably avoid exceeding 450 ppm of CO2 simply due to a non-functioning economy, though we also won’t be able to build alternatives at anything near the rate I describe above.
  • Managed descent: there are a lot of things that need to be done just right to manage our descent.  First, we’d need policy-based solutions, either in the form of a carbon tax (or the equivalent) or energy quotas.  Second, we’d need to stabilize swings in oil prices as I discussed before.  Third, we’d need to invest in alternatives that have the highest capacity yield per unit time.  From what I can tell, solar thermal is one of the best options, as it doesn’t require particularly advanced technology and therefore could probably be ramped up quickly.  It is however only viable in desert regions.  My preference would be to target solar thermal, wind, and algae fuel as the three main alternative sources; solar PV can help at the household scale.

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Responses to “The roads to our alternative energy future”

  1. The so called “renewable” energies are still business as usual. They are not renewable, no green, not clean and not sustainable. There are massive fossil fuel inputs and other nonfuel mineral inputs into these “renewables”. But there is this implicit dream of a continued material wealth that is a further illusion.

    Solar and Wind are not renewable. The energy from solar and from wind is of course renewable but the devices used to capture the energy of the sun and wind is not renewable. Nor are they green or sustainable.

    An oak tree is renewable. A horse is renewable. They reproduce themselves. The human-made equipment used to capture solar energy or wind energy is not renewable. There is considerable fossil fuel energy embedded in this equipment. The many components used in devices to capture solar energy, wind energy, tidal energy and biomass energy – aluminum, glass, copper, rare metals, petroleum in many forms to name a few – are fossil fuel dependent.

    Wind used by sailing ships and old style “dutch” wind machines is renewable and sustainable.
    From: Energy in the Real World with pictures of proof.

  2. Thanks for the comment. I agree regarding the terminology, which is why I didn’t use the words ‘renewable’ or ‘green’ or ‘clean’ or ‘sustainable’ anywhere in the post. We have two broad categories of choices on energy: to change sources or to change behavior. Here I wanted to explore the former to show that even if we wanted to do it, we wouldn’t succeed.

    I think you’re right that old-style Dutch windmills were sustainable. I think it’s also possible to make solar thermal electricity in a sustainable way, though it’s not sustainable at the moment (the metals required can be completely recycled and can be machined using ancient techniques if required). Photovoltaics and modern wind turbines are most definitely not renewable in the long term.

  3. I’m happy to discover this blog (a friend sent a link); I like your perspective careful thinking, and avoidance of cant. (As a one-time major in logic, I also like your title and the reasons for it.)

    One additional consideration I’d like to see factored in: conservation. While it’s a small one at the moment, there are many movements underway to reduce our “energy footprint”, and even in the “green mainstream”, the idea of “reduce, reuse, recycle” is gaining traction and action. To what extent, at what rate? I don’t know, but it might reduce the 15TW target somewhat. (It also has the virtue of immediate feasibilty, with low initial energy investment.)

  4. Thanks! So I should say that in this post I intentionally left out conservation. Maybe I’m beating this idea into the ground, but I’m trying to very carefully dismantle the notion that alternatives can allow us to keep running everything the way we’re running it without any change in behavior (i.e. without significant conservation). If changing sources isn’t going to resolve the issue, we need to look at changing behavior like you mention.

    I think when it comes to electricity it should be no problem to save 20-50% (depending on the region in question) with a public conservation effort – there’s a fair bit of low-hanging fruit. But transportation and agriculture are much harder and slower to transition to efficient alternatives. We may end up doing something that I don’t have a good word for – giving up certain practices, habits, etc. despite their utility just for the sake of saving energy (and money). (Maybe that’s also conservation, though I generally think of conservation as finding an equivalent alternative that is more efficient rather than just doing without.)

  5. Barath, I’d love to see a post where you talk more about your opposition to nuclear. I’m personally on the fence about it. I’ve read estimates that are even more pessimistic about the prospects for other “renewables” (wind, solar, etc.). On the other hand, I’m not very happy about the political context require for nuclear to operate (massive security state), though I think worries about accidents and waste tend to be overblown.

  6. Hi Matt – I should write about it sometime… A decade ago I used to think nuclear was a decent option given that at least it’d help on the climate change front, and statistically it causes fewer deaths per joule than coal power. Three things, broadly, have changed my mind. First: oil depletion. In a permanently declining global economy, the resources (mostly financial, though military resources are important like you mention) to keep plants well maintained are going to be scarce. Nicole Foss said it well – that after studying nuclear safety in Eastern Europe and Russia she concluded that nuclear power is incompatible with hard times. Second: waste storage. I think it is possible for us to store waste for the short term. It’s the longer term that is a bit more doubtful. Watching the documentary Into Eternity on Finland’s waste storage plans reminded me of a few things: a) Finland is a small country, and yet the scale of the waste site is huge, b) planning for the 100 years it’ll take to finish the waste site is hard enough (will there be the money needed to complete it?) let alone the hundreds of thousands it needs to survive, and c) they’ve been working on this for a decade already, while no other country has even the beginnings of a solution. (The documentary was a bit sad – Finland has assembled a number of expert, sincere people trying to solve a problem that you sense they realize cannot be solved.) Third: scale, cost, and durability. Nuclear isn’t particularly cheap when you compare it to alternatives (though cost estimates vary wildly) and is difficult to scale up quickly. It’s also not a technology that fails well. Even barring a catastrophic failure, at some point the whole plant has to be decommissioned and many of its parts stored as waste. Solar thermal and hydro are better options for baseload generation, and they’re generally very durable. Mirrors can be replaced/cleaned/etc. on an ongoing basis and without any advanced technology.