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Tag Archives: embedded energy debts

Are renewables enough?

By Dave Elliott

Richard Heinberg from the Post Carbon Institute raised some interesting issues in a lengthy paper at: http://www.postcarbon.org/our-renewable-future-essay/ For example, he says ‘renewable energy technologies currently require fossil fuels for their construction and deployment, so in effect they are functioning as a parasite on the back of the older energy infrastructure. The question is, can they survive the death of their host?’

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Energy return on energy invested

by Dave Elliott

There is inevitably some energy ‘embedded’ in energy generation systems, and it is useful to compare the energy needed to build and run plants relative to the useful energy out, but estimating ‘Energy Returns of Energy Invested’ (EROEIs) can be tricky. The ratios can range up to 200:1 or more, and down to single figures- very worryingly since then it is hardly worth running the plant.

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Renewable breeders

Renewable energy isn’t cheap, but prices should fall as markets build and technology develops. Indeed the basis of ‘learning curve’ theory is that this is what happens, over time. So why are some renewables getting more expensive- off shore wind for example?

One reason is that materials, like steel and aluminium, have been getting more expensive, in part reflecting the increased costs of (conventional) energy – these are very energy intensive materials. Some of those price rises were just blips (e.g. linked to the oil crisis last year), but the long-term trend for fossil (and fissile) fuels must surely always be up, since they are finite reserves. So the old technology undermines the new. At some point in the future we will be using renewable energy to produce/process these and other materials, so the continual price escalation problem will be avoided. But that’s some way off.

Certainly we will need an initial fossil fuel input to kick off a renewable energy future – so as to build the new renewable-energy technologies and produce the materials used in their construction. So some say that net emissions will increase if we try to expand renewables quickly. That ignores the fact that we will have to replace the existing fossil plants anyway in the years ahead, as they get old and are retired. Moreover, the energy (and carbon) debt from replacing the existing system with renewables should be less that either building more fossil plants, or even than going nuclear e.g. the embedded energy content of wind turbines is low – typically you get around 80 times more energy out over their lifetimes operation than is needed for their construction. By comparison, according a 2002 Hydro Quebec study, the output from nuclear plants over their lifetime is only around 16 times the energy needed for their construction and for the (energy intensive) production/processing of their fuel. Even more dramatically, the equivalent figure quoted for coal was 7 and gas CCGT 5. That for PV solar was initially about 9 – PV cell production is energy intensive – but it has been improving. Similarly for wind and other renewables – the energy/carbon debts are falling.

High energy (and therefore carbon) debts are only incurred when fossil, or to a lesser extent nuclear, fuels are used to build renewables: fossil fuels are obviously the worst, but the review by Ben Sovacool (Energy Policy 36 (2008) pp2940–2953) suggests that a nuclear system generates about seven times more CO2 over its lifetimes than wind turbines. However, after the high carbon input phase, the energy for building more renewables can come from these initial renewables. In effect we would then have renewable breeders. There are already some PV powered PV manufacturing plants – solar breeders.

That said, the rate of ramp up needs debate: what rate of new renewables growth could be sustained by the existing renewables – including providing the energy needed for producing basic materials?

Some say, rather bleakly, that we won’t even be able to get to that point: with peak oil, peak gas, peak uranium and even peak coal, looming, we just won’t have the energy to start ramping up renewables seriously – or for anything! Some add that this at least means that climate change will not be a problem! But others argue that, while Peak Oil and Gas now seem very likely soon, and Peak Uranium not far off (see the German Energy Watch Group’s study), there is still plenty of coal, so that is what is likely to be used- and, tragically, can be, given slow progress on a global climate agreement.

While it might be possible to reduce the impacts by Carbon Capture and Storage, rather than just burning the remaining fossil fuels off carelessly, we really ought to use whatever is left to start to build the new renewable energy system. Using these fuels to build a nuclear system, which is the only other supply option on the table, seems to be very short-sighted – given the energy intensive nature of the nuclear fuel cycle and the relatively limited uranium reserves. Though, if all else fails, and in the worst case and there isn’t enough fossil fuel, you could say that nuclear plants might, in the interim, provide some of the energy we need to start to build up the renewables system. More sensibly though, we should try to cut energy demand, so leaving more fossil energy to build the initial renewables.

Could it be done – will there be enough energy to support the development of a full renewable system? At the most obvious level if there is not enough energy to replace our existing plants with new plants of whatever type, then we are all doomed. But if we choose renewables for the future, it would be good not to incur massive emission debts. That rather depends in part on which renewables we choose – some are more energy intensive than others. It also depends on how quickly we need to ramp up renewables: if it could be done more slowly, then they can bootstrap themselves in energy terms, to some extent. But given the climate crisis, we may have to move faster than that. In which case, demand reduction and also possibly Carbon Capture and Storage, would become even more important, while we are still stuck in a mainly fossil-fuelled economy.

For the Hydro Quebec study see: L.Gagnon, C. Belanger and Y. Uchiyama ‘ Life Cycle assessment of electricity generation options: the status of research in the year 2001′ Energy Policy 30 (2002) pp 1267–1278.

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